The impact of alternative mission models on the future orbital debris environment

In reviewing discussions of future directions for space activity, it becomes obvious that there are a large number of groups formulating a wide diversity of plans for the future use of space. These plan alternatives are being made to account for user needs, technology development constraints, economic constraints, and launch support, and each of the plans will have direct or indirect effects on the orbital debris environment in terms of mass to orbit, deposition of operational debris, and control of accidental breakups. Thus it is important to develop the ability to project future debris states for a range of possible space traffic scenarios. The impact that these possible traffic environments would have on space operations forms the basis for studies of alternative options for the usage of space. In this paper, the effects on the orbital debris environment of a base-line mission model and two alternatives are investigated, using a numerical debris environment simulation code under development at JSC.     

Radioactive satellites: Intact reentry and breakup by debris impact

There is a substantial mass of radioactive material in nuclear reactors or radioisotope thermal generators (RTGs) in orbit about the earth. This paper examines the reentry of intact nuclear fuel cores and RTGs and the fragmentation and subsequent radioactive debris cloud deposition and evolution resulting from the impact of orbital debris upon an orbiting reactor, fuel core, or RTG. To assess the intact reentry, decay rates and a predicted decay date using historical and projected orbital decay data, are estimated. The current NASA debris environment model is utilized to estimate impact rates and debris cloud evolution of a fragmentation event. Results of these analyses are compared and concepts are tendered which would tend to minimize the radiological debris hazard to personnel and structures both on the earth's surface and in low earth orbit.     

Density and mass distributions of orbital debris

Area-to-mass ratios for orbital debris tracked by the U.S. Space Command were calculated from observed changes in apogee and perigee altitude due to atmospheric drag. The area-to-masses observed for the orbital debris were similar to those found for debris from laboratory breakups, and suggest that much of the debris is composed of crumpled thin plates or of insulation material with low effective density. Areas for the debris objects were derived from radar cross-section data. Object masses were calculated from the ratio of the RCS-derived area to the area-to-mass ratio. Analysis of the distributions of fragment masses from the breakups suggests that in many cases, only a portion of the initial object breaks up into small fragments.