NASA Langley Research Center
Hampton, Virginia

Ionizing Radiation Modelling

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The LDEF satellite provided the unique opportunity to investigate long-term radiation exposure of spacecraft materials in the low-Earth orbit (LEO) environment. LDEF incorporated thirteen experiments designed specifically to measure some aspect of the space radiation environment. The LDEF mission was particularly important to radiation model validation for the following reasons: various types of detectors were aboard, providing an extensive data set; the long mission duration enabled the data to have unparalleled statistical accuracy; and the LDEF spacecraft had a very stable flight orientation, allowing unprecedented data to be obtained on the directionality of the charged trapped particles in the space environment. To study this radiation environment, detectors and analyses of radiation sources and the induced radioactivity of the LDEF were utilized. Numerous detectors were located about the circumference of LDEF and at various shielding depths. Some of the experiments onboard the LDEF were specifically designed to measure the radiation environment while other experiments were designed to monitor radiation environmental effects near a component. These measurements include dosimetric studies on the directional aspects, energies, and magnitudes of particle radiation in LEO. Quantitative results from these measurements should provide an accurate means of confirming environment flux models, assessing the accuracy of radiation environment models, calculations, and techniques for predicting radiation encountered on future LEO missions, particularly those of extended duration.

This comparison process will allow adjustment of the models and accurate extrapolation of the environment to any LDEF coordinate, as well as to other spacecraft. This becomes especially useful since the LDEF orbit was essentially the same as that planned for the International Space Station. Consequently, the radiation measurements on LDEF will play a significant role in the design and construction of radiation shielding of the Space Station, and indeed on other long-term, near-Earth orbital space missions.

As a result of expanded near-Earth orbital space missions, spacecraft designers and engineers have a need for accurate radiation models. Several radiation models, such as the Siegen LET code, the Vette AP-8, and AE-8 trapped particle models and the CREME model were utilized to evaluate the data from the LDEF. The LDEF Ionizing Radiation Special Investigation Group plans to release a radiation model that incorporates the data gathered from the LDEF. In addition, a list of current radiation models has been compiled.

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