"[Arms Control Today] has become indispensable! I think it is the combination of the critical period we are in and the quality of the product. I found myself reading the May issue from cover to cover."

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Co-Director of Program on Science and Global Security, Princeton University
Open Skies Treaty

Open Skies Treaty Flights Resume in 2019

The United States conducted an airborne surveillance mission over Russia under the auspices of the 1992 Open Skies Treaty on Feb. 21, the first routine treaty flight since 2017. Following agreed procedures, all treaty parties received advance notification of the mission, and six Russian officials flew on the unarmed U.S. aircraft “to monitor all phases of the flight,” said Defense Department spokesperson Lt. Col. Jamie Davis.

Using an OC-135B observation aircraft, shown here in 2000, the United States conducted an Open Skies Treaty flight over Russia in February. It was the first routine treaty flight since 2017. (Photo: Mike Freer/Touchdown Aviation)Last year, there were no regular treaty flights because of a dispute over on-board observers that was resolved in October. There was, however, one “extraordinary flight” on Dec. 6 over Ukraine, requested by Ukraine shortly after a Russian attack on Ukrainian naval vessels in the Black Sea.

The United States has accused Russia of violating the treaty by applying excessive restrictions on surveillance flights over Kaliningrad, a sensitive Russian enclave between Poland and Lithuania, but U.S. officials expressed hope that the dispute could be settled. Andrea Thompson, U.S. undersecretary of state for arms control and international security, said on Sept. 18 that Russia has “made overtures that suggest” it could resolve the alleged violation. (See ACT, January/February 2019.)

The Open Skies Treaty, which entered into force in 2002, aims to increase confidence and transparency between the United States, Russia, and European nations by allowing unarmed observation flights over the entire territory of its participants for information-gathering purposes. The 34 parties have yearly quotas on overflights and must make the collected information available to all treaty parties.—SHERVIN TAHERAN

Open Skies Treaty Flights Resume in 2019

Open Skies Treaty: A Quiet Legacy Under Threat

January/February 2019
By Alexandra Bell and Anthony Wier

On a pleasant day in August 2017, a low-flying jet pierced secure airspace near the White House, the Capitol, and the Pentagon that had been mostly off-limits since the Sept. 11, 2001, terrorist attacks. Surprise turned to suspicion when news reports revealed the midday flight was a Russian military aircraft taking photographs.

A U.S. Air Force OC-135B aircraft, one of two modified Boeing 707s used for Open Skies flights, prepares to take off September 14, 2018, at Offutt Air Force Base, Nebraska. (Photo: Charles J. Haymond/U.S. Air Force)Was this some outgrowth of President Donald Trump’s campaign call for friendlier relations with Moscow? No. The Russian Tupolev Tu-154 had U.S. permission to fly over Washington that day because of an idea President Dwight Eisenhower had in 1955 and a treaty President George H.W. Bush forged in 1992.

The little-known Open Skies Treaty provided the authority for that surveillance flight and many like it elsewhere across the Euro-Atlantic region. The United States carries out similar surveillance flights over Russia and other treaty member states using two U.S. Air Force OC-135B observation aircraft. Yet despite its long history of enhancing mutual understanding and lowering military tensions, the 34-nation pact, centered around transparency and information sharing, has operated mostly unseen and unknown by the public.

Now, with several disputes hampering aspects of the treaty’s implementation and a U.S. administration openly questioning other bilateral and multilateral arms control agreements, the Open Skies Treaty is at risk. This is troubling because abandoning the treaty would destroy concrete national security benefits. It would deny the United States real-time, comprehensive images of Russian military facilities. It would pull the rug out from under long-standing U.S. allies. It would sap the confidence that is built through the treaty’s intense but cooperative implementation process. Above all, ending the Open Skies Treaty would be one more move by Trump and his national security adviser, John Bolton, to squander an arms control and national security inheritance that Bush and other Republican presidents worked so hard to hand down.

The Concept

In July 1955, Eisenhower shocked the Soviet Union and the world. In a bid to calm superpower tensions and lower fears of all-out surprise attacks, Eisenhower offered to allow unarmed Soviet aircraft to make unlimited surveillance flights over U.S. territory if the Soviet Union would permit U.S. planes to do the same over Soviet territory. Just a few months after Sen. Joseph McCarthy (R-Wis.) had spun the country into a red-scare frenzy, a scheme to let communist Soviet spy planes into U.S. airspace seemed sure to go over poorly.

Instead, the American public loved the idea. Eisenhower’s highly publicized offer brought him some of the highest approval ratings of his presidency.1 Senate Majority Leader Lyndon Johnson (D-Tex.) praised the Republican president’s gambit. Eisenhower’s approach, Johnson said, would “separate the warmongers from the peacemakers” at a time when the “American people yearn for peace.”2

Decades would pass, however, before Eisenhower’s vision could become reality. For years, Moscow shunned Eisenhower’s proposal with a suspicion bordering on paranoia. It finally took another war vet to use a Cold War’s thaw to bring the vision to life. In May 1989, Bush spoke to the new graduates of Texas A&M University.3 In sweeping remarks dreaming of a path beyond the Cold War, he revived the long-forgotten Open Skies transparency plan.

Yet, Bush went even further. He called for a regime built “on a broader, more intrusive and radical basis.” His key twist was to propose applying overflight rights and duties to all of NATO and the Warsaw Pact, stretching from Vancouver to Vladivostok. As Bush put it, Soviet willingness to embrace the Open Skies idea could prove their commitment to real change. Moscow balked again, but by 1992, a newly formed Russian government finally agreed to open its entire territory to observation and overflight. Twenty-four states signed the new Treaty on Open Skies in Helsinki on March 24, 1992.4 Eventually, membership would rise to 34 states.

At its core, the treaty aims to lower the temptation and fear of surprise attack by guaranteeing that there will be photographic evidence of any major military preparations and movements across the Euro-Atlantic region. Each state-party must allow a certain number of flights over its own territory and then may conduct an equal number of flights over the territories of other states-parties.

Observing countries give very short notice of their specific flight plan. Each party’s cameras must be verifiably limited to a resolution well below state-of-the-art technology, even for 1992. The cameras just need to be good enough to distinguish a tank from a truck. The treaty explicitly permits a range of imagery, including optical and video cameras, as well as infrared and synthetic aperture radars, while barring collection of any other electromagnetic signals. All imagery collected from overflights is then made available to any state-party.

The treaty is simple in concept but excruciatingly detailed in its operation. The implementation process carries its own confidence-building benefit by creating more opportunities for interaction among parties.

U.S. Ratification

The Bush and Clinton administrations each thought the Open Skies Treaty provided valuable national security advantages. Before the United States could become a party to the treaty, however, the U.S. Senate had to give its advice and consent. Given the current congressional atmosphere, one might expect that a treaty signed by a just-defeated Republican president would have had trouble winning approval from a Democratic-controlled Senate.

Fortunately, things were different in the early 1990s. Both sides of the aisle queried administration officials, worked through a few concerns, and signed off with a few minutes of floor debate and without a single opposing vote.

Russian and American representatives sign an agreement on August 5, 2006, before a U.S. flight over Russia conducted under the Open Skies Treaty. (Photo: OSCE)The Senate Armed Services Committee concluded that the treaty represented “the broadest international effort to date to promote openness and transparency of military forces and activities.”5 Even so, senators knew that the treaty was not the most important treaty they had ever considered. They knew that the United States had intelligence capabilities that far outstripped any other potential treaty partners. They understood that U.S. satellites could generally see more than what the treaty’s resolution limits would allow.

What they did not know was that Open Skies Treaty aircraft would become the best tool available for imaging significant parts of Russia.6 Senators also did not fully grasp then what experience has taught since, that it is a lot easier to use pictures acquired through Open Skies Treaty flights instead of sensitive satellite sources to gain diplomatic advantage. The conflict in Ukraine has put this aspect of the treaty’s value on display. By early 2014, the United States and its allies had already been able to use more than 10 Open Skies Treaty overflights covering “thousands of square miles” of Ukrainian and Russian territory to collect photos of Russian forces and military movements.7 These photographs could be shared among European governments without the usual delays or concerns that accompany sensitive intelligence declassification. As recently as December 2018, the United States and Ukraine again partnered to take advantage of the treaty to collect shareable, incontrovertible imagery following a Russian attack on Ukrainian vessels in the Sea of Azov.8

Senators did understand that the treaty would help build transatlantic transparency, confidence, and stability. The Senate backed the treaty so unreservedly because European allies valued it.9 The United States’ security partners, after all, do not have the same imaging capabilities as the United States. For most European allies, Russian tanks have just a border to cross, not a wide ocean. Those allies need and want U.S. backing in securing the rights of European countries to periodically fly east and take a look around.

After the other countries met their own treaty approval requirements, the treaty came into force in 2002. Since then, the United States, Russia, and 32 other countries have flown 1,426 picture-snapping flights over each other’s territories.10 The United States and its allies have been able to fly more than 500 times over Russian territory with Russian permission.11

Current Disputes

Implementation issues arise with any arms control treaty. For the Open Skies Treaty, these questions are managed through the Open Skies Consultative Commission. With 34 parties and more than 100 pages of detailed rules, the commission has seen its share of disputes. Frustrations have risen over the last few years on a couple of key issues, mostly having to do with Russians activities.12

Unlike Russia’s violation of the Intermediate-Range Nuclear Forces (INF) Treaty, from which Trump currently plans to withdraw the United States in early 2019 unless Moscow returns to compliance, the U.S. concerns regarding the Open Skies Treaty have focused on specific practices that do not fundamentally undermine what the United States and its allies gain from the treaty.

U.S. Air Force Master Sgt. David Dines changes out the film aboard an OC-135B Open Skies observation aircraft during pre-flight checks January 16, 2010, at Joint Base Andrews, Md. (Photo: Perry Aston/U.S. Air Force)One ongoing dispute relates to flights near the border between Russia and Georgia. Article VI says that flights cannot happen within 10 kilometers of “the border with an adjacent State that is not a State Party.” Russia defies most of the world by asserting that South Ossetia and Abkhazia are independent states. To be consistent, Russia also has to deny treaty overflights along those disputed borders. In addition, Russia has created general implementation problems for Ukraine.

The Open Skies Treaty thus has become collateral damage in Russia’s deteriorating relationship with its neighbors. Yet, Russia is not the only country to prevent flights near a sensitive border. In 2016, Turkey prevented a Russian flight from getting too close to the Syrian border, a source of heavy Russian complaints.13 In all of these cases, problems are connected to broader national disputes.

More troubling is Russia’s unilateral imposition of a 500-kilometer sublimit for certain observation flights over Russia’s Kaliningrad exclave, despite the limitation having no basis in the treaty. Russia is allowing treaty-compliant planes to fly over Kaliningrad, just not for the flight distances technically permitted. The Russians imposed the restriction because some past flights over Kaliningrad have zig-zagged across the small territory, creating problems for civilian flights and air traffic control. One 2014 overflight by Poland causing such problems has been cited as the origin of the dispute.14

Based on this cumulative activity, the United States determined in 2016 that Russia has not been meeting its obligations and has therefore limited certain Russian overflight privileges here.15 Specifically, the United States has restricted flights under the treaty over the Pacific Fleet in Hawaii and the missile defense interceptor fields
at Fort Greely, Alaska.16

Although such reciprocal measures might be a natural response, by themselves they do not actually resolve disputes. The United States and Russia nevertheless have been able to find solutions in some cases. For instance, in its April 2018 report to Congress on treaty compliance, the Department of State stated that a long-standing disagreement about how to deal with overflights during major events had been settled.17 The April 2017 report confirmed that previous U.S. concerns about altitude restrictions over Chechnya had also been resolved.18

Such progress has been complicated by those in the United States who seem happy to impede the treaty. The United States has caused particular trouble with regard to Russian moves to upgrade its treaty observation aircraft and replace film cameras with digital sensors. Congress has fueled the challenges to new Russian equipment. As early as 2014, the U.S. House of Representatives led Congress to require a report at least 30 days prior to signing off on any Russian proposal to modify or replace its treaty observation aircraft or sensor.19 The next year, the House pushed Congress to triple that warning time, unilaterally imposing an artificial three-month diplomatic cooling-off period.20 In August 2018, Congress defied administration objections and passed restrictions virtually guaranteed to force the United States to oppose any state-party’s bid to use infrared or synthetic aperture radar sensors in exactly the way the treaty envisions.21

On the heels of this congressional direction, in early September 2018, the Trump administration caught allies and Congress by surprise when it blocked the consultative commission against certifying a new Russian Open Skies plane and its associated digital sensors. The United States eventually relented, but the incident served as a reminder of the administration’s disrespect for multilateral agreements that allies support.22

September’s diplomatic dust-up had followed a late 2017 act of apparent neglect that resulted in no regularly planned Open Skies flights for 2018. Unlike in previous years, the United States and other partners had failed to coordinate on a plan for navigating a long-running dispute between Russia and Georgia. As a result, the treaty states-parties did not reach agreement on a regular schedule of flights for 2018.23 The same mistake did not happen in October 2018, and a regular program of flights is back on schedule for 2019.24

Not content to stop at Russian aircraft, Congress has gotten in the way of upgrades to U.S. observation aircraft, as well. The Department of Defense has been seeking funds to overhaul and replace the 1960s-era OC-135B aircraft and its film-based cameras. According to Secretary of Defense Jim Mattis, in 2017 the United States could not complete roughly one-third of its scheduled Open Skies missions over Russia.25 In May 2018, the Omaha World-Herald revealed one U.S. flight crew’s harrowing experience during a 2016 mission over Russia, when an equipment failure caused one unplanned landing and then a cabin fire forced an emergency landing on the second attempt to leave Russia.26

The Republican-controlled House Armed Services Committee nevertheless led Congress in 2018 in putting restrictions on the funding for replacing the aging aircraft and its outdated film camera unless the administration imposes reciprocal measures for Russia’s compliance shortfalls.27 In a hopeful turnaround for the treaty, however, a month after imposing those restrictions, Congress nevertheless appropriated nearly $150 million for two replacement observation aircraft.28

All this adds up to a few positive signs and a treaty that will still be in serious danger without a more concerted effort to actually fix the problems and get matters back on track. It would be reckless to keep going down this route; none of what has been going wrong with the Open Skies Treaty should be enough to risk losing what is right with it.

A Worthy Fight

For the last 16 years, the United States made the most of the treaty, overflying Russia nearly three times as often as the Russia overflew the United States.29 Whatever the treaty’s shortcomings, the United States should strive to preserve a right for nations across the transatlantic region to collectively acquire images that distinguish tanks from trucks in all weather. Despite the problem areas, the overwhelming majority of Russia is available for overflights. With tensions between Russia and NATO on the rise, the treaty’s goal to provide mutual transparency is more important than ever.

Some U.S. critics have dismissed the value of imagery obtained under the treaty.30 They assert that the United States can get the same or better pictures from its own intelligence satellites while other countries could rely on intelligence shared by Washington or use commercial satellite digital imagery. Conversely, in 2016 testimony before the House Armed Service Committee, the director of the Defense Intelligence Agency, Lieutenant General Vincent Stewart, mused that Russia could use processing techniques on treaty-obtained digital imagery to somehow gain an unfair advantage.31

The critics’ contentions are all faulty. The U.S. government had the chance to thoroughly examine the new Russian sensor and aircraft after the initial questions were raised. It certified that both fully fit within the treaty’s guidelines. It is also difficult to reconcile the call for relying solely on commercial digital imagery with the fear about processing lower-resolution, treaty-obtained digital imagery. Russia presumably could apply the same processing techniques to commercially obtained digital satellite imagery as would be applied to imagery acquired through the treaty.

As for U.S. flights over Russia, satellite imagery can surpass the limited resolution of cameras aboard Open Skies flights, but planes enjoy much more flexibility in choosing flight paths. The three to four days’ warning that observed countries get before a satellite overpass gives them ample time to move military assets. Treaty flights provide only 24 hours’ notice, increasing the odds that overflights capture an accurate assessment. Planes can also double back to provide a more comprehensive set of images than fixed-orbit satellites can.

Danish jets accompany a Russian An-30 aircraft during an Open Skies Treaty observation flight over the territory of Denmark on  June 12, 2008. (Photo: OSCE)Moreover, every party, observers and observed, can see the same set of certified Open Skies pictures. Any time the United States challenges Russia over new misbehavior in the region, Russia will look to exploit the public mistrust that still lingers from faulty U.S. claims about Iraq. The United States benefits immensely from having common Open Skies images that offer an indisputable level of authenticity and do not force the United States to expose its own intelligence means. Besides, 15 years after Iraq, many poorer, smaller allies would be loathe to lose Open Skies imagery and become the United States’ imagery intelligence client-state.

The treaty-mandated collaboration helps build confidence in its own right. The treaty forces countries’ military and government officials to work with one another, jointly solve air traffic or other logistical questions, inspect planes together, and confront problems in a broadly inclusive, transatlantic diplomatic framework. All these acts and the choice by the larger powers to submit themselves to them increase mutual trust and predictability.

This is why U.S. allies are voting for the Open Skies Treaty with their wallets, investing large sums in new Open Skies planes and digital sensors. They reject suggestions of nefarious activities connected to overflights; no treaty party has ever tried to employ prohibited technology during a flight. They know that the incredibly intrusive pre-flight inspection process, in which an aircraft is all but taken apart, should remove concerns that any observing party is somehow capturing unauthorized information. They appreciate that the treaty even lets a nervous observed country insist that its own Open Skies plane be used for an observation flight.

Mattis also apparently values the national security benefits of the treaty enough to invest more in it. “In order to maximize U.S. benefits from the Treaty,” Mattis wrote, “the United States needs to recapitalize and modernize its sensors and aircraft.”32 Mattis’s advocacy looks more and more likely to set up a showdown at some point with Bolton. When that happens, the fate of a national security legacy passed down from Eisenhower and Bush may hang in the balance.

A Squandered Inheritance?

Bush used his 1989 Open Skies proposal to test the Soviet Union’s commitment to changing its relationship with the world. The U.S. approach toward the treaty now will test its own commitment to a once-honored U.S. strategy of using adroit diplomacy and collective action to secure key national security interests.

It is no coincidence that Bush, the last World War II military veteran to serve as president, valued an arms control concept put forward by Eisenhower, the first World War II vet to occupy the Oval Office. They, along with President John Kennedy, another combat veteran of that war, grasped the urgency of averting modern great-power war because they survived the worst conflict the world had ever known. They understood the true costs of war. They knew that avoiding war between great powers was at least as important as any thoughts about “winning” such a war.

To be sure, the Open Skies Treaty by itself will not guarantee that major conflicts will never return to the Euro-Atlantic region. Yet, the treaty joins other arms control agreements and a larger institutional order to form a safety net that has kept the world from falling back into the chaos and destruction of great-power war. There can be no doubt that, with each and every discarded international agreement, the inherited safety net frays and the United States slips further down an uncertain and unsafe path.

Opponents of arms control thrive on attacking the shortcomings of each treaty or agreement one by one. The compliance problems are easy to see, while most of a treaty's benefits only truly reveal themselves in the shadow left by their absence. The full potential of each individual treaty or agreement can only be seen if it sits within a larger, complementary ecosystem of other agreed rules and behaviors.

More difficult still to prove, but perhaps most important of all, is the benefit that comes from the spirit of collaboration and mutual problem solving required of the leaders who create and sustain arms control treaties and agreements. As valuable as the Open Skies Treaty has been and will continue to be, the real inheritance that Bush left was the example he set in forging the treaty in the first place. He was fundamentally committed to working cooperatively with heavily armed adversaries to avoid the mutual catastrophe of war, even when doing so meant assuming new obligations and denying himself the fantasy that instead he should simply aim to destroy those adversaries.

Walking away from a treaty that Eisenhower imagined and that Bush built would cost more than the national security insights lost and the alliance resentments generated. Rejecting the treaty would be one more step away from the spirit of confidence, patience, and problem solving that made the treaty possible in the first place.

The Open Skies Treaty has existed mostly out of sight, but its dissolution would be felt across the Euro-Atlantic region. As the United States continues to reflect on the passing of a president who led us out of a Cold War, it is important to sustain the legacy he left behind.



1. “Legal Agreement Pertaining to the Oral History Interview of Harold E. Stassen,” National Archives and Records Administration, February 4, 1994, p. 7, https://www.eisenhower.archives.gov/research/oral_histories/oral_history_transcripts/Stassen_Harold_519.pdf (interview of April 29, 1977); See FiveThirtyEight, “How Popular Is Donald Trump?” n.d., https://projects.fivethirtyeight.com/trump-approval-ratings/ (accessed October 25, 2018).

2. W.W. Rostow, Concept and Controversy: Sixty Years of Taking Ideas to Market (Austin: University of Texas Press, 2010), p. 166.

3. George H.W. Bush, “Commencement Address at Texas A&M University,” May 12, 1989, https://millercenter.org/the-presidency/presidential-speeches/may-12-1989-commencement-address-texas-am-university.

4. The Treaty on Open Skies, March 24, 1992, https://www.osce.org/library/14127?download=true.

5. “Treaty on Open Skies: Report,” Executive Report 103-5, 103rd Congress, 1st Session, August 2, 1993, p. 141.

6. Bureau of Arms Control, Verification, and Compliance (AVC), U.S. Department of State, “Key Facts About the Open Skies Treaty,” June 6, 2016, https://2009-2017.state.gov/t/avc/rls/2016/258061.htm.

7. U.S.-Russia Nuclear Arms Negotiations: Ukraine and Beyond; Joint Hearing Before the Subcommittee on Terrorism, Nonproliferation, and Trade and the Subcommittee on Europe, Eurasia, and Emerging Threats of the Committee on Foreign Affairs, 113th Cong. 13 (2014) (testimony of Anita E. Friedt, principal deputy assistant secretary for nuclear and strategic policy, AVC).

8. U.S. Department of Defense, “DOD Statement on Open Skies Flight Over Ukraine,” December 6, 2018, https://dod.defense.gov/News/News-Releases/News-Release-View/Article/1703977/dod-statement-on-open-skies-flight-over-ukraine/.

9. 139 Cong. Rec. 10801 (1993) (remarks of Senator Claiborne Pell [D-R.I.]).

10. U.S. Delegation, Open Skies Consultative Commission, “Open Skies Treaty Observation Flights 2017,” OSCC.DEL/2/18, May 8, 2018, https://www.state.gov/documents/organization/282711.pdf. The total number includes an extraordinary flight flown on December 6, 2018.

11. AVC, “Key Facts About the Open Skies Treaty,” June 6, 2016, https://2009-2017.state.gov/t/avc/rls/2016/258061.htm.

12. AVC, “2018 Report on Adherence to and Compliance With Arms Control, Nonproliferation, and Disarmament Agreements and Commitments,” April 2018, p. 8, https://www.state.gov/documents/organization/280774.pdf (hereinafter 2018 AVC report); AVC, “2017 Report on Adherence to and Compliance With Arms Control, Nonproliferation, and Disarmament Agreements and Commitments,” April 14, 2017, https://www.state.gov/t/avc/rls/rpt/2017/270330.htm#OST (hereinafter 2017 AVC report).

13. “Turkey Dismisses Russia’s Charges Over Breaking Aviation Treaty,” Hurryiet Daily News, February 4, 2016.

14. U.S. government officials, discussions with author, Washington, D.C., November 2018

15. Brett Forrest and Nathan Hodge, “In Tiff With Russia, U.S. Moves to Restrict International Military Flights Over Hawaii,” The Wall Street Journal, September 28, 2017.

16. Aaron Mehta, “U.S., Russia Remain at ‘Impasse’ Over Open Skies Treaty Flights,” Defense News, September 14, 2018.

17. 2018 AVC report.

18. 2017 AVC report.

19. Carl Levin and Howard P. “Buck” McKeon National Defense Authorization Act for Fiscal Year 2015, Pub. L. No. 113–29, sec. 1242.

20. National Defense Authorization Act for Fiscal Year 2016, Pub. L. No. 114–92, sec. 1244.

21. John S. McCain National Defense Authorization Act for Fiscal Year 2019, Pub. L. No. 115–232, sec. 1242.

22. Kingston Reif, “U.S. Reverses Course on Open Skies Treaty,” Arms Control Today, October 2018, https://www.armscontrol.org/act/2018-10/news/us-reverses-course-open-skies-treaty.

23. Ibid.; U.S. government officials, discussions with author, Washington, D.C., November 2018.

24. Open Skies Consultative Commission, “Decision No. 2/18: Distribution of Active Quotas for Observation Flights in the Year 2019,” OSCC.DEC/2/18, October 22, 2018, https://www.state.gov/documents/organization/287236.pdf.

25. Jim Mattis, Letter to Senator Deb Fischer, May 22, 2018, https://www.fischer.senate.gov/public/_cache/files/b2df2cf7-3828-4d81-aa57-2963ce8d70b0/sd-response-to-senator-fischer-regarding-the-open-skies-treaty-osd070739-18.pdf (hereinafter Mattis letter).

26. Steve Liewer, “Despite Danger to Offutt Crews, U.S. House Drops New Open Skies Jets From 2019 Budget,” Omaha World-Herald, May 16, 2018.

27. Center for Arms Control and Non-Proliferation, “Analysis of Fiscal Year 2018 National Defense Authorization Bill: HR 2810,” n.d., https://armscontrolcenter.org/wp-content/uploads/2017/11/NDAA-conference-analysis-111417.pdf.

28. Office of Senator Deb Fischer, “Fischer, Fortenberry, Bacon Applaud Open Skies Funding in FY2019 Defense Funding Bill,” September 14, 2018, https://www.fischer.senate.gov/public/index.cfm/2018/9/fischer-fortenberry-bacon-applaud-open-skies-funding-in-fy2019-defense-funding-bill.

29. AVC, “Key Facts About the Open Skies Treaty.”

30. Edward R. Royce, Devin Nunes, and William M. “Mac” Thornberry, Letter to President Barack Obama, June 14, 2016.

31. World Wide Threats; Hearing Before the Committee on Armed Services, 114th Cong. 13 (2016), https://www.govinfo.gov/content/pkg/CHRG-114hhrg99649/pdf/CHRG-114hhrg99649.pdf (testimony of Lt. Gen. Vincent R. Stewart, director, Defense Intelligence Agency).

32. Mattis letter.


Alexandra Bell is senior policy director at the Center for Arms Control and Non-Proliferation. Anthony Wier is legislative secretary for nuclear disarmament and Pentagon spending at the Friends Committee on National Legislation.



With tensions between Russia and NATO on the rise, the treaty’s goal to provide mutual transparency is more important than ever.

U.S. Conducts Special Open Skies Flight

January/February 2019
By Kingston Reif

The United States and several allies on Dec. 6 conducted an “extraordinary flight” over eastern Ukraine under the Open Skies Treaty, the first and only treaty flight worldwide during 2018.

A U.S. Air Force OC-135B Open Skies aircraft parked on a ramp at Offutt Air Force Base, Neb., September 14, 2018. (Photo: U.S. Air Force)The flight followed a Russian attack in late November on Ukrainian naval vessels in the Black Sea and as Ukraine said Russia has been increasing its forces near its border with Ukraine.

The U.S. Defense Department said U.S., Canadian, French, German, Romanian, UK, and Ukrainian observers were aboard the OC-135B aircraft during the observation flight, which was requested by Ukraine.

“The timing of this flight is intended to reaffirm U.S. commitment to Ukraine and other partner nations,” the Defense Department said in a Dec. 6 news release.

“Russia's unprovoked attack on Ukrainian naval vessels in the Black Sea near the Kerch Strait is a dangerous escalation in a pattern of increasingly provocative and threatening activity,” the statement added.

The treaty, which entered into force in 2002 and has 34 states-parties, aims to increase confidence in and transparency of military activities, particularly in Europe, by allowing unarmed aerial observation flights over the entire territory of its participants for information-gathering purposes. The parties have yearly quotas on overflights and must make the information they acquire available to all treaty parties.

For example, the treaty permits up to 42 overflights of Russia by states-parties, of which 16 can be flown by the United States.

A dispute between Georgia and Russia over the inclusion of Russian observers on treaty flights over Georgia prevented agreement on quotas for 2018, thereby freezing flights for all member states.

But the treaty includes a provision allowing for two states-parties “on a bilateral and voluntary basis to conduct observation flights over the territory of each other.” The last such extraordinary observation flight over Ukraine took place in 2014 as part of the U.S. response to Russia’s annexation of Crimea.

Normal flights appear set to resume in 2019. States-parties at an Oct. 22 meeting of the Open Skies Consultative Commission, the treaty’s implementing body, agreed to active quotas for observation flights this year.

In recent years, disputes over implementation and concerns from some U.S. officials and lawmakers about the value of the treaty have threatened to derail the pact.

The agreement on quotas for 2019 followed a U.S. decision in September not to certify a new Russian aircraft outfitted with an upgraded digital electro-optical camera for flights under the treaty, a decision that was reversed several days later. (See ACT, October 2018.)

Washington for several years has raised numerous concerns about Russian compliance with the pact. The State Department’s annual compliance report released in April determined that Russia is violating the treaty by restricting observation flights over Kaliningrad, which is a sensitive Russian enclave between Poland and Lithuania, to no more than 500 kilometers, and within a 10-kilometer corridor along Russia’s border with the Georgian border-conflict regions of South Ossetia and Abkhazia.

The United States said the 500-kilometer restriction is about half the distance needed to fully cover Kaliningrad and, in response, has placed restrictions on some of Russia’s treaty flights.

Andrea Thompson, U.S. undersecretary of state for arms control and international security, told the Senate Foreign Relations Committee on Sept. 18 that “recently Russia has resolved one violation of its obligations and has made overtures that suggest it could resolve another.” But she added that Russia had refused to address the violation related to Kaliningrad.

The Open Skies Treaty has also become a point of contention in Congress. (See ACT, July/August 2018.)

The fiscal year 2019 defense authorization act, signed into law by President Donald Trump on Aug. 13, waters down language in the original U.S. House of Representatives version of the bill that would have blocked the Air Force’s budget request to replace the aircraft that the United States uses to conduct Open Skies Treaty flights, including over Russia. Instead, the law conditions funding necessary to acquire an upgraded digital imaging system for treaty flights and implement certain decisions of the treaty’s implementing body.

Treaty dispute with Russia grounded routine transparency overflights last year.

GOP Takes Aim at Surveillance Treaty

July/August 2018
By Kingston Reif

Republicans on a key House committee are ratcheting up their campaign to cripple the Open Skies Treaty despite protests from the Pentagon and U.S. allies that such a move would benefit Russia.

An OC-135B Open Skies aircraft takes off from Offutt Air Force Base, Neb.  (Photo: Josh Plueger)The House Armed Services Committee proposed in May to block the Air Force’s request to replace the aircraft that the United States uses to conduct treaty flights, including over Russia. But in a letter to Sen. Deb Fischer (R-Neb.), the top Republican on the Senate Armed Services strategic forces subcommittee, Defense Secretary Jim Mattis said that, despite Russian violations of the treaty, “it is in our nation’s best interest to remain a party” to the pact.

“In order to maximize U.S. benefits from the Treaty, the United States needs to recapitalize and modernize its sensors and aircraft,” Mattis added. “The 1960s-era U.S. Open Skies aircraft are ill-suited to extreme operating environments in Russia and experience regular, unplanned maintenance issues, often resulting in mission delays or cancellations.”

The Treaty on Open Skies, which entered into force in 2002 and has 34 states-parties, aims to increase confidence in and transparency of military activities, particularly in Europe, by allowing unarmed aerial surveillance flights over the entire territory of its participants for information-gathering purposes. The parties have equal yearly quotas of overflights and must make the information they acquire available to
all treaty parties.

The treaty permits up to 42 overflights of Russia by states-parties, of which 16 can be flown by the United States.

Washington for several years has raised numerous concerns about Russian compliance with the pact. The State Department’s annual compliance report released in April determined that Russia is violating the treaty by restricting observation flights over Kaliningrad, which is a sensitive Russian enclave between Poland and Lithuania, to no more than 500 km, and within a 10-kilometer corridor along Russia’s border with the Georgian border-conflict regions of South Ossetia and Abkhazia.

In response, the United States has placed restrictions on some of Russia’s treaty flights.

Separate from the compliance concerns, treaty critics in Congress argue the Russia’s flights, which now employ more advanced sensors and cameras as allowed by the treaty, amount to spy missions.

Lt. Gen. Vincent Stewart, then-director of the Defense Intelligence Agency, told the House Armed Services Committee in March 2016 that he has “great concern about the quality of the [digital] imagery” for intelligence collection purposes and “would love to deny the Russians” that capability. (See ACT, March 2016.)

The Pentagon is in the process of transitioning to the more advanced digital sensors in its treaty flights over Russia. Even so, critics claim that commercial satellite imagery can provide higher-quality photos and videos than those taken on U.S. treaty flights.

In his May letter to Fischer, Mattis countered that the imagery produced on treaty flights “is verifiable and unclassified, which allows for its use in international or bilateral fora.” He noted that, in 2014, treaty imagery was “a key visual aid during U.S. engagement with allies and Russia regarding the military crisis in Ukraine.”

Meanwhile, the two OC-135B aircraft that the United States uses for treaty flights are increasingly unreliable, resulting in mission delays and cancellations. In 2017 the United States completed only 64 percent of its scheduled Open Skies missions over Russia, according to Mattis.

The House-passed version of the fiscal year 2018 National Defense Authorization Act would have barred the Pentagon from acquiring an upgraded digital imaging system for treaty flights. The Senate version of the bill did not include such a provision.

The Trump administration strongly objected to the House proposal. In a statement of policy on the bill, the White House said the prohibition would “prevent the United States from keeping pace with Russian Open Skies aircraft sensor upgrades, fully implementing the Open Skies Treaty, and increasing the value of the treaty to United States national security.”

Following negotiations between the two chambers, the final version of the authorization act conditioned funding for the new cameras and sensors on the receipt of two certifications. (See ACT, December 2017.) The first certification requires the defense secretary to confirm that the new cameras and sensors “will provide superior digital imagery as compared to digital imagery” commercially available to the Defense Department. The second certification requires the president or secretary of state confirm that Washington has imposed costs on Russia for its violation of the treaty. Neither certification has been provided to Congress.

The House has taken an even more aggressive approach this year, turning its attention toward preventing the Pentagon from replacing the OC-135B aircraft. The chamber’s version of the fiscal year 2019 National Defense Authorization Act, which passed the House in May, would eliminate the Pentagon’s $222 million request to buy new planes.

In addition, the bill would prevent the United States from participating in or implementing decisions made at the Open Skies Consultative Commission, the pact’s implementing body, to approve requests made by parties to the treaty to upgrade their digital sensor systems until several requirements are met.

These requirements include a certification that Russia has returned to compliance with the treaty and the submission of a report on the value of the treaty. Among the required elements of the report is “a plan, and its estimated comparative cost, to replace the treaty architecture with an increased sharing of overhead commercial imagery, consistent with United States national security, with covered state parties, excluding the Russian Federation.”

The Trump administration once again objected to the House proposal. In its statement of policy on the House bill, the White House said that “modern, capable, and cost-effective aircraft” are needed to replace the current unreliable OC-135Bs.

In contrast, the Senate version, which passed in June, would condition funding to upgrade the digital imaging system until the administration provides the certifications required by the fiscal year 2018 bill.

House and Senate leaders are hoping to reconcile differences in the bills and send a final version to the president by the end of July.

In the Senate, the fight for funding is being led by the two Republicans from Nebraska, who have a home-state interest. The OC-135Bs are based at Offutt Air Force Base near Omaha.

Fischer told the Omaha World-Herald in May that “if we don’t have the planes to complete the mission, we’re not hurting the Russians.… We’re hurting ourselves.”

Rep. Don Bacon (R-Neb.) echoed similar sentiments in an interview with the Daily Beast. “While Russia has chosen not to comply with some provisions [of the treaty], they generally adhere to the rest,” he said. “We need them to return to full compliance. Defunding our own aircraft doesn’t hurt them, it only hurts us.”

Anthony Wier, a former State Department and Senate official who worked on Open Skies Treaty implementation issues, told Arms Control Today in a June 21 interview that the effort to hollow out the treaty is based on the theory that there are alternative ways to collect the imagery it provides. But Wier, who is currently at the Friends Committee on National Legislation, noted that the agreement provides the United States and its allies “with imagery we cannot get any other way” and that the flights strengthen ties between the United States and its allies and reassure non-NATO members on Russia’s periphery.

Undermining the treaty, he continued, would further alienate the European allies of the United States, who are seething in the wake of Trump’s unilateral withdrawal from the Iran nuclear deal.

“We stay in Open Skies not to do favors for the Russians or anybody else, but because being able to fly a camera low and slow over Russian territory many times a year is in America’s interest,” Wier said.

The original version of this article misstated the nature of the U.S. concern regarding Russia's restriction of Open Skies Treaty flights over Kaliningrad. 

Critics of the Open Skies Treaty seek to block the Pentagon’s request for funding to modernize U.S. reconnaissance aircraft and sensors.

Nuclear Restraint Agreements Under Serious Threat



Volume 9, Issue 7, September 5, 2017

Since the dawn of the nuclear age over 70 years ago, rarely has the world faced as difficult an array of nuclear weapons-related security challenges as it is facing now. Unfortunately, Congress will soon enact legislation that could further imperil the global nuclear order.
The Senate is scheduled to take up the Fiscal Year (FY) 2018 National Authorization Act as early as this week. The House approved its version of the NDAA July 14 by a vote of 344-81. Both bills contain several problematic provisions that if enacted into law would deal a major, if not mortal, blow to several longstanding, bipartisan arms control and nonproliferation efforts and increase the risks of renewed nuclear arms competition with Russia.

U.S. President Ronald Reagan and Soviet General Secretary Mikhail Gorbachev sign the Intermediate-Range Nuclear Forces Treaty in the East Room of the White House on December 8, 1987. (Photo credit: Ronald Reagan Presidential Library)Tensions between the U.S. and Russia have worsened over the past few years, thanks to Moscow’s election interference, annexation of Crimea, continued destabilization of Ukraine, alleged violation of the 1987 Intermediate Nuclear Forces Treaty (INF) and support for the Assad regime in Syria. Nevertheless, the two countries continue to share common interests. In particular, as the possessors of over 90 percent of the roughly 15,000 nuclear weapons on the planet, they have a special responsibility to avoid direct conflict and reduce nuclear risks. The downward spiral in relations makes these objectives all the more urgent.
While some meaningful cooperation continues, such as adherence to the 2010 New Strategic Arms Reduction Treaty and implementation of the 2015 Iran nuclear deal, there is no ongoing dialogue on further nuclear risk reduction steps.
Instead of rushing to hasten their demise, Congress must seek to preserve and strengthen the existing architecture of arms control and nonproliferation agreements, key pillars of which have their origin in the vision of President Ronald Reagan. These agreements constrain Russia’s nuclear forces, provide for stability, predictability, and transparency in the bilateral relationship, and have only increased in value as the U.S.-Russia relationship has deteriorated.
Below is a summary of the current status and arguments in support of four key agreements put at risk by the Senate and/or House NDAAs. 

The 2010 New Strategic Arms Reduction Treaty (New START)
Background: The New Strategic Arms Reduction Treaty (New START) requires that the United States and Russia each reduce their deployed strategic nuclear forces to no more than 1,550 warheads and 700 delivery systems by 2018. The agreement, which is slated to expire in 2021, can be extended by up to five years if both Moscow and Washington agree.
Current Status: So far both sides are implementing the agreement and there are no indications that they do not plan to continue to do so. Russia has indicated that it is interested in beginning talks with the United States on extending the treaty, but the Trump administration has yet to respond to these overtures. In January phone call with President Putin, President Trump reportedly dismissed the idea of an extension and called the treaty a “bad deal.” The House-passed version of the Fiscal Year 2018 National Defense Authorization Act (NDAA) would prohibit the use of funds to extend the New START treaty unless Russia returns to compliance with the 1987 Intermediate Range Nuclear Forces (INF) Treaty.

At-a-Glance Factsheet: https://www.armscontrol.org/factsheets/NewSTART

Key Points:

  • New START caps the size of Russia’s nuclear arsenal and provides the United States with additional tools to monitor Russia’s forces. The treaty includes a comprehensive suite of monitoring and verification provisions that help ensure compliance with treaty limits and enable the United States to verify the size and composition of the Russian nuclear stockpile, which aids U.S. military planning.
  • The deterioration of the U.S.-Russian relationship has only increased the value of New START. The treaty provides for bilateral stability, predictability, and transparency, thereby bounding the current tensions between the world’s two largest nuclear powers.
  • The U.S. military and U.S. allies continue to strongly support New START. For example, in March 2017, Gen. John Hyten, the commander of U.S. Strategic Command, told the House Armed Services Committee (HASC), “I am big supporter of the New START Agreement.” Hyten added that “bilateral, verifiable arms control agreements are essential to our ability to provide an effective deterrent.”
  • Connecting New START extension with INF treaty compliance is senseless and counterproductive. By “punishing” Russia’s INF violation in this way, the United States would simply free Russia to expand the number of strategic nuclear weapons pointed at the United States after New START expires in 2021. If the treaty is allowed to lapse, there will be no limits on Russia’s strategic nuclear forces for the first time since the early-1970s. Moreover, the United States would have fewer tools with which to verify the size and composition of the Russian nuclear stockpile.

The 1987 Intermediate-Range Nuclear Forces (INF) Treaty
Background: The 1987 Intermediate-Range Nuclear Forces (INF) Treaty required the United States and Soviet Union to eliminate and permanently forswear all nuclear and conventional ground-launched ballistic and cruise missiles with ranges of 500-5,500 kilometers. Russia and the United States destroyed a total of 2,692 short/medium/intermediate-range missiles by the 1991 deadline.
Current Status: The United States has accused Russia of testing and deploying ground-launched cruise missiles in violation of the treaty. Moscow denies it is violating the agreement, and instead has accused Washington of breaching the accord. Both the House-passed and Senate Armed Services Committee versions of the FY 2018 NDAA would authorize programs of record and provide funding for research and development on a new U.S. road-mobile GLCM with a range of between 500 and 5,500 kilometers. The House bill also includes a provision stating that if the president determines that Russia remains in violation of the treaty 15 months after enactment of the legislation, the prohibitions set forth in the treaty will no longer be binding on the United States. A similar provision could be offered as an amendment to the Senate bill.

At-a-Glance Factsheet: https://www.armscontrol.org/factsheets/INFtreaty
Key Points:

  • The United States and Russia need to work to preserve the INF Treaty. This should include using the Special Verification Commission, the treaty’s dispute resolution mechanism, to address mutual concerns. The Trump administration should make it clear to Moscow that so long as Russia remains in violation of the treaty, the United States will pursue steps to reaffirm and buttress its commitment to the defense of those allies threatened by the treaty-noncompliant missiles.
  • Development of a new GLCM sets the stage for Washington to violate the agreement and would take the focus off Russia's violation. Russia could respond by publicly repudiating the treaty and deploying large numbers of noncompliant missiles without any constraints.
  • Development of a new GLCM is militarily unnecessary and Pentagon has not asked for one. The United States can legally deploy air- and sea-launched systems that can threaten the same Russian targets. There is no reason to believe that development of a new GLCM will convince Russia to return to compliance. A new GLCM would also take years to develop and suck funding from other military programs for which there are already requirements. The administration's statement of policy on the House NDAA objected to the INF provision on requiring a new GLCM.
  • NATO does not support a new GLCM and attempting to force it upon the alliance would be incredibly divisive. It is thus a weapon to nowhere. A divided NATO would also be a gift to Russia.
  • Mandating that the United States in effect withdraw from the INF treaty if Russia does not return to compliance by the end of next year raises constitutional concerns. If Congress can say the United States is not bound by its obligations under the INF Treaty, what is to stop it from doing the same regarding other treaties?

The 1990 Treaty on Open Skies
Background: The Treaty on Open Skies, which entered into force in 2002 and has 34 states parties, aims to increase confidence in and transparency on the military activities of states, particularly in Europe, by allowing unarmed aerial surveillance flights over the entire territory of its participants for information gathering purposes. The parties have equal yearly quotas of overflights and must make the information they acquire available to all Treaty parties.
Current Status: The United States has raised numerous concerns about Russia’s compliance with the treaty. Republican lawmakers have voiced concern that Russian flights under the treaty, which now employ more advanced sensors and cameras as allowed by the treaty, amount to spy missions. The House-passed version of the FY 2018 NDAA would annually bar, for each of the next five years, any U.S. Open Skies Treaty skies flights until Pentagon and intelligence community submit a plan for all of the treaty flights in the coming year. The bill would also bar DOD from acquiring a more effective, more timely, more reliable digital imaging system for conducting flights over Russian territory.

At-a-Glance Factsheet: https://www.armscontrol.org/factsheets/openskies

Key Points:

  • The Open Skies Treaty provides a significant contribution to the security and stability of North America and Europe. According to Principal Deputy Assistant Secretary of State for Nuclear and Strategic Policy Anita E. Friedt, almost a dozen U.S. and NATO member flights over Ukraine and Western Russia in 2014 during the Ukraine crisis “resulted in valuable data and insights.” The treaty mandates information-sharing about military forces that increases transparency among members, thereby contributing to stability and improving each participating state’s national security.
  • U.S. allies continue to value and rely on the Open Skies Treaty for imagery collection. The United States and its allies typically carry out many more overflights than Russia. These flights strengthen ties between the United States and its allies and reassure non-NATO members on Russia’s periphery.
  • Russia would gain a unilateral advantage as a result of restricting funding for upgrading aircraft used by the United States for treaty observation flights. This would stymie U.S. efforts to match Russian sensor upgrades, thereby limiting the value of the Open Skies treaty to U.S. national security.
  • The Russian sensors and cameras in question do not pose a threat to U.S. security. According to Vice Admiral Terry Benedict, director of Navy Strategic Systems Programs, all states party to the Open Skies treaty are permitted to certify new sensors and aircraft. Furthermore, he said, “the resolution of Open Skies imagery is similar to that available in commercial satellite imagery.” He added that Russian information compiled as a result of Open Skies flights is “of only incremental value” among Russia’s many means of intelligence gathering. 

The Comprehensive Test Ban Treaty Organization (CTBTO)
Background: The Comprehensive Test Ban Treaty Organization (CTBTO) is the the intergovernmental organization that promotes the 1996 Comprehensive Test Ban Treaty (CTBT), which has yet to enter force, and maintains the global International Monitoring System (IMS) to deter and detect nuclear test explosions.
Current Status: The United States currently contributes nearly a quarter of the annual CTBTO budget. In April 2017, Secretary of State Rex Tillerson joined with other Foreign Ministers at the G-7 foreign minister summit in a statement expressing support for the CTBTO. The Trump administration’s FY 2018 budget request would fund the U.S. contribution to the CTBTO at roughly the same level as the Obama administration. The House-passed version of the FY 2018 NDAA would prohibit funding for the CTBTO and calls on Congress to declare that the September 2016 UN Security Council Resolution 2310 does not “obligate…nor does it impose an obligation on the United States to refrain from actions that would run counter to the object and purpose” of the CTBT.

At-a-Glance Factsheet: https://www.armscontrol.org/factsheets/test-ban-treaty-at-a-glance

Key Points:

  • The CTBTO and IMS support and provide detection capabilities that supplement U.S. national intelligence capabilities to detect nuclear testing. Reducing U.S. funding for the CTBTO would  adversely impact the organization’s ability to operate and maintain existing nuclear test monitoring stations. This is due to the fact that a wide range of organization’s personnel and assets directly or indirectly support the IMS.
  • The CTBTO is a neutral source of information that can help to mobilize international action against any state that violates the global norm against nuclear testing. U.S. action to restrict funding could prompt other states to reduce their own funding for the CTBTO or lead states to withhold data from CTBTO monitoring stations that are based in their territory, thus undermining the capabilities of the system to detect and deter clandestine nuclear testing. Contrary to what the Cotton-Wilson bill implies,
  • Resolution 2310 (which was endorsed by 42 states, including Israel) does not impose any new obligations on the United States. Rather, it encourages states to “provide the support required” to the CTBTO and the IMS, and urges states to refrain from nuclear testing and urges those states that have not ratified to do so. It also takes note of a Sept. 15 joint statement by the five permanent Security Council members that formally “recognized” that a nuclear explosion would “defeat the object and purpose of the CTBT.” 
  • Asserting that the United States is not required to respect our obligations as a CTBT signatory would signal to other states that that the United States may be seeking to back out of its commitment to a global and verifiable nuclear test ban and is considering the resumption of nuclear testing. With North Korea having conducted a sixth nuclear test explosion, it is essential that the United States reinforce, not undermine, the CTBTO and the global nuclear testing taboo. 

—KINGSTON REIF, director for disarmament and threat reduction policy


Instead of rushing to hasten their demise, Congress must seek to preserve and strengthen these four key pillars of arms control and nonproliferation.

Country Resources:

The Open Skies Treaty at a Glance

October 2012

Contacts: Daryl Kimball, Executive Director, (202) 463-8270 x107

Updated: October 2012

Signed March 24, 1992, the Open Skies Treaty permits each state-party to conduct short-notice, unarmed, reconnaissance flights over the others' entire territories to collect data on military forces and activities. Observation aircraft used to fly the missions must be equipped with sensors that enable the observing party to identify significant military equipment, such as artillery, fighter aircraft, and armored combat vehicles. Though satellites can provide the same, and even more detailed, information, not all of the 34 treaty states-parties1 have such capabilities.  The treaty is also aimed at building confidence and familiarity among states-parties through their participation in the overflights.

President Dwight Eisenhower first proposed that the United States and the Soviet Union allow aerial reconnaissance flights over each other's territory in July 1955. Claiming the initiative would be used for extensive spying, Moscow rejected Eisenhower's proposal. President George H.W. Bush revived the idea in May 1989 and negotiations between NATO and the Warsaw Pact started in February 1990.

Treaty Status: The treaty entered into force on January 1, 2002. Twenty-six of the treaty’s initial 27 signatories have ratified the accord and are now states-parties. Since the treaty entered into force, Bosnia and Herzegovina, Croatia, Estonia, Finland, Latvia, Lithuania, Slovenia, and Sweden have become states-parties. Russia conducted the first observation flight under the treaty in August 2002, while the United States carried out its first official flight in December 2002. In 2008, states-parties celebrated the 500th overflight and since then the number of flights flown has risen to more than 800.

Territory: All of a state-party's territory can be overflown. No territory can be declared off-limits by the host nation.

Flight Quotas: Every state-party is obligated to accept a certain number of overflights each year, referred to as its passive quota, which is loosely determined by its geographic size.2 A state-party's active quota is the number of flights it may conduct over other states-parties. Each state-party has a right to conduct an equal number of flights over any other state-party that overflies it. A state-party's active quota cannot exceed its passive quota, and a single state-party cannot request more than half of another state-party's passive quota.

Process: An observing state-party must provide at least 72 hours' advance notice before arriving in the host country to conduct an overflight. The host country has 24 hours to acknowledge the request and to inform the observing party if it may use its own observation plane or if it must use a plane supplied by the host. At least 24 hours before the start of the flight, the observing party will supply its flight plan, which the host has four hours to review. The host may only request changes in flight plans for flight safety or logistical reasons. If it does so, the two states-parties have a total of eight hours after submission of the original flight plan to agree on changes, if they fail, the flight can be cancelled. The observation mission must be completed within 96 hours of the observing party's arrival unless otherwise agreed.3 Although state-parties are allowed to overfly all of a member’s territory, the treaty determines specific points of entry and exit, and refueling airfields. The treaty also establishes ground resolution thresholds for the onboard still and video cameras. The aircraft and its sensors must undergo a certification procedure before being allowed to be used for Open Skies in order to confirm that they do not exceed the allowed resolutions.

Aircraft: The treaty lays out standards for aircraft used for observation flights. Aircraft may be equipped with four types of sensors: optical panoramic and framing cameras, video cameras with real-time display, infra-red line-scanning devices, and sideways-looking synthetic aperture radar. For the first three full years after the treaty entered into force, the observation aircraft had to be equipped with at least a single panoramic camera or a pair of optical framing cameras. The states-parties may now agree on outfitting the observation planes with additional sensors.

Data: A copy of all data collected will be supplied to the host country. All states-parties will receive a mission report and have the option of purchasing the data collected by the observing state-party.

Treaty Implementation: The Open Skies Consultative Commission (OSCC), comprised of representatives of all states-parties, is responsible for the implementation of the Open Skies Treaty. The OSCC considers matters of treaty compliance, decides on treaty membership, distributes active quotas, and deals with any questions that may arise during the implementation of the treaty.

The 2nd Review Conference for the Open Skies Treaty was held in Vienna on June 7-9, 2010 under the chairmanship of the United States. The Conference’s Final Document paves the way for the use of digital cameras and sensors in the future by requesting states-parties consider the technological and financial aspects of converting to digital systems. The document also encourages the expansion of the Open Skies Treaty to other countries, particularly those in the Organization for Security and Cooperation in Europe, where the OSCC is headquartered.

Images of Open Skies flights are available at: http://www.osce.org/photos/show_photos.php?a=1&grp=429&limit=1&thumb=1&pos=0.



1. Belarus, Belgium, Bosnia and Herzegovina, Bulgaria, Canada, Croatia, the Czech Republic, Denmark, Estonia, Finland, France, Georgia, Germany, Greece, Hungary, Iceland, Italy, Latvia, Lithuania, Luxembourg, the Netherlands, Norway, Poland, Portugal, Romania, Russia, Slovakia, Slovenia, Spain, Sweden, Turkey, Ukraine, the United Kingdom, and the United States. Kyrgyzstan has signed, but not ratified the treaty.

2. For example, Russia, which shares its quota with Belarus, and the United States both have quotas permitting 42 flights per year, while Portugal is only obligated to allow two flights annually. Countries are not required to exhaust their flight quotas. In 2009, the United States flew a total of thirteen flights, twelve over Russia and one over Ukraine.

3. This limit can be extended by 24 hours if the host insists that the observing party use the host's aircraft and demonstration flight is conducted.

Conventional Arms Issues

Subject Resources:

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Realizing the Full Potential of the Open Skies Treaty

Sidney D. Drell and Christopher W. Stubbs

The Open Skies Treaty, which entered into force in 2002, provides a mechanism for enhancing arms control transparency, activity monitoring, and confidence building by allowing unrestricted, short-notice, aerial reconnaissance overflights.

This article explores the importance of realizing the full potential of the treaty to making progress in reducing the numbers and dangers of nuclear weapons, goals that have been endorsed by many world leaders. This effort will require expanding the membership of the treaty on a global scale and implementing modern technology for data collection and analysis.

When they first met on April 1, 2009, President Barack Obama and Russian President Dmitry Medvedev, the leaders of the two states with the largest nuclear arsenals, officially committed their countries “to achieving a nuclear-free world, while recognizing that this long-term goal will require a new emphasis on arms control and conflict resolution measures and their full implementation by all concerned nations.” Toward that end, Russia and the United States resumed formal negotiations toward a step-by-step process of new and verifiable reductions in their strategic offensive arsenals, culminating a year later with the signing of the New Strategic Arms Reduction Treaty (New START). That treaty calls for modest reductions in deployed strategic forces and a commitment to move ahead with further and broader reductions in the two countries’ respective nuclear arsenals. In particular, New START extends and simplifies the verification protocols and cooperative measures of the original START, which had expired. The new treaty requires data exchanges and transparency measures that are more comprehensive than those of its predecessor.

The progress made in this area of verification is breathtaking when one considers the confrontational situation 30 years ago with the former Soviet Union. It augurs well for efforts to verify deep reductions in nuclear weapons and even to abolish them. To make progress toward such goals, it will be necessary to negotiate multinational agreements for significantly more transparency and cooperation for detecting covert efforts to violate treaty restrictions on weapons activities.[1]

Projecting the state of science and technology in a world with a greatly reduced number of nuclear weapons and ultimately no nuclear weapons is necessarily speculative. The discussion in this article is based on the assumption that nuclear arms control and verification technologies most likely will exhibit evolutionary rather than revolutionary progress. In this context, it is suggested that the Open Skies Treaty, upgraded as discussed below, in conjunction with other elements of the verification system, is promising for strengthening the international community’s ability to detect covert, illicit attempts to develop nuclear weapons or weapons-grade material. Yet, without a revolutionary new verification methodology, it seems unlikely to overcome the challenge of providing robust standoff detection of fissile materials encased in a deeply buried and unattended nuclear warhead. In the absence of necessary maintenance work, such systems lose military value over time. More pertinent to national security concerns will be the ability to detect potentially threatening activities involving nuclear weapons and materials, particularly as the arsenals decrease. It is the standoff detection of such activities by an expanded and upgraded treaty that is of particular interest.

Such activities would take place against a backdrop that is likely to include the following:

• Nuclear power will continue to play a role in meeting energy demands, despite the problems at Fukushima. Even with a tightly controlled and monitored nuclear fuel cycle at known sites, there is a need to develop and implement verification methods to detect a covert attempt to produce weapons-grade fissile material. At the front end of the fuel cycle, this means searching for uranium-enrichment facilities; at the back end, it means searching for spent fuel reprocessing facilities.

• The number, capabilities, and resolution of commercial and scientific remote-sensing satellites all are likely to increase, driven by the need for climate change monitoring, land and resource management and stewardship, and support of geological and atmospheric sciences. These data can help support the verification and monitoring program regimen.

Implementation of the Treaty

The Open Skies Treaty represents a remarkably successful implementation of shared technical means of verification and confidence building. The concept of Open Skies,[2] which was first proposed by President Dwight Eisenhower at the height of the Cold War in 1955, provides a mechanism for transparency and confidence building by allowing for short-notice, aerial reconnaissance overflights. The Soviet Union vehemently and immediately rejected the proposal, which was then largely ignored for more than three decades as U-2 overflights (1956-1960) and photoreconnaissance satellites (starting with Corona in 1960) proved effective in piercing the Iron Curtain. The descendants of those satellites remain an important part of the United States’ national technical means.

In 1989, near the end of the Cold War, the negotiations on the Conventional Armed Forces in Europe (CFE) Treaty—putting limitations on deployments of conventional forces in the Warsaw Pact and NATO countries—renewed interest in the Open Skies idea, with the motivation of using overflights to verify compliance with CFE provisions. This led to a speech by President George H.W. Bush calling for negotiation of an Open Skies treaty. His idea was quickly expanded by Canadian Prime Minister Brian Mulroney to include not just the United States and the Soviet Union, but all of NATO and the Warsaw Pact.

This idea caught fire. Following the conclusion of the CFE Treaty in 1990, an accord was negotiated, thereby resurrecting Eisenhower’s Open Skies idea as a formal treaty. Twenty-seven states signed the treaty in 1992, but it did not enter into force until January 2002, after Russia ratified it.

Under the treaty, each party has a quota for the number of flights it may initiate annually; that number is equal to the number it must accept over its own territory. The treaty provides for reciprocal verification overflights, on 24 hours’ notice, over any and all portions of the 34 states currently participating in the treaty. The United States and Russia (including Belarus) have the right to conduct and are committed to accept 42 annual overflights with trajectories that can extend over distances comparable to the distances between the borders of the inspected country. In particular, up to 21 overflights can be of each other, with the balance taken up by other parties to the treaty. At present, the Open Skies aircraft designated by the individual countries are equipped with film-based aerial reconnaissance cameras. Russia is in the process of outfitting new airframes with digital cameras, which is consistent with the treaty.

The treaty currently allows data to be acquired, subject to certain established resolution restrictions, with visible and infrared cameras, as well as with synthetic aperture radar (SAR, all-weather imaging radar), and the resulting data are available to all treaty participants. Between August 2002 and December 2010, 739 Open Skies flights were conducted.[3]

The second review conference for the Open Skies Treaty was held in Vienna in June 2010 to review and evaluate the treaty implementation thus far and to explore how the agreement might evolve in the future. The presentations at the review conference explored both augmentation of the sensors carried by the Open Skies-certified aircraft and the potential application of Open Skies collection capabilities to problems that are beyond the scope of the current treaty, such as natural disaster assessment and wildfire monitoring.[4]

The suite of sensors allowed under the treaty currently comprises optical and infrared cameras and SAR. The treaty currently limits the ground resolution obtained in overflights at optical, infrared, and radio wavelengths to 30, 50, and 300 centimeters, respectively.[5] Final notification of the desired flight path is provided 24 hours before takeoff. Mutual inspection of the aircraft and its sensors is permitted as a means to prevent a country from being subjected to any covertly added sensors. A country that has been notified of an upcoming flight over its territory also has the “taxi” option of using its own aircraft to carry out the data collection mission, if it so chooses. The crew aboard the flight always includes personnel from the inspecting and the inspected countries.

Treaty implementation is overseen by the Open Skies Consultative Commission, which is composed of representatives from the member states. Periodic review conferences are held to administer the treaty and address issues that might arise.

Article IV of the treaty anticipates the possibility of an evolution of the sensor suite, stating that “[t]he introduction of additional categories and improvements to the capabilities of existing categories of sensors provided for in this Article shall be addressed by the Open Skies Consultative Commission pursuant to Article X of this Treaty.”[6]

The treaty stipulates that decisions by the commission shall be on the basis of consensus, which is defined as no party raising an objection to an impending decision.

Exploiting Opportunities

Because the Open Skies collection platforms are aircraft, they provide technical verification opportunities that simply are not possible from satellites, for example, airborne collection of trace gas and particulate samples. These data are important in searching for covert programs to develop weapons of mass destruction (WMD); the fact that Open Skies allows for full, unrestricted, territorial access is an important feature. Obtaining gas and particulate samples would require adding new capabilities to the Open Skies sensor suite, but the treaty spells out a clear path for enhancing the instruments. Particulate and gas collection and analysis are mature and demonstrated technologies and would become increasingly important for remote monitoring of nuclear material production activities as nuclear arsenals shrink in the longer-term future. The parties to the treaty should consider augmenting Open Skies sensor capabilities and increasing multiagency coordination of standoff detection instrumentation research and development with Open Skies platform capabilities.

Even though infrared and SAR imaging are allowed under the current treaty, U.S. Open Skies aircraft currently do not carry infrared cameras or a radar system. U.S. Open Skies aircraft should carry the full complement of currently allowed Open Skies sensors with contemporary technology. Having the Open Skies system operating at full capacity not only enhances the U.S. capability for monitoring nuclear weapons activities under New START, but also provides added assurance to the country’s intelligence collection systems over a substantial fraction of the globe.

In particular, the United States should replace its current film-based cameras with digital imaging systems. Installation of modern digital cameras is long overdue and will facilitate full dissemination and exploitation of Open Skies images. Digital images can be more easily georegistered (aligned with map coordinates) and thereby fused with other data sources. Increased resolution, if future negotiations allow it, can be achieved by simply flying the aircraft lower and will not require new instruments and cameras. This approach is far more cost effective than achieving high-resolution imaging from orbit. It is also limited in practice by the need to avoid air traffic congestion and the desire to maintain a sufficiently broad width of the reconnaissance ground swath. (For a given camera system, there is a trade-off between resolution and field of view. Flying lower achieves higher resolution but diminishes the extent of cross-track coverage.)

As noted above, the current spatial resolution for the optical wavelength surveillance systems on Open Skies collection aircraft is essentially comparable to what can be obtained from commercial imaging satellites. It is an important foundation on which to build a system of shared technical means of the future, primarily because of the potential for continuing advances in the sensor suite.

Expanding the group of signatory nations would allow verification access to an increasing fraction of the globe. Open Skies is an unclassified system. Both its sensors and the information it produces can be shared with all participating countries. At present, there is a nearly decade-old U.S. presidential directive that prevents the Department of State from pursuing expanded Open Skies participation. The U.S. government should re-evaluate this policy; in the past, it managed to negotiate reciprocal access with precisely those countries among the Warsaw Pact that were of prime concern.

There are several distinct and substantial advantages to building enhanced verification capabilities based on the success of the Open Skies Treaty.

1) Open Skies is an existing treaty with a track record of success. It allows the international community to expand verification capabilities using an existing framework. Building on an existing international agreement is more straightforward than embarking on a new one. As noted earlier, the structure of the Open Skies Treaty is very well suited to evolving verification needs, the most important of which are the collection of atmospheric gases and particulate samples, which are not accessible from satellites.

2) The size, weight, and power constraints for advanced sensor capabilities are minimal with existing Open Skies aircraft. The Open Skies collection platform currently used by the United States, the OC-135B, is essentially a Boeing 707 airframe that can accommodate the deployment of innovative sensor technologies that might be larger and heavier than currently available technologies and require more power and bandwidth to operate. Next-generation sensors will need to abide by the treaty’s principle that all parties have the right to install commercially available sensors that can be certified for comparable performance.

3) The treaty produces unclassified data that may be shared among the parties for government use so that all states, both former nuclear-weapon states and countries that always have been non-nuclear-weapon states, can benefit in the future from the verification collections. This reduces information inequities among countries and avoids the problems associated with the sharing of classified data that are collected by states that wish to protect sensitive sources and methods. Since the treaty’s entry into force, the United States has requested copies of film from 84 missions conducted by other parties and processed 23 requests for imagery obtained during U.S. missions.

4) Although broader WMD considerations are beyond the scope of this paper, one could readily imagine augmented Open Skies sensors designed to search for evidence of biological or chemical weapons programs. In some cases, such as active laser spectroscopy, the same instruments could provide nuclear and non-nuclear WMD verification.

Specific Technical Opportunities

This section highlights the potential technical opportunities for enhancing the verification capabilities of the Open Skies sensor suite and, where appropriate, identifies the research and development needed to support these options. Because the goal of the section is to map out the technical opportunities, it presents concepts that span a range of levels of intrusiveness. It is not intended to be an exhaustive or comparative survey of all possible methods for detecting covert uranium-enrichment or plutonium-recovery efforts, but rather is meant to illustrate the potential benefits of enhancing Open Skies for future verification applications.[7]

The verification opportunities presented below eventually must be carefully assessed in terms of their technical readiness, their verification utility, and the likely political (U.S. and foreign) barriers to adoption. The Open Skies verification effort would presumably augment and complement other methods, such as on-site inspections and wide-area monitoring, methods that are employed today by the Comprehensive Test Ban Treaty Organization’s International Monitoring System.

One important verification application of enhanced Open Skies is the problem of covert fissile material production. For covert enrichment programs, the analysis below will concentrate on the detection of uranium and its compounds, while for plutonium, it will focus on how to exploit the krypton-85 (Kr-85) signature of reprocessing.

Atmospheric Gas Sampling. The detection of trace gases has long been considered to be a potentially useful method for detecting clandestine production of fissile materials.[8] The ability to collect and store gas samples along an aircraft’s flight path would be a powerful augmentation to the Open Skies collection suite. The aircraft’s ability to enter and exit the suspect territory rapidly allows for the gas analysis to be performed on the ground in an appropriate laboratory setting with minimal delay.

A particularly interesting verification method is to search for the unstable noble gas isotope Kr-85, which is produced in the consumption of uranium in reactors and is released when fuel rods are reprocessed for plutonium extraction. By monitoring Kr-85, researchers have claimed the ability to sense plutonium separation activity of a few hundred grams per week from a standoff distance of 39 kilometers.[9] Thus, an Open Skies flight should have the ability to map out a swath of terrain that spans tens of kilometers on either side of the flight path. This is probably not enough area coverage per flight to perform a rapid survey of an entire large country, but it should allow for samples to be collected from sites that are suspected (from image analysis or other sources) of harboring clandestine reprocessing activity.

Given the 24-hour notification time, the detailed flight plan (altitude and path) can take wind forecasts into account, and the flight can be tailored to maximize the system’s sensitivity to detect emanations from a region of particular interest. One measurement challenge for an airborne Kr-85 sampling system is the varying natural background concentration. Therefore, the task is to discriminate spatial and temporal variation in pre-existing backgrounds from the signature arising from weapons-related activities. Making a differential measurement of Kr-85 concentration along the flight path should facilitate this. A ground-based network of Kr-85 sensors is likely to be an element in a verification protocol for “nuclear zero,” and the combination of ground-based and aircraft-collected data will be more powerful than either data set in isolation.

Scientists currently do not have a detailed understanding of the propagation and diffusion of noble gases from reprocessing activity, especially if conducted underground, but deeply buried facilities will have an increased diffusion timescale compared to activities on the surface. Thus, even if reprocessing were shut off in response to an Open Skies overflight notification, one would not anticipate an instantaneous termination of detectable Kr-85.

On the U.S. side, the sister aircraft to the OC-135B Open Skies collection platform is the WC-135 Constant Phoenix, which apparently already has a gas sample capture and storage capability.[10] The implementation of an atmospheric gas sampling scheme is not technically demanding and could be undertaken in short order. The samples presumably would be subjected to laboratory analysis on the ground.

Particulate/Aerosol Sampling. The Constant Phoenix also has a particulate sampling capability. Adding this verification technique to the Open Skies aircraft is therefore presumably a fairly straightforward undertaking. An automated particulate sampler has been developed for use in verifying the Comprehensive Test Ban Treaty.[11] This is a mature technology.

The collected particulates can be analyzed for any hint of weapons-grade fissile materials. In particular, the radionuclides that adhere to particulates and aerosols can be analyzed to determine the ratios of the isotopes of elements of interest, which is extremely valuable information for plutonium and uranium. The results from studies focusing on the releases from covert fuel-cycle facilities imply that a monthly Open Skies aerosol collection flight over a region the size of the Middle East, in conjunction with high-sensitivity laboratory analysis techniques, should provide good monitoring of clandestine fissile material production activity over such a region.[12] The studies consider only fixed ground stations, but an Open Skies flight can collect aerosols along the entire flight path and from an optimized altitude.

Higher-Resolution Optical and Infrared Imaging. The ability to increase imaging resolution would be significant from a verification standpoint.[13] Attaining better resolution from orbit requires larger-diameter mirrors. The satellite cost scales faster than the square of the mirror diameter,[14] while the resolution increases only linearly with diameter. High-acuity imaging from space therefore is very expensive. From airborne platforms, one can just fly lower to obtain sharper images; the ground resolution distance is simply proportional to the aircraft’s height above the ground. This makes the acquisition of high-resolution images from aircraft much more affordable than from space. The highest resolution images of urban areas in Google Earth are from aerial photography, not from commercial satellite images.[15]

The high-resolution camera system currently used on the U.S. Open Skies collection platform, the KA-91C camera, is operated from an altitude of 35,000 feet in order to abide by the treaty’s stipulations on ground resolution.[16] The potential for higher-resolution imaging already exists and will continue to exist if and when the Open Skies participants change from film to digital imaging systems. Maximum allowable ground resolution and minimum allowable flight altitude were topics of considerable discussion.[17] Although the political challenges of obtaining higher resolution images from Open Skies platforms should not be underestimated, the technical aspects of this upgrade are fairly straightforward: the parties simply need to agree to take aerial photography from lower flight altitudes.

Laser-Illuminated Time-Resolved Imaging Spectroscopy. Various techniques are under development for the optical standoff detection of uranium and its compounds. A full exploration of the dual challenges of signal-to-noise ratio (sensitivity) and discrimination (rejection of natural backgrounds and clutter) is beyond the scope of this article.

Activity Monitoring With SAR. An advantage of radar imaging with SAR is its unique all-weather, day and night access to targets of interest. This could play a valuable role in monitoring activity and detecting changes at suspect sites, such as possible weapons caches. Further work should be pursued on this potential.


Implemented in the waning days of the Cold War era, the Open Skies Treaty is a laudable example of transparency and confidence building and can provide an important framework for implementing broader verification methods in a nuclear-zero era.

Toward achieving that goal, the United States should initiate diplomatic and technical steps to implement a modern upgraded suite of all three currently allowed Open Skies Treaty sensors (optical, infrared, and SAR), work to enhance the scope of collections undertaken from treaty platforms, and expand international participation in the treaty.

Sidney D. Drell is a theoretical physicist and arms control expert. He is a professor emeritus at the SLAC National Accelerator Laboratory and a senior fellow at the Hoover Institution at StanfordUniversity. Christopher W. Stubbs is a professor of physics and of astronomy at HarvardUniversity. Both authors are active as scientific advisers to the U.S. government. They have benefited from conversations with George Shultz, Rose Gottemoeller, and Raymond Jeanloz. Stubbs wishes to thank the Hoover Institution for the Visiting Annenberg Fellow appointment under which this work was carried out.


1. The scope of this paper specifically excludes technical issues that are unique to countering nuclear terrorism. Preventing a nuclear version of the September 11 attacks is a top priority but a different technical problem from the elimination of existing national nuclear weapons arsenals. Continuing reductions in the number of nuclear devices that must be safeguarded and steady progress in limiting access to fissile materials will help to suppress the likelihood of a nuclear terrorist event. However, the classical concept of strategic deterrence is likely of little use in countering an attack by suicidal nonstate actors using weapons of mass destruction. In the nuclear terrorism context, a nuclear arsenal (and the radioactive materials within it) is arguably more of a liability than an asset.

2. Not to be confused with Open Skies agreements that pertain to civil aviation and landing rights.

3. For a listing of Open Skies flights through June 4, 2010, see www.osce.org/secretariat/68315.

4. See, for example Mike Betts and Don Spence, “Potential Non-Treaty Applications for Open Skies Assets” (presentation, 2nd Open Skies Review Conference, OSCC.RC/11/10, June 2, 2010).

5. The ground resolution obtained by Open Skies images is stipulated in the treaty. At visible wavelengths, it is roughly comparable to that obtained by commercial satellites and presumably inferior to that of U.S. national technical means (NTM). This may be one reason that U.S. engagement and investment in Open Skies is currently rather precarious, because it adds little to current NTM satellite capabilities.

6. Article X of the Open Skies Treaty defines the structure, responsibilities, and function of the Open Skies Consultative Commission. The prospect of an enhanced sensor suite is explicitly cited in this section of the treaty as well. Changes and additions to the sensor systems require only commission approval and do not require an amendment to the treaty.

7. An interesting opportunity that this article does not explore is the possibility for “bi-static” techniques, with two Open Skies aircraft operating in tandem. One aircraft could contain an optimized light source, and the other a detector system. The atmosphere between the aircraft could then be sampled in transmission, at high spectral resolution and high signal-to-noise ratio.

8. See Paul R.J. Saey, “Ultra-Low-Level Measurements of Argon, Krypton and Radioxenon for Treaty Verification Purposes,” ESARDA Bulletin, No. 36 (2007).

9. Martin B. Kalinowski et al., “Conclusions on Plutonium Separation From Atmospheric Krypton-85 Measured at Various Distances From the Karlsruhe Reprocessing Plant,” Journal of Environmental Radioactivity, Vol. 73, No. 2 (2004): 203. See also Martin B. Kalinowski, Heiner Daerr, and Markus Kohler, “Measurements of Krypton-85 to Detect Clandestine Plutonium Production,” INESAP Bulletin, No. 27 (December 2006).

10. U.S. Air Force, “WC-135 Constant Phoenix,” February 11, 2009, www.af.mil/information/factsheets/factsheet.asp?id=192.

11. See S.M. Bowyer et al., “Automated Particulate Sampler for Comprehensive Test Ban Treaty Verification (The DOE Radionuclide Aerosol Sampler/Analyzer),” IEEE Transactions on Nuclear Science, Vol. 44, No. 3 (June 1997): 551.

12. On uranium-conversion facilities, see R. Scott Kemp, “Initial Analysis of the Detectability of UO2F2 Aerosols Produced by UF6 Released From Uranium Conversion Plants,” Science and Global Security, Vol. 16, No. 3 (2008): 115-125. On uranium-enrichment and spent fuel reprocessing facilities, see P.W. Krey and K.W. Nicholson, “Atmospheric Sampling and Analysis for the Detection of Nuclear Proliferation,” Journal of Radioanalytical and Nuclear Chemistry, Vol. 248, No.3 (2001): 605-610.

13. See Sidney D. Drell and Raymond Jeanloz, “Nuclear Deterrence in a World Without Nuclear Weapons,” in Deterrence: Its Past and Future, eds. George Shultz, Sidney Drell, and James Goodby (Stanford, CA: Hoover Institution Press, 2011), pp. 21-29.

14. This is because of the added weight and volume needed to accommodate a larger primary mirror. The typical cost scaling assumption is D2.5, where D is the mirror diameter.

15. Google, “Imagery Partner Program,” 2011, http://maps.google.com/help/maps/imagery/.

16. U.S. Air Force, “OC-135B Open Skies,” September 28, 2007, www.af.mil/information/factsheets/factsheet.asp?id=120.

17. See Mark David Gabriele, “The Treaty on Open Skies and Its Practical Applications and Implications for the United States” (Ph.D dissertation, RAND Graduate School, 1997).


The Open Skies Treaty is a good example of transparency and confidence building. If the parties agree to update the treaty by expanding its membership and using modern technology for data collection and analysis, it can provide an important framework for implementing broader verification methods in a nuclear-zero era.


Open Skies Treaty Enters Into Force

Wade Boese

On January 1, the Open Skies Treaty entered into force, paving the way for its 26 state-parties to officially begin unarmed reconnaissance flights over each others’ territories later this year.

For any given year, the number of flights that a country may conduct over others and has to permit over its own territory is limited by a quota system loosely based on the size of a country’s territory. For example, Russia, which shares its quota with Belarus, and the United States are obliged to permit up to 42 reconnaissance flights over their territories annually, although Portugal only needs to permit two. All states-parties have a reduced number of flights that they must allow during the first round of treaty flights, which extends until the end of 2003.

A U.S. government official said treaty flights are not expected to begin until this August because the planes to be used in conducting the flights must be checked out and certified as treaty compliant. This certification period is tentatively scheduled to occur from mid-April to July.

As part of the plane certification, inspectors will check whether the plane’s sensors, which are supposed to be capable of enabling an observing party to distinguish between tanks and trucks on the ground, match the specifications of those permitted by the treaty. Under the treaty, a plane ultimately may be equipped with optical cameras, video cameras, infrared line-scanning devices, and sideways-looking synthetic aperture radar (SAR). Initially, states-parties are likely to employ cameras only and will gradually incorporate the other permitted sensors. No country even has a SAR to use at this time, according to the U.S. government official.

NATO and former members of the Warsaw Pact, which dissolved during the treaty’s two-year negotiations, signed the accord in March 1992. The treaty was originally intended to help ease distrust between the two blocs and be a tool for verifying other agreements. A January 9 State Department press release stated that the treaty “is still expected to be a useful element of the European security framework,” adding that it will provide “increasing transparency, mutual understanding, and cooperation, among its parties.”

Now that the treaty has entered into force, members of the Organization for Security and Cooperation in Europe not party to the accord may apply to accede. If no state-party objects to a country’s application, the country may join the treaty. Finland, Sweden, and Cyprus have expressed interest in acceding. After July 1, any other country may also ask to join the accord.

Open Skies Treaty to Enter Into Force

On November 2, Russia and Belarus deposited their instruments of ratification for the Open Skies Treaty, triggering the 60-day countdown for the accord’s entry into force on January 1, 2002.

Negotiated by NATO and former members of the now-defunct Warsaw Pact and signed in 1992, the Open Skies Treaty permits countries to conduct unarmed reconnaissance flights over the territories of other treaty parties. Aircraft used in the flights will have to meet certain specifications and will be equipped with sensors, such as cameras and infrared devices, sensitive enough to enable the observing party to distinguish between tanks and trucks on the ground.

The treaty allocates each state-party a quota of flights that it must permit over its territory annually. For example, the United States and Russia, which shares its quota with Belarus, each have a quota of 42 flights, while smaller countries, such as Spain and Bulgaria, have to allow only four flights per year.

Under the treaty, however, states-parties only need to permit up to 75 percent of their flight quota from the date of entry into force to the end of the following year. Thus, states-parties will have until the end of 2003 to conduct the first round of reduced annual flights.

Treaty signatories have been conducting practice flights, and more than 350 trial missions have taken place since 1996, according to the Organization for Security and Cooperation in Europe (OSCE).

Kyrgyzstan is the only country of the 27 treaty signatories that has not ratified the treaty, but its ratification is not required for the accord’s entry into force. For the first six months after entry into force, other OSCE members not party to the treaty may apply to join the accord, and after that any country may request to accede to the treaty. Finland and Sweden, both of which are OSCE members, announced on November 5 that they want to join the treaty.

Russia, Belarus Move Toward Open Skies Treaty Ratification

Wade Boese

As expected, Russia’s upper house of parliament, the Federation Council, gave its approval of the Open Skies Treaty on May 16, a little less than a month after the Russian Duma, the more powerful, lower house, approved the accord on April 18. (See ACT, May 2001.) Russian President Vladimir Putin subsequently signed the legislation, ratifying the accord on May 28.

In Belarus, which had adopted the position that it would act on the treaty once Russia did, the lower house of parliament overwhelmingly approved the treaty 86-2 on May 3, and the upper house followed suit on May 17.

Kyrgyzstan is the only other country of the 27 signatories that has not ratified the treaty. However, its ratification is not needed for the treaty to enter into force, which will happen 60 days after both Moscow and Minsk have deposited their instruments of ratification.

Negotiated by NATO and the former members of the Warsaw Pact and then signed in March 1992, the Open Skies Treaty permits states-parties to fly unarmed reconnaissance missions over each other’s entire territories. The sensors aboard the aircraft, including cameras, will enable the observing party to distinguish between tanks and trucks.

Each state-party is obliged to receive only a certain number of flights per year over its territory, referred to as its passive quota, and is restricted to the number of flights it may conduct over other states-parties, which is a country’s active quota. All countries with a passive quota of eight or more must ratify the treaty for it to enter into force, which is why Russia and Belarus—the two share a quota of 42—must complete ratification before the accord becomes legally binding.

By the terms of the treaty, the first allocation of overflights, in which states-parties need only receive up to 75 percent of their passive quota for overflights, is good from the date of entry into force until the end of the following year. Therefore, if Moscow and Minsk quickly deposited their instruments of ratification within the next few months, the treaty would enter into force this year and states-parties would have only through the end of 2002 to get their observation aircraft certified, which could take several months, and conduct the first round of overflights. If the two capitals deposit their instruments of ratification later this year so that entry into force falls during early 2002, states-parties will have all of 2002 and 2003 to get the treaty running, allowing themselves a more leisurely schedule for getting aircraft certified and conducting the first round of overflights.


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