Global Courant 2023-04-11 19:00:44
Extreme cold is merciless to machines. Liquids thicken into useless goo. Rubber seals stiffen and crack.
The problems pile up as the temperature drops. Metal becomes brittle and threads contract. Batteries stop working, adhesives stop sticking, and LCD screens go black as their liquid crystals freeze.
And that’s just here on Earth.
When NASA’s new lunar rover lands on the moon’s south pole next year, it will encounter a whole new kind of cold.
Temperatures there hover around minus 280 degrees Fahrenheit (minus 173 degrees Celsius). In the permanent shadows of polar craters, it can drop to minus 388 F (minus 233 C).
For context, the Vostok station in Antarctica holds the record for the lowest temperature ever recorded on this planet: minus 128.6 F (minus 89.2 C), recorded July 21, 1983. A typical day on the moon is about 150 degrees colder than the coldest it has ever been on Earth.
Previous rovers for the moon and Mars — which is also cold, averaging minus 80 F — are equipped with built-in heaters that turn on at the start of the lunar or Martian day and take several hours for the machines to warm up enough to begin their daily tasks.
That takes time and energy, two precious commodities on any space mission. But what if you could build a rover that doesn’t require warm-up time?
“If you can work more hours in a day, you could get more information,” he said Lacie Fradet, a project engineer at Motiv Space Systems in Pasadena, which is working with NASA’s Jet Propulsion Laboratory to make this happen. If they manage to build an arm that can operate in extremely cold regions, “we’ll be able to go places we haven’t been before.”
The first step towards that vision becomes reality in Motiv’s air-conditioned cleanroom: a slender robot arm whose angles resemble those of a praying mantis.
The Cold Operable Lunar Deployable Arm, or COLDArm, bears a striking resemblance to a praying mantis.
(Dania Maxwell/Los Angeles Times)
This is the Cold Operable Lunar Deployable Arm, a robotic arm that can operate in the cold of the lunar poles. Motiv builds it with parts supplied by JPL in La Cañada Flintridge. If COLDArm passes all the tests here on Earth, the project’s next goal is to secure a spot on NASA’s Commercial Lunar Payload Servicesa program that allows U.S. companies to send technology to the lunar surface for testing or conducting scientific experiments.
The 2-meter-long arm is just one part of a future lunar rover, but it’s crucial. The arm is the main tool for scooping up samples from the lunar surface. If it fails, so does the mission.
Motiv previously built the robotic arm on Perseverance, the robber currently exploring Jezero crater on Mars. The 2 meter long arm contains crucial instruments such as SHERLOCwhich searches for evidence of past microbial life, and the X-ray spectrometer known as PIXL.
If COLDArm proves successful, it could boost the amount of experiments that can be conducted in the colder regions of our solar system.
JPL has experience building machines that can function in temperatures on Mars down to -202 F (minus 130 Celsius), said Ryan McCormickCOLDArm’s principal investigator.
“But getting even colder,” he said, “is a big challenge.”
Ryan McCormick, JPL’s principal investigator for COLDArm, says designing a robotic arm system that can function in the extremely cold temperatures of the moon’s south pole “is a major challenge.”
(Dania Maxwell/Los Angeles Times)
Many lubricants and adhesives that work on Mars will degrade in the cold of a lunar night. Certain electronics that worked fine for the Mars rovers — which can take advantage of the heat trapped by the thin Martian atmosphere — don’t work on the moon either.
COLDArm is made of bulk metallic glassa class of metals whose atomic arrangement is more similar to that of glass, making them stronger and more durable than steel or ceramic.
Project engineer Lacie Fradet with COLDArm, which is made of solid metal glass to improve its function in temperatures down to minus 280 degrees Fahrenheit.
(Dania Maxwell/Los Angeles Times)
Bulk metallic glass requires no wet lubricant at the joints. That’s crucial, because wet lubricants freeze solid at minus 94 F (minus 70 C) — a practically tropical temperature compared to the cold of the lunar poles. Previous rover arms had to be built with small heating elements at each joint to keep the lubricant at a pliable temperature. Bulk metallic glass makes that unnecessary, Fradet said.
In addition, COLDArm’s motor controllers are equipped with an updated voltage converter that can function in extremely cold environments without additional cables or insulation, McCormick said.
In March, the Motiv team disassembled the arm and tested its various parts in a thermal vacuum of less than 100 Kelvin, or roughly minus 175 C. (Extreme cold has its own temperature units, with zero Kelvin representing the point at which molecules stop moving .)
A close-up of one of COLDArm’s large metal glass joints.
(Dania Maxwell/Los Angeles Times)
All parts functioned in both the extreme cold and vibration tests designed to simulate launch conditions, McCormick said. The next step is to reassemble the arm and make sure it works as a whole under those conditions.
Adding to the complexity is the fact that temperature on the moon functions in a very different way than on Earth, said planetary scientist JPL Laura Kerber. The moon has no air to redistribute heat, so when light hits the moon’s surface, it gets super hot — up to 250 F at the equator. It’s super cold without that light.
Given the Moon’s position relative to the Sun, the interiors of craters at the South Pole remain in constant shadow. That makes them about as cold and dark as anything in the solar system.
“In those permanently shadowed areas, all they see is the cold of space,” Kerber said. “Technically, it’s so hard to make something that can survive in those really, really cold, permanently shadowed craters.”
That’s a big deal for NASA’s Volatiles Investigating Polar Exploration Rover, better known as ADDERwhich will land on the moon’s south pole in late 2024 to search for water ice.
The strongest hints of water on the moon are in the most deeply shaded areas. Those places are too cold for VIPER, but he will walk around them and collect samples from the environment, where the suggestions of water are weaker but still significant.
Navigating the moon’s extreme temperatures has been challenging since the earliest lunar missions. That’s a big part of why Neil Armstrong and Buzz Aldrin flew 150,000 miles for a relatively short walk around their spacecraft: It was just too hot at Apollo 11’s landing site in the Sea of Tranquility to continue.
“We were working in a near-perfect vacuum, with temperatures well above 200 degrees Fahrenheit,” said Neil Armstrong. told NPR in 2010. “NASA officials limited our working time on the surface to 2¾ hours during that initial surface exploration to make sure we wouldn’t succumb to hyperthermia.”
