When NASA’s most powerful rocket ever attempts its first flight this month, its largest payload will be three instrument dummies that will embark on a 42-day trip to the moon and back. They are replacements for the astronauts the 98-meter-tall rocket known as the Space Launch System (SLS) is supposed to take to the moon as soon as 2025 as part of NASA’s Artemis program. But there will be other travelers when SLS lifts off on August 29: 10 CubeSats, satellites no bigger than a small briefcase, to study the Moon, asteroids and the radiation environment of deep space.
The researchers who built these satellites have more than the usual launch nerves: Half of them may not have enough power to launch their missions. Stuck in the rocket for more than a year due to launch delays, their batteries have depleted to a level where some may not be able to charge and deploy their solar panels. “The longer we wait, the greater the risk,” said Morehead State University’s Ben Malphrus, principal investigator of Lunar IceCube, one of the CubeSats with power problems.
At stake is not just data, but a test of CubeSats as deep space probes. “We’re in a transition phase from being a curiosity and a learning tool to being a platform for real science,” says Malphrus. CubeSats are easy to assemble from standardized parts—from frugal ion propulsion systems to pint-sized radio transmitters—supplied from a growing commercial base. This allows researchers to focus on developing instruments capable of collecting new data — if they can squeeze it into a CubeSat package.
Small size and standardization also make CubeSats inexpensive. At millions of dollars apiece, compared to hundreds of millions for a larger, standalone 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 in a briefing earlier this month.
Several SLS CubeSats will focus on the lunar ice, which has intrigued researchers since NASA’s Lunar Prospector detected a signal suggesting water in the late 1990s. Using a neutron detector, he peered into cold, permanently shadowed regions in polar craters. In many of them, the probe found a curious suppression of neutrons – best explained by the extra hydrogen in the top meter of soil.
Researchers assume that much of the hydrogen is water ice delivered by ancient comet or asteroid impacts and trapped in the coldest and darkest lunar niches. But hydrogen can also be implanted by the solar wind. When hydrogen ions in the wind collide with oxygen-bearing minerals in the lunar soil, it creates hydroxyl, which can be transformed into water through subsequent reactions. If the Moon contains enough water, it can be used for agriculture and life support and split into hydrogen and oxygen for rocket fuel. “It will be more economical than bringing it from Earth,” says Hannah Sargent, 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 rises just 12 to 15 kilometers above the South Pole. Over the course of 280 passes with its neutron detector, the team hopes to map the excess hydrogen at a resolution of 20 to 30 kilometers, about twice as good as Lunar Prospector. “We can distinguish one [deep crater] from another,” says Hardgrove. Craters without hydrogen or enrichments outside the cold hides may indicate a relatively recent impact that blew up the ice and redistributed it, he says.
Lunar IceCube will carry a spectrometer that can detect the infrared signatures of water or hydroxyl. Because the device depends on reflected light, it will be most sensitive to signs of hydroxyl and water in sunny regions at lower latitudes. “They really look [effect of] the solar wind, day after day,” said Benjamin Greenhagen, a planetary scientist at Johns Hopkins University’s Applied Physics Laboratory.
When NASA launches its giant rocket to the moon, it will also carry 10 small satellites beyond low Earth orbit. Some of the missions may have had power problems at launch after half of the satellites were not allowed to recharge their batteries.
|NAME||PURPOSE||LEAD DEVELOPER||BATTERY PROBLEMS|
|ArgoMoon||Observe the launch of Cubesats, rocket stage||The Italian Space Agency|
|BioSentinel||Study radiation effects on yeast||NASA (Ames Research Center)|
|CuSP||Study the solar wind and magnetic fields||Southwest Research Institute||x|
|horseman||Image of Earth’s plasmasphere||The Japanese Space Agency|
|LunaH card||Explore the lunar ice||Arizona State University||x|
|Lunar Ice Cube||Explore the lunar ice||Morehead State University||x|
|LunIR||Test a new infrared spectrometer||Lockheed Martin||x|
|NEA Scout||Fly to an asteroid with a solar sail||NASA (Marshall Space Flight Center)|
|GET DAMAGED||Place a small lander on the lunar surface||The Japanese Space Agency|
|Team Miles||Test plasma engines||Miles Space Citizen Scientists||x|
Some of the CubeSats are headed beyond the Moon. After SLS leaves Earth orbit and releases the probes, the Near-Earth Asteroid Scout (NEA Scout) will develop a thin solar sail the size of a racquetball court. Powered by photons, it will navigate to 2020GE, a miniature asteroid between 5 and 15 meters in diameter. In about 2 years, it should come within 800 meters of the asteroid for a 3-hour flight. Many larger asteroids are loosely bound piles of debris, but NEA Scout will test the expectation that the weak pressure of sunlight has rotated 2020GE too quickly to hold any debris, says Julie Castillo-Roguez, principal investigator of the NEA Scout at NASA’s Jet Propulsion Laboratory.
BioSentinel, led by Sergio Santa Maria, a biologist at NASA’s Ames Research Center, will carry yeast strains 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 flares and galactic cosmic rays—a real concern for astronauts traveling to the Moon or Mars. From solar orbit beyond the Moon, BioSentinel’s optical sensors will measure the health of yeast strains as they accumulate radiation damage by measuring cell growth and metabolism.
BioSentinel, NEA Scout and three other CubeSats were given permission to recharge their batteries during their long wait aboard SLS. But five others were unlucky, including LunaH Map and Lunar IceCube. Some could not be reloaded without being removed from the rocket; in other cases, NASA engineers feared that the process could cause ejecta to damage the rest of the rocket. “We have to be very aware of the risk to the core mission when we interact with these CubeSats,” said Jacob Blacher, NASA’s principal investigator.
Hardgrove says LunaH Map’s battery reserve is probably 50% and the threat to the mission is high because at 40% the CubeSat will not be able to go through a set of initial operations and maneuvers before the solar panels can deploy and start recharging the batteries. He says he pushed hard for the chance to reload but was turned down by NASA officials. “You can’t agree to take illegal travelers and then kill them,” he says. However, he understands that CubeSats are secondary payloads and settles for rolling the dice. “This wouldn’t be a CubeSat mission if you weren’t worried.”