The failure could take many forms next week when NASA’s state-of-the-art rover, Perseverance, hits the surface of the Red Planet. Here’s what needs to go well – and how things can go quickly sideways – when Perseverance tries to make its long-awaited landing.
For NASA, entry, landing and landing (EDL) a Perseverance Thursday, February 18 shows many potential points of failure. NASA has SAPS that “hundreds of things have to go well” for the rover to survive seven minutes of terror. We can’t take a safe landing as such: as NASA points out, only “about 40% of the missions ever sent to Mars – by any space agency – have been successful.”
In short, Perseverance will have to go from speeds reaching 20,000 km / h at a pace of walking for a few minutes. Moreover, you will have to do this autonomously, as it takes almost 11 minutes for the radio signals to reach Earth. To complicate matters, NASA is launching two new technologies for the mission, both related to the EDL phase and both unproven.
All three phases – entry, descent and landing – present their own unique challenges.
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The rover, located inside the descent stage, will be separated from the cruise stage, which, with its solar panels, radios and fuel tanks, will no longer be needed. The ship will then have to orient itself so that its heat shield is oriented forward, a task made possible by the small thrusters located on the aft hull. During atmospheric entry, the ship’s heat shield will have to withstand temperatures reaching 2,370 degrees Fahrenheit (1,300 degrees Celsius). A structural failure at this stage would be catastrophic, ending the mission before it has a chance to begin.
Indeed, previous missions to the Red Planet failed right on the Martian threshold. In 1999, NASA’s Mars Climate Orbiter entered a much too low orbit, causing the spacecraft to burn into the atmosphere. The failure was in the end followed to a conversion error, in which the pound-second imperial units were not converted to the standard Newton-second metric. Hate him when that happens.
If the descent stage will survive the atmospheric entry, it will still have to face air pockets of varying density that could take it away from the course. A guided entry will be made to avoid this problem, in which the descent stage will trigger small thrusters to compensate.
The 21.5 meter wide parachute will follow. If the parachute runs smoothly and does not get tangled, the descent stage will suddenly decelerate to 1,600 km / h, which is still extremely fast (remember, Mars has a very thin atmosphere). The deployment of this supersonic parachute will depend on a new unproven technology called Range Trigger, which will calculate the distance to the landing site and trigger the parachute to unfold at the right time. This is expected to occur approximately 240 seconds after atmospheric entry, when the descent stage is approximately 7 miles (11 km) above the surface. Perseverance will say goodbye to its heat shield about 20 seconds after the parachute, introducing another potential point of failure.
This is a critical stage – one with unfortunate historical precedents. During failed landing from ESA’s Schiaparelli mission in 2016, the descent stage prematurely ejected the parachute and heat shield, the result of a software error. A computer on board thought it was just a few feet off the ground, but in reality the descent was somewhere between 1.25 and 2.5 miles (2-4 km) above the surface. You can imagine what happened next. The convicted landing Schiaparelli was traveling at about 300 km / h when he broke into the Martian rule.
With the heat shield gone and the rover finally exposed to the Martian atmosphere, another new technology will begin, called Relative navigation on the ground. The correct execution of this instrument will be critical, because the chosen landing place, a crater, is quite dangerous.
“Jezero is 28 miles wide, but in this stretch there are a lot of potential dangers that the rover can encounter: hills, rock fields, dunes, the crater walls themselves, to name just a few,” Andrew Johnson said. The main robotics systems engineer at NASA’s Jet Propulsion Laboratory, said in a Press release. “So if you land on one of these dangers, it could be catastrophic for the entire mission.”
Here’s how NASA describe the new instrument, which should allow the landing craft to determine its position relative to the surface with a degree of accuracy of approximately 40 meters or less.
Relative ground navigation allows the rover to make more accurate estimates of its position relative to the ground during the descent. […] Using images from Mars orbiters, the mission team creates a map of the landing site. The rover stores this map in its new computer “brain”, designed specifically to support navigation on the ground. Descending on the parachute, the rover takes pictures with the surface approaching quickly. To find out where he is going, the rover quickly compares the landmarks he sees in the images with his map on board. Armed with the knowledge of where he is going, the rover is looking for another map on board of safe landing areas to find the safest place he can reach. The rover can avoid dangerous terrain with a diameter of up to about 1,100 feet (about three dimensions of football field from head to toe) by deviating to safer ground.
The parachute should slow down to about 200 miles per hour (320 km / h), requiring one last step to slow down: motorized descent with eight tiny retro-missiles. After dropping the parachute, the rover, still attached to the back shell, will cruise to the surface from an initial height of 2,100 meters.
About 12 seconds before touching and at a very reasonable speed of 2.7 km / h, it will be time to maneuver skycrane. The back cover will lower the rover using three 20-foot-long, 66-foot cables, during which time the rover’s legs and wheels will move into their landing position. Perseverance, feeling an imminent landing, will give up the cables, and the descent stage will close and will collapse – hopefully – far.
Lots of moving parts, including some projectiles, make this an extraordinarily complicated dance. The heat shield, parachute and rear casing may damage or interfere with the landing and / or performance of the Perseverance.
Again, history provides another example of a mission that is currently failing, namely NASA’s Mars Polar Lander, which, like the Mars Climate Orbiter, died in 1999 (it was not an excellent year for NASA). Conformable GODMOTHER, “The most likely cause of the failure was the generation of false signals when the lander’s legs unfolded during the descent”, which “falsely indicated that the spacecraft touched Mars when, in fact, it was still descending” , causing “the main engines [to] closed prematurely “, resulting in the fall from the Martian surface.
If something goes wrong during the landing, Swati Mohan will be among the first to know because she is driving, navigation and control operations lead for Mars 2020 Mission. Swill be in control of the NASA mission tracking the rover’s progress and health during landing.
“Real life can always throw you curved balls. So, we will monitor everything during the cruise phase, we will check the power of the camera, we will make sure that the data flows as expected “, said Mohan in a Press release. “And once we get the signal from the rover that says, ‘I’ve landed and I’m on stable ground,’ then we can celebrate.”
The rover, though modeled on Curiosity, has many new features, including a number of cameras and the ability to look under surface with radar penetrating the ground. The rover will land at Jezero Crater, where it will look for signs of ancient life. If life once existed on Mars, a place like Jezero Crater – a former lake and river delta – would have been an ideal place for microbes to live. In addition to this important astrobiological work, Perseverance will study the weather and Martian geology, will deploy a small helicopter called Ingeniousness and collects samples for a future mission.
NASA will have a live landing coverage stream, which is scheduled for Feb. 18 at 3:30 p.m. ET (12:30 PM PT). We will watch and hope for The best.