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Issue 6: Preservation of Space

International Guidelines for the Preservation of Space as a Unique Resource


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Another factor contributing to the calculation of collision rate is the relative cross-sectional area of projectiles and targets. While Figures 2 and 3 indicate two roughly equivalent peaks in spatial density at around 800-1000 km and 1400-1500 km altitude, more collisions are expected to take place at the lower altitude. This is because the objects resident at and about that altitude are significantly larger (many being derelict SL-16 R/B), and hence present more "target area", than are the spacecraft around 1400-1500 km altitude. This has been confirmed by high fidelity long-term computer modeling of the evolution of the environment.

Computer models, based on measurements of the environment (including the analysis of objects returned from space), are used to project an "average" environment due to objects smaller than those depicted in Figures 2-5.

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Fig. 6: The modeled environment for 1 mm-1 m impactors; target orbit is 400 km circular, 51.6∞ inclination (similar to the ISS nominal orbit).

Figure 6 depicts the output of the NASA ORDEM2000 computer model (Ref. X7). As may be seen, the cumulative flux due to the debris population 1 mm and larger in size is five (5) orders of magnitude larger than the cataloged population.

3. Effects Upon Spacecraft

As of this writing (November 2003), there has been only one (1) recognized accidental collision between cataloged objects: the French Cerise satellite's gravity gradient stabilization boom was cut by a piece of French debris produced by the 1986 fragmentation of an Ariane R/B third stage. All other historical (alleged) collisions were conducted as military anti-satellite or ballistic missile defense tests. The vast majority of fragmentations have been accidental explosions.

These explosions range in severity from mission survivable (e.g. a battery box explosion aboard the NOAA 8 spacecraft) to the catastrophic, in which a body is totally destroyed in the blast. Therefore, this section will concentrate on the effects of impacts on spacecraft.

A qualitative assessment of impact effects is provided in the following table, after Ref. X1.

Diameter of Impactor [cm] Effect
< 0.01 Surface erosion
< 0.1 Potentially serious damage to spacecraft
0.3 at 10 km/s relative velocity (typical in low Earth orbit) Equivalent to being struck by a bowling ball traveling at 60 mph (88 ft/s)
1.0 at 10 km/s relative velocity Equivalent to being struck by a 400 lb safe traveling at 60 mph
Table II. Effects of particles of a given size upon spacecraft surfaces

It is illustrative in a quantitative sense to examine the dependency of the probability of impact or penetration upon environmental and physical variables. Environmental variables are those dependent upon the orbital characteristics of the target (and projectile) objects, such as the relative velocity between the two; physical variables include the mass densities of the materials constituting the two objects.

The effect of the incident flux may be characterized by the Poisson probability of one or more (n ≥ 1) impacts of size 'd' and larger is:

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Where F(d, v) is the size and velocity-dependent flux, dA is the differential unit of surface area, n is the number of impacts, and integrals are performed over both surface area and the velocity distribution.

A common figure of merit for estimating the hazard to spacecraft (for example, in calculations performed for the International Space Station [ISS] and the space shuttle fleet) is the probability of no penetration, or PNP. The PNP may be expressed using the Poisson statistic P0 = exp(-N), where:

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The variable T is the surface thickness, ø is the impact angle measured from surface normal, v is the relative velocity, f(v) is the fraction of velocities between v and v + dv, p is a mass density, A is the area of the exposed surface, and t is the elapsed time of exposure. The subscripts 't' and 'p' refer to target and projectile, respectively, and the set (issue pic) are, in general, non-integer rational numbers. Additional dependencies relating to target yield and tensile strengths[12] or other material characteristics[13] may be manifest. Multi-layer shielding and body self-shielding can modify these relations.

Impacts in MEO and GEO occur at correspondingly lower velocities. However, even in GEO, the average relative velocity is on the order of 500 m/s, with a maximum around 1.5 km/s. As such, and to apply a terrestrial measure, these are commensurate with being struck by either "standard" or "high velocity" ammunition.

While the debris population accounts for roughly half of all objects tracked and cataloged by the US, simple calculations reveal that the impact rate of these cataloged objects onto a one m2 target, per year, is minuscule. However, small untracked debris do present a meaningful hazard to spacecraft because of accelerated aging of spacecraft components, degradation of sensitive surfaces such as mirrors, optical surfaces, radiators, and solar panels, and the potential for a 'mission kill' should a single-point failure mode be susceptible to impact by small debris. The STS-50 mission provides an example of component degradation[4], as segments of the radiator assembly were required to be replaced following approximately 10 days of flight with the payload bay facing in the direction of the velocity vector (the so-called "ram" direction). Shuttle flight deck windows are also replace with a frequency of (on average) one outer pane per mission. High pressure propellant lines, pressurized storage vessels, and exposed cable bundles provide additional examples of single-point failure mode elements on small spacecraft.


  • Appendix A: An Orbital Debris Bibliography (PDF, 180 KB)
  • Appendix B: Space Situational Awareness via Space Surveillance (PDF, 2.3 MB)
  • Appendix C: US Government Guidelines (PDF, 124 KB)


  1. Anonymous, "Meteoroid Environment Model-1969 [Near Earth to Lunar Surface]". NASA SP-8013 (1969).
  2. Anonymous, Natural Environment for Space Station Design, Revision A. NASA SSP-30425/A (June 1989).
  3. Reynolds, R.C., G.W. Ojakangas, and P.D. Anz-Meador, "Defining Orbital Debris Environmental Conditions for Spacecraft Vulnerability Assessment". J. Spacecraft Rockets 29, no 1 (January-February 1992): 57-63.
  4. Christiansen, E.L. et al., "Assessment of High Velocity Impacts on Exposed Space Shuttle Surfaces". In Proceedings of the First European Conference on Orbital Debris, W. Flury ed. (Darmstadt, Germany: ESA SD-01, 1998): 447-52.
  5. Anz-Meador, P.D. and A.E. Potter, "Density and Mass Distributions of Orbital Debris". Paper IAA-94-IAA.6.4.689, presented at the 46th Congress of the International Astronautical Federation, Jerusalem, Israel, 9-14 October 1994.
  6. Reinhardt, A., Wm Borer, and K. Yates, "Long Term Orbital Debris Environment Sensitivity to Spacecraft Breakup Parameters" DRAFT. Presented at the World Space Congress, Washington, D.C., September 1992.
  7. Kessler, D.J., "Impacts on Explorer 46 from an Earth Orbiting Population". In Orbital Debris, D.J. Kessler and S.-Y. Su, eds., NASA CP-2360 (1985): 220-32.
  8. Oliver, J.P. et al., "Estimation of Debris Cloud Temporal Characteristics and Orbital Elements". Adv. Space Res. 13, no. 8 (August 1993): 103-6.
  9. Bernhard, R.P., and D.S. McKay, "Micrometer-sized Impact Craters on the Solar Maximum Satellite: The Hazards of Secondary Ejecta". In Lunar and Planetary Science XIX, Part 1 (Houston: Lunar and Planetary Institute, 1988): 65-6.
  10. Stansbery, E.G., D.J. Kessler, T.E. Tracy, M.J. Matney, and J.F. Stanley, "Haystack Radar Measurements of the Orbital Debris Environment", NASA JSC-26655 (20 May 1994).
  11. Anz-Meador, P.D., "A Model of the Thermal and Electrical Properties of Cosmic Dust Particles". Ph.D. dissertation, Baylor University, Waco, Texas, 1989.
  12. Watts, A.J., and D. Atkinson, "Dimensional Scaling for Impact Cratering and Perforation". Presented at the 3rd LDEF Post-Retrieval Symposium, Williamsburg, VA, 1993.
  13. McDonnell, J.A.M., and K. Sullivan, "Hypervelocity Impacts on Space Detectors: Decoding the Projectile Parameters". In Hypervelocity Impacts in Space, J.A.M. McDonnell, ed. (Canterbury, UK: University of Kent Press.
  • X1. Interagency Group (SPACE), for the National Security Council, "Report on Orbital Debris", Washington, D.C., February 1989.
  • X2. Galicia, G.E., B.D. Green, M.T. Boies et al., "Particle Environment Surrounding the Midcourse Space Experiment Spacecraft". J. Spacecraft Rockets 36, no. 4 (July-August 1999): 561 ff.
  • X3. Dushek, O., W.K. Hocking, and N. Mitchell, "Investigation of the Possible Detection of Earth-Orbiting Particulates by SKiYMET Meteor Radars". Can. Undergrad. Phys. J. 1, no. 2 (January 2003): 7-11.
  • X4. Office of Science & Technology Policy, "Interagency Report on Orbital Debris". Washington, D.C., November 1995.
  • X5. Anz-Meador, P.D., History of On-Orbit Satellite Fragmentations, 12th ed. NASA JSC-29517, Houston, Texas, USA. 31 July 2001.
  • X6. Flury, W., A. Massart, T. Schildknecht et al., "Searching for Small Debris in the Geostationary Ring - Discoveries with the Zeiss 1-metre Telescope". ESA Bulletin no. 104 (November 2000): 92 ff.
  • X7. Liou, J.-C., M.J. Matney, P.D. Anz-Meador et al., "The New NASA Orbital Debris Engineering Model ORDEM2000". NASA TP 2002-210780, Houston, Texas, USA. May 2002.
  • X7A. Portree, D.S.F. and J.P. Loftus Jr., Orbital Debris and Near-Earth Environmental Management: A Chronology. NASA Ref. Pub. (RP) 1320, December 1993.
  • X8. Hõrz, F., G. Cress, M. Zolensky, T.H. See, R.P. Bernhard, and J.L. Warren, "Optical Analysis of Impact Features in Aerogel From the Orbital Debris Collection Experiment on the Mir Station", NASA/TM-1999-209372, August 1999.
  • X9. Mandeville, J.C., "Cosmic Dust and Orbital Debris: Collection on MIR Space Station", Adv. Space Res. 11, no. 12 (1991): (12)93-(12)96.
  • X10. Mandeville, J.C., and L. Berthoud, "Hypervelocity Impacts on Space retrieved Surfaces: LDEF and MIR". In Hypervelocity Impacts in Space, ed. J.A.M. McDonnell (Canterbury, UK: U. of Kent at Canterbury, 1991): 196-199.

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Issue No. 6:
Satellite Security

Winter 2004

General Editor Introduction

From the Guest Editor


Security Issues
p. 1
, p. 2

Threats to Satellite Communication
p. 1
, p. 2

Signal Security
p. 1
, p. 2

Current Development

Space-Based Weaponry
p. 1
, p. 2

Preservation of Space p. 1, p. 2

Critical Perspectives

Security and Performance

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