Proximity Operations in Space

The Case for a Code of Conduct

Michael Katz-Hyman

Twelve hundred kilometers above the Pacific Ocean an intricate dance is about to take place. A small 50 kg satellite approaches ever so slowly towards an oblong shaped communications satellite. Their dance involves no humans and no direction from the ground; however, the steps to their dance have been choreographed hundred of times over during weekly meetings and computer simulations. The smaller satellite will approach its partner, coming within six meters, before backing away and circling around her. Once complete, the satellite will move away, completing the difficult orbital ballet it was designed for.

This kind of autonomous operation can be essential in space – certainly not necessarily a bad thing nor should it surprise anyone. Close proximity operations, autonomous or human controlled, are a promising method that could be used to reduce both the costs and the danger of human repair missions. As long as satellites or other space operations require on-orbit assistance, proximity operations will be part of space flight and exploration. But close proximity operations could also be a prelude to space weapons – a fact that has received an increased amount of attention recently.

Not as Planned

The dance described actually occurred on April 16, 2005… but failed. The satellite slowly approached its partner and came within 20 meters. However, flight controllers on the ground, who were not controlling the rendezvous but merely monitoring it, knew something was wrong. The satellite computers were indicating that it had placed itself into a “retirement phase” and was moving itself into an orbit that would eventually lead to it burning up in the atmosphere.[1] The mission was over. It wasn’t until four days later that flight controllers knew what actually happened – a collision.

The small satellite, which was called DART – Demonstration of Autonomous Rendezvous Technology – bumped into an experimental communication satellite known as MUBLCOM. Initially ground controllers just thought the satellite ran out of fuel as it approached MUBLCOM and bailed from the mission early so as to avoid a disaster. But shortly thereafter engineers at Orbital, the company which built both the $95 million DART and the MUBLCOM satellite,[2] noticed that MUBLCOM was in a higher orbit than it was before the encounter. Four days later US Air Force Space Command, which maintains surveillance on over 10,000 objects in space, confirmed this observation.[3] DART hit MUBLCOM and pushed it into a higher orbit. Luckily, for both craft, no damage was detected.[4]

The accident demonstrates the dangers of close quarters operations of satellites. Due to extremely high launch costs, still currently around $10,000 per kilogram, designers and engineers design satellites with the lightest materials possible, which means they are also very fragile. Combine this with the fact that satellites in low earth orbit are traveling at speeds exceeding seven kilometers per second, a collision in space can be catastrophic.

This case illustrates a subtle, but extremely important fact of operations in space. When something goes wrong it may take days or even months before you know what happened and why (in some cases you may never know). The main space surveillance networks run by the US and Russian governments are not perfect, there are large gaps in the number of sensors in the southern hemisphere, and many times satellite orbital data is not updated for days.[5]

One of Many

DART is far from being the only close proximity satellite in space. In the United States, there are a number of other autonomous or human controlled spacecraft that are being designed to inspect or repair satellites. Unlike DART, some of these are military projects. XSS-11 (Experimental Satellite Series), which was launched in April 2005, has been conducting “proximity operations” around various spacecraft and pieces of debris.[6]Another satellite called ASTRO (Autonomous Space Transport Robotic Operations) is being built by Boeing for the Defense Advanced Research Projects Agency (DARPA) of the US Department of Defense to test the possibility of on-orbit servicing.[7] All three of these programs have been mentioned as possible precursors to a “service tug” that may be used to de-orbit the Hubble Space Telescope when its mission eventually ends.[8] In addition, as long as there are space shuttles or space stations, close proximity operations in space will be a fact of life.

Outside the United States, other nations are also working on autonomous operations in space and satellites designed to operate in close quarters. Russia, in fact, already has the ability to conduct autonomous docking operations with its Soyuz and Progress spacecraft – used to ferry crew members and supplies to the International Space Station.[9] The European Space Agency (ESA) is also working on an autonomous cargo supply ship much like Progress called the Automated Transfer Vehicle.[10]

Private industry is also investing in proximity operations that could have a number of uses. Surrey Satellite Technology of the United Kingdom launched SNAP-1 in 2000, which has the ability to perform “remote inspection.”[11] The SNAP-1 satellite was also launched on the same rocket as a Chinese satellite, Tsinghua-1, which led to some speculation that China was also working on proximity operations.[12]

Ambiguity of Intention

Any satellite that is capable of moving close to a satellite is capable of impacting the satellite or interfering with it. This is well understood within the US Air Force, and a 1999 committee tasked with advising the Air Force on microsatellite work recommended “the deployment, as rapidly as possible, of XSS-10-based satellites to intercept, image and, if needed, take action against a target satellite.”[13]

It is also reasonable to infer that any nation with advanced space capabilities can adapt a satellite with onboard navigation equipment to attack another satellite. A direct ascent style weapon may be even easier, using a medium-range ballistic missile and a pellet cloud or simple homing vehicle. Nations with this capability would include not only the United States which last tested a direct ascent weapon in 1985, but Russia, which had its own co-orbital anti-satellite program in the 1970s, China, and perhaps France, Japan, and India.

The existence and maturation of technologies for close proximity operations that are inherently dual-use – they can be used for peaceful as well as hostile purposes in space – is obviously a hard problem. The difference between a satellite performing proximity operations and one performing kinetic kill anti-satellite warfare is only the fact that the former does not impact its target.

Dual-use operations in space could fuel offensive military space programs, lead to hedging strategies that erode cooperation, and reduce a nation’s space assurance. We define space assurance as the political strategy and physical environment that best ensures space is used for commercial, scientific, and military benefit.[14] This erosion of space assurance will especially be the case if there are no rules that distinguish between satellites used to attack versus satellites that are designed to inspect and repair or codes that govern how responsible nations are to operate in space.

The Code of Conduct

Codes of conduct, or rules of the road, are well tested methods to codify what many times are de facto behaviors of responsible actors. From local traffic laws to international agreements on responsible handling of missile components, codes and rules promote responsible behaviors while clarifying those rules which are inappropriate to break.

By encouraging responsible behaviors and setting a precedent for mitigating dangers, nations have been able to ensure both safe passage and freedom of action on the ground, in the air, and at sea. One prime example of such set of rules was laid out in the 1972 Incidents at Sea Agreement (IncSea). Signed by the heads of the navies of the United States and the Soviet Union, the agreement formalized a number a rules and codes for military ships operating in close proximity. Under the agreement, ships operating near vessels of an opposing navy would ensure that they did not interfere with the formations of that navy. It also ensured that navies would not use bright search or signal lights to blind the bridges of opposing ships or simulate attacks on opposing ships.

IncSea went a long way to easing some of the tensions of the Cold War and was so successful that more than thirty other navies adopted similar agreements.[15] Even in the mid 1980s, when Soviet-American relations were at a low point, the US Secretary of the Navy credited IncSea as making naval cooperation one area of relations “better rather than worse” and that the number of incidents at sea was “way down” from its previous levels in the 1960s and 1970s.[16] IncSea was also agreed to at the executive level and in the United States did not require a contentious and lengthy ratification process. Even though the agreement was conceived under this informal framework, it continues to have the same standing as a treaty under international law.

Space deserves a similar agreement. In 2004 the Stimson Center, in conjunction with NGO experts in the United States, drafted a Model Code of Conduct for Responsible Space Faring Nations.[17] While the Center is currently in the process of drawing in NGOs and legal and technical experts from other nations to draw up a more rigorous Code, the initial draft serves as a possible blueprint for what rules of the road in space may look like. The Model Code lays out a number of rules which would have a security-enhancing and stability-increasing effect on operations in space, including the use of autonomous satellites and proximity operations.

Avoid Collisions and Pre-notify Dangerous Maneuvers

Dangerous maneuvers can be misinterpreted as attacks or preparation for attacks. In addition, they can lead to debris generation if a collision occurs. Minimizing and notifying other states of planned maneuvers which may come close to other satellites is key. Under the Model Code, space-faring nations agree to avoid such dangerous maneuvers. If a mission requires a satellite to approach or to dock with another nation’s spacecraft, nations agree to pre-notify each other of such maneuvers.

In the case of autonomous satellites and proximity operations, having clear guidelines on the proper behavior of satellites along with an improved space surveillance network will enhance the security of on-orbit satellites. One way to implement this would be with special caution areas around satellites. This would not prohibit close proximity operations but states maneuvering a satellite within the special caution zones would need to pre-notify and explain their actions. On the sea, this has meant that not only do naval ships not enter such areas without notification, but when they are near such areas they keep an open channel of communication. While the technical implementation of such areas in space would be challenging, they would provide an extra buffer in between very fragile satellites.

Debris Mitigation and Traffic Management

The US Air Force Space Surveillance Network currently tracks nearly 10,000 named objects in space and approximately 4,000 pieces of unnamed or unidentified space junk.[18] While the majority of such space trash is from second stage rockets bodies and various other launch debris, collisions in space may soon exceed these problems.[19] Some studies have also suggested that small amounts of additional debris in certain orbits could also cause such orbits to have so called “runaway environments,” meaning the rate of debris generation by collisions exceeds the rate of debris removal from an orbit by natural processes.[20] While more scientific research must be conducted on debris, it is clear that our goal should be to minimize any debris creation, especially creation of such debris in orbits with lengthy decay times or already high populations.

Stimson’s Model Code of Conduct calls on nations to follow the debris guidelines set out by the Inter-Agency Space Debris Coordination Committee. This includes ensuring satellites have the ability, like DART, to move themselves into a decaying orbit or into a graveyard orbit before its end-of-life. NASA has been a leader in mitigation, publishing guidelines that apply to all missions in 1995,[21] and the US Department of Defense follows guidelines laid out in December 2000.[22] The European Union has also agreed to a Code of Conduct on space debris, with the French Space Agency (CNES) as its charter signatory.[23] Russia and Japan also have debris mitigation standards.[24]

A full international code of conduct should also encompass developing space faring nations such as India and China. While some may argue that such mitigation procedures increase the cost of space activity, this must be balanced with the fact that it will be increasingly more expensive to deal with space debris as the problem gets worse.

In tandem with debris mitigation, the Model Code also calls on nations to implement traffic management in earth orbit. Currently the 140 year old International Telecommunications Union (ITU) only manages orbital slots in the geosynchronous orbit – no such organization manages low earth orbits.[25] As a general rule, in low-earth orbit, satellites stay in predictable orbits (sometimes with the help of station-keeping engines). However, with the introduction of autonomous or navigable satellites a comprehensive management system should be established to ensure satellites do not collide, are not placed in overly crowded orbits, and to resolve electromagnetic spectrum assignment disputes between nations.

Simulated Attacks and Space Weapons

A set of rules of the road that build up confidence between nations operating in space, thereby creating an environment of space assurance, would be undermined if space weapons were flight-tested or deployed.[26] Tests of these weapons may also create debris further exacerbating the problems highlighted above.

International cooperation is essential to today’s space operations. Nations, including the United States, rely on each other to distribute costs, provide expertise, and to launch and track satellites. Flight-testing or deploying weapons in space or simulating attacks in space will undermine cooperation by undermining nations’ confidence in their space assets. It will also undermine cooperation on the ground, as nations adjust their own force postures in response to strategic considerations in space.[27]

Rules of the Road Increase Security

Established and agree-upon rules in space will increase security for all nations. If there are understood acceptable behaviors of satellites it will be easier to identify when nations break such rules. It will also be politically easier to form coalitions to respond to such breaches. It will encourage nations to invest in the peaceful uses of space and to develop spacecraft that are potentially transformational, such as autonomous satellites, but not strategically provocative since they will adhere to responsible behaviors. Rules of the road which prevent dangerous actions will increase space assurance and therefore a nation’s ability to operate in space. In short, rules of the road increase the freedom of action of nations as opposed to limit it.

A Code of Conduct would enhance, not restrict, a space-faring nation’s benefits and capabilities in space. It would not preclude prohibited actions – no legal code can prevent illegal acts – but the code would clarify illicit behavior as well as promote good behavior. In the case that a nation or actor breaks such rules, states will have the political and military means to take action. Most space faring nations have residual capabilities that could be ground-tested for anti-satellite missions, and can act as a hedge against unwise choices of other nations. This is in addition to already demonstrated jamming capabilities and an ability to target ground stations with conventional weapons.

We live by codes of conduct that govern most walks of life, from traffic codes to penal codes. Most nations, including the United States, also support codes of conduct to ensure the safe operation of military forces on the ground and at sea in addition to codes which support the non-proliferation of missiles and weapons of mass destruction materials. A Code of Conduct for space would not have to be negotiated like a treaty at the United Nations Conference on Disarmament, which requires its 66-member body to reach consensus to even begin negotiations. Interested space faring nations can agree to a code on a bilateral or multilateral basis in any combination of countries they choose. Furthermore, these codes can also be at the executive level, not requiring a formal ratification process such as the one required in the United States.

Outer space deserves rules of the road and those concerned with the safety and security of satellites should work hard to convince nations of this important goal. International cooperation, scientific achievement, and economic growth all depend on a robust and safe environment in space. As new technologies are developed that increase the capabilities and opportunities of this realm, we would be wise to consider and implement responsible rules for how such technologies should be used.

  1.  On Orbit Anomaly Ends DART Mission Early, NASA News Release 05-051, April 16, 2005.
  2.  DART Demonstrator To Test Future Autonomous Rendezvous Technologies in Orbit, NASA Facts FS-2004-08-113-MSFC, Marshall Space Flight Center, Huntsville, Alabama, September 2004.
  3.  Brian Berger, Fender Bender: NASA’s DART Spacecraft Bumped Into Target Satellite, Space News, April 22, 2005.
  4.  This is a preliminary conclusion; a Mishap Investigation Board was formed by NASA after the accident with a mandate to return a report within 75 days. Today, the report remains “under review” at NASA headquarters. Kim Newton, Marshall Flight Center, phone conversation, January 9, 2006.
  5.  Theresa Hitchens, Future Security in Space: Charting a Cooperative Approach, Center for Defense Information, September 2004, p. 31.
  6.  Leonard David, Military Micro-Sat Explores Space Inspection, Servicing Technologies, Space.com, July 22, 2005; www.space.com/businesstechnology/050722_XSS-11_test.html.
  7.  Jeffrey Lewis, Autonomous Proximity Operations: A Coming Collision in Orbit?, University of Maryland, March 11, 2004.
  8.  Brian Berger, NASA Proposes $300 Million Tug To Deorbit Hubble, Space News, November 24, 2003.
  9.  David Portree, Mir Hardware Heritage, NASA Reference Publication 1357, Johnson Space Center, March 1995, p. 3.
  10.  Automated Transfer Vehicle, European Space Agency, December 7, 2005; www.esa.int/SPECIALS/ATV/index.html.
  11.  Snap, Surrey Satellite Technology Ltd., http://zenit.sstl.co.uk/index.php?loc=47.
  12.  Jeffrey Lewis, op.cit.
  13.  Matt Bille, Robyn Kane, and Mel Nowlin, Military Microsatellites: Matching Requirements and Technology, AIAA-2000-5186, September 19-21, 2000, p. 9.
  14.  For more on the concept of “space assurance” see Michael Krepon with Christopher Clary, Space Assurance or Space Dominance? The Case Against Weaponizing Space, Henry L. Stimson Center, 2003.
  15.  Michael Krepon, Ground rules for Space, Bulletin of the Atomic Scientists, May/June 2005, p. 68.
  16.  Incidents at Sea Agreement, US State Department, Bureau of Arms Control; www.state.gov/t/ac/trt/4791.htm.
  17.  The full text of the Model Code of Conduct can be found at www.stimson.org/space.
  18.  Space-Track.org, Air Force Space Command at www.space-track.org and Theresa Hitchens, op.cit., p. 26.
  19.  J.-C. Liou and N.L. Johnson, Risks in Space from Orbiting Debris, Science, Vol. 311, January 20, 2006, p. 340.
  20.  Donald Kessler and Phillip D. Anz-Meador, Critical Number Of Spacecraft In Low Earth Orbit, presented at the Third European Conference on Space Debris, March 2001; http://webpages.charter.net/dkessler/files/CriticalNumberofSpacecraftinLow.pdf.
  21.  Guidelines and Assessment Procedures for Limiting Orbital Debris, NASA Safety Standard 1740.14, August 1995.
  22.  Theresa Hitchens, op.cit., p. 33.
  23.  Code Of Conduct For Space Debris Mitigation, CNES Press Release, December 1, 2004; www.cnes.fr/html/_455_465_3018_.php. The text of the code can be found at www.stimson.org/wos/pdf/eurocode.pdf.
  24.  See A. Kato, Debris Mitigation activities in NASDA, Advances in Space Research, Vol. 23, Issue 1, 1999, pp. 227-230, and IADC Space Debris Mitigation Guidelines, IADC 02-01, Inter Agency Debris Coordination Committee, October 15, 2002.
  25.  For more on the ITU see www.itu.int/ITU-R/.
  26.  Currently, there is no agreed upon definition for a space weapon. For the purposes of the Model Code, the Stimson Center has adopted one that defines space weapons as direct attacks on satellites from other satellites or from Earth, and attacks on earth from dedicated satellites in space. Implicitly absent from this definition is military equipment designed to jam communications between satellites and ground stations since these are attacks on the communications links as opposed to the satellites themselves. For more on this definition, see Michael Krepon with Christopher Clary, op.cit, p. 29.
  27.  For an analysis of how the main effect of any US space weapons plans would be an increase in proliferation, see Michael Krepon with Michael Katz-Hyman, Space Weapons and Proliferation, Nonproliferation Review, Monterey Institute for International Studies, Volume 12, No. 2, 2005.