The Mars Perseverance rover incorporates new design advances since Curiosity landed on the Red Planet, including a Mars Helicopter. Tech Briefs spoke with NASA’s Keith Comeaux, Deputy Project Chief Engineer, to learn more about these new technologies.
Tech Briefs: The Mars 2020 spacecraft will employ an entry, descent, and landing (EDL) process similar to Curiosity’s but with some new technology. How will this technology improve EDL?
Keith Comeaux: We have a new algorithm — a software change — that the autopilot uses to decide when to open the parachute. On MSL, we opened the parachute when we were in the right velocity range independent of where we were respective to our target. This time, we’ll open the chute right when we’re approaching our target so we get a more accurate chute opening where we want to land. That’s going to shrink our landing ellipse quite a bit. The second improvement is including the lander vision system, which has a map of our landing site onboard that is pre-populated with risky zones and safe zones.
The rover is going to take some pictures as its coming down on the parachute and correlate those pictures to the map it has in its brain and choose one of the safe sites that we’ve pre-designated. By studying the landing side for years now, the team has done a very detailed risk analysis of where those safe sites are within our landing site. So, those two technologies in particular have really improved our capability to zero in on a very interesting place for our scientists but to do it in a way that we can deliver the system safely to that site.
Tech Briefs: New cameras could provide the first-ever view of a Mars landing. What do you expect to see — what questions do you hope to answer?
Comeaux: MSL had 17 different cameras — one of which was a landing camera — that took some images as we were descending. Most of what you saw was a simulation but there are a few snapshots of the videos of the heat shield falling away. Those were taken from a camera called MARDI [Mars Descent Imager]. A landing camera, which is in the same position as MARDI was, will be used to take images as the spacecraft is coming down. An entirely new camera system — a commercial camera system called EDL Cams — includes a rover down-look camera, which is on the bottom of the rover looking down at our landing site, and an up-look camera on the top deck of the rover looking up at the descent stage.
When the spacecraft starts the skycrane maneuver, we’ll see the rover drop away from the descent stage, we’ll see the descent stage pop off the rover, and we’ll see it move away. We also have a descent stage down camera, which is on the bottom of the descent stage. When skycrane starts, the rover will fall away from the descent stage and we’ll capture a video of that as well as the content of the landing site. With that camera in particular, I’m very interested in seeing the results because it’ll show the rover from the point of view of the descent stage as it’s touching down on the ground. We’ve got a lot of questions about what happens with the thrusters used by the descent stage. There’s been a lot of concern about the thrusters kicking up a lot of dust and rocks as well as potentially damaging the rover.
Finally, there are three parachute up-look cameras at the top of the back shell. When the parachute is deployed, these cameras are rotated in position in the ring around where the parachute is ejected from, providing three different angles of the parachute inflating at Mars. That’s a very interesting engineering problem because there are very few occasions that we get to actually record a supersonic parachute inflating. We’ve done some high-altitude tests to understand that better but this will be the first time we actually get to record it at Mars. We might have to wait a while for it because it’s a pretty high data volume that’s going to get stored in the memory banks and it’ll take a while to downlink it all. But the engineering return on those cameras is going to be pretty incredible.
Tech Briefs: Let’s talk about Perseverance. Again, it’s very similar to Curiosity but heavier and with some major differences, including a new, more capable wheel design.
Comeaux: Yes, we designed the wheels for Curiosity with what we knew about how to design wheels to support the size of the rover but Mars threw us a curveball. The terrain included rocks that were embedded in the bedrock and kicked up by the wind, creating very sharp points. When Curiosity rolled over them, they didn’t break or move out of the way. The rover put all its weight on those points and punctured the wheels. And over time, there were enough punctures that cracks started to develop and grew into pretty big holes. The wheels actually still work just as well as they were designed to at the start of the mission.
Over time, the mission operators learned how to avoid the terrain that causes degradation of the wheels. We know we’ve got plenty of life left in the Curiosity wheels but for Perseverance, we wanted to do better. Now we have wheels that are slightly narrower, just a tiny bit larger in diameter, and most importantly, there is more tread with a little bit of a wave in it — a little curve if you look at them closely — that gives them stiffness to prevent crack propagation and puncturing in the first place. We tested them just as we did the Curiosity wheels and we concluded that these design features meet the need if we again face the same type of terrain we saw with Curiosity.
Tech Briefs: What enhancements were made to improve navigation and hazard avoidance?
Comeaux: There’s a lot of onboard software that allows us to detect hazards as we’re driving across Mars including an algorithm that enables the Mars drivers on the ground to actually select sites that they want the rover to get to. The rover will take pictures as it goes and do the onboard processing of those stereo images to determine where the obstacles are and navigate a path around those obstacles to get through to the destination. The Rover Compute Element interfaces engineering functions of Perseverance with the same computer we’re using for the lander vision system during entry, descent, and landing. But once we’re on the surface of Mars, we have an extra computer, so we chose to put it to use in helping us navigate the surface. All of the images taken with the cameras up on the mast — the NAVCAMs — will get piped to that computer and processed to choose a path through the obstacles.
Tech Briefs: One of the new aspects of the rover is the addition of the Mars helicopter, Ingenuity. Why does the helicopter remain under Perseverance’s power for two months after landing and what are the goals for the helicopter once it is deployed?
Comeaux: The mission operation plan is to choose a safe site to deploy the helicopter once we’ve landed. The extra time on the rover allows us to do all of our initial checkouts of the rover and then navigate to a flat place where we can drop off the helicopter and begin its operations. We’ll be operating the helicopter in a 30-day period in which we’ll stay focused on the helicopter and maybe do some science on the side — the real objective will be operating the helicopter. The two months spent on Perseverance is basically to allow us time to check out the rover and then find a good spot for helicopter operations.
During that period, the helicopter stays tucked underneath the rover on rover power because its battery is really not powerful enough to operate on its own for a long period of time. Once we deploy Perseverance, it will drive off and Ingenuity will deploy from underneath the rover. Perseverance will need to drive away from the helicopter the same day so that the Sun can get on the solar panels above the helicopter blades. We can recharge the battery and be ready for the overnight cold — it will have to use the heaters to stay warm overnight. During the day, it’ll charge up. And then when the conditions are right during the daytime in terms of Sun, wind, and temperature, we’ll start helicopter objectives.
Basically, Ingenuity is a technology demonstration to show that we can operate a flying machine on Mars, which is pretty incredible. We’ll take pictures of the helicopter as well as from the helicopter looking down at Mars.
Visit the Mars 2020 mission web site here .