November 19, 2013
Radiation Hazards Of Deep Space Travel Quantified By Researchers
April Flowers for redOrbit.com - Your Universe Online
Comprehensive findings on space-based radiation as measured by a detector aboard NASA’s Lunar Reconnaissance Orbiter (LRO) have been published by a team of scientists led by the University of New Hampshire. The findings, published in a special edition of Space Weather, provide critical information on the radiation hazards that will be faced by astronauts on extended missions to deep space such as those to Mars.
"These data are a fundamental reference for the radiation hazards in near Earth 'geospace' out to Mars and other regions of our sun's vast heliosphere," says CRaTER principal investigator Nathan Schwadron of the UNH Institute for the Study of Earth, Oceans, and Space (EOS).
For both humans and satellites, the space environment poses significant risks because of harmful radiation from galactic cosmic rays and solar energetic particles that can easily penetrate typical shielding and damage electronics. There is an increased risk of cancer when this radiation impacts biological cells.
Such hazards were not sufficiently understood to determine if long missions outside low-Earth orbit can be accomplished with acceptable risk until the CRaTER's long-term radiation measurements were derived using a material called "tissue-equivalent plastic"—a stand-in for human muscle capable of gauging radiation dosage.
The new measurements provide quantified, radiation hazard data from lunar orbit. They can be used to calculate radiation dosage from deep space down to airline altitudes, and will be crucial in developing techniques for shielding against space-based radiation dosage. UNH space scientists' efforts to develop the first Web-based tool for predicting and forecasting the radiation environment in near-Earth, lunar and Martian space environments, as well as a space radiation detector that possesses unprecedented performance capabilities, have been vitally enhanced by the new measurements.
PREDICCS, a near real-time prediction/forecasting tool, integrates numerical models of space radiation and a host of real-time measurements being made by satellites currently in space for the first time. The tool provides hourly updates of the radiation environment and archives the data weekly, monthly, and yearly— an historical record that provides a clear picture of when a safe radiation dose limit is reached for skin or blood-forming organs, for example.
CRaTER allows the researchers the opportunity to test the capabilities of PREDICCS to accurately describe the lunar radiation environment. Dose rates produced by PREDICCS were compared to those measured by CRaTER during three major solar energetic particle events that occurred in 2012.
The new detector at UNH is called DoSEN - Dose Spectra from Energetic Particles and Neutrons. It measures and calculates the absorbed dose in matter and tissue resulting from the exposure to indirect and direct ionizing radiation, which can change cells at the atomic level and lead to irreparable damage. Schwadron is the lead scientist for both PREDICCS and DoSEN.
"DoSEN is an innovative concept that will lead to a new generation of radiation detectors, or dosimeters, to aid in understanding the hazards posed by the radiation environment of space," says Schwadron. "The ability to accurately understand these hazards will be critical to protect astronauts sent beyond low-Earth orbit on extended space missions."
Two advanced, complementary radiation detection concepts that present fundamental advantages over traditional dosimetry are combined by DoSEN. Energy and the charge distribution of energetic particles that affect human and robotic health are measured by the dosimeter in a way not presently possible with current technology. The radiation hazard is significantly impacted by protons, heavy ions, and neutrons.
"Understanding how different particles such as neutrons and heavy ions pose hazards will be extremely important in completely characterizing the types of environments we will operate in," Schwadron says. "For example, on the moon, there are additional hazards from neutrons that are created by high-energy radiation interacting in the lunar soil and radiating outward from the surface."
CRaTER discovered the "backsplash" of protons known as the moon's radiation "albedo," which is caused by the partial reflection of galactic cosmic rays off the moon's surface creating a one-two punch of deadly radiation. This can be used to peer below the lunar surface like a geological probe.
Harlan Spence, CRaTER deputy lead scientist and director of EOS, says, "Until now, people have not had the 'eyes' necessary to see this particular population of particles. With CRaTER, we just happen to have the right focus to make these discoveries."