BOX 6-1 Design Responses to the Debris Hazard: Three Examples

International Space Station: Because of the extremely high value of the spacecraft and the desire to protect the people that will inhabit it, the International Space Station design requirements are that the probability that debris impact will cause a critical failure must be less than 0.5% per year.

Geostationary Communications Spacecraft: Due to the low perceived hazard in the geostationary orbit, no spacecraft in GEO are known to have design requirements specifically for protection against debris impacts, though they are designed to survive the micrometeoroid environment.

RADARSAT: The RADARSAT spacecraft is designed to be launched into an orbital regime with a high debris flux. The response of the RADARSAT designers is presented in some detail at the end of this chapter.

ESA, the National Space Development Agency of Japan, and the Russian Space Agency in the design of the International Space Station (Kessler et al., 1994). A simplified version of this model, accessible on the EnviroNET database (Lauriente and Hoegy, 1990), can predict the cumulative debris flux of a given size on a spacecraft surface in any LEO. The ESA Reference Model for Space Debris and Meteoroids is also available in an analytic form useful for spacecraft designers (Sdunnus and Klinkrad, 1993).

Once the debris flux and the distribution of impact angles have been estimated, the number of impacts on specific spacecraft components can be predicted. This process involves determining the location of each component relative to all the others and to the incoming space debris, to see how components shield one another and to determine where and at what angles debris is likely to strike each component. NASA's BUMPER probability analysis code (Christiansen, 1993), which was developed for the analysis of Space Station Freedom and has since been applied to the U.S. shuttle orbiter, LDEF, Mir, and the proposed International Space Station, can be used to link the debris (and meteoroid) environment with the spacecraft's geometry and penetration equations to determine the perforation hazard to each part of the spacecraft and to size shielding to prevent such perforations. However, BUMPER can only predict perforation hole size; it cannot predict other types of impact damage.

Other models, analyses, or impact tests are needed to assess the probability of component failures due to impact damage effects. As described in Chapter 5, this can be accomplished through numerical or analytical methods, by subjecting some components to actual hypervelocity impacts, or through a combination of both approaches. As described in



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