A mission to return samples from the planet Mars is still many years away and, officially, not on the calendar. That hasn't stopped the ESA from producing a proof-of-concept prototype of the scientific “box of delights,” which could one day bring bits of the Red Planet back to Earth for study.
Returning samples from Mars would be a technological achievement only exceeded by actually landing astronauts there. It would involve a small fleet of unmanned spacecraft operating in concert. Key to this is the development of a multifunctional sample container that can keep Martian samples safe and in pristine condition at sustained temperatures of less than -10° C (14° F).
In this case, the ESA has created a fully functional metal sphere 23 cm (9 in) in diameter and weighing less than 5 kg (11 lb). Its function isn't to act as a mere container, but also as a way of protecting its valuable cargo against contamination and the rigors of a month’s long journey through the vacuum of space to Earth followed by re-entry in the Earth’s atmosphere, and ending in a rather violent landing. Added to this, it must be self-powered and act for a few days as a miniature spacecraft in its own right.
Exactly how a Mars sample return mission would work is still up in the air, but the basic idea is that an orbiter would be sent to Mars first, which would drop a lander or rover to descend to the surface. Once there, it would collect soil and air samples and hold them until a second mission arrives from Earth.
A second rover would collect the samples from the first and take them back to its lander, where the sample container sits in an ascent launcher. The rover would then place 11 sealed cylindrical sample receptacles, which includes one air sample, inside the container. The container would then be launched into orbit around Mars, where another unmanned spacecraft would home in on the container's radio beacon and laser reflectors several days later.
Like Russian dolls, or a particularly frustrating Christmas present, the container would then be sealed in a larger biocontainer to prevent any Earth microbes from contaminating the samples or Martian germs running amok on Earth. This is particularly important because current plans call for the sample container to land without a parachute at speeds in excess of 20,000 mph (32,000 km/h). No wonder it’s designed to withstand an impact of 400 g's.
"Because there is the potential, however remote, that the samples contain alien life, we have to comply with strict planetary protection protocols not to bring them into contact with Earth’s biosphere," says Benoit Laine, Head of the ESA’s Thermal Analysis and Verification section. "In effect, the parachute technology is not reliable enough – which means the container must be able to withstand a crash landing without parachute. The mission design therefore does not include any parachute, and the capsule literally falls from Mars onto Earth, decelerated only by the pressure on the heat shield through Earth’s atmosphere, and by the impact at landing."
Despite such a mission not likely to take place for many years, the team, which is coordinated by the future missions preparatory office of the ESA’s Directorate of Science and Robotic Exploration, plans to continue to refine the sample container design in preparation for any potential future Mars sample mission.