a more detailed and accurate assessment as described above. ORSAT has been used numerous times, providing great utility to mission programs.5

The use of ORSAT and DAS for assessing the survivability of reentering debris will increase as debris continues to reenter and concerted efforts are made to remove derelict hardware from orbit. As with other model developments, NASA uses IADC deliberations to perform cross-program comparisons of ORSAT with ESA’s equivalent model(s).6 Although mathematical results for reentry object disintegration are found to be very similar between the two models, the inconsistent definition of “casualty” between ESA and NASA makes it difficult to easily compare results. ESA considers a “casualty” to be a person who is killed by a reentering object, whereas NASA (within ORSAT and DAS) considers a “casualty” to be a person who is injured by a reentering object. As a result, ORSAT is more conservative than the ESA reentry survival model; it predicts a higher probability of a “casualty” from the same reentry events. Updating ORSAT to provide the probabilities for both injury and death as standard outputs would require only a simple coding change.

Finding: The reentry hazard programs used by NASA and the European Space Agency to determine the risk to people on the ground from reentering debris differ in how those thresholds are defined. NASA’s Object Reentry Survival Analysis Tool defines a “casualty” as personal injury, whereas ESA models equate a “casualty” with death.

Recommendation: NASA should update the Object Reentry Survival Analysis Tool so that it provides the probabilities of both injury and death as standard outputs.

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5 For examples of the use of ORSAT by mission programs, see J.P. Rustick and W.C. Rochelle, Reentry Survivability Analysis of GENESIS Spacecraft Bus, LMSEAT 33557, December 2000; J.P. Rustick and W.C. Rochelle, Reentry Survivability Analysis of Earth Observing System (EOS)Aqua Spacecraft, LMSEAT-33622, March 2001; R.N. Smith and W.C. Rochelle, Reentry Survivability Analysis of Compton Gamma Ray Observatory (CGRO), JSC-28929, NASA Johnson Space Center, Houston, Tex., March 2000; R.N. Smith, R.M. DeLaune, and J. Dobarco-Otero, Reentry Survivability Analysis of the Genesis Spacecraft Bus for Off-Nominal Trajectories, JSC-62665 Rev. A, NASA Johnson Space Center, Houston, Tex., August 2004; R.N. Smith and W.C. Rochelle, Reentry Survivability Analysis of Earth Observing System (EOS)Aura Spacecraft, LMSEAT-33712, July 2001, p. 12; R.N. Smith, J. Dobarco-Otero, J.J. Marichalar, and W.C. Rochelle, Tropical Rainfall Measuring Mission (TRMM)Spacecraft Reentry Survivability Analysis, JSC-29837, NASA Johnson Space Center, Houston, Tex., September 2002, p. 4; R.N. Smith, J. Dobarco-Otero, and W.C. Rochelle, Reentry Analysis of Gamma-ray Large Area Space Telescope (GLAST) Satellite, JSC-49775, NASA Johnson Space Center, Houston, Tex., July 2003, p. 6; R.N. Smith, K.J. Bledsoe, and J. Dobarco-Otero, Reentry Survivability Analysis of the Hubble Space Telescope (HST), JSC-62599, NASA Johnson Space Center, Houston, Tex., May 2004; R.N. Smith, J. Dobarco-Otero, and R.M. DeLaune, Reentry Survivability Analysis of Shuttle External Tank Debris, JSC-62683, NASA Johnson Space Center, Houston, Tex., December 2004; and R.N. Smith, J. Dobarco-Otero, and R.M. DeLaune, Reentry Survivability Analysis of the Terra Satellite, JSC-63042, NASA Johnson Space Center, Houston, Tex., June 2005, p. 3.

6 W. Rochelle et al., “Results of IADC Reentry Survivability Benchmark Cases: Comparison of NASA ORSAT 5.0 Code with ESA SCARAB Code,” presentation at the 17th IADC meeting, Darmstadt, Germany, October 1999.



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