The first series of radiation data collected inside the International Space Station (ISS) has been transmitted from space to scientists on Earth eager to assess its potential biomedical impacts and implications for future research.

The data were collected in May by radiation detectors on the ISS known as thermoluminescent detectors (TLDs). An onboard electronic reader read the data earlier this month and ISS astronaut James Voss transmitted it to scientists on Earth. The TLDs are part of a set of radiation-monitoring hardware known as the Passive Dosimeter System (PDS), which was developed by the Space Station Biological Research Project at NASA Ames Research Center and the Hungarian Space Office. The ability to accurately measure and monitor radiation exposure is important both to crew health and to future scientific research on the ISS.

The international space station. Photo: NASA

"This is very good news," exulted project science lead Kristofer Vogelsong of Lockheed Martin Engineering and Sciences at NASA Ames, in the heart of California's Silicon Valley. "The quality of the data indicates that the reader is functioning normally." Space Shuttle Discovery ferried the TLDs to the ISS in March.

The Passive Dosimeter System is a flexible, easy-to-use radiation monitoring system that is available for use by researchers from the U.S. or ISS partner nations. It complements existing dosimeters used in routine ISS operations. The dosimeters can be placed anywhere in the ISS to provide an accurate measurement of the radiation levels at their locations.

Vogelsong said the data indicate that all 12 TLDs currently in use are in perfect condition. The detectors are a third-generation version of dosimeters that flew on the Russian space stations Salyut 7 and Mir, and on the space shuttle.

NASA scientists expect to receive a preliminary interpretation soon of the radiation dose onboard the ISS from the Hungarian Space Office. A complete picture of the space station's radiation environment will not be available until a second type of dosimeter, known as Plastic Nuclear Track Detectors (PNTDs), is returned to Earth on an August space shuttle flight. The data from the TLDs will be combined with the data from the PNTDs and other radiation monitors as part of the Dosimetric Mapping Experiment (DOSMAP) to characterize the space radiation environment on board the space station. The DOSMAP experiment is being conducted by Dr. Guenther Reitz and is managed by the Space and Life Sciences Directorate at NASA's Johnson Space Center, Houston.

The PNTDs -- thin sheets of plastic similar to the material used for some eyeglass lenses -- were delivered to the ISS last April. The PNTD surface becomes pitted with tiny craters as heavy charged ions pass through it. After the detectors are returned to Earth, the plastic will be etched to enlarge the craters, which will be counted and their shapes and sizes analyzed using a microscope. This information is used to improve the accuracy of the radiation dose the TLDs have recorded and to improve the estimate of the biological effects of the radiation. Eril Research, San Rafael, CA, developed and will analyze the PNTDs.

Each TLD, which resembles a fat fountain pen, contains calcium sulfate crystals inside an evacuated glass bulb. The crystals absorb energy from incident ionizing radiation (protons, neutrons, electrons, heavy charged particles, gamma rays and x-rays) as the radiation passes through them. This process results in a steady increase in the energy level of the electrons in the crystal.

"We are happy the Passive Dosimeter System appears to be working well," said PDS payload manager Robert Jackson of Ames. "We expect that support to the DOSMAP experiment will be followed in future years by continued use for many experiments on the space station."