SLS Could Launch a Sample Return Mission to Phobos and Deimos
by Andy Tomaswick

NASA’s next colossal rocket, the Space Launch System (SLS), recently had its first successful flight back in November after years of development. Much of that development was done by aerospace contractors like Northrop Grumman and Boeing, so it is a good bet that engineers at those companies want the SLS to be seen as a success. One measure of its success will be how many missions it manages to help launch successfully – the more missions, the better. To help plan out some of those missions, a pair of Boeing engineers wrote a paper describing an outline of a sample return mission to Phobos and Deimos. And, of course, it would be launched by the SLS.


Phobos and Deimos, Mars’ two moons, are unique in various ways. Phobos itself is estimated to be ? hollow; it has a massive crater on its side that takes up almost half the surface, which was named Stickney after the maiden name of the wife of the astronomer who discovered it. Even better – it is the closest moon to its host planet. Deimos is slightly less interesting but could still serve as a functional forward base for future exploration of the Red Planet.

To get there requires some power, though. Launching any craft, let alone one with enough fuel to get back to the Earth after landing on a body would be difficult. However, as Benjamin Donahue and Matt Duggan, two of Boeing’s SLS engineers, explain in a paper, the SLS could not only get such a mission to the Martian system but also launch an Orion crew module simultaneously.

There’s a mission already in the works from JAXA to bring back a piece of Phobos, as explained by this UT video.

The SLS has another payload system called (with a bit of tongue-in-cheek) the Universal Spacecraft Adapter (USA). It allows other spacecraft to co-manifest with an Orion capsule on an SLS mission. In the case of the Phobos / Deimos sample return mission, the vehicle would have four different parts.

First up would be the Mars aerobrake module, allowing the vehicle to slow to a highly elliptical parking orbit in the Martian system. It makes that orbital transition after using Earth’s Moon and the Earth itself for a gravity assist on the way to Mars. Once it arrives and completes its aerobraking duties, it is discarded.

Which leaves open the descent module. It is responsible for landing the craft on the surface of both Phobos and Deimos. It carries along with it the other two components of the vehicle and the science packages, which could include small rovers. It has engines powerful enough to stop the vehicle from slamming into the side of the Martian moons, but eventually runs out of fuel after the descent to Deimos (the second moon to be visited).

After samples are collected on both Phobos and Deimos (and their science payloads are left behind), the ascent module takes over by blasting off of Deimos and orienting towards Earth. It then separates from the last of the four modules, the Earth Return Capsule (ERC).


Depictions of the Launch and Cruise Configurations of the Phobos / Deimos sample return mission.
Credit – Donahue & Duggan

The ERC is responsible for the journey back to Earth and their re-entry. It primarily consists of a heat shield and some maneuvering thrusters and only takes up a small percentage of the total weight of the package. However, it is arguably the most critical phase of the mission, as, without it, the samples never successfully return to where they can be analyzed.

So far, the engineers have mapped out reasonable routes and trajectories, including delta v calculations for the mission, as well as the expected weight of each of the given components. However, there wasn’t much detail on what samples would be the mission’s goal to find, nor any indication that any major space agency would support the mission.

But with the advent of the SLS and other superheavy launchers like Starship, these types of missions will no longer be prohibitively expensive in some cases. It’s just a matter of time before we visit the surface of these two extraordinarily unique moons.

Learn More:
Donahue & Duggan – A Phobos and Deimos Sample Return Mission Launched as a Co-manifested Payload on the NASA SLS Launcher
UT – What Could We Learn From a Mission to Phobos?
UT – JAXA’s Ambitious Mission to Phobos Will Even Have European-Built Rover
UT – Want To Explore Mars? Send Humans To The Moons Of Mars First: Phobos And Deimos

Lead Image:
The Mars Reconaissance Orbiter (MRO) captured this image of Phobos and the Stickney crater in 2008.
Credit: NASA/JPL-Caltech/University of Arizona

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