They may look like typical flash drives, but the six Timepix detectors plugged into laptops on the International Space Station (ISS) are far from ordinary.
“These units work 24/7 to characterize the space radiation environment in various locations of the space station,” said Lawrence Pinsky, John and Rebecca Moores Professor of Physics at the University of Houston and head of the team analyzing the data received from the detectors. “The devices allow the space radiation environment to be assessed in real time.”
The detectors, consisting of a chip bonded onto a sensor, have been in use on the space station since October 2012 with raw data from each device coming to UH daily for analysis.
The Timepix chips were developed through the Medipix 2 and 3 international collaborations at CERN, the European Organization for Nuclear Research. UH is a member of these scientific collaborations. Only one other U.S. institution is involved, the Space Sciences Laboratory at the University of California, Berkeley.
“Our devices detect charged particles, photons and neutrons,” Pinsky said. “These particles are very high energy and are penetrating the craft and its occupants. The particles go through the detector and through its components, depositing energy as they do. The energy can be analyzed to determine the detailed characteristics of each track, particle-by-particle.”
Pinsky’s team at UH receives data for every charged particle penetrating the detector and can characterize each particle by charge and energy as well as direction.
“For example, each individual snapshot frame of the radiation has the latitude, longitude and altitude of the space station at that moment appended to it,” Pinsky said. “The astronauts can look up the radiation dose record of each laptop. There is a variance between the six laptop locations due to the variation in the spacecraft shielding from place to place inside the ISS.”
The UH team compares the Timepix data with the data gathered by the current device used to monitor the radiation environment on the space station, the Tissue Equivalent Proportional Counter.
“The idea is to demonstrate that our new technology is capable of replacing the device currently used for radiation detection and monitoring,” Pinsky said.
The primary sources of radiation are galactic cosmic rays, solar particle events and radiation trapped in the Earth’s magnetic field.
“We can tell you exactly what is present, the kind of particles and their energy spectrum,” he said. “We use that data to calculate risk based on the current standards set by National Council of Radiation Protection.”
Radiation exposure is considered a risk in spaceflight, especially long-duration missions, as accumulated doses can increase the risk of cancer later in life. Space radiation may also play a role in increased cardiovascular disease and central nervous system damage.
As mission lengths extend and crews travel outside of Earth’s orbit, the radiation exposures will change. Because the device fully characterizes the radiation field rather than providing limited dosimetric information, it provides the flexibility needed for future missions.
“The Timepix raw data will allow us to calculate the dose equivalent for humans based on whatever standard endpoints for risk might be used in the future,” Pinsky said.
As a result of the Timepix project on the space station, Pinsky’s team at UH has been collaborating with NASA Johnson Space Center to design a radiation detector to fly on the first test flight of NASA’s new Orion spacecraft.
Known as battery-operated independent radiation detector or BIRD, two identical devices will fly on the Orion module flight test currently scheduled for December 2014. The uncrewed flight test will take Orion 3,600 miles above Earth on a 4.5-hour mission to test many of the systems necessary for future human missions into deep space.
The BIRD sensor will record radiation levels throughout the mission for comparison to the mission telemetry after the completion of the flight. This will reveal how much and where the radiation was encountered.
“The space station only goes through the edge of the trapped radiation belts surrounding Earth,” Pinsky said. “Because Orion is going up higher, the craft will go through the meat of the radiation belt and will see much higher radiation.”
Pinsky says the chips on the detectors have been tested at accelerators on Earth that mimic space-like radiation. “We’ve subjected the chips to as much as 40 times the expected radiation in space and haven’t lost a pixel,” he said.
On future missions, Orion will carry astronauts farther into the solar system than ever before, including proposed destinations such as an asteroid or to Mars. The planned radiation monitors on board will include UH-supplied Medipix-based devices.
Kathy Major, College of Natural Sciences and Mathematics