With the Perseverance safely on Mars, now collecting rock and soil samples from the surface, it’s now time to plan the next stage of the mission: the return of the samples to Earth. The Mars Sample Return mission will be an unprecedented one in the history of space exploration, marrying decades of scientific knowledge and with cutting-edge technology. It will comprise separate, coordinated robotic missions requiring NASA and the European Space Agency (ESA) to combine their expertise.
A NASA lander will first deliver a fetch rover along with a Mars ascent vehicle (MAV) to the Martian surface. Once the samples (prepped by Perseverance) are picked by the rover, it will be loaded into a canister and transferred to the MAV, which will lift off from Mars and carry the samples into orbit.
Meanwhile, an Earth return orbiter mission will be underway, timed to intercept the samples and transfer them to an Earth entry capsule, to be delivered to a handling facility. If all goes well, the fetch rover and MAV will leave Earth in 2026, and the samples will arrive in the early 2030s.
Coordinating and facilitating a robotic lift-off from an alien planet is a new challenge for scientists and engineers. The technology to make that happen will be built by the Maryland-based aerospace company Northrop Grumman Corporation.
“[We are] providing the solid rocket propulsion that will launch the MAV into space for the first part of its journey home,” says Mike Lara, director of strategy and business development. “Our propulsion technology is critical in order to return these samples back to Earth.” The company has a legacy of supporting space exploration. In the 1960s, Northrop Grumman’s heritage company TRW designed and built the lunar modules, the module’s descent engine and abort guidance system for the Apollo program, in which sample return was also a major part.
Anita Sengupta, an aerospace engineer from the University of Southern California’s Department of Astronautical Engineering, says the main challenges while developing propulsion for the MAV is that systems will have to be designed to account for the differences in gravity and atmosphere on Mars compared to Earth.
“The gravity on Earth is about three times as high,” she says. “[And] Mars has a surface pressure…about 1 percent of that of Earth… So in a sense…the rocket to be able to lift off with the same amount of payload is going to be a lot smaller on Mars.” But that doesn’t make it any easier: “The real challenge is the fact that it all has to be done autonomously… There isn’t a crew of people on the ground [for exigencies, so]…it has to work right the first time.”
Successful rocket launches are challenging even on Earth, Lara says, and weather or technical glitches can result in a launch being called off in the final seconds. With the time delay in communications between Earth and Mars being about 20 minutes for a round trip message, there will be no such option: once the countdown starts, there is no going back.
The team building the solid rocket propulsion engines also must consider that along with its thin atmosphere, Mars is really cold, about –40°C. That means engineers must design propulsion system to protect the rocket for over a year—the fetch rover is expected to spend about 18 months retrieving samples—and keep it just warm enough to successfully launch when the time comes. Lara adds, “[O]ur rocket motors will need to withstand that low temperature storage in near vacuum conditions.”
Despite the extreme conditions on Mars, Sengupta says that the team isn’t going into this mission blind, “Physics and engineering [are] about being able to model and predict… Because we have the ability to…run computer simulations, because we have the ability to do tests and scale them for the differences…we have a physics-based understanding [that] is quite the opposite of blind.” For instance, computational fluid dynamics simulations help scientists see ahead of time how something will perform in a particular environment.
Plus, she adds, there would be a system redundancy aspect to the design, which means that if something doesn't work as intended, there will be a fallback. "You can add margin to the design to make you are more successful," she says.
Finally, while there has never have been a propulsive ascent from Mars, there are lessons from Apollo’s lunar lift-off and other missions, Sengupta says. “We learn from every single mission that’s happened before we build on it for the next mission. It’s really an issue of understanding the physics…down to the component level.”