Scientists have long tested solar power in space, but it could soon arrive on the Moon – in the form of rovers equipped with solar panels. On unmanned lunar missions, these tiny robotic vehicles will test the limits of how humans fuel their explorations, navigate the moon’s surface, and create potential human habitats far from home.
The team behind them includes Mike Provenzano, director of planetary mobility for Pittsburgh-based Astrobotic. Under a contract with NASA, the robotics company has scheduled unmanned missions to the moon with the rover in tow for next year. The first mission, Peregrine 1, is scheduled for the end of 2021.
These trips will represent a milestone in space: they will mark the first visit of the United States to the Moon in 50 years.
A light but powerful Rover
The smallest of Astrobotic’s vehicles, the CubeRover is similar in size to a microwave oven and weighs up to 5 pounds – and will include a solar panel mounted on its top. Their fleet also includes the slightly larger MoonRanger, which weighs around 24 pounds.
Once the rover reaches the moon, the team hopes it will venture from the landing gear into water ice search near the moon’s south pole, says Provenzano. In recent years, scientists found forms of water across the surface of the moon.
The CubeSAT has since served as a standardized building block for larger satellites made up of multiple cubic modules. Due to its size and shape, the CubeRover can carry payloads of the same size as the CubeSAT, it explains, so space partners can plan larger shipments based on the familiar CubeSAT unit. The designers of the CubeRover thus hope to set a standard for the “lunar economy” and interplanetary freight delivery. (Watch a video of NASA testing CubeRover mobility.)
More ambitiously, Astrobotic wants the CubeRover “to democratize access to the moon, making it easier for business and academic groups to engage in these scientific missions” and to design their own experiments for the surface of the moon, explains Provenzano. . Partners aboard Peregrine 1 will come from six countries and will include DHL and the Mexican Space Agency, Espacial Mexicana Agency.
Chuck Taylor, program director for vertical solar panel technology (VSAT) at NASA’s Langley Research Center, began pursuing off-planet solar energy research about seven years ago. It was a happy coincidence, he said. After working with the Navy in systems engineering, he joined NASA’s space power program. With expertise in autonomous systems, the Langley Center is leading NASA’s solar energy effort, partnering with solar cell experts at NASA’s Glenn Research Center.
For polar missions, Taylor considered placing large solar panels high enough on masts to supply solar power. This would involve solar panels aligned vertically, unlike those that are common on Earth.
The rule of thumb is that if you’re at the South Pole, the angle of the sun’s ray is very low on the horizon, Taylor explains. Cliffs and other terrain features, or a nearby lander, could cast shadows on low horizontal panels.
Once the solar panels capture the energy, it can be stored in batteries or transferred to electric vehicles. This transfer occurs either by cables (“tried and true”, says Taylor) or by more recent methods, notably radiant power with lasers.
It will be difficult to transform the vision of the sun-powered rovers running across the lunar surface (as in Ad Astra) in reality. The main obstacles, says Provenzano, include the extreme temperatures of the moon, the radiation on its surface and moon dust.
But first, the equipment must survive the launch. Solar panels are delicate and must resist disintegration when the rocket leaves Earth, and later when the lander descends towards its destination. Cedric Corpa de la Fuente, avionics engineer with Astrobotic’s planetary mobility team, prepares to test a “structural model” – a replica of the solar panels – under launch-vibration conditions in the laboratory to verify that the panels of the rover can hold up.
The lunar night presents perhaps the biggest obstacle for rovers and panels. The dark side of the moon is brutal: a lunar day lasts 14 Earth days, and during lunar night temperatures drop for two weeks, shipwreck at minus 280 degrees Fahrenheit. In order for a rover to survive such intense cold, it must store enough energy for continued use during that long period of darkness. The vehicle will also need enough horsepower to run heaters that help the equipment withstand the frost. And during the long lunar day, the panels must withstand warmer temperatures than anywhere else on Earth.
Then there is the dust. When moon sand, or regolith, stains solar panels, it can reduce the energy they store and cause them to overheat. Regolith consists of approximately 50 percent silicon dioxide and is very abrasive. Provenzano notes that this can wreak havoc on the rover’s gaskets and seals, and can cause sparks in the equipment.
As pandemic restrictions eased this spring, testing at Astrobotic resumed to simulate the rover’s navigation in such harsh moonlight and dust conditions. Teams are monitoring how dust affects the movement of the rover and its solar panel, and how regolith clogs the panels.
Navigation presents another headache, as rovers can’t rely on Google Maps or GPS like we do on Earth journeys. During landing, the lander’s cameras will take a series of photos to create a high-resolution map of the area surrounding the site where it lands. Once deployed, the rover will take its own photos for easy orientation. Then, software using stereo vision and visual odometry (the process of determining position and orientation by analyzing images from the camera) will create local maps that correlate with the high-resolution ones from the lander.
This navigation technique is somewhat similar to that of the ancient Polynesians, who compared the movements of ocean currents and stars. The team will also track the position of the sun, adds Corpa de la Fuente, and they will project laser patterns on the surface in order to build 3D surface maps.
Once on the moon, the rover needs enough juice to venture out of the lander. This is why Astrobotic is developing a contactless docking station with WiBotic, a company specializing in industrial and underwater wireless charging. With smart docking software, a rover can locate a charging concentrator on its own and, once in range, start charging.
The smaller rover should be able to recharge in as little as 90 minutes, thanks to a 125-watt charging system and a battery similar in size to a rechargeable drill. Rangers could recharge themselves by forming a network, a concept known as “swarm technology.”
They can also be delivered with accessories: the British company Spacebit has developed mini-rover robots to fit inside a CubeSat. Their Asagumo rover is a four-legged robot weighing around 2 pounds; they plan to launch a demo on Peregrine 1 (see video).
Overall, there is plenty to keep the mission team busy. “There are so many ways a spaceship can die,” Provenzano whispers. But the rover’s potential is exciting. “If it finds water ice, it will be the first rover to find this on another planetary body. So we’re super excited.
Unmanned lunar road tests may also contain lessons for adventures elsewhere in the solar system, including on Earth. For example, moon-friendly wireless chargers can be useful in “harsh radiation environments” like nuclear power plants, says Provenzano, where they can power sensors to monitor temperature and pressure more efficiently than conventional hard-wired methods. .