Mars Sample Return: The mission that will bring home a piece of another planet
An ESA scientist tells us why we’re bringing samples home from Mars.
We want to bring something back from Mars. That’s the thinking behind a programme so ambitious that it will take two space agencies and several missions to pull it off. To find out what’s at stake, and how we’ll get a sample from the Red Planet, we spoke to ESA’s Dr Albert Haldemann.
He's the ExoMars Payload and Assembly, Integration and Verification Team Leader at ESA, and he coordinates with NASA to keep the two agencies working smoothly together.
Tell us about the Sample Return mission.
The Mars Sample Return mission is the first mission – programme actually, because more than one craft is required – to return samples from another planet. We have samples from the Moon returned by the Apollo missions, by the Russian rover and most recently by the Chinese. And we’ve returned samples from asteroids [via missions run] by the US and Japan.
But we’ve yet to return a sample from Mars. That’s the objective. The first step is the Perseverance rover, which is beginning to collect samples after NASA landed it successfully on Mars in February this year.
The Mars Sample Return programme is a joint endeavour between NASA and the European Space Agency (ESA), although NASA is leading it. NASA will be responsible for the rockets that will launch from the surface of Mars and put the samples in Mars orbit. But ESA is responsible for the Earth Return Orbiter, which is basically going to be the first interplanetary spacecraft.
It’ll go from Earth to Mars, go into orbit around Mars, rendezvous with the sample craft in Mars orbit, capture the sample and then come back to Earth. It won’t enter Earth orbit, but it’ll release the NASA-built entry capsule containing the samples once it’s near enough. Only the entry capsule will come back to Earth, not the Earth Return Orbiter.
The plan is to essentially have the capsule perform a controlled crash. So we’ll target the crash site, then have the Earth Return Orbiter release the samples and fly away. It’ll deviate so that it flies past Earth and goes into a graveyard orbit around the Sun.
But prior to all this, Perseverance will be on Mars collecting samples. Those samples will be put in caches on the surface. In 2026 NASA will launch another rocket to Mars containing a lander that’s carrying the Mars Ascent Vehicle and the Sample Fetch Rover.
The lander will land on Mars and release the Fetch Rover, which will pick up the caches of rock samples that have been collected by Perseverance. The Fetch Rover will then bring them back to the lander, where they’ll be put in the Mars Ascent Vehicle and launched into Mars orbit.
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Launching rockets from Earth is tricky enough. Launching one from Mars sounds incredibly difficult.
Yes, there are plenty of challenges, especially as the launch will have to be carried out automatically.
The rocket will be a two-stage, solid-fuelled rocket, and that will carry the Orbiting Sample container – or OS, essentially a football-sized sphere. When the rocket gets into orbit, it’ll eject the OS and leave it orbiting Mars.
We’re still working on how best to make sure we can find it. Our baseline is that we make it shiny and use cameras to spot it from a distance of a few thousand kilometres, which is what the Earth Return Orbiter will be at as it makes its approach.
It seems doable, but everybody’s still a little worried. So we’re considering about radio beacons, laser range finders and stuff like that. But there are a lot of challenging steps, which is what makes this fun for engineers who have to build all of these things and make them work.
What would it mean to the astronomical community to get a sample of Mars back to Earth?
We’ve sampled Mars from afar with our robots, rovers and landers. And we have samples from meteorites that were blown off Mars and landed on Earth. We know that’s where they came from, thanks to isotopic analysis of the rocks. A few of them contain gas bubbles that are dead ringers for Mars’s atmosphere, which we measured with Viking 1 and 2 back in 1976 and 1977.
So if we already have samples from Mars, why go and bring back more? Well, firstly we can’t tell precisely where these Martian meteorites came from on Mars. We have some hypotheses, but we don’t know. Secondly, although we have high-powered instruments and spectrometers on Perseverance, and other Mars rovers, those instruments are miniaturised so they can make the trip; they’re not as high-performance as the instruments we have in our labs on Earth.
Also, some of the rocks that will be obtained by Perseverance in the Jezero Crater aren’t represented in the meteorite samples. Those kind of rocks don’t survive being blown off of a planet, we think. And yet they’re key to the geologic history of Mars. And because of the delta in Jezero Crater, the rocks from there might have been associated with liquid water and so are most likely to contain evidence of past life or organic materials of a past environment on Mars.
Whether we decide that means there was or wasn’t once life on Mars, we don’t know yet. Let’s wait for the evidence.
What sort of things will you be looking for in the samples?
That’s down the road. But in order to analyse them, we’re going to take extraordinary precautions. Because Mars is considered potentially inhabitable – we’ve seen that there are underground environments that may contain liquid water – for these first samples we’ll use the most stringent planetary protection measures.
The samples will be contained within rugged metal test tubes that are as inert as possible so we don’t contaminate the contents. They’ll be packaged inside the OS, which has multiple shells. Then, when the OS gets up to the Earth Return Orbiter, it’s packaged inside the entry capsule that will also have multiple shells. And when the capsule gets back to Earth, it’ll be picked up and bagged before being taken to a special facility for unpacking.
We’ll X-ray the test tubes to see the mineralogy of the contents before we open them. Some of the samples may also undergo very high-energy synchrotron examination to look at their compositions.
Only once we’re convinced that it’s safe to do so will we open the capsules, and we’ll do that in a controlled way too. Then other, more advanced geochemical procedures will be applied to the samples to look at the details and see if there are any organic materials along with the mineral.
The Sample Fetch Rover looks like it’s going to have inflatable tyres on its wheels. Why?
Yeah, they do look like inflated tyres. They’re not, though – they’re actually a wire mesh made with memory metal that allows us to make a bigger wheel that can be compressed in a smaller package for launch. The tyres do expand, but they don’t inflate through air. When we get to Mars, they’re released and allowed to expand to their full size. The reason for that is the Sample Fetch Rover will need to cover a lot of ground quickly, and larger wheels will help it do that.
We’re also going to use just four wheels instead of the six we’ve had in previous designs. Six wheels is very efficient for rough terrain. Four wheels with big tyres, like you see on dune buggies, are also okay for rough terrain, especially if you know what the terrain is like, which we will, to some extent, because we have Perseverance on the ground already essentially doing reconnaissance.
Are you worried about contamination from the Mars samples?
Personally, I’m not worried about Mars contamination. I think Earth and Mars have been ‘sharing spit’ for billions of years. But my opinion is irrelevant compared to what the public and political perception is of this risk. So we need to address that. It’s going to be a heck of a challenge, I think, especially given what we’ve seen with COVID as far as the general public’s confidence in scientific authority is concerned. We’ve already taken our lesson from that.
And we welcome the challenge because we need to understand what the samples from Mars mean, if we ever want to have astronauts go there and come back. We need a detailed understanding of what planetary protection means if we have the ambition, as many do, to have astronauts – human beings – go further into the Solar System and then be able to come back to Earth.
The Mars Sample relay
1. Land, explore, drill
Launched in July 2020, NASA’s Perseverance rover successfully landed in the Jezero Crater on Mars in February 2021. The roughly hatchback-sized rover represents the first leg of humanity’s first round trip to another planet.
The rover will use its drill to collect rock and soil samples and store them on the planet’s surface.
2. Seal and deposit
Any samples Perseverance collects will be in sealed tubes that the rover will deposit on the planet’s surface, essentially leaving a trail of breadcrumbs behind it as it explores the Martian surface.
Future missions to Mars – collaborative efforts by NASA and ESA – will follow the trail left by Perseverance, to retrieve the samples and return them to Earth.
3. Set off the second wave
The next stage will get underway in 2026, when NASA launches another mission to Mars that will carry a lander containing the rover, rocket and capsule needed to collect the samples gathered by Perseverance and launch them on their journey back to Earth.
The lander will aim to set down in the Jezero Crater, where Perseverance began its journey.
4. Unfold and unload
After the lander has successfully touched down on the Red Planet, it’ll deploy its solar panels to power up the ESA-designed Fetch Rover.
The rover (a four-wheeled vehicle, slightly smaller than Perseverance) will then unfold itself and deploy from the lander before beginning to follow the trail of samples left behind by Perseverance.
5. Grab and go
The Fetch Rover will follow in Perseverance’s tracks to collect the samples that have been deposited on the surface. Once a sample has been located, a robotic arm will deploy to collect it and store it inside the rover, before it moves on to find the next one.
Once enough samples have been collected, the Fetch Rover will return to the lander.
6. Hand over the samples
Once the Fetch Rover has arrived back at the lander, the same arm it used to collect the sealed samples will transfer them into the nose cone of the Mars Ascent Vehicle, stowed inside the lander.
If there are additional samples that the Fetch Rover was unable to collect, they could be brought to the lander directly by Perseverance.
7. Blast off for home
Once the samples are loaded onto the Mars Ascent Vehicle, the small rocket will be launched from the lander into Mars orbit.
The gravity on Mars is about a third of that on Earth, so it’s easier for objects to reach escape velocity, hence the rocket can be much smaller. It’s expected to be a maximum of 3m tall and around 50cm in diameter.
8. Pick up and drop off
The Mars Ascent Vehicle will carry the container of samples into orbit around Mars and release it. Another spacecraft, the Earth Return Orbiter, will detect the sample container and collect it, before returning to Earth.
Once there, the Earth Return Orbiter will drop the sample container into Earth’s atmosphere... if everything goes according to plan.
- This article first appeared in issue 367 of BBC Science Focus Magazine – find out how to subscribe here
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