Failure could take many forms next week when NASA’s next-gen rover, Perseverance, reaches the surface of the Red Planet. Here’s what has to go right – and how things can go sideways quickly – when Perseverance tries to make its long-awaited landing.
For NASA, it’s the entry, exit, and landing (EDL) of Persistence on Thursday February 18 presents numerous potential points of failure. NASA has said that “hundreds of things have to go just right” for the robber to kill seven minutes of terrorWe can’t take a safe landing for granted: As NASA notes, only “about 40 percent of missions ever sent to Mars – by a space agency – have been successful.” Which one, yikes.
Basically, persistence will have to transition from speeds of 12,500 miles per hour (20,000 km / h) to a walking pace over the course of a few minutes. In addition, it will have to do this autonomously, as it takes almost 11 minutes for radio signals to reach Earth. To complicate matters, NASA is introducing two new technologies to the mission, both related to the EDL phase and both unproven.
All three stages – entry, descent, and landing – present their own unique challenges.
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Nestled in the descent, the rover will separate from the cruise staircase, which with its solar panels, radios and fuel tanks will no longer be needed. Next, the spacecraft will have to orient itself so that the heat shield is facing forward, a task made possible by small thrusters on the backshell. During atmospheric entry, the spacecraft’s heat shield will have to withstand temperatures of 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.
Previous missions to the Red Planet have indeed failed on the doorstep of Mars. In 1999, NASA’s Mars Climate Orbiter entered orbit far too low, burning the spacecraft in the atmosphere. The failure was ultimately traced to a conversion error, where imperial units of pound seconds were not converted to the standard metric Newton seconds. Hate it when that happens.
Should the descent phase survive the atmospheric input, it will still have to contend with variably dense air pockets that could keep it off course. To avoid this problem, a guided entry will be performed where the descent stairs will fire small thrusters to compensate.
The rollout of the 70-foot-wide (21.5-meter) parachute is next. If the parachute unfolds properly and doesn’t get entangled, the descent phase will abruptly slow to 1,000 miles per hour (1,600 km / h), which is still lightning fast (remember, Mars has a super-thin atmosphere). Deployment of this supersonic parachute relies on an unproven new technology called Range trigger, which calculates the distance to the landing site and activates the parachute at exactly the right time. This is expected to occur approximately 240 seconds after atmospheric arrival, when the descent phase is approximately 11 km above the surface. Perseverance will say goodbye to the heat shield about 20 seconds after the parachute has deployed, introducing a new potential point of failure.
This is a critical phase – one with regrettable historical precedents. During the failed landing from ESA’s Schiaparelli mission in 2016, the parachute and heat shield were prematurely ejected during the descent, the result of a software glitch. An onboard computer thought it was only a few feet above the ground, but in reality the descent was anywhere from 1.25 to 2.5 miles (2-4 km) above the surface. You can imagine what happened next. The doomed Schiaparelli lander was traveling at about 185 miles per hour (300 km / h) when it crashed into the regolith of Mars.
With the heat shield gone and the rover now finally exposed to the atmosphere of Mars, another new technology, called Terrain-relative navigationThe correct implementation of this tool will be critical as the chosen landing site, a crater, is quite dangerous.
“Jezero is 45 kilometers wide, but within that expanse there are many potential hazards that the rover could encounter: hills, rocky fields, dunes, the walls of the crater itself, just to name a few,” Andrew Johnson, principal robotic systems engineer at NASA’s Jet Propulsion Laboratory, said in a press release“So if you hit one of those dangers, it could be disastrous for the entire mission.”
Here’s how NASA describes the new tool, which allows the landing craft to determine its position relative to the surface with an accuracy of nearly 40 meters or less.
Terrain-Relative Navigation allows the rover to make much more accurate estimates of its position relative to the ground during descent. […] Using images of Mars orbiters, the mission team creates a map of the landing site. The rover stores this map in its new computer brain, which is specially designed to support Terrain-Relative Navigation. The rover descends on its parachute and takes pictures of the rapidly approaching surface. To find out where it is going, the rover quickly compares the landmarks it sees in the images with the map on board. Armed with the knowledge of where he is going, the rover searches for another map on board with safe landing zones to find the safest place he can reach. The rover can avoid dangerous ground up to about 335 meters in diameter (about the size of three football fields end-to-end) by diverting itself to safer ground.
The parachute should slow the descent to about 200 miles per hour (320 km / h), requiring one last step to slow down: powered descent with eight small retro missiles. After the parachute is put on the water, the rover, still attached to its backshell, will float to the surface from an initial height of 2,100 meters.
About 12 seconds before landing, and at the very reasonable speed of 2.7 miles per hour (2.7 km / h), it’s time for the skycrane maneuver. The backshell will lower the rover using three 20-meter cables, during which time the rover’s legs and wheels will move into their landing position. Persistence, sensing an impending landing, will release the cables, and the descent staircase will fly off and – hopefully – crash far away.
Lots of moving parts, including some projectiles, clearly make this an extremely complicated dance. The heat shield, parachute, and backshell are all at risk of damaging or otherwise disrupting the landing and / or the execution of Perseverance.
Again, history offers another example of a mission that failed at this point, namely NASA’s Mars Polar Lander, which, like the Mars Climate Orbiter, died in 1999 (not a great year for NASA). According to NASA, the “ most likely cause of the disturbance was the generation of false signals when the lander’s legs were deployed during descent, ” which “ falsely indicated that the spacecraft hit Mars when in fact it was still descending ” , eliminating the engines [to] shut down prematurely, ”causing the lander to fall to the surface of Mars.
Should something go wrong during landing, Swati Mohan is one of the first to know, as she is the lead guidance, navigation and control operations for the Mars 2020 mission. S.he will be with NASA Mission Control to monitor the rover’s progress and health during the landing.
“Real life can always throw you crooked balls. So we keep an eye on everything during the cruise phase, check the power to the camera and make sure that the data is flowing as expected, ”Mohan said in a statement. press release“And as soon as we get that signal from the robber that says, ‘I’ve landed and I’m on stable ground,’ then we can celebrate.”
The rover, although modeled after Curiosity, has many new features, including an array of cameras and the ability to see underneath the surface with ground penetrating radar. The rover will land at the Jezero crater, where it will look for signs of old life. If life had ever existed on Mars, a place like Jezero Crater – a former lake and river delta – would have been an ideal place for microbes to hang out. In addition to this important astrobiological work, Perseverance will also study the weather and geology of Mars and deploy a small helicopter called Ingenuity, and collect monsters for a future mission.
NASA will have a live stream of the landing scheduled for February 18 at 3:30 p.m. ET (12:30 p.m. PT). We’ll watch and hope for the best.