To the casual observer, a rover landing on Mars can seem like old news, believe it or not. Especially after all the successes of NASA. But many probably do not know the so-called “Martian curse”. The fact is that many of the spaceships attempting to land there fail and crash.
Next, the NASA Perseverance Rover wields the glove of Mars Curse. She will attempt her long-awaited landing in Jezero Crater on February 18th. The folks at NASA gave the Perseverance rover some finely tuned tools to get it safely to the Martian surface and defeat the Martian curse.
“So if you land on any of these hazards it could be disastrous for the entire mission.”
Andrew Johnson, senior robot systems engineer at NASA’s JPL
The Perseverance Rover ends up in Jezero Crater because NASA believes it can do the best science there. The aim of the mission is to look for signs of old life and to collect samples for a possible return to earth. The Jezero crater is an ancient, dry paleo lake. It contains both preserved sediments and a delta. According to NASA, the crater is “one of the oldest and most scientifically interesting landscapes Mars has to offer”. Scientists believe if there is fossilized evidence of ancient life, they could find it in Jezero.
The Jezero crater on Mars is the landing site for NASA’s Mars 2020 rover. Photo credit: NASA / JPL-Caltech / ASU
But it is also dangerous to land in it.
“Jezero is 28 miles wide, but at that distance there are many potential hazards the rover could encounter: hills, rock fields, dunes, the walls of the crater itself, to name a few,” said Andrew Johnson, director of robotic systems engineer at NASA’s Jet Propulsion Laboratory in Southern California. “So if you land on any of these hazards it could be disastrous for the entire mission.”
About 60% of all spaceships sent to Mars fail. Perseverance uses what is known as “Terrain Relative Navigation” (TRN), a technology first used in cruise missiles to avoid the same failure. On the whole, TRN consists of two elements: a boarding pass of the landing area with heights and hazards and a navigation camera. When Perseverance approaches its landing ellipse, the camera compares its real-time images with the boarding pass and orders the lander’s missiles to steer the vehicle away from known hazards.
Overall, the rover’s autonomous landing system is known as the “Landing Visions System” (LVS).
“For Mars 2020, the avalanche transceiver will use the position information to find out where the rover is relative to safe spots between these hazards. And in one of those safe places the rover lands, ”Johnson said in a press release.
This type of system has been in development for some time. NASA’s OSIRIS-REx used one in its risky sampling maneuver at the asteroid Bennu. This system was called Natural Feature Tracking (NFT), and it effectively guided the spaceship to Bennus’ underground littered with boulders. The OSIRIS-REx mission was successful and the samples should arrive on Earth in September 2023.
But a system like Perseverance’s can’t do without a lot of hard work and lead time. It’s been in development for several years and hopefully all of that development and testing is paying off.
A prototype of the Lander Vision System for NASA’s Mars 2020 project was tested on this December 9, 2014 flight of a “Xombie” vehicle from Masten Space Systems in Mojave Air and Space Port, California. Photo credit: NASA / Photo: Tom Tschida
Swati Mohan is the director of guidance, navigation and control operations for Mars 2020 at JPL. The first two test phases were hardware and simulation and were both carried out in a laboratory. In the press release, Mohan said, “There we test every condition and variable we can. Vacuum, vibration, temperature, electrical compatibility – we put the hardware through its paces. ”
Once the hardware has undergone all of these tests, it’s time for simulations. “Then we use the simulation to model various scenarios that the software algorithms can encounter on Mars – a day that is too sunny, a very dark day, a windy day – and ensure that the system behaves as expected regardless of these conditions”, said Mohan.
After that, the system was ready for flight tests. But not autonomously. Instead, it was tested on a helicopter, where it was used to estimate the helicopter’s altitude and position.
This illustration shows Jezero Crater – the landing site of the Mars 2020 Perseverance Rover – as it may have looked like on Mars billions of years ago when it was a lake. An inlet and an outlet are also visible on both sides of the lake. Photo credit: NASA / JPL-Caltech
“That brought us to some level of technical readiness as the system could monitor a variety of terrains but didn’t have the same type of descent as Perseverance,” said Johnson. “It was also necessary to demonstrate an avalanche transceiver on a rocket.”
The avalanche transceiver system was repeatedly tested in the field with a rocket. This rocket, the Masten Space System Xombie, served as a test bench for avalanche transceivers from 2014. NASA’s Flight Opportunities Program funded these tests.
“The tests on the rocket almost removed any remaining doubts and answered a critical question for avalanche transceiver operation in the affirmative,” said Nikolas Trawny of JPL, a payload and pointing control systems engineer who worked closely with masts on the 2014 field tests . “We knew then that the avalanche transceiver would work during the high-speed vertical descent typical of Mars landings.”
“The tests that Flight Opportunities are supposed to offer were really unprecedented in NASA at the time,” said Johnson. “But it has proven so valuable that this type of flight test is now expected to be conducted. For LVS, these rocket flights were the cornerstone of our technological development efforts. “
“And as soon as we get the signal from the rover that says, ‘I’ve landed and on solid ground,’ we can celebrate.”
Swati Mohan, Head of Leadership, Navigation and Control for Mars 2020 at JPL.
The LVS system is complex. It can not only bring the Perseverance rover to the surface, but also in the most economical way possible. The fuel for the lander’s missiles is obviously limited so there really is only one chance to get it right. Overall, the system was successfully tested and is only a few days away from the actual business: the landing in the Jezero crater.
But even with all the thorough tests of the autonomous system, there can still be surprises. Real life is always different from simulations, and while NASA trusts the system, they are still ready to respond to and adapt to problems or changing conditions.
“Real life can always throw curve balls. So we will monitor everything during the cruise phase, check the power to the camera and make sure the data is flowing as expected, ”Mohan said. “And as soon as we get the signal from the rover that says, ‘I’ve landed and on solid ground,’ we can celebrate.”
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