Bacon, John B.

Greene, Benton R.

Marichalar, Jeremiah J.

Matney, Mark J.

Opiela, John N.

English

NASA Technical Reports Server

National Aeronautics and Space Administration
Operational and Technical Updates to the 
Object Reentry Survival Analysis Tool 
NASA Orbital Debris Program Office
Safety Team
J. Bacon (NASA Lead)
B. Greene
J. Marichalar
J. Opiela
C. Ostrom (Contract Lead)
M. Matney
C. Sanchez
A. Smith
R. Toledo-Burdett
https://ntrs.nasa.gov/search.jsp?R=20200002044 2020-05-24T04:31:11+00:00Z
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• ORSAT History
• Model Updates
• AutoORSAT
• Satellite Test Case
• Conclusions
• Future Work
Agenda
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ORSAT
All photos courtesy The Aerospace Corporation 
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ORSAT History
• Originally developed in 1994 (version 4.0) to estimate 
DCA for reentering satellites
• Version 5.X developed from 1999-2003
• Version 6.0 complete in 2005
• Version 6.1 complete in 2008
• Version 6.2 and 6.2.1 developed 2017-2019
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Model Updates (1/5)
• CFRP and GFRP
– Previous models assumed no residual 
strength existed in FRP
– Tests conducted by ODPO and others 
indicate that survivability is much 
higher [1-7]
– Examples in the media of COPV found 
on the ground after reentries of 
spacecraft and upper stages [8-10]
– “Two-material model” proposed in [7]
• If material > 1mm thick, assume fiber 
fraction will survive to ground
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The Basic Effect:
(and why it precedes the nodal crossing)
Dives into 
atmosphere
Atmosphere “falls 
away” faster than 
decay rate for most 
objects that survive 
passage through the 
“wall of air”.  
Unlikely to decay in 
next ¼ orbit
Objects that 
survive the 
previous pass 
have perigee 
near equator, 
and rapidly-
rising density 
on the approach
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When Ratio’ed to Uniform Spacing, the Spacings
of Entry ArgLats Make a “Compression Curve”
A value above 1 shows more rarified entries 
than uniform spacing would predict
A value below 1 shows more 
concentrated entries than uniform spacing would predict
The white average 
curve is the prior 
reported result.  
The physics 
behind the scatter 
is the current 
study
Peak 
compression 
slightly 
precedes the 
nodal 
crossings
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Model Updates (2/5)
• Entry Conditions
– Research over past 15-20 years indicates that reentry is not equally 
likely in time around an orbit (“latitude bias”) [11-16]
– This bias also creates a bias in conditions at entry interface [17]
– Effect is not same with varying inclination (or season, or beta) [18]
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Model Updates (3/5)
• Breakup altitude
– “Standard” ORSAT assumption is that spacecraft and rocket bodies 
breakup at 78 km (42 nmi) altitude, based on an Aerospace report 
[19]
– Same report suggests that catastrophic breakup occurs when surface 
radiative equilibrium temperature reaches melting point of structure
– New ORSAT functionality allows for computation of breakup altitude 
based on this criterion for each set of entry conditions
– Objects may now breakup >78km (CubeSats), others lower (steel 
frames)
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Model Updates (4/5)
• Radiation models
– ORSAT 6.0 used “Jones-Park” [20]
– ORSAT 6.1 added both “Tauber-Sutton” [21] and the program QRAD 
[22-23]
– All these models produce minimal effects on entries from circular LEO
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Model Updates (5/5)
• Atmosphere model
– MSISe-90 was upgraded to NRLMSISE-00 for analysis of controlled 
entries
• DCA Update
– New model only requires area of object (previous Opiela-Matney 
model required both area and perimeter [24])
– RMSE 1% better with new model
• Source code
– Upgraded from F77 to F95
– Removed parametric study functionality from within ORSAT proper
– Improved file IO – new “speed mode”
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AutoORSAT
• Python wrapper developed by Greene and Smith [24]
• Improved parametric study capability 
– ORSAT internal function could only do univariate studies
– Parallel processing
• Allows simplification of ORSAT code
– Use Fortran for heavy lifting, python for “accounting”
• Combined with computer cluster, >100K runs per hour
– Cf. ORSAT 6.0 – 1 run in ~3-6 hours
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Satellite Test Case (1/)
• 1100 kg S/C
– 150 unique components
• 98.0° inclination
• 8640 trajectories simulated in 
GMAT to generate the entry 
conditions
– Varying time of year, RAAN, dithered 
BC
• “Standard” ORSAT analysis for 
comparison
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Satellite Test Case (2/)
• STD ORSAT
– 43 surviving components
– 26 m2 DCA
– Ec 1:2700 (using equal temporal likelihood-based population density)
• AutoORSAT
– DCA between 21-29 m2, depending on conditions
– Ec depends on where objects land (latitude binning)
– Average Ec 1:3300
– Median Ec better than 1:10K (Compliant?)
– Worst Ec ~1:500
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Satellite Test Case (3/)
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Conclusions
• ORSAT 6.2.1 up to 100x faster than v6.0 (single-thread)
• AutoORSAT allows for significant exploration of 
parametric space
• Simplification and update allows for faster development 
going forward and more robust code
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Future Work
• Design-for-demise (D4D)
– Sensitivity to breakup altitude (see Lips [25])
• Statistics!
– Ability to quickly see effects of each parameter (which to ignore and 
which to refocus on)
• Improving FRP ablation/demise models
• Hollow object modeling
– Currently all objects treated as solid, but with less area if hollow
– New models for transitional flow being developed (see Marichalar 
[26])
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Questions
Thanks for your time!
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References (1/3)
1. 31st ISTS – “Experimental Investigation of Material Demisability in 
Uncontrolled Earth Re-entries”
2. 8th IAASS – “ABOUT THE DEMISABILITY OF PROPELLANT TANKS
3. DURING ATMOSPHERIC RE-ENTRY FROM LEO”
4. ODQN 22-3 – “Spacecraft Material Ablation Testing at UT Austin”
5. ODQN 23-3 – “Testing and Modeling the Demisability of Fiber-
Reinforced Plastics”
6. 6th ESDC -- "Modelling the Thermal Decomposition of Carbon Fibre
Materials During Re-entry“
7. 10th IAASS – “Demisability of Various Reinforced Polymer Components 
of Reentering Orbital Debris: Phase I Test Results”
8. https://www.campograndenews.com.br/cidades/objeto-que-caiu-em-
chacara-e-tanque-de-combustivelestrangeiro-diz-aeb
9. https://www.reuters.com/article/us-australia-spacejunk/australian-farmer-
finds-mystery-space-junkidUSSYD8466320080328
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References (2/3)
10. https://timesofindia.indiatimes.com/city/madurai/Mysterious-object-
inspectedby-ISRO-officials/articleshow/55380486.cms
11. 9th IAASS – “Casualty Risk Reduction by Semi-Controlled Reentry”
12. 9th IAASS – “Oblate-Earth Effects on the Calculations of Ec During 
Spacecraft Reentry”
13. 8th IAASS – “Statistical Issues for Calculating Reentry Hazards” 
14. 7th ESDC – “Fast Re-Entry Deorbitation with Acceptable Risk Level”
15. 3rd IAASS – “Statistical Issues for Uncontrolled Reentry Hazards”
16. 4th IAASS – “Statistical Issues for Uncontrolled Reentry Hazards: Empirical 
Tests of the Predicted Footprint for Uncontrolled Satellite Reentry Hazards”
17. 10th IAASS – “Effect of Latitude Bias in Entry Angle on Ground Casualty 
Risk from Naturally Decaying Space Objects”
18. 10th IAASS – “Seasonal- and Beta-Angle-Dependent Latitude Bias 
Variations in Natural Decays”
19. “Aerospace Report No. ATR-92(2835)-1, Review of Orbital Reentry Risk 
Predictions"
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References (3/3)
20. Hamilton, Gupta, Jones “Flight Stagnation-Point Heating Calculations on 
Aeroassist Flight Experiment Vehicle”, 1991 JoS
21. Tauber and Sutton. “Stagnation-Point Radiative Heating Relations for 
Earth and Mars Entries”
22. Page et al. “Radiative Transport in Inviscid Nonadiabatic Stagnation-
Region Shock Layers“, 1968
23. JSC-26059 – “User's Manual for QRAD Entry Radiation Program”
24. 1st IOC – “Development and Analysis of the Automated Object Reentry 
Survival Analysis Tool’s Parametric Study Wrapper
25. 10th IAASS – “Probabilistic Casualty Risk Assessment and Labeling for 
the Re-Entry of Spacecraft Components”
26. 1st IOC – “Estimating Drag and Heating Coefficients for Hollow Reentry 
Objects in Transitional Flow Using DSMC”


Operational and Technical Updates to the Object Reentry Survival Analysis Tool

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