The latest evidence of potential biological activity on ancient Mars further underscores the importance of studying soil samples from the planet in Earth's laboratories. However, after almost half a century of planning, a mission to bring rocks from Mars is yet to be implemented. Still, the search for a pathway to a Martian sample return mission continues.
Last year, Russia agreed to launch the European ExoMars rover and to build its landing system. Following liftoff on a Proton rocket in 2018, ExoMars will traverse the distance between the two planets with the help of a cruise stage designed to provide power and attitude control during the journey. Upon reaching the Red Planet, the rover will penetrate its atmosphere inside a special aerodynamic cocoon. It will help to slow down the spacecraft before splitting into two halves and letting the platform holding the rover complete the landing under rocket power.
In case of a successful mission, the Russian and European space programs could acquire not only a great scientific harvest but also a flight-tested hardware for future Mars landings. One of the most likely candidates to benefit from the engineering heritage of the ExoMars project would be a Mars sample return mission. Although it would be much more complex than the delivery of a rover, the sample-return mission architecture can be formed by replacing the mobile vehicle on the landing platform with a return rocket. After loading samples, the vehicle would lift off from the surface, starting its journey back to Earth. The USSR used a similar strategy in the 1960s and 1970s, when a common lander was used for the delivery of rovers and sample return vehicles to the Moon.
In January 2014, Russian engineers presented a concept of a Mars sample return mission known as Expedition-M (Ekspedition-M). Even though, the Expedition-M project has been under consideration for a number of years, its latest incarnation was based on the design developed for ExoMars. The borrowed hardware included the cruise stage, a slightly modified aerodynamic descent module and the rocket-powered landing platform.
The two-launch mission scenario relying on Proton rockets included a second spacecraft, which would enter the orbit of Mars and rendezvous with the ascent vehicle returning from the surface. It would then head back to Earth with the samples. The most unusual and controversial phase of the mission involved the transfer of the samples between the two spacecraft. The capsule with Martian rocks would be first ejected from the ascent vehicle in the Martian orbit. The Earth-return spacecraft would then home-in on the capsule and "swallow" it with a funnel-like receptacle. As a result, the Mars ascent rocket and the Earth-return vehicle would never make physical contact, as it was envisioned in practically all previous scenarios for such a mission. Russian planners proposed to test this risky capsule transfer method during a mission to the Martian Moon Phobos, which could follow the ExoMars around 2022 and precede the Expedition-M currently anticipated as early as 2024.