National Aeronautics and Space Administration The Disposal of Launch Vehicle Orbital Stages Nicholas L. Johnson Chief Scientist for Orbital Debris 28 October 2009

National Aeronautics and Space Administration 2 Disposal Objectives The responsible disposal of launch vehicle orbital stages is required to control the growth of the orbital debris population. In addition to the U.S. Government Orbital Debris Mitigation Standard Practices, international orbital debris mitigation guidelines applicable to launch vehicle orbital stages have been adopted by the Inter-Agency Space Debris Coordination Committee (IADC) and the United Nations. The three principal objectives for launch vehicle orbital stage disposal are –Passivation (currently addressed by FAA regulations) –Limitation of time in high value orbital regions, i.e., LEO and GEO –Limitation of risk of human casualty from reentries, i.e., risk < 1 in 10,000

National Aeronautics and Space Administration 3 Growth of Launch Vehicle Stages in Earth Orbit Abandoned launch vehicle stages continue to accumulate in Earth orbit.

National Aeronautics and Space Administration 4 Long-term Consequences of Large Objects in Earth Orbit Without proper post-mission disposal, accidental satellite collisions will significantly increase the Earth satellite population.

National Aeronautics and Space Administration 5 Launch Vehicle Stages as Sources of Additional Debris In addition to the direct contribution of intact launch vehicle stages to the orbital debris environment, smaller, more numerous debris can be generated via –Intentional or unintentional release of debris during normal operations e.g., multiple payload adaptors, small motor covers, degradation of vehicle elements –Explosions of derelict stages Prior to 2007, launch vehicle explosions represented the greatest source of hazardous orbital debris –Collisions of derelict stages with other resident space objects 2005 collision of 31-year-old U.S. rocket body with another piece of debris

National Aeronautics and Space Administration 6 USG Orbital Debris Mitigation Standard Practices The USG Orbital Debris Mitigation Standard Practices were first developed in 1997, presented to industry in January 1998, and adopted via a USG Interagency process in early Standard Practice 4-1 addresses launch vehicle disposal options. The basic options for launch vehicle stages are –Leave stage in orbit which will result in reentry within 25 years, taking into account potential human casualty risks on Earth –Leave stage in disposal orbit above LEO and below GEO, avoiding the GPS altitude regime –Leave stage in disposal orbit above GEO

National Aeronautics and Space Administration 7 Standard Practice 4-1 “4-1.Disposal for final mission orbits: A spacecraft or upper stage may be disposed of by one of three methods: a. Atmospheric reentry option: Leave the structure in an orbit in which, using conservative projections for solar activity, atmospheric drag will limit the lifetime to no longer than 25 years after completion of mission. If drag enhancement devices are to be used to reduce the orbit lifetime, it should be demonstrated that such devices will significantly reduce the area-time product of the system or will not cause spacecraft or large debris to fragment if a collision occurs while the system is decaying from orbit. If a space structure is to be disposed of by reentry into the Earth’s atmosphere, the risk of human casualty will be less than 1 in 10,000. b. Maneuvering to a storage orbit: At end of life the structure may be relocated to one of the following storage regimes: I. Between LEO and MEO: Maneuver to an orbit with perigee altitude above 2000 km and apogee altitude below 19,700 km (500 km below semi-synchronous altitude II. Between MEO and GEO: Maneuver to an orbit with perigee altitude above 20,700 km and apogee altitude below 35,300 km (approximately 500 km above semi-synchronous altitude and 500 km below synchronous altitude.) III. Above GEO: Maneuver to an orbit with perigee altitude above 36,100 km (approximately 300 km above synchronous altitude) IV. Heliocentric, Earth-escape: Maneuver to remove the structure from Earth orbit, into a heliocentric orbit. Because of fuel gauging uncertainties near the end of mission, a program should use a maneuver strategy that reduces the risk of leaving the structure near an operational orbit regime. c. Direct retrieval: Retrieve the structure and remove it from orbit as soon as practical after completion of mission.”

National Aeronautics and Space Administration 8 IADC Space Debris Mitigation Guideline The IADC Space Debris Mitigation Guidelines are essentially derived from the U.S. Government Orbital Debris Mitigation Standard Practices and were adopted in 2002 by the 11 IADC member agencies. Guideline 5.3 addresses launch vehicle stage post-mission disposal. –For objects passing through LEO: “Whenever possible spacecraft or orbital stages that are terminating their operational phases in orbits that pass through the LEO region, or have the potential to interfere with the LEO region, should be de-orbited (direct re-entry is preferred) or where appropriate manoeuvred into an orbit with a reduced lifetime. Retrieval is also a disposal option. “A spacecraft or orbital stage should be left in an orbit in which, using an accepted nominal projection for solar activity, atmospheric drag will limit the orbital lifetime after completion of operations. A study on the effect of post-mission orbital lifetime limitation on collision rate and debris population growth has been performed by the IADC. This IADC and some other studies and a number of existing national guidelines have found 25 years to be a reasonable and appropriate lifetime limit …”

National Aeronautics and Space Administration 9 IADC Space Debris Mitigation Guideline (continued) –For objects near GEO: “Spacecraft that have terminated their mission should be manoeuvred far enough away from GEO so as not to cause interference with spacecraft or orbital stage still in geostationary orbit. The manoeuvre should place the spacecraft in an orbit that remains above the GEO protected region. “The IADC and other studies have found that fulfilling the two following conditions at the end of the disposal phase would give an orbit that remains above the GEO protected region: 1. A minimum increase in perigee altitude of 235 km + (1000·C R ·A/m) where C R is the solar radiation pressure coefficient, A/m is the aspect area to dry mass ratio (m 2 kg -1 ) 235 km is the sum of the upper altitude of the GEO protected region (200 km) and the maximum descent of a re-orbited spacecraft due to luni-solar & geopotential perturbations (35 km). 2. An eccentricity less than or equal to 0.003”

National Aeronautics and Space Administration 10 United Nations Space Debris Mitigation Guidelines The United Nations Space Debris Mitigation Guidelines were developed within the Committee on the Peaceful Uses of Outer Space and adopted in 2007, followed by endorsement of the General Assembly the same year. Guideline 6 addresses launch vehicle stage disposal in LEO: –“Spacecraft and launch vehicle orbital stages that have terminated their operational phases in orbits that pass through the LEO region, should be removed from orbit in a controlled fashion. If this is not possible, they should be disposed of in orbits which avoid their long-term presence in the LEO region. “When making determinations regarding potential solutions for removing objects from LEO, due consideration should be given to ensure that debris which survives to reach the surface of the Earth does not pose an undue risk to people or property, including through environmental pollution caused by hazardous substances.”

National Aeronautics and Space Administration 11 United Nations Space Debris Mitigation Guidelines (continued) Guideline 7 addresses launch vehicle stage disposal in GEO: –“Spacecraft and launch vehicle orbital stages that have terminated their operational phases in orbits that pass through the GEO region, should be left in orbits which avoid their long-term interference with the GEO region. –“For space objects in or near the GEO region, the potential for future collisions can be reduced by leaving objects at the end of their mission in an orbit above the GEO region such that they will not interfere with, or return to, the GEO region.”

National Aeronautics and Space Administration 12 LEO Commercial Communications Satellite Missions Iridium (operational orbit 780 km) –95 spacecraft launched using four different launch vehicles from three countries –28 orbital stages inserted, but only one remains in orbit (due to malfunction) Proton orbital stages de-orbited over Pacific Ocean Delta, Long March, and Rokot orbital stages moved to lower disposal orbits Globalstar (operational orbit 1415 km) –52 spacecraft launched using Delta and Soyuz launch vehicles –19 of 21 orbital stages have already decayed –Eight additional Soyuz stages were de-orbited into Pacific from altitude near 900 km Orbcomm (operational orbit km) –41 spacecraft launched as primary or secondary payloads using Pegasus and Cosmos launch vehicles –Nine orbital stages used for dedicated missions (37 spacecraft); 1-2 orbital stages will fail to meet 25-year guideline: one due to lower stage malfunction At least 95% compliance with 25-year rule, excluding two malfunctions

National Aeronautics and Space Administration 13 Recent U.S. Experience: Delta 2 second stage From January 1990 through September 2009, 133 Delta 2 second stages were left in Earth orbits. –97 have already reentered – 1 more expected to reenter within 25 years of launch – 2 were left in disposal orbits above LEO –29 were left in orbits within LEO exceeding 25 years (all but 2 launched in 1990’s*) – 4 have no publicly available data Overall rate of compliance with 25-year rule beginning in 2001: 100%, excluding one mission in 2003 with a secondary DoD mission For NASA missions, the Delta 2 second stage routinely performs a post- payload delivery maneuver, leaving stage with a lifetime of less than 1 year. –Example: NOAA 19 inserted into orbit of 847 km by 866 km in 2009 NOAA 19 Delta 2 second stage maneuvered to 177 km by 819 km; reentered within 2.5 months –Two Delta 2 second stages (one in 2008 and one in 2009) were left in disposal orbits above LEO (payload destinations were 1330 km circular and Earth escape, respectively)

National Aeronautics and Space Administration 14 Delta 4 and Atlas 5 The Delta 4 and Atlas 5 vehicles have flown relatively few missions to date. Of 24 cataloged stages in Earth orbits: –4 have already reentered –6 were left in orbits above LEO –9 have no publicly available orbital data –5 left in orbits with perigee in LEO

National Aeronautics and Space Administration 15 Predicted Lifetimes of Orbital Stages Traversing LEO: Missions in Year 2000 Orbital Stages Launched in 2000 (last year before USG Standard Practices) USA: 68% All: 73%

National Aeronautics and Space Administration 16 Recent NASA Study for FAA During the summer of 2009, the NASA Orbital Debris Program Office collected statistics on the compliance of all launch vehicles with the 25-year rule for the period January 2004 through June 2009.

National Aeronautics and Space Administration 17 Recent NASA Study for FAA (continued)

National Aeronautics and Space Administration 18 Recent NASA Study for FAA (continued)

National Aeronautics and Space Administration 19 Recent NASA Study for FAA (continued)

National Aeronautics and Space Administration 20 Recent NASA Study for FAA (concluded)

National Aeronautics and Space Administration 21 Origin of Reentry Risk Metrics NASA Safety Standard (August 1995) first established the guideline for all LEO spacecraft and launch vehicle orbital stages to remain in orbit for no more than 25 years after end of mission for the purpose of protecting the space environment for future operations. The most practical and cost-effective strategy for compliance is disposal of the vehicle in a low altitude orbit from which a natural, uncontrolled reentry will occur within the allotted time. However, such uncontrolled reentries shift on-orbit satellite collision risks to human casualty risks on Earth. To limit human casualty risks from surviving satellite debris, NASA developed a specific risk criterion and risk assessment process.

National Aeronautics and Space Administration 22 Reentry Risk Criterion In NASA Safety Standard , a total debris casualty area metric was established: where N is the number of objects that survive reentry and A i is the area of the surviving piece in m 2. The term 0.6 represents the square root of the average cross-sectional area of a standing person, as viewed from above. Debris with impacting kinetic energies less than 15 Joules are no longer considered. Total human casualty expectation, E, can then be defined as E = D A x P D where P D is equal to the average population density for the particular orbital inclination and year of reentry. A fundamental human casualty risk threshold of 1 in 10,000 per reentry event was adopted by NASA in 1995, which was equivalent to a debris casualty area of no more than 8 m 2 averaged over all inclinations for that year.

National Aeronautics and Space Administration 23 Reentry Risk Evaluation Process Reentry risk assessments are required for all NASA programs and projects in conjunction with the Preliminary Design Review (PDR) and Critical Design Review (CDR) milestones. Applies to spacecraft, launch vehicle orbital stages, large mission-related debris, and objects intentionally released from the International Space Station. NASA maintains two levels of reentry risk assessment software: DAS (Debris Assessment Software) and ORSAT (Object Reentry Survival Analysis Tool) DAS is publicly available and can be used by program/project personnel. ORSAT is a higher fidelity, more capable model run by trained specialists at the NASA Johnson Space Center.

National Aeronautics and Space Administration 24 ORSAT Summary Table for Terra Spacecraft: Surviving Components * * * * * Less than 15 joules

National Aeronautics and Space Administration 25 Launch Vehicle Orbital Stage Assessments NASA has evaluated the uncontrolled reentry risk potential for several launch vehicle orbital stages: –Pegasus third stage (Orion 38): Compliant with 1 in 10,000 reentry risk (Orion 38’s used as final stages for Taurus and Minotaur-4 are also likely compliant) –Delta 2 second stage: Slightly non-compliant reentry risk (limited number left to launch) –Delta 4 second stage: Highly non-compliant reentry risk –Atlas 5 Centaur stage: Highly non-compliant reentry risk NASA has not yet evaluated the Falcon series of launch vehicles.

National Aeronautics and Space Administration 26 Options for Delta 4 and Atlas 5 To avoid the uncontrolled human casualty reentry risks associated with Delta 4 and Atlas 5 second stages, three basic options are available: –Leave stage in long-lived disposal orbit with perigee above 2000 km Utilized by NASA Delta 4 launches of GOES spacecraft (GOES 13 and 14) to GEO; to be utilized by NASA Atlas 5 launches of TDRS spacecraft (TDRS K and L) –Send stage into Earth escape trajectory Natural consequence for NASA Atlas 5 deep space missions, e.g., to Mars and Pluto Utilized by DoD Atlas 5 launch of DMSP 18 to LEO –Execute a controlled reentry Utilized by DoD Delta 4 launch of DMSP 17 to LEO Being planned for a future NASA Atlas 5 mission

National Aeronautics and Space Administration 27 Summary International consensus exists for the proper disposal of launch vehicle orbital stages, including passivation, short-term presence in LEO and GEO, and limitation of reentry risks. –All topics are addressed by the U.S. Government Orbital Debris Mitigation Standard Practices. Overall, U.S. launch vehicle operators are doing a good job in all three areas. –Formal evaluations for all commercial space missions would be beneficial. The greatest challenge is the reentry risk for Delta 4 and Atlas 5 orbital stages.