When NASA’s most powerful rocket ever attempts its first flight this month, its highest profile payload will be three instrumented mannequins, setting off on a 42-day journey beyond the Moon and back. They are stand-ins for the astronauts that the 98-meter-tall rocket, known as the Space Launch System (SLS), is supposed to carry to the Moon as soon as 2025, as part of NASA’s Artemis program. But there will be other voyagers along for the ride when the SLS lifts off on 29 August: 10 CubeSats, satellites no bigger than a small briefcase, to probe the Moon, asteroids, and the radiation environment of deep space.
The investigators who built those satellites have more than the usual launch jitters: Half of them may not have enough power to begin their missions. Stuck within the rocket for more than a year because of launch delays, their batteries have drained to a level where some may be unable to boot up and unfurl their solar panels. “The longer we wait, the higher the risk,” says Ben Malphrus of Morehead State University, principal investigator for Lunar IceCube, one of the CubeSats with power concerns.
At stake is not just data, but a test of CubeSats as deep-space probes. “We’re in the transition phase from being a curiosity and a training tool to being a platform for real science,” Malphrus says. CubeSats are easy to assemble out of standardized parts—from thrifty ion propulsions systems to pint-size radio transmitters—supplied by a growing commercial base. That lets researchers focus on developing instruments capable of gathering novel data—if they can shrink them into a CubeSat package.
The small size and standardization also make CubeSats cheap. At millions of dollars a pop compared with hundreds of millions for a bigger, stand-alone satellite on its own rocket, they can take on riskier missions, including hitchhiking on the unproven SLS. “When it comes to CubeSats, failure is an option,” Bhavya Lal, NASA’s associate administrator for technology, policy, and strategy, said at a briefing earlier this month.
Several SLS CubeSats will focus on lunar ice, which has intrigued researchers ever since NASA’s Lunar Prospector discovered a signal suggestive of water in the late 1990s. Using a neutron detector, it peered into frigid, permanently shadowed regions in polar craters. In many, the probe detected a curious suppression of neutrons—best explained by extra hydrogen in the topmost meter of soil.
Researchers assume much of the hydrogen represents water ice delivered by ancient impacts of comets or asteroids and trapped in the coldest, darkest lunar recesses. But the hydrogen could also be implanted by the solar wind. When hydrogen ions in the wind strike oxygen-bearing minerals in lunar soil, it creates hydroxyl, which can be transformed into water through subsequent reactions. If the Moon holds enough water, it could be used for agriculture and life support, and split into hydrogen and oxygen for rocket propellant. “That will be more economical than bringing it from Earth,” says Hannah Sargeant, a planetary scientist at the University of Central Florida.
The Lunar Polar Hydrogen Mapper (LunaH Map), an SLS CubeSat led by Craig Hardgrove of Arizona State University, Tempe, will attempt to improve on Lunar Prospector’s maps with a daring orbit that swoops just 12 to 15 kilometers above the South Pole. Over the course of 280 passes with its neutron detector, the team hopes to map excess hydrogen with a resolution of 20 to 30 kilometers, about twice as good as Lunar Prospector. “We can distinguish one [deep crater] from another,” Hardgrove says. Craters lacking hydrogen, or enrichments outside the frigid hideouts, might indicate a relatively recent impact that blasted out ice and redistributed it, he says.
Lunar IceCube will carry a spectrometer that can detect the infrared fingerprints of either water or hydroxyl. Because the device depends on reflected light, it will be most sensitive to signs of hydroxyl and water in sunlit regions at lower latitudes. “They’re really looking at the [effect of] the solar wind, day by day,” says Benjamin Greenhagen, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory.
When NASA launches its giant Moon rocket, it will also carry 10 small satellites beyond low-Earth orbit. Some of the missions could have power issues on startup, after half of the satellites were not permitted to recharge their batteries.
|NAME||PURPOSE||LEAD DEVELOPER||BATTERY ISSUES|
|ArgoMoon||Monitor release of Cubesats, rocket stage||Italy’s space agency|
|Bio Sentinel||Study radiation effects on yeast||NASA (Ames Research Center)|
|CuSP||Study solar wind and magnetic fields||Southwest Research Institute||X|
|EQULEUS||Image Earth’s plasmasphere||Japan’s space agency|
|LunaH Map||Study lunar ice||Arizona State University||X|
|Lunar IceCube||Study lunar ice||Morehead State University||X|
|LunIR||Test novel infrared spectrometer||Lockheed Martin||X|
|NEA Scout||Fly to asteroid with a solar sail||NASA (Marshall Space Flight Center)|
|OMOTENASHIA||Put tiny lander on the lunar surface||Japan’s space agency|
|Team Miles||Test plasma thrusters||Miles Space citizen scientists||X|
Some of the CubeSats are headed beyond the Moon. After the SLS leaves Earth’s orbit and releases the probes, Near-Earth Asteroid Scout (NEA Scout) will unspool a thin solar sail the size of a racquetball court. Propelled by photons, it will navigate to 2020GE, a miniature asteroid between 5 and 15 meters across. About 2 years from now, it should sail as close as 800 meters to the asteroid in a 3-hour flyby. Many larger asteroids are loosely bound rubble piles, but NEA Scout will test the expectation that the faint pressure of sunlight has spun up 2020GE too fast for it to hold any rubble, says Julie Castillo-Rogez, NEA Scout’s science principal investigator at NASA’s Jet Propulsion lab.
BioSentinel, led by Sergio Santa Maria, a biologist at NASA’s Ames Research Center, will carry strains of yeast in hundreds of microscopic wells, NASA’s first test of the biological effects of radiation beyond low-Earth orbit since the last Apollo mission in 1972. Unprotected by Earth’s magnetic field, organisms are more vulnerable to DNA damage caused by solar outbursts and galactic cosmic rays—a real concern for astronauts traveling to the Moon or Mars. From a Sun-orbiting perch beyond the Moon, optical sensors on BioSentinel will gauge the health of the yeast strains as they accumulate radiation damage by measuring cell growth and metabolism.
BioSentinel, NEA Scout, and three other CubeSats were allowed to recharge their batteries during their long wait aboard the SLS. But five others were out of luck, including both LunaH Map and Lunar IceCube. Some could not be recharged without removing them from the rocket; in other cases NASA engineers feared the process might spark discharges that could harm the rest of the rocket. “We have to be very cognizant of the risk to the primary mission when we interface with these CubeSats,” says Jacob Bleacher, NASA’s chief exploration scientist.
Hardgrove says LunaH Map’s battery reserve is probably at 50% and the threat to the mission is high, because at 40% the CubeSat will not be able to run through a set of initial operations and maneuvers before the solar panels can unfurl and begin to recharge the batteries. He says he pushed hard for the opportunity to recharge but was rebuffed by NASA officials. “You can’t agree to take stowaways and then kill them,” he says. Still, he understands that the CubeSats are secondary payloads and is resigned to rolling the dice. “It wouldn’t be a CubeSat mission if you weren’t anxious.”