The failure could take many forms next week when NASA’s next-generation rover, Perseverance, hits the surface of the red planet. This is what should go well — and how things could quickly go awry — when perseverance tries to achieve the long-awaited landing.
For NASA, the entry, descent and landing (EDL) of Perseverance on Thursday, February 18 presents numerous potential points of failure. NASA has done it dit that “hundreds of things have to go well” for the rover to survive the seven minutes of terror. We can’t take for granted a safe landing: as NASA points out, only “about 40 percent of the missions sent to Mars — by any space agency — have been successful.” Quina, yikes.
In short, Perseverance will have to go from speeds that reach 20,000 km / h and a speed of walking over several minutes. In addition, it will have to do so autonomously, as radio signals take almost 11 minutes to reach Earth. To complicate matters, NASA is releasing two new technologies for the mission, both related to the EDL phase and both unproven.
The three phases (entry, descent and landing) present their own challenges.
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The rover, located within the descent stage, will be separated from the cruise stage, which will no longer be needed with its solar panels, radios and fuel tanks. The spacecraft will then have to be oriented so that its thermal shield is oriented forward, a task possible thanks to the small thrusters located in the rear casing. During atmospheric entry, the spacecraft’s heat shield will have to withstand temperatures reaching 2,300 degrees Fahrenheit (1,300 degrees Celsius). A structural failure at this stage would be catastrophic and would end the mission before it had a chance to begin.
In fact, previous missions to the red planet have failed at the Martian gate. In 1999, NASA’s Mars Climate Orbiter entered too low an orbit, causing the spacecraft to burn into the atmosphere. The failure was finally layout to a conversion error, in which the imperial units of pounds-seconds were not converted to Newton’s standard metric-seconds. Hate it when that happens.
If the descent stage survives the atmospheric entry, you will still have to struggle with varied and dense air pockets that could deviate from the course. A guided entry will be made to avoid this problem, in which the descent stage will fire small thrusters to compensate for them.
The deployment of the 21.5-meter-wide parachute is as follows. If the parachute unfolds properly and does not get tangled, the descent stage will slow down sharply to 1,600 km / h (1,000 miles per hour), which is still incredibly fast (remember, Mars has a very fine atmosphere). The deployment of this supersonic parachute will depend on a new untested technology called Rank trigger, which will calculate the distance to the landing point and activate the parachute that will be deployed at the right time. This is expected to happen approximately 240 seconds after atmospheric entry, when the descent stage is about 11 km above the surface. Perseverance will be fired from its heat shield about 20 seconds after the parachute is deployed, introducing another potential point of failure.
This is a critical stage, with unfortunate historical precedents. During the failed landing from ESA’s Schiaparelli mission in 2016, the descent stage prematurely expelled the parachute and heat shield, the result of a software problem. An on-board computer thought it was a few feet off the ground, but in reality the descent stage was between 2.4 km and 1.25 and 2.5 miles above the surface. You can imagine what happened next. Schiaparelli’s terrifying convict was traveling at 300 km / h at about 185 miles per hour when he crashed into the Martian regolith.
With the thermal shield gone and the rover finally exposed to the Martian atmosphere, another new technology will begin, called Navigation relative to the terrain. The correct execution of this tool will be crucial, as the chosen landing point, a crater, is quite dangerous.
“Jezero is 28 miles wide, but within that extent there are many potential dangers the rover could encounter: hills, rock fields, dunes, the walls of the crater itself, to name just a few,” Andrew Johnson, principal robotics system engineer from NASA’s jet propulsion laboratory said in a Press release. “So if you land in one of those dangers, it could be catastrophic for the whole mission.”
This is how NASA is describes the new tool, which should allow the landing craft to determine its position relative to the surface with a degree of accuracy close to 40 meters or less.
Terrain navigation allows the rover to make much more accurate estimates of its position relative to the ground during the descent. […] Using images from orbits of Mars, the mission team creates a map of the landing site. The rover stores this map in its new computer “brain”, specifically designed to support terrain-related navigation. Going down on his parachute, the rover takes pictures of the rapidly approaching surface. To find out where it’s headed, the rover quickly compares the landmarks it sees in the images to the built-in map. Armed with the knowledge of where he is heading, the rover looks for another map aboard safe landing areas to find the safest place he can get to. The rover can avoid dangerous terrain up to about 335 meters in diameter (approximately the size of three end-to-end football fields), by diverting to safer terrain.
The parachute should slow down the descent to 320 km / h at about 200 miles per hour, requiring one last step to slow down: the descent powered by eight tiny retro rockets. After leaving the parachute, the rover, still attached to its rear casing, will cross to the surface from an initial height of 2,100 meters (6,900 feet).
About 12 seconds before the touchdown, and at a very reasonable speed of 1.7 miles per hour (2.7 km / h), it will be time to maneuver the elevator. The rear casing will lower the rover using three 20-meter-long cables, so that the rover’s legs and wheels will move to their landing position. Perseverance, which detects an impending landing, will let go of the cables, and the descent stage will zip up and hopefully crash.
There are many moving parts, including some projectiles, that make it an extraordinarily complicated dance. The heat shield, parachute, and rear casing are at risk of damaging or otherwise interfering with Perseverance landing and / or performance.
Again, the story provides another example of a mission that fails at this point, namely NASA’s Mars Polar Lander, which, like the Mars Climate Orbiter, died in 1999 (it wasn’t a big year for NASA). In accordance with NASA, the “most likely cause of failure was the generation of false signals when the lander’s legs unfolded during the descent,” which “falsely indicated that the spacecraft had touched Mars when in fact it was still descending,” causing the engines [to] closed prematurely “, which causes the lander to fall to the Martian surface.
If something goes wrong during the landing, Swati Mohan will be among the first to know, as she is guide, navigation and control of operations for the March 2020 Mission. Swill be in control of NASA’s mission tracking the rover’s progress and health during landing.
“Real life can always throw you curved balls. Therefore, we will monitor everything during the cruise phase, check the power of the camera and make sure that the data flows as expected “, said Mohan in Press release. “And once we get that signal from the rover that says, ‘I’ve landed and I’m on stable ground,’ we can celebrate.”
The rover, although based on Curiosity, has many new features, including a variety of cameras and the ability to look below. the surface with radar penetrating the ground. The rover will land in Jezero Crater, where it will look for signs of ancient life. If life ever existed on Mars, a place like Jezero Crater — an ancient lake and river delta — would have been an ideal place to pass microbes. In addition to this important astrobiological work, Perseverance will also study the climate and Martian geology, will deploy a small helicopter called Ingenuity, and collect samples for a future mission.
NASA will feature a live broadcast of the landing cover, which is scheduled for Feb. 18 at 3:30 p.m. ET (12:30 p.m. PT). We will be watching and waiting for him better.