Safer Spaceflight to Mars

By Michael Lucibella

APS April Meeting, Savannah
Recent discoveries about the dangers of radiation exposure during interplanetary travel have prompted the National Aeronautics and Space Administration (NASA) to make radiation protection a fundamental part of spacecraft design. To get a better understanding of these risks, a team at the Marshall Space Flight Center is building a comprehensive database of simulated cosmic-radiation effects using a long-established particle physics tool.

“We need to think about radiation from the early stages of design, just like we think about oxygen, temperature, pressure and so on,” said Nasser Barghouty of NASA’s Marshall Space Flight Center. “You need the nuclear-physics tools to estimate how much radiation is inside a certain structure, inside the suit, inside your liver, and so on and so forth.”

“Once you leave the protective atmosphere of Earth, you are bombarded by space radiation from the very low energy up to the highest energy,” adds Mohammed Sabra, also of NASA’s Marshall Space Flight Center.  

To assess the hazards, the space agency is integrating the program Geant4 (for “geometry and tracking”) into the design process for spacecraft. Geant4 has been a mainstay for years, helping nuclear physicists simulate collisions at the LHC, SLAC, and the Tevatron. The program also calculates how different types and energies of radiation affect different materials, spacecraft, and even the crew.

Sabra and Barghouty used Geant4 to calculate the effectiveness of two shapes, a slab of aluminum and a spherical shell of aluminum, against a bombardment of iron nuclei. They presented the results of these simulations at the 2014 APS April Meeting. They hope to refine these simulations of basic shapes into the designs of a full spacecraft.

“If you go to Mars and back, that’s a two-and-a-half-year trek, and the radiation level is lethal for any human being in a typical spacecraft,” Barghouty said.

The best way to shield against this onslaught of cosmic radiation is not obvious, but the researchers say that the most important first step is to find out how the building materials of a spacecraft react to being immersed in such a hazardous environment. Geant4, as well as other programs, have previously been used to simulate a narrow range of materials reacting to specific kinds of radiation. Now, the NASA team is working on how to put together a broad database of effects.

“[W]e are performing the simulations for all biologically significant cosmic-ray nuclei (protons through iron) and for all targets of interest to mission designers, from gallium arsenide used in solar-cell materials, to tungsten in microelectronics, to water and polymers for shielding purposes, and over a large energy range,” Barghouty said.

“The real danger is we really don’t know the exact biological effects of these heavy ions on a cell or a tissue. That’s a complete unknown,” Barghouty said. “We can calculate a lot of things, but how do you translate that to real effects on humans as opposed to electronics and so on. That’s another side of the challenges being addressed.”