Space Debris Mitigation Policy

As awareness of space debris and its potential threats to operational satellites continues to evolve,
so too do policies regarding its removal.

First published Fall 2015, Crosslink® magazine.

Space debris mitigation policies are designed to limit or reduce the growth of the debris population in Earth orbit and reduce risks to satellites. These policies are also designed to limit risks to people on the ground in the case of debris reentries. Space debris policy is developed by using observational and analytical information to identify the sources of debris, and within the constraints of cost and technical feasibility, to identify and codify the best means to maintain acceptable risk levels.

Space debris is defined as any nonfunctioning human-made object orbiting Earth. This distinguishes it from operational payloads and natural meteoroids that pass through Earth’s orbit. It can include debris from explosions and collisions, as well as dead satellites and used rocket upper stages.

Historically, the space debris environment is a product of launched objects (including satellites, spent stages, and operational debris) and fragments from on-orbit breakups and degradation. As the debris population increases, there is growing potential for on-orbit collisions, which increases the cost of satellite designs and operations. The larger the debris population, the greater the burden on systems such as the Space Surveillance Network (SSN), which tracks and catalogs Earth-orbiting objects.

In addition, the processes of conjunction assessment and collision avoidance become significantly more complicated with increases in the number of objects that must be analyzed. In the world of space today, more maneuvers are necessary for operational satellites to avoid potential collisions, which use precious fuel and interfere with mission operations.

Debris, particularly from explosions and collisions that cannot be tracked or avoided, pose hazards to operational satellites. Depending on its size and orbit, debris can degrade and even disable satellites. An example of this is the French Cerise satellite, which had a gravity gradient boom severed by impact with a piece of fragmentation debris. Although satellite control was recovered, operational lifetime was significantly reduced by the event. Another example is the Iridium 33 satellite, which was permanently disabled by a collision with the nonoperational satellite Cosmos 2251.

Understanding and Mitigating Debris Sources

Guidelines and policies for debris mitigation address the control of several broad classes of problems. One of the earliest recognized sources of debris was the release of operational debris, which is debris that is produced in the course of running a mission. This includes lens caps, explosive bolts, and debris from other separation and deployment mechanisms. These types of debris have proven to be easy to control through spacecraft design. For example, some satellites are now designed to retain their lens caps after deployment. Likewise, separation and deployment mechanisms have been redesigned to avoid releasing their component pieces. Most recently, hardware design modifications have identified ways to eliminate the release of debris shed from launch vehicle upper stage motor nozzles.

Collisions and accidental explosions of satellites and upper stages have historically been one of the major sources of debris, particularly debris that can be mission-ending through secondary collisions with other space objects, but is too small to track by the SSN. Explosions occur for many reasons, but all had some type of residual energy source on board the vehicle after its end of mission. This may have been due to a valve failure between the residual fuel and oxidizer tanks, a charged battery, or propellant or gas in a sealed tank that was heated by the sun until it burst under pressure. Mitigation for this type of problem focuses on making safe space vehicles and upper stages at end of life by removing any residual energy sources. This may involve shorting electrical systems, venting/depleting unused propellants and pressurants, and spinning down momentum wheels and other moving parts. Once the energy sources are removed, there is no means to initiate an explosive event.

Over the long term, it is collisions between objects on orbit that are likely to be the major source of debris. Space vehicle collision avoidance maneuvers may be conducted during a satellite’s mission lifetime, but this is not the case after it has been passivated at end of life. Assessments are now made during a satellite’s design to determine the probability of damage—based on exposure to its operational orbit debris environment—to components critical to postmission disposal maneuvers. If components are found to be vulnerable, relatively inexpensive shielding can be added to the design, or components can be relocated to safer areas on the satellite. This helps to ensure that postmission disposal can be completed and the satellite can successfully conduct a controlled reentry or maneuver to its planned long-term disposal orbit.

For satellites that are unable to maneuver, collisions may occur, even during operations. In an effort to mitigate this threat, assessments are conducted prior to launch to determine launch dates and orbital parameters that minimize the probability of collisions with large objects that could cause a catastrophic breakup.

Overall, to control the long-term growth of the debris environment, it is critical to limit the amount of nonoperational mass left in Earth orbit. Deorbiting an object such as a launch vehicle upper stage or placing a satellite on a limited lifetime orbit after end of mission, typically with a lifetime of 25 years or less, will remove objects from operational orbits and eliminate them as possible sources of debris. Long-term disposal orbits do not remove mass from orbit, but do move objects from the most populated regions of space, reducing the probability of debris generation in those critical operational orbits.

History of Debris Mitigation and Prevention Policy

In the early days of space programs, there was little or no concern about space debris—the entire focus was on accomplishing the mission. However, as the use of space grew, so did awareness of the impact debris has on the space environment. A 1978 article by NASA’s Donald Kessler and Burton Cour-Palais first discussed the potential of orbital debris becoming self-perpetuating, and NASA began to address these issues in the 1980s. Department of Defense (DOD) debris mitigation practices evolved in concert with NASA, perhaps most notably in attempts to prevent Delta rocket body breakups. In fact, the original Delta program office was located at NASA’s Goddard Space Flight Center (GSFC). In May 1981, pieces from a Delta second stage explosion were recorded and later found to make up approximately 27 percent of the tracked objects with orbital periods under 225 minutes. GSFC notified the manufacturer, McDonnell Douglas Space Systems Company, of the explosion and requested a determination of the cause. An assessment of the events found that the residual fuel and oxidizer on board were causing the explosions. The missions then began depleting or venting the excess fuel and oxidizer, which eliminated future explosions. This was one of the first debris mitigation efforts.

The United Nations Committee on the Peaceful Uses of Outer Space (UNCOPUOS) began considering space debris in the late 1980s. Studies by Aerospace, NASA, and other organizations over the next decade increased knowledge of the potential manifestations of the growing space debris hazard and its effects on spacecraft and satellite architectures, resulting in new requirements and changes to spacecraft design, operations, and end-of-life standard practices. In 1988, U.S. national space policy for the first time included statements on the need to minimize the creation of orbital debris. This was followed by a 1989 U.S. government interagency report on orbital debris.

The International Academy of Astronautics published a paper on space debris in 1992 that offered immediate debris mitigation recommendations. In 1993, the Inter-Agency Space Debris Coordination Committee (IADC) was established to provide a forum for spacefaring nations to exchange technical information related to the growth and mitigation of orbital debris.

On Sept. 14, 1996, a new U.S. national space policy was established, declaring that it was in the best interest of all nations to minimize debris, and that the United States would take a leading role in the international development of debris minimization policies and associated research. The initial U.S. Government Orbital Debris Mitigation Standard Practices (USGODMSP) document, which contained specific guidelines for satellite operators for disposal and debris mitigation, was developed in 1997, and formalized into practice by the U.S. government in 2001.

The IADC released its first set of debris mitigation guidelines in 2002 as an international consensus on approaches to controlling debris growth. Many countries now regularly launch objects into space, and efforts are under way to standardize guidelines for such practices, including those of the IADC and the USGODMSP. The intent is to develop a consistent set of rules that apply to all countries and satellite operators. Other nations have also implemented their own guidelines; France has even adopted many of these guidelines into law.

The scientific and technical subcommittee of UNCOPUOS adopted a set of guidelines for orbital debris mitigation in 2007 that were largely based on the 2002 IADC guidelines. The General Assembly of the United Nations included mitigation guidelines in a general resolution in 2008.

In 2010, U.S. national space policy established requirements that the United States continue to follow the USGODMSP, consistent with mission requirements and cost effectiveness, in the procurement and operation of spacecraft, launch services, and testing and experiments in space. Each year, the U.S. Air Force’s Space and Missile Systems Center (SMC) develops an “exception to policy” package for the Office of the Secretary of Defense’s (OSD) approval, which provides the USGODMSP compliance status of each mission to be launched in the following calendar year, as well as an update on the strategy and progress for elimination of noncompliances within the next 5 to 7 years.

U.S. Air Force Instruction (AFI) 91-217 (first approved in 2010, with an update published in April 2014) provides detailed debris mitigation requirements for Air Force missions. It also requires SMC space program offices to prepare a mission-specific space debris assessment report and end-of-life plan for approval by the program executive officer prior to each launch. These documents are the results of required space debris mitigation assessments usually performed or validated by The Aerospace Corporation.

Aerospace published the SMC Space Debris Handbook in 2002, as well as later standards for satellite disposal in low Earth orbit (LEO) and geosynchronous Earth orbit (GEO), to ensure that space debris mitigation requirements are integrated into system designs early in the acquisition lifecycle. Aerospace continues to develop satellite disposal strategies for debris mitigation and prevention alternatives for the sustainability of space.

Policy/Guideline Scope and Comparison

The primary international organization involved in debris guidelines development is the IADC. It is a forum represented by thirteen multinational space agencies organized to coordinate mitigation activities related to human-made and natural space debris. The IADC is not a regulatory body, but provides consensus guidelines and supporting technical analyses to encourage effective debris mitigation practices worldwide. Aerospace has represented the DOD as a member of the NASA delegation to the IADC for 20 years.

The IADC advises the UNCOPUOS on space debris issues. IADC guidelines are frequently referenced as space-faring countries develop their own space debris policies and regulations.

NASA was the first organization within the United States to develop a set of guidelines specifically for space debris mitigation. The current NASA requirement, NPR 8715_006A, specifies compliance with a set of practices for limiting orbital debris, and applies to all NASA centers and contractors. The NASA Technical Standard 8719.14 specifies the detailed engineering and technical requirements associated with NPR 8715_006A.

The DOD uses a number of different documents to govern its debris mitigation practices. The overarching rules come from the national space policy, which references the USGODMSP, with implementing instructions and directives for space policy (DODD 3100.10) and space support (DODI 3100.12). U.S. Strategic Command Instruction SI 505-4 specifies the need for satellite disposal and provides criteria and options for postmission disposal. AFI 91-217 defines acceptable levels of risk, specifies associated debris mitigation measures, and requires documentation of implementation efforts throughout the acquisition lifecycle, operation, and disposal of the system.

Commercial launches are regulated by the Federal Aviation Administration (FAA), which is charged with ensuring the protection of public health, safety, and property, as well as the national security and foreign policy interests of the United States through its commercial launch licensing process. These regulations apply to all commercial launch vehicle stages and their components through insertion of the payload(s) into orbit. FAA certification requires that an applicant demonstrate that the risk level associated with debris from a proposed launch meets the public risk criteria for unplanned explosions. Applicants must also show plans for keeping in contact with the payload after payload separation. FAA certification also depends on applicants’ plans for the mitigation of risks from reusable and reentering vehicles. However, the FAA does not currently regulate orbiting launch vehicle upper stage disposal strategies, including defining long-term disposal orbits, and limiting human casualty expectation to less than one in ten thousand.

The Federal Communications Commission (FCC)

has also developed orbital debris mitigation rules focused on communications satellites in Earth orbit. Applicants for FCC authorization to operate communication satellites that will transmit to U.S. receiver systems must submit documentation for their debris mitigation strategy, including limiting operational debris produced during the mission, and limiting the probability that the satellite will become a source of debris. An end-of-life plan (EOLP) is also required that details the postmission disposal strategy including the quantity of fuel, if any, that will be reserved to perform post-mission disposal maneuvers. For GEO orbit satellites, the EOLP must disclose the altitude selected for a postmission disposal orbit, the calculations that are used in deriving the disposal altitude, and the expectation of casualty if planned postmission disposal involves atmospheric reentry of the satellite.

Compliance Challenges and Solutions

Basic space debris mitigation and prevention practices can present difficult challenges for policy and government decision makers. Space sustainability is considered a top priority by the international community, but it is a largely unfunded mandate. Regulations on commercial launches are not always in line with U.S. government requirements. The resolution of these conflicts and the compromises and trades that must take place to satisfy as many requirements as possible drive a considerable amount of work in day-to-day debris mitigation efforts at SMC.

One of the major challenges is attempting to maximize mission performance of a space system while complying with space debris mitigation requirements within a limited budget. This is especially challenging with respect to the fuel budget of a satellite. For example, moving a given satellite to a postmission disposal orbit requires utilization of propellant that could otherwise be used to provide satellite station-keeping and increase the satellite’s mission lifetime. In terms of the entire space system architecture, going this route could increase the number of launches needed to meet user requirements, which would subsequently increase the overall risk associated with launch activities.

A conflict within the debris mitigation polices themselves is between the requirement to mitigate collision risk in LEO by reducing orbital lifetime or by controlled deorbiting of objects from LEO, and the requirement to limit the risk of human casualty on the ground from debris that survives reentry. Technological solutions include new satellite designs that have fewer components that survive reentry (design for demise) or that ensure that the satellite is able to conduct a controlled reentry into Earth’s atmosphere. In terms of policy, what is critical is to find the correct balance between the risk on the ground and the risk in space.

The increase in the launching of small satellites/CubeSats by both the commercial and government space industries is presenting a unique challenge because the small size of these satellites can make them difficult to track. They also frequently lack propulsion and maneuver capability and are often launched as high-risk missions with expected high failure rates. Many small satellites, sometimes 20 to 30 CubeSats from one launch vehicle, are launched into LEO, a densely populated regime, and left on orbit at the end of their missions with an expectation of reentering Earth’s atmosphere within 5 to 10 years. Although they are indeed capable of a catastrophic collision with highly valued assets, the overall incremental collision risk from small satellites has been assessed as low because of their low total mass and small collision areas. There is currently no specific debris mitigation and prevention guidelines for small satellites.

Because the field of orbital debris research is relatively new and mitigation approaches even more recent, there
are many areas of this field that are not thoroughly understood, or can only be modeled with limited accuracy. This can add to the difficulty of identifying mitigation plans and assessing compliance. Some of these areas include estimation of orbital lifetime, prediction of debris quantity and characteristics generated from collisions and explosions, representation of the existing subtrackable debris environment, and projection of growth in the future debris population. Aerospace and NASA, as well as other organizations around the world, continue to conduct research to better understand these topics.

One of the most effective ways to optimize space debris mitigation and prevention at SMC is to put hard requirements on contracts for new system designs. The earlier that debris mitigation alternatives are considered, the more easily and less expensively they can be accommodated, and the more options that become available. However, long lead times result in significant delays in implementing debris mitigation procedures that require mission and/or hardware design changes. These changes can take many years to implement because of costs and technical challenges. For example, there is a significant lead time in terms of procurement of launch services using existing launch vehicles.

An illustration of the effects of lead times and operational lifetimes can be seen with GEO satellites. The first guidelines for disposal of GEO satellites were issued in the early 2000s, but it was not until more than a decade later that substantial international compliance rates were achieved. This amount of time was needed to allow satellites that implemented
the guidelines shortly after their creation to reach their end-of-life and require disposal.

Similar considerations can be given to legacy space systems. Frequently, one of the difficulties in meeting debris mitigation requirements is the need for the proper disposal of an upper stage. The mission of an upper stage is to deliver its payload to a particular orbit, which may leave it with insufficient fuel to be able to be disposed of properly. One means of accomplishing compliance could be a requirement early in the launch vehicle procurement process (2 to 3 years prior to launch) that the payload be kept at a mass low enough so that the launch vehicle upper stage would have sufficient remaining fuel to perform a controlled reentry. Another option to consider is that the delivery of a given satellite and disposal of its upper stage be made requirements of the mission. It would then be possible to reallocate the portion of the delivery of the satellite to its mission orbit so that both missions could be accomplished. In either of these scenarios, the compliance rate of Air Force payloads would be higher, and the risk of human casualty from reentering debris decreased. Aerospace is currently assisting the Air Force’s SMC Launch Systems Directorate and its space program offices with feasibility studies that consider these compliance alternatives.

Conclusions

The goal of space debris mitigation guidelines is to ensure that safe and cost-effective space operations can be maintained into the future. Space debris mitigation guidelines are developed based on analyses of existing patterns in satellite construction, operations, and patterns of use. As technologies change, new uses for satellites are found, new approaches for operating satellites are developed, and the requirements for debris mitigation will also change. Continuing efforts are needed to evaluate the effects of changes in the satellite industry on the orbital debris environment and on the associated mitigation approaches. Policies then need to be adapted to enable the most efficient and effective approaches to mitigation and prevention.

Over the last three decades, orbital debris has progressed from a nearly unknown problem to a recognized issue being addressed at the international level. As understanding grows, it has become clear that steps must be taken to control the growth of the debris environment and limit its effects on space operations. Policies have been established in the United States and around the world to codify the proper procedures to control debris environment growth. The most efficient way to control and reduce the effects of space debris is the strict adherence to mitigation policies. Because of the long lead times involved with developing space systems, implementation can be slow, but progress is being made. Researchers continue to better understand the problems in a rapidly evolving space operations environment. Aerospace has been heavily involved in these efforts since the early days of recognizing the orbital debris problem, and continues to be integral in developing the necessary technical mitigations and scientifically sound policy recommendations to control orbital debris for the sustainability of space.  End

About the Authors

Marlon E. Sorge_200x200Marlon E. Sorge, Senior Project Engineer, Space Innovation Directorate, joined Aerospace in 1989. He has worked on space debris issues for more than 25 years, encompassing fragmentation modeling, risk assessments, debris environment projection, mitigation techniques, and policy development. He also coordinates Aerospace’s debris research program. He has a B.S. in physics and an M.S. in aeronautical and astronautical engineering from Purdue University.

VojtekMary Ellen Vojtek, Senior Project Engineer, Engineering and Integration Division, joined Aerospace in 2007. She supports the SMC Specialty Engineering Division in the areas of space debris and environmental compliance assessments, and conducts policy interpretation for various SMC programs and projects. She has a B.S. in chemical engineering from the University of Pittsburgh and an M.S. in civil and environmental engineering from the University of California, Los Angeles.

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—Marlon Sorge, Mary Ellen Vojtek, and Charles Griffice