NASA Langley Research Center
Hampton, Virginia

Measurement Objectives

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The primary objective of the LDEF ionizing radiation experiments was to take measurements which will lead to a better understanding of the space radiation environment and result in more accurate models of the ionizing radiation environment. The scope of these measurements encompasses: the determination of the irradiation of experiment materials which accompanied the detectors; the measurement of shielding and locational effects; the measurement of the directional properties of LET spectra; the measurement of short range recoil particles; and overall, the measurement of the trapped charged particles. These measurements provide data to map the radiation environment which are then compared with calculations from modelling of the incident radiation and propagation through the shielding. Ionizing radiation measurements on LDEF provide a unique opportunity for reducing present uncertainties in models used in defining the space radiation environment. The improved models will enable more accurate radiation designs and design margin assessments for future missions in low Earth orbit which in turn will help reduce risk and cost.

Risk assessments are necessary for the long-term assurance of the health and safety of the International Space Station and other space crew members. Risk estimations are usually based on measurements of the charged particle radiation environment external to the spacecraft and on transport code calculations of the radiation environment internal to the spacecraft. Measurements of the spacecraft radiation environment are also essential to validate transport codes based on 3-D mass models and in some cases to provide direct data for risk estimation. The remarkably detailed investigation of the charged particle radiation environment of the LDEF satellite will enable more accurate predictions of single event upsets (SEUs) in microelectronics, and especially more accurate assessment of the risk contributed by different components of the radiation field (i.e., galactic cosmic rays, trapped protons, secondaries and heavy recoils) which affect the health and safety of crew members.

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