Mars Helicopter? Really?

Transcript

Theme song by Destin Heilman

MISSION CONTROL: Tango Delta nominal. Yeah. EDL comm configured. RIMU stable. UHF telemetry. RIMU stable. Touchdown confirmed! We're safe on Mars. [CHEERS] [APPLAUSE]

ERIC: That is the sound of a robot landing on another planet, at least what it sounds like from the control room at NASA. You just heard the reaction to the Curiosity rover's successful touchdown on Mars in 2012.

And last week, we talked about how the next Mars rover, Perseverance, will attempt to make a similarly dramatic landing in February of 2021.

This week on Pulsar, we're answering your questions about what the rover hopes to accomplish during its mission. I'm your host, Eric. Thanks to Facebook Boston for supporting this episode of Pulsar.

My guest this week is Rich Rieber, the lead mobility systems engineer for the Perseverance rover. Rich, thanks so much for joining me.

RICH: Thank you for having me. I'm looking forward to it.

ERIC: So to start off with, the big question is, why are we sending this robot to Mars?

RICH: So Perseverance launched on July 30, and she's currently on her way to Mars. She'll be landing in mid-February in Jezero Crater, which is an amazing fan delta coming out of, basically, the Mississippi River of Mars.

And so what's nifty about river deltas is they act as giant concentrators for the surrounding area, so you have a little bit of the entire watershed of that big river across Mars. All the water will wash stuff down into the river and deposit it into the delta.

So the goal of Mars 2020 is actually to go find evidence of life, and where best to do that is in a river delta. A vast swath of the Martian surface is concentrated in this river delta. So if we want to answer the question, yes or no, was there life on Mars, there's no real better place to go than the delta of Jezero Crater.

The way we're going to answer this question, we have a suite of instruments that all help us give context to samples. So the whole front third of the rover is a sample collection system. It has this matrix of about 30 or 40 test tubes.

And so what we'll do is, at places that are really interesting, we can collect a sample, put it in this test tube, and at various points in the mission, we're going to create a sample depot.

So we'll drop all these tubes on the ground, and in 2026, we're going to launch a sample return mission. We're going to have a little fetch rover that's going to go pick these up, bring these back to a Mars ascent vehicle, and then bring these tubes back to Earth. So this will be the first ever Mars sample return mission.

ERIC: And so you can do a whole lot more with those samples if you had them on Earth?

RICH: Oh, yeah. The infrastructure we have in Earth-based laboratories is much greater than anything we could send to Mars, so those samples are going to be really powerful data points to have.

ERIC: A couple of people during our launch viewing party wanted to know, is this mission going to help pave the way for humans to explore Mars any time soon?

RICH: Oh, undoubtedly. Starting with entry descent and landing, we have half a dozen video cameras that are going to be taking data of entry descent and landing. And one of the things that the team is really excited to see is high-speed video of the parachute inflation.

We know these parachutes work at Mars because we have multiple instances of them behaving properly. So we said, great. They work at Mars. We're going to use these parachutes.

But what we realized was we tried to recreate the Martian atmosphere and do some parachute deployment tests, and the only place you can recreate the Martian atmosphere is at about 100,000 foot altitude. So at 100,000 feet on Earth is where you get a similar Martian atmosphere. What we did-- this is the most Rube Goldberg device ever-- we sent a weather balloon up to 100,000 feet.

That then dropped this kick motor, basically a small rocket, that launched this doohickey up to, basically, space. And then it re-entered, and we popped a parachute somewhere about 100,000 feet.

And we looked at the parachute inflation. And what we found was that failed, and we didn't know why. The parachute community has crunched all the numbers. What they see doesn't match the physics that they believe governs parachute inflation.

And so their only conclusion is that the physics is wrong. So our understanding, our knowledge of parachute inflation at Mars, is wrong. And so by capturing high-speed trinocular vision-- that's three cameras-- we should be able to understand why the parachutes inflate at Mars and help correct our understanding of the physics.

ERIC: Well, knowing exactly what's going on with the parachutes will definitely be important for using them for humans. How about once the rover is on the ground? Are there any experiments that are going to be useful for getting ready to explore with humans someday?

RICH: Inside the rover chassis, we have an instrument called MOXIE. What's nifty about MOXIE is they're sucking in the Martian atmosphere, which is 99% carbon dioxide, and they're running it through this thingy that will split the carbon off from the oxygen and produce oxygen. So oxygen, we need-- well, duh-- to breathe, but it's also a primary component for rocket fuel.

So if you ever want to leave Mars, you're going to need an oxidizer. And so now we can create our own oxygen. So MOXIE is basically a precursor to allowing future astronauts to live off the land, so to speak.

ERIC: So there's no available oxygen on Mars, but if astronauts can make it out of the carbon dioxide that's in the Martian air, they don't have to bring it from Earth.

RICH: Yeah, mass is king in space flight. For every ounce you can save in your spacecraft or in what you send to Mars ends up being a huge cost-saver.

ERIC: Can you tell us what part of the rover that you focus on, specifically?

RICH: So I'm the mobility systems engineer for Mars 2020, so my job governs everything that affects how the rover drives. And that's actually a pretty broad swath of engineering disciplines. So that's everything that deals with driving wheels, motors, the suspension, but also the software that allows us to drive.

One of the other areas I'm focused on is our ground-penetrating radar called RIMFAX. RIMFAX has an antenna that sits just below the back of the rover, and we plan on taking soundings every 10 centimeters as we drive. So we have a close coupling with the mobility software saying, this is how far we've driven, and the RIMFAX software saying, hey, let's take a sounding.

But also, in order to interpret that data, the RIMFAX scientists need a really accurate understanding of where the rover drove. So we have this question of being able to reconstruct the rover traverse after we drove it, using a wide variety of different data sets to say, this is where the rover was, to an accuracy of one meter. We've never had that level of accuracy.

We've been able to localize the endpoints of every drive to within about 50 centimeters, but now we need to be able to do it anywhere along the drive within one meter. And so what we can do is we can then take that traverse, sketch it on top of our orbital maps, and now we have a really good understanding of where the rover drove. I'm actually really excited to see what the science and the robotics community can do with that data set.

ERIC: That's really cool, a ground-penetrating radar on Mars. What kind of things will that be able to tell us?

RICH: So what RIMFAX will do is when you add up all of the data from all the different soundings is we get a cross-section of the ground. And what you're doing is you're looking at the radar reflections underground. And what that gives you is a map of the geological strata, so the different layers underground.

What the team is going to be able to do is follow the geological strata and see how things underground change as we drive. And so from that, they can get a really good understanding of Jezero Crater and everything along our traverse. I'm actually really excited for that data set.

One of the test data sets they did is they took their radar, and they strapped it on the back of an ATV. And they drove around what's called a star dune, so this is a dune that's formed from sand being blown in from multiple directions. It doesn't have a stereotypical single ridge on the dune. It has like five or six ridges.

They drove their radar around this sand dune, and they were able to get an understanding of the aeolian history of the sand dune. Aeolian means "wind." Sand dunes are formed from wind depositing sand, and so what they could do is look at the different density of the sand.

And they could say, this part of the dune was created when wind was blowing from the East, and this part of the dune was created from wind blowing from the West. And by looking at the different layers, they could come up with a wind history of that dune and a rough age of when the winds were out of that direction. So that was a really cool analysis they did from one of their field tests with the radar.

And so I'm just imagining what they're going to be able to figure out of Jezero Crater from that data.

ERIC: That will be really cool. And finally, we get this question a lot, so I wanted to hear what your answer would be. What part of this mission are you most excited about?

RICH: Helicopter. Pew!

ERIC: Yes, exploring Mars by helicopter. Give us the what, the how, and the why of Ingenuity, the drone that will attempt to fly around on Mars.

RICH: Well, the why is why not? This is a funny story. So about seven or eight years ago, I was working on a project called SMAP, which is an Earth-orbiting radar. And I'm outside the test bed, and there's this engineer, who's probably been here since the '50s. And he's got this big stack of papers, and the papers go everywhere, all over the parking lot.

So you know, being a good Samaritan, I help him pick up all his papers. And I look at the cover, and it says Mars helicopter. And I look at him like, Mars helicopter? He's like, yeah, we've got this idea of building a helicopter for Mars.

And I look at him like, you know the atmosphere is like 1% as thick. Just Reynolds number, which is a key metric of aerodynamics. And he's like, yeah. The Reynolds number works out. You need like 5,000 rpms on a rotor that's two meters in diameter or something like that.

And I'm like, huh. And then he spent like 10 minutes describing to me in the parking lot their concept for this helicopter. And I'm like, this could really work. So that was my introduction to the Mars helicopter. It was eight years ago in a parking lot.

The helicopter is actually going to be really nifty. We're only signing up for five test flights, but it could be revolutionary in terms of future science missions or shuffling payload around between human settlements on Mars. Imagine, instead of having a fetch rover, you have a fetch helicopter to go bring our samples back. It could be really cool. I'm really excited about that helicopter.

ERIC: Later this week, in our next episode, I'll continue my conversation with Rich, focusing on how Perseverance will move around on Mars. Until then, keep asking questions.