MARS DROPBOX? Should Phobos (or alternatively Deimos) serve as an international collection point for samples gathered on the surface of Mars? (Image taken from the electronic poster.)
Current plans for bringing samples to Earth from Mars involve three distinct steps. First is a rover with the capability to cache samples: this will be the Mars 2020 rover, now in its initial stages of development.
Second is a special lander carrying a small “fetch rover” that collects the cached samples and brings them to the lander, which then sends them up into Martian parking orbit. The third step sends a spacecraft to Mars to collect the orbiting samples and deliver them to Earth. All these are robotic spacecraft, and for budgetary purposes, several years could easily intervene between each step.
But what if the second step deposited the samples on the surface of Phobos, Mars’ larger moon, instead of sending them into orbit around Mars or directly to Earth?
That’s the suggestion of Philip Stooke (University of Western Ontario). He presented the idea (PDF) in a poster talk (PDF electronic version here) at the 45th Lunar and Planetary Science Conference in The Woodlands, Texas.
Using Phobos as a dropbox offers several advantages, he argues. It has only weak gravity, so landing a sample collection there will be easy, using airbags for example. Also, Phobos could serve as a place where Mars missions by other space agencies could drop off samples they collect.
In Stooke’s scenario, a mission with a human crew would retrieve the samples from Phobos. This would serve as a rehearsal for a crewed landing mission to Mars, much as Apollo 10 was the dress rehearsal for the actual first lunar landing by Apollo 11.
“Human flights to Mars will be extremely risky and expensive,” he says, “making a rehearsal mission both necessary for system testing yet hard to justify in scientific terms.” Thus he is proposing to combine both sample return and rehearsal into a decade-long program of robotic sample collection that culminates in a human flight to Phobos to collect and return the samples.
An added advantage, says Stooke, is that Phobos itself is a good target for samples to collect. Besides original Phobos material, the moon’s regolith is littered with rocks thrown off Mars by large impacts. The retrieval crew would scout for these for when they arrive to collect the samples.
Finally, he notes that parking samples on Phobos does not commit anyone to a crewed mission to Mars: “If human Mars exploration is eventually deemed impossible, a flagship-class robotic mission to Phobos can gather the samples instead.”