Furthermore, the system is what Pisacane calls "active" and can take real-time measurements of radiation levels, alerting astronauts immediately if they are at risk. Spacesuits and spacecraft equipped with the microdosimeter sensors could help enable astronauts to take protective action at the onset of enhanced radiation.

But before the device is ready for manned missions, it will be tested on numerous satellites over the course of about five years. Pisacane hopes that with each trip, the device--which is powered by AA batteries and already uses only one watt of power when continuously collecting data--will become even smaller, using less power with increased reliability. The microdosimeter will make its first trip to space on March 8, when it will go up on STP-1, the launch vehicle, as an experiment on the MidSTAR satellite built by the USNA. The satellite will contain three microdosimeter sensors, one outside and two inside, one of which will be coated with polyethylene, a substance whose permeability is similar to that of human tissue, and thus can simulate the effects of radiation on the human body. All three sensors will be connected to an electronic output module that will collect and store data for transmission to the ground.

The central challenge in creating one of these devices is to make it accurate. "There are a lot of elements that go into making it work," says Pisacane, "and all this has to be designed, parts have to be manufactured, we have to identify electrical components and get them on the board--some of them are so small you can hardly see them."

Indeed, the things you have to do in order to develop very small, low-mass, and low-power-consumption devices for space flight are exceptionally tricky, explains Cary Zeitlin, a staff scientist at the Lawrence Berkeley National Laboratory and former principal investigator of the Martian Radiation Environment Experiment (MARIE). The MARIE project, which was funded by NASA, built a particle telescope to measure radiation levels on Mars and was sent aboard the Odyssey for testing in 2001. Although the technology suffered from hardware difficulties after a large solar event, it was able to gather dosage information and was a beginning step in detection efforts on Mars. "Pisacane's group is doing a variation on the standard type of dosimeter, and it's a new way of measuring radiation doses that I think is a novel application," says Zeitlin.

While extremely important to manned space missions, the microdosimeter is meant to have Earth-based applications as well. It can help people who work with nuclear power, with nuclear compounds, in medical and industrial applications, and in those areas in which it is important to know the levels of radiation, says Jay Buckey, team lead for the NSBRI Technology Development Team and professor of medicine at Dartmouth Medical School. "This technology is an excellent and very worthwhile way to track radiation exposure and an improvement of what we have now," he says.