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Construction of the International Space Station is now a reality with the start of permanent human presence. Radiation presents a serious risk to the health and safety of the astronauts with the clear requirement for estimating their exposures prior to and after the flight. Over the last few years, a tissue equivalent proportional counter (TEPC) has been flown at a fixed mid-deck location onboard Shuttle flights in 51.65° inclination flights. These flights have provided data that covers the expected changes in the radiation exposure due to changes in altitude, and solar activity from the solar minimum to the solar maximum of the current 23rd solar cycle. Comparison with data acquired by a TEPC flown on the Mir has been made and shows excellent agreement. Based on this data a simple function of the solar deceleration potential has been developed to predict 90 days ahead of time of observations, the internal galactic cosmic radiation dose rate to ± 10% throughout the solar cycle.

A new radiation measurement system for the realtime measurement of absorbed depth dose and dose-equivalent from space radiation within a phantom is being developed. The head and torso of the “average male” phantom (height 175 cm, weight, 73.5 kg) will be instrumented with active and passive radiation dosimeters and flown as an experiment on a Shuttle mission in 1996. The unique dosimetry system, which utilizes both pulse height analysis and internal data storage, is described. The active systems will be supported with a large number of passive dosimeters (lithium fluoride thermoluminescent detectors and CR-39 plastic nuclear track detectors) distributed throughout the phantom. Previous earlier measurements of space radiation dose distribution within a phantom head are reviewed. Unfortunately, results from both passive and active radiation measurement systems on the head-torso phantom experiment are not yet available.

Longer on-orbit crew stay times anticipated during the construction and habitation of the International Space Station (ISS) will necessarily require the development of a new generation of radiation measurement instrumentation. The planned orbit of 51.6° inclination at 470 km will result in significantly higher daily crew exposures than experienced during the bulk of previous U.S. space missions. In addition, the National Commission for Radiation Protection and Measurement (NCRP) is revising the guidelines for crew radiation exposures. It is anticipated that the new guidelines will call for dose and dose-equivalent limits that are substantially less than those currently used in the space program. The cornerstone elements of the planned radiation measurement instrumentation for the ISS are a tissue-equivalent proportional counter (TEPC) and a directional charged particle spectrometer. These active systems will be supported by NASA's standard passive (thermoluminescent) dosimetry system.

Current dosimetric practices do not provide comprehensive classification of high-energy charged particle radiation, so that the ability to adequately project health risk to astronaut crews is limited. To address this shortcoming in dosimetry for Space Station missions, a new generation of active radiation monitors is being developed to supplement traditional dosimetry. One active monitor is a Tissue Equivalent Proportional Counter (TEPC) to measure the linear energy transfer (LET) spectrum of space radiation. Two versions of a second type of active monitor, the Charged Particle Directional Spectrometer (CPDS), will be deployed, one internal and one external to the Station. The CPDS consists of a stack of lithium-drifted silicon detectors used to classify the radiation by particle charge and energy. The comprehensive data set obtained by using the TEPC and the CPDS permits significant improvement in assessing crew radiation exposures.