If all goes as planned, an Atlas V-541 rocket will launch from Cape Canaveral, Florida, this morning carrying a new rover to Mars. Named Perseverance, this rover will look for ancient signs of life on the Red Planet, hoping to determine whether humans could survive there. We'll leave it to others to explain why man would want to live on Mars when we've got a perfectly good planet right here. We're better equipped to answer more practical questions. Like: Why can't we just launch a golf cart into space and drive it on Mars? What makes a rover different from a vehicle you'd use here on Earth?
To help answer these questions, we talked to John Grant, a geologist for the Center for Earth and Planetary Studies at the National Air and Space Museum, and Rich Rieber, mobility systems engineer for Perseverance at NASA's Jet Propulsion Laboratory in Pasadena.
Grant was a co-leader in the process for selecting the site in the Jezero crater where Perseverance will land in February, should everything go as planned. He was also involved with the Spirit, Opportunity, and Curiosity rovers. Rieber's job is to make sure Perseverance can get where it needs to go to carry out its mission—an expert in off-planet off-roading.
"The main thing is, if you get a flat tire on the moon or Mars, there's nobody there to replace it," Grant says. "So we design for the worst case—surviving the biggest bump or the biggest temperature swing. And sometimes we can devise workarounds. We had bum wheels on Spirit, but the engineers figured out how to drive it backward." Rieber says NASA learned from prior rovers' wheel problems, leading to what he calls Perseverance's "sick rims."
Consider the growsers—what we would think of as the tread. Compared to Curiosity, Perseverance's wheels have double the growsers, 48 to 24. "That gives it better traction and makes it stronger," Rieber says. "That's one of the places where durability meets traction. The growsers have a very slight sine wave shape, four to five millimeters, but that adds an insane amount of rigidity. It has to get traction in sand but survive bedrock."
Scientific goals dictate the design of the rover, but the vehicle's limitations define the mission. There may be some intriguing geological formation at the peak of a 50-degree incline, but you're not driving up there. "We'll get images down and start planning, and multiple groups will want to go to different places, but if the engineers say we can't get there, we can't get there," Grant says. "You can't keep everybody happy all the time."
NASA
You probably can't go check out a site 200 miles from your original drop zone, either, because Perseverance tops out at a little less than 0.1 mph. It's the ultimate low-range rock-crawler: six motors, six-wheel drive, four-wheel steering, and the ability to drive over a 15.7-inch-tall rock. The Jet Propulsion Lab tested Perseverance's systems in the “Mars Yard”—essentially a parking lot filled with rocks and sand—using a rover named Scarecrow, because it had no brain. The Mars Yard is a good place to suss out the physical limitations of the platform, as well as potential problems with both hardware and software.
"My coworker got Scarecrow high-centered on a rock and snagged a suspension pivot, and we had to lift it out with a crane," Rieber says. "Another time, we got into a situation where the rover would only do Zoolander turns—it would only turn right. You told it to go left and it would go right 270 degrees to get there. It turned out it had a bad gyro package."
The Mars Yard was also the setting for some of the testing on Perseverance's self-driving capabilities, which are key to its (relative) speed. NASA uploads a plan for each Mars day and the rover needs to navigate its way through it, because—contrary to popular perception—you can't sit on earth and drive a rover on another planet in real time.
"We don't joystick the rover," Rieber says. “We don't have a steering wheel. There's no cool drone operator interface, because of latency. Our one-way light time is seven minutes. So it takes seven minutes for the image to get to you, seven minutes for you to send a command and seven minutes to see what happens. And that goes to 22 minutes when Mars is on the opposite side of the sun. So what we do is take the entire instructions for a Mars day, a sol, and send it up every morning. Then we have five or six hours when the rover has to operate by itself."
One key to Perseverance's guidance is a stereo camera system (think Subaru EyeSight), but its processing power is actually pretty minimal. "The processor we're using is like a Pentium 1," Rieber says. "It's like an early '90s computer. And that's because of all the radiation. The tighter you pack transistors on a chip, the more susceptible they are to radiation. But we've stripped down the code and we were able to make this rover less paranoid, less of a scaredy cat." In an elegant bit of recycling, the landing computer gets reprogrammed to become the navigation computer once landing is complete.
Perseverance will be powered by a 10.6-pound chunk of plutonium-238. NASA has estimated how much radiation spectators will be exposed to if the rocket explodes on launch. It's 210 millirem, which is about equivalent to getting a head CT scan.
The plutonium gives off heat as it decays, and that heat is converted to a constant 110 watts of electrical power by a 99-pound thermoelectric generator on the rover's aft end. A pair of rechargeable lithium-ion batteries store additional energy, allowing the rover to draw up to 900 watts—1.2 horsepower—for short stretches. Think of it as an IndyCar push-to-pass system for a really long, really slow race.
Perseverance's planned mission is scheduled to span at least 687 days, or one Martian year. The plutonium should last about 14 years, but previous Mars rovers have far outlasted NASA's expectations. The Curiosity rover, which landed on Mars in 2012 with the same mission length as Perseverance, is still doing research there today. Which begs the question: Why not add solar panels to the 2260-pound rover to potentially extend its mission indefinitely? Because, as with any vehicle, you can't have everything.
"You're flying right up to the mass limit of what you can fly," Grant says. "A lot of people asked, 'Why not put on windshield wipers?' back when the solar-powered rovers would get dust on the panels. It would be nice to fly a lot of other instruments, too. But the bigger the thing you try to land on Mars, the harder it gets. You have to consider what you really need to accomplish the mission." So no underbody neon or kickin' sound system on Mars. For now.
Anatomy of a Rover
NASA
NASA has spent around $2.4 billion on this mission so far, with the bulk of that going into developing its new rover. Perseverance is about the size and shape of a small car and weighs as much as a Mazda Miata. But there's a lot more to it than those modest dimensions would suggest. Here are a few of its notable features:
Antennas
Mars rovers are no good if they can't talk to Earth. Perseverance has three antennas. One communicates with Mars orbiters. One can pivot to point directly at Earth so the rover doesn't have to reorient itself and waste energy. The third receives signals and has a low data-transfer rate but can talk to NASA no matter which direction it's pointing.
Robotic Arm
NASA designed this mechanism with a drill that'll bore the surface and collect rock samples. The rover will then store these rocks in a cache on Mars in the hope that a future mission will allow these samples to come to Earth. Until that happens, the arm has a terrain scanner, called SHERLOC, and a camera, called WATSON, to document its findings. The N in WATSON is for engineering.
Body
After President Obama announced cuts to the Mars Exploration Program in 2012, NASA decided to build Perseverance on the same basic structure as the Curiosity rover but gave it new wheels and software and a more sophisticated robotic arm.
Wheels
Each of the rover's six wheels sits at the end of a length of titanium tubing. The wheels themselves are aluminum and have ridges for traction. The curved titanium spokes give the wheels some spring. Pneumatic tires are not a viable option.
Eyes and Ears
Perseverance has a couple microphones, one of which works with a camera and laser setup to determine the chemical composition of rocks on Mars. The camera scans for rocks that could contain evidence of past life on Mars. The laser then vaporizes these rocks, and based on the resulting noises, scientists can understand the mass and makeup of the specimen in question. The other mic is designed to record the descent and landing of the craft, but NASA doesn't expect it to survive beyond that.
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The Link LonkJuly 30, 2020 at 05:00PM
https://www.caranddriver.com/features/a33457653/perseverance-nasa-mars-rover/
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https://news.google.com/search?q=Red&hl=en-US&gl=US&ceid=US:en
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