Results of time-resolved radiation exposure measurements made during U.S. Shuttle missions with a tissue equivalent proportional counter.

Time-resolved radiation exposure measurements inside the crew compartment have been made during recent Shuttle missions with the USAF Radiation Monitoring Equipment-III (RME-III), a portable four-channel tissue equivalent proportional counter. Results from the first six missions are presented and discussed. The missions had orbital inclinations ranging from 28.5 degrees to 57 degrees, and altitudes from 200-600 km. Dose equivalent rates ranged from 40-5300 micro Sv/dy. The RME-III measurements are in good agreement with other dosimetry measurements made aboard the vehicle. Measurements indicate that medium- and high-LET particles contribute less than 2% of the particle fluence for all missions, but up to 50% of the dose equivalent, depending on the spacecraft's altitude and orbital inclination. Iso-dose rate contours have been developed from measurements made during the STS-28 mission. The drift rate of the South Atlantic Anomaly (SAA) is estimated to be 0.49 degrees W/yr and 0.12 degrees N/yr. The calculated trapped proton and Galactic Cosmic Radiation (GCR) dose for the STS-28 mission were significantly lower than the measured values.