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NSSDC/WDC-A-R&S 91-29 The NASA/National Space Science Data Center Trapped Radiation Environment Model Program (1964-1991) James I. Vette November 1991 National Space Science Data Center (NSSDC) World Data Center A for Rockets and Satellites (WDC-A-R&S) National Aeronautics and Space Administration Goddard Space Flight Center Greenbelt, Maryland 20771 Contents L Introduction ........................................................................................................................... 1 2. Historical Background and Purpose of Program ................................................................... 3 3. Philosophy and Approach ...................................................................................................... 5 4. Summary of Accomplishments ............................................................................................. 7 5. A View of the Future .............................................................................................................. 11 Knowledge of Trapped Protons .................................................................................... 1] Knowledge of Energetic Electrons ............................................................................... 13 Prospective Data for Near-Term Modeling ................................................................. 16 The Long-Term View .................................................................................................... 18 6. Appendix: Chronology of and Remarks on TREMP Development ..................................... 21 The AE-1 Model ........................................................................................................... 21 The AP- 1, AP-2, and AP-3 Models ............................................................................... 22 The AP-4 Model ........................................................................................................... 23 The AE-2 Model ........................................................................................................... 23 The AE-3 Model ........................................................................................................... 25 The AP-5 Model ........................................................................................................... 26 The AP-6 Model ........................................................................................................... 27 The AP-7 Model ........................................................................................................... 27 The AE-4 Model ........................................................................................................... 28 The AE-5 Model ........................................................................................................... 29 The Starfish Decay Model ........................................................................................... 29 The AE-5 1975 Projected and the AE-6 Models ........................................................... 30 The AP-8 Model ........................................................................................................... 30 The Non-Model AEI-7 ................................................................................. .,.,_.,............ 31 The Inner Zone Electron Study .................................................................... :_._;_i.:._....... 31 The AE-8 Model .................................................................................................. ._-...... 32 Errors in the Models .......................................................................................... ,......... 33 Table 1. Experimental Data Used in the Trapped Radiation Model ...... Environment Program ............................................................................... 34 Table 2. Summary of Data Usage in Trapped Radiation Environment Models ...... 41 7. References ............................................................................................................................. 43 Acronyms and Abbreviations ...................................................................................................... 47 PRECEDI.NG PAGE BLANK NOT RLMED t w m 1 INTRODUCTION cial satellite on October 4, 1957, humankind had opened a new frontier for its activities. It was necessary to understand this new environment to learn how to survive for specific intervals of time, since future endeavors would require the placement of new equipment and, eventually, humans into that environment to successfully pursue these goals. The first satellites of both the U.S.S.I_ and the United States carried instruments capa- ble of measuring energetic charged particles, so by mid-1958 it was established that the geo- magnetic field was capable of trapping particles to produce a radiation belt. Thus, the trapped radiation environment was a reality that became a factor in all space program planning. This document will detail the major effort that NASA, initially with the help of the United States Air Force (USAF), carried out for 27 years to synthesize the experimental and theoretical results of space research related to energetic charged particles into a quantitative description of the terrestrial trapped radiation environment in the form of model environments. In this document the effort will be called the Trapped Radiation Environment Modeling Program (TREMP). In chapter 2 the historical background leading to the establishment of this program is given. Also, the purpose of this modeling program as established by the founders of the program is discussed. This is followed in chapter 3 by the philosophy and approach that has been applied in this program throughout its lifetime. As will be seen, this philosophy led to the continuation of the program long after it would have expired. The highlights of the accomplishments are presented in chapter 4. A view to future possible efforts in this arena is given in chapter 5, mainly to pass on to future workers the differences that are perceived from these many years of experience. Chapter 6 is an appendix that details the chronology of the developments of TREMP. Finally, the references, which document the work accomplished over these years, are presented in chapter 7. 1t 2 Most of the scientific instruments HISTORICAL that had been flown in space from October 4, 1957, to July 9, 1962, were concerned with energetic pro- tons and electrons. A general un- BACKGROUND derstanding of this environment was available from the results of these measurements. However, there could be large differences, at AND PURPOSE least by a factor of 10, when at- tempting a quantitative compari- son between various measure- ments. This was apparent to the OF PROGRAM National Aeronautics and Space Administration (NASA) and the USAF as they received proposals from contractors in response to requests for proposals (RFPs) concerning new space projects. The engineering responses to such a variance in the radiation environment caused great diffi- culty in evaluating such proposals, This resulted from the fact that spacecraft shielding, power design, orbit selection, and operating lifetime were influenced by the radiation environment. Thus, the need to obtain a "best" and uniform quantitative description of the trapped radiation environment (TRE) from the available measurements was highly desirable to a number of ele- ments of several countries' space programs. In 1958 the U.S. began the testing of one kiloton nuclear detonations at altitudes above 200 kin. Three such explosions produced short lived artificial radiation belts. Hess {1968) has pro- vided an unclassified history of these and the additional four artificial belts produced by the U.S.S.R. and the U.S. in 1962. By far the most dramatic of the seven was the U.S. Starfish det- onation on July 9, 1962. This 1.4 MT bomb, detonated at 400 Mn above Johnston Island in the Pacific Ocean, injected enough fission spectrum electrons {energies up to about 7 MeV) to increase the fluxes in the inner Van Alien belt by at least a factor of 100, and effects out to 5 Earth radii were observed. These electrons would dominate the inner zone for five years and would be detectable, in specific energy-space pockets, for about eight years. Shortly after Star- fish ten satellites were affected by the radiation damage. For example, Ariel I went out of oper- ation one week after Starfish, and TRAAC ceased shortly thereafter. The Orbiting Solar Obser- vatory (OSO) 1 suffered power degradation but was able to operate at least another year. Telstar 1, which was launched on July 10, 1962, lasted less than one year because of radiation damage, although it was planned to last for several years. Starfish had thrust the radiation problem to the forefront. There was now an extreme interest in understanding the radiation belts from a quantitative standpoint as well as from the phys- ics. Besides the satellites mentioned above, InJun 1 and Cosmos V were in orbit prior to Star- fish. Using the data from these five or six satellites, Wilmot Hess, then chief of the Theoretical Division at Goddard Space Flight Center (GSFC), began making models of the inner belt, both for electrons and protons. These models were denoted as E I, E2, etc., and P 1, P2, etc., and were distributed informally by letter. 9- 3 PRECEDfNG P_GE BLANK NOT FILMED mEMP Two satellites were launched specifically to study Starfish as soon as possible following the initial results; these were Explorer 15 (October 27, 1962) by NASA

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