Pacific Northwest Laboratory detectors map safe space travel
August 05, 1994
RICHLAND, Wash. –
Astronauts are exploring the depths of space and airline passengers are flying near the speed of sound, but as travel takes us farther and faster we face a new concern -- cosmic radiation. To enable NASA to gather first-of-a-kind data on the types and amounts of cosmic radiation to which humans are exposed, researchers at the U.S. Department of Energy's Pacific Northwest Laboratory are developing special detectors for several U.S. and Russian space exploration missions in 1994.
Scientists at PNL are making final adjustments to two instruments. The tissue-equivalent proportional counter simulates a human cell nucleus and records the energy deposited, and resulting tissue damage, when cosmic radiation passes through the body's cells. The counter is capable of identifying and recording a full spectrum of energy every second. The charged-particle directional spectrometer characterizes the radiation by identifying the types, amounts and direction of cosmic rays. The TEPC is housed in a casing about the size of a cellular phone, and the spectrometer is slightly larger.
Prototypes of both the TEPC and spectrometer have been tested in space. In 1993, the PNL-developed detectors were tested on three U.S. space shuttle missions including the Endeavor mission in May. Most recently, a TEPC instrument was placed in the shuttle cargo bay during the March 1994 Columbia mission to measure radiation outside crew quarters.
In coming months, several new, modified versions of both detectors will be supplied to NASA to gather data on various missions throughout 1994. These detectors will have expanded capabilities, including memory to store months of data and will be smaller and lighter -- an important consideration in space exploration with launch costs estimated at $5,000 per pound.
Current plans call for the instruments to be placed inside crew quarters and outside the shuttle to determine dose to humans and equipment in both environments. Data collected will be instrumental in determining the parameters of manned space missions.
"The Earth's atmosphere acts as a filter, protecting humans from various types and amounts of natural background radiation," said Leslie Braby, project manager of PNL's space dosimetry program. "As space travel, and even some commercial air travel, moves us out of this buffer zone, we need to characterize the radiation our bodies are coming in contact with -- especially as we plan for extended manned experiments in space."
A unique version of the TEPC recently was delivered to NASA for its joint experiment with the Russian space program on the Mir Space Station. The instrument is expected to be placed in Mir crew quarters to gather data on human and equipment radiation exposure for approximately two years.
NASA will apply data from the detectors to verify and improve models currently used to estimate human exposure to cosmic radiation. Also, the detectors will track location shifts of high radiation areas in our atmosphere that result from trapped radiation zones and solar flares.
"Some areas of our atmosphere have radiation levels up to 100 times greater than others," Braby said. "The detectors will supply NASA with the data to map the safest space travel routes and to determine the best positioning of the U.S. Space Station Freedom." The mapping capability was illustrated during prototype testing on a previous shuttle mission when data from a detector identified a "new" trapped radiation zone caused by a large solar flare.
Detectors also have been tested on airplanes to track radiation levels encountered on commercial flights. Technological advances that result in faster and higher air travel also put passengers in contact with additional types and amounts of natural background radiation. In addition, flight crews and other frequent flyers have expressed increased interest in quantifying and characterizing their in-flight exposures. PNL-developed detectors may be adapted to record radiation levels encountered on each flight.
Technology for the detectors was an outgrowth of PNL's 25-year microdosimetry program funded by DOE to determine the effects of different types of radiation on the human body. Such expertise has made PNL a primary source of cosmic radiation dosimeters for the U.S. space program -- work to date totalling more than $1 million.