FIGURE 3.2 International Space Station (ISS) exposure to radiation. Twenty-four hours of ISS ground track overlaid with the magnetic shielding boundaries for quiet and active storm conditions and the South Atlantic Anomaly. The quasi-latitudinal pair of high-latitude lines in each hemisphere indicates the low-latitude borders of areas accessible to radiation from solar energetic particle (SEP) event zones. The higher-latitude line in each hemisphere represents quiet conditions and the lower-latitude line represents disturbed conditions. SOURCE: NRC, 2000, Figure 1.5, p. 14, originally provided by Ronald E. Turner, ANSER Corporation.

instruments to measure dose (tissue equivalent proportional counter [TEPC]),2 and record the charge, energy, and directionality of particles (charged particle directional spectrometer [CPDS]).3 Passive dosimeters are mounted throughout the ISS and space shuttle (RAM) and are also worn by crew members throughout the mission (CPD). The TEPC and CPDS display the average dose rate and other parameters in real time for use by the crew, and transmit data to Mission Control so that SRAG personnel can constantly monitor the radiation environment inside the spacecraft. The TEPC is portable, enabling the mapping of the internal spacecraft radiation environment. The TEPC and RAM are flown on both the ISS and the space shuttle; the CPDS is flown only on the ISS.


The TEPC measures the dose that a small volume of human tissue would absorb if the tissue were at the detector’s location. The instrument incorporates a spectrometer that performs real-time calculations and a liquid crystal display.


The CPDS is a stack of energy-loss and position-sensitive silicon detectors and a Cerenkov counter, designed to measure the charge, energy, and direction of a particle that passes through the instrument. Currently, there are four CPDS instruments in use onboard the ISS. The intra-vehicular charged particle directional spectrometer (IV-CPDS) is designed to be used inside the ISS, with liquid crystal displays and mounting and power options for both the U.S. and Russian segments. The remaining three CPDS instruments are mounted outside the ISS and form the extra-vehicular charged particle directional spectrometer (EV-CPDS). The EV-CPDS instruments are arranged in such a way that one points forward along the velocity vector (EV1), one points aft along the antivelocity vector (EV3), and the third points up along the zenith direction (EV2). The EV-CPDS instruments have no liquid crystal displays and are coated with a special material to allow the instruments to survive the extreme temperatures in space.

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