Extreme cold is cruel to machines. The liquid thickens into a useless slime. Rubber gaskets harden and crack.
The problems pile up as the temperature drops. The metal becomes brittle and the wire shrinks. Batteries stop working, adhesives stop sticking, and LCD screens turn black as their liquid crystals harden.
And that’s just here on Earth.
When NASA’s new lunar probe lands on the moon’s south pole next year, it will encounter a whole new type of cold.
The temperature there hovers around minus 280 degrees Fahrenheit (minus 173 degrees Celsius). In the perpetual darkness of polar craters, temperatures can drop to minus 388 F (minus 233 C).
For context, Antarctica’s Vostok Station holds the record for lowest temperature ever recorded on this planet: minus 128.6 F (minus 89.2 C), recorded on July 21, 1983. A typical day on the moon is about 150 degrees colder than the coldest ever on Earth land.
Previous rovers for the moon and Mars – also cold, averaging minus 80 F – have been equipped with built-in heaters that turn on early in the lunar or Martian day and take several hours to get warm enough let the machine start their daily work.
That comes at the expense of time and energy, two precious commodities in any space mission. But what if you could build a self-driving car with no warm-up time?
“If you can work more hours in a day, you will be able to get more information,” says Lacie Fradet, a project engineer at Motiv Space Systems in Pasadena, is working with NASA’s Jet Propulsion Laboratory to make this a reality. If they succeed in building an arm that can work in extreme cold, “we’ll be able to go places we’ve never been before.”
The first step towards that vision is to materialize in Motiv’s climate-controlled clean room: a sleek robotic arm whose corners resemble a praying mantis.
This is the Cold Operable Lunar Deployable Arm, a robotic arm capable of operating in the cold of the lunar poles. Motiv is building it using parts supplied by JPL in La Cañada Flintridge. If COLDARm passes all the tests here on Earth, the next goal of the project is to secure a spot on NASA. Commercial Moon Load Servicea program that allows US companies to send technology to the lunar surface to test or conduct science experiments.
The 6.5-foot (2-meter) arm is just one part of a future lunar rover, but it’s an important one. The arm is the main instrument for sampling from the lunar surface. If it fails, so does the quest.
Motiv previously built Robot arm ABOVE Persistlounger currently exploring Mars’ Jezero . crater. The 7 foot long arm holds important tools like SHERLOClooking for evidence of past microbial life and an X-ray spectrometer known as PIXL.
If COLDARm proves successful, it could further increase the number of tests that can be conducted in colder regions of our solar system.
JPL has experience building machines that can operate in Martian temperatures as cold as minus 202 F (minus 130 degrees C). Ryan McCormickCOLDARM principal investigator.
“But getting colder,” he said, “is a big challenge.”
Many of the lubricants and binders that work on Mars will metamorphose in the cold of the moonlit night. Some of the electronics that work well for Mars rovers – which can take advantage of the heat trapped by Mars’ thin atmosphere – won’t work on the moon either.
COLDARM is made of bulk metal glassa metal whose atomic arrangement closely resembles that of glass, making them harder and more durable than steel or ceramic.
Bulk metal glass does not require wet lubricants at its joints. That’s important, because wet lubricants freeze at minus 94 F (minus 70 C) – the actual tropical temperature compared to the cold of the lunar poles. Previous rover arms had to be built with small heaters at each joint to keep the lubricant at a pliable temperature. The bulk metal glass makes that unnecessary, says Fradet.
In addition, COLDARM’s motor controllers have been equipped with updated voltage converters that can operate in extremely cold environments without the need for large amounts of additional cables or insulation, McCormick said.
In March, the Motiv team disassembled the arm and tested its various components in a thermal vacuum set below 100 Kelvin, or close to minus 175 C. (The cold pole has its own temperature unit, with 0 Kelvin. denotes the point at which the molecules stop moving.)
McCormick says all components operate in both extreme cold and vibration testing is designed to simulate launch conditions. The next step is to reassemble the arm and make sure it functions as a whole under those conditions.
Adding to the complexity is the fact that temperature works in a completely different way on the moon than it does on Earth, says JPL planetary scientist Laura Kerber. The moon has no air to redistribute heat, so when light hits the moon’s surface, it becomes super hot—up to 250 F at the equator. Without that light, it was very cold.
Given the moon’s position relative to the sun, the interior of its south pole craters remains in constant darkness. That makes them as cold and dark as anything in the solar system.
“In those permanently obscured regions, all they see is the coldness of space,” says Kerber. “Technically, it’s hard to make something that can survive inside those real, very cold, permanently obscured craters.”
That’s a big deal for NASA’s Polar Explorer, or VIPERis expected to land on the moon’s south pole by the end of 2024 in search of water ice.
The clearest signs of water on the moon are in the regions with the deepest shadows. Those places are too cold for VIPER, but it will circumnavigate them and collect samples from the surrounding area, where the hint of water is weaker but still significant.
Navigating the moon’s extreme temperatures has been a challenge since the first lunar missions. That’s a big part of the reason Neil Armstrong and Buzz Aldrin flew 240,000 miles in one relatively short wandering around their spacecraft: It was simply too hot at the Apollo 11 landing site in the Sea of Tranquility to go further.
“We are operating in a near-perfect vacuum, with temperatures above 200 degrees Fahrenheit,” Neil Armstrong tell NPR in 2010. “NASA officials limited our surface work time to 2 and a half hours during that first surface expedition to ensure that we didn’t expire because of hyperthermia. .”