The effects of vacuum and (gamma) -irradiation as well as their joint effects on electrical and optical properties of phototransistors and imaging charge coupled devices are discussed. These effects will be related not only to bulk effects, but also to surface effects which are enhanced due to vacuum environments.
Over the past several years the interest in orbital debris has grown due to the hazard it poses to operating satellites. Models of the debris environment depend upon accurate assessments of the masses and sized of debris particles. Utilizing data from several hypervelocity impact tests and other sources, a mass-diameter relationship is determined for debris ranging in size from sub-millimeter particles to objects as large as derelict rocket bodies and inactive satellites. The accuracy of the mass-diameter relationship is examined and conclusions are reached.
The key to conducting an accurate damage assessment of a structure that has been impacted by an orbital debris particle is the use of a robust assessment methodology. To accurately determine total structure damage, a damage assessment methodology must include the effects of descrete impacts by solid debris cloud fragments as well as impulsive loadings due to molten and vaporous debris cloud material. As a results, the amount of debris cloud material in each of the three states of matter must be known to accurately assess total damage due to a high speed orbital debris impact. This paper presents a first-principles based method to calculate 1) the amount of material in a debris cloud created by a perforating hypervelocity impact that is solid, molten, and vaporous, 2) the debris cloud leading edge, trailing edge, center-of-mass, and expansion velocities, and 3) the angular spread of the debris cloud material. The predictions of this methodology are compared with those of empirically based damage assessment schemes as well as against numerical and empirical results obtained in previous studies of debris cloud formation.
Orbital debris penetration of manned spacecraft is accompanied by a number of atmospheric effects that can pose a serious hazard to spacecraft and crew survival. These atmospheric effects can include overpressure, light flash, and temperature rise as hot particles from the penetration process impinge into the atmosphere of a manned spacecraft. This paper reports the results from a series of tests sponsored by the Marshall Space Flight Center and recently completed at the University of Alabama in Huntsville Aerophysics Research Center to study these effects. In these tests, a light gas gun was used to fire orbital debris particle simulants from 0.375 to 0.625 inches in diameter through target simulants into a large test chamber simulating the interior cabin of a spacecraft at 1 atmosphere. The test chamber was instrumented with pressure transducers, light sensors, and temparature gauges to measure the level of blast hazard associated with differing target and penetrator conditions at various distances from the target site. The mitigating effects of interior equipment racks and spall blankets were also measured. This report discusses the relationship between observed overpressure, light, and temperature effects and the hazard level that would be expected to cause crew injury.
The Space Transportation System (STS) fleet has flown more than sixty missions over the fourteen years since its first flight. As a result of encounters with on-orbit particulates (space debris and micrometeoroids), 177 impact features (chips) have been found on the STS outer windows (through STS-65). Forty-five of the damages were large enough to warrant replacement of the window. NASA's orbital operations and vehicle inspection procedures have chnaged over the history of the shuttle program, in response to concerns about the orbital environment and the cost of maintaining the space shuttle. These programmatic issues will be discussed, including safety concerns, maintenance issues, inspection procedures, and flight rule changes. Examples of orbital debris impacts to the shuttle windows will be provided. There will also be a brief discussion of the impact properties of glass and what design changes have been considered to improve the impact properties of the windows.
The purpose of this study is to examine the sensitivity of the orbital debris environment to fragmentation model parameters. Seven modeling parameters are varied to examine their impact on the future debris environment. Simulations for the future debris state up to the year 2081 are compared with evolution runs using 'standard' breakup models. Fragments from satellite-satellite collisions are shown to dominate the future evolution of the debris environment. Several parameters significantly affect the future environment evolution. This shows that further work to improve fragmentation model is warranted. By improving all aspects of debris modeling it could be shown that our models for the environment are accurate and justify taking measures to reduce our polluting of the orbital environment.
Determining the hazards from debris generating events is a design and safety consideration for a number of space systems, both currently operating and planned. To meet these and other requirements, the US Air Force Phillips Laboratory Space Debris Research Program is developing a simulation platform called the Debris Analysis Workstation (DAW) which provides an analysis capability for assessing a wide variety of debris studies. DAW integrates several component debris analysis models and data visualization tools into a single analysis platform that meets the needs for DoD space debris analysis, and is both user friendly and modular. This allows for studies to be performed expeditiously by analysts that are not debris experts. DAW has gone from concept to reality with the recent deliveries of Versions 0.1 to 0.4 to a number of customers. The current version of DAW incorporates a spacecraft break-up model, drag inclusive propagator, a collision dispersion model, a graphical user interface, and data visualization routines, which together provide capabilities to conduct missile intercept range safety analyses. Work is progressing to add new capabilities with the incorporation of additional models and improved designs. The existing tools are in their initial integrated form, but the 'glue' that will ultimately bring them together into an integrated, user-friendly system, is an object oriented language layer that is scheduled to be added in 1995. Other candidate component models that are under consideration for incorporation include additional orbital propagators, error estimation routines, dispersion models, and other breakup models. At present, DAW resides on a SUN workstation, although future versions could be tailored for other platforms, depending on the need.
In this paper we consider the implications for the orbital debris environment of introducing a constellation of satellites into low Earth orbit. We consider not only the impact that the orbital debris population will have on the satellites, but also the possible effect of the space system on the environment. Using standard population models we estimate the collision risk that the current orbital debris environment will present to a variety of generic constellation designs, and investigate the consequences of a collision-induced breakup of one of the constellation elements for operational satellites residing both within, and outside, the constellation. We apply state-of-the-art developments in the method of probabilistic continuun dynamics to estimate the short term collision hazard, and the classical Kessler approach to estimate the long term collision risk. We assess the probability of a collision-induced cascade fragmentation occuring within the system and its possible consequences for the extermal satellite population. We find that for large constellation sizes, the likelihood of a collision- induced breakup of a satellite is significant, although the probability of a collisional cascade within the constellation remains small by comparison.
To better characterize the orbital debris environment, improvements must be made to the overall sensitivity of the orbital debris surveillance system. There are many ways to improve the sensitivity of the optical system: through hardware and software improvements, and through observing techniques. AMOS has been investigating algorithms for processing video data as a technique for improving the sensitivity of the optical sensors. This paper discusses preliminary results for two different approaches to the sensitivity issue, and the potential for implementing them in real time.
Results of debris environment projections are of great importance for the evaluation of the necessity and effectiveness of debris mitigation measures. EVOLVE and CHAIN are two models for debris environment projections that have been developed independently using different conceptual approaches. A comparison of results from these two models therefore provides a means of validating debris environment projections which they have made. EVOLVE is a model that requires mission model projections to describe future space operation; these projections include launch date, mission orbit altitude and inclimation, mission duration, vehicle size and mass, and classification as an object capable of experiencing breakup from on-board stored energy. EVOLVE describes the orbital debris environment by the orbital elements of the objects in the environment. CHAIN is an analytic model that bins the debris environemnt in size and altitude rather than following the orbit evolution of individual debris fragments. The altitude/size bins are coupled by the initial spreading of fragments by collisions and the following orbital decay behavior. A set of test cases covering a variety of space usage scenarios have been defined for the two models. In this paper, a comparison of the results will be presented and sources of disagreement identified and discussed. One major finding is that despite differences in the results of the two models, the basic tendencies of the environment projections are independent of modeled uncertainties, leading to the demand of debris mitigation measures--explosion suppression and de-orbit of rocket bodies and payloads after mission completion.
The National Oceanic and Atmospheric Adiministration (NOAA) is the world's largest civil operational environmental space agency. NOAA is also the largest holder of atmospheric and oceanographic data in the world. An overview of NOAA's operational satellite programs is presented. These programs include the Geostationary Satellite Program, the Polar-orbiting Satellite Program, and the Landsat Program. The Geostationary Satellite Program includes the Geostationary Operational Environmental Satellite series. A discussion of NOAA's policy to mitigate geosynchronous orbit debris is also provided. The Polar Program includes the NOAA K-N' satellite series and the newly converged NOAA and Department of Defence operational polar-orbiting satellite programs. A discussion of the status of the converge polar satellite program is provided. The Landsat Program includes the plans of the new Landsat Program Management which is composed of NOAA, NASA, and the US Geological Survey. The Landsat 7 spacecraft and ground system are discussed.
Since the launch of the first Sputnik in 1957, the number of space debris in orbit is progressively increasing, up to a point that is today considered serious. Scientists quickly became aware of this phenomena and started studying the evolution, mitigation, and characterization of space debris. But jurists are today confronted with a situation that the United Nations Outer Space Treaties did not foresee. The purpose of the presentation is to look at the existing international public law and examine how it may help to characterize and/or mitigate the space debris population. After having briefly described the problem caused by space debris, the first part will study the United Nations Space Treaties and in particular the principles of responsibility and liability as laid down in the 1967 Outer Space Treaty and the 1972 Liability Convention, which should allow us to conclude that there is an urgent need for a new international convention of space debris. The second part will then focus on the several proposals made concerning space debris and will lay down a set of general principles of the legislation on space debris.
NASA has adopted a policy to limit the generation of orbital debris, as stated in NASA Management Instruction 1700.8. To implement this policy, NASA sponsered the development of a handbook to assist in performing debris assessments, and this project has lead to the developemnt of a NASA safety standard, which is undergoing final review. This paper is a review of the guidelines and rationale sections taken from the standard.