NASA’s Moonlight is ready to search for the moon’s water ice

Water ice is known to exist beneath the lunar regolith (crushed rock and dust), but scientists still don’t understand whether surface ice covers the floors in these cold craters. To find out, NASA sent the Lunar Flashlight, a tiny satellite (or SmallSat) no bigger than a briefcase. Descending low over the moon’s south pole, it will use lasers to shine a light on these dark craters – much like a gold prospector searching for hidden treasure by shining a flashlight into a cave. The mission will launch aboard a SpaceX Falcon 9 rocket in mid-November.

“This launch will put the satellite on a trajectory that will take about three months to reach its science orbit,” said John Baker, the mission’s project manager at NASA’s Jet Propulsion Laboratory in Southern California. “Then the Lunar Flashlight will try to find water ice on the surface of the Moon in places that no one else has been able to see.”

Fuel efficient orbits

After launch, mission navigators will guide the spacecraft past the moon. It will then be slowly pulled back by gravity from Earth and the Sun before settling into a wide, circumnavigation orbit to collect science. This nearly rectilinear halo orbit will bring it within 42,000 miles (70,000 kilometers) of the Moon at its farthest point, and on its closest approach the satellite will skim the surface of the Moon, coming within 9 miles (15 kilometers) above the lunar south pole.

Small satellites carry a limited amount of propellant, so fuel-intensive orbits are not possible. The nearly rectilinear halo orbit requires much less fuel than traditional orbits, and Lunar Flashlight will be only the second NASA mission to use this type of trajectory. The first is the technology and navigation experiment of NASA’s Cislunar Autonomous Positioning System (CAPSTONE), which will arrive in orbit on November 13, making its closest pass over the Moon’s North Pole.

“The reason for this orbit is to be able to get close enough for Lunar Flashlight to shine its lasers and get a good return from the surface, but also to have a stable orbit that consumes little fuel,” said Barbara Cohen, Lunar Flashlight principal investigator at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

As a technology demonstration, Lunar Flashlight will be the first interplanetary spacecraft to use a new type of “green” fuel that is safer to transport and store than commonly used space fuels such as hydrazine. This new fueldeveloped by the Air Force Research Laboratory and tested on a a previous NASA technology demonstration mission, burns through a catalyst rather than requiring a separate oxidizer. That’s why it’s called a monopropellant. The satellite’s propulsion system was developed and built by NASA’s Marshall Space Flight Center in Huntsville, Alabama, with integration support from the Georgia Tech Research Institute in Atlanta.

Lunar Flashlight will also be the first mission to use a four-laser reflectometer to search for water ice on the Moon. The reflectometer works by using near-infrared wavelengths that are easily absorbed by water to identify ice on the surface. If the lasers hit bare rock, their light will reflect back to the spacecraft, signaling the absence of ice. But if the light is absorbed, it would mean that these dark pockets do contain ice. The greater the absorption, the more ice there can be on the surface.

Lunar water cycle

The water molecules are thought to come from comet and asteroid material impacting the lunar surface and from interactions of the solar wind with the lunar regolith. Over time, the molecules may have accumulated as a layer of ice in “cold traps.”

“For the first time, we will make definitive measurements of surface water ice in permanently shaded regions,” Cohen said. “We will be able to link the Lunar Flashlight observations with other lunar missions to understand how extensive this water is and whether it can be used as a resource by future explorers.”

Cohen and her science team hope that the data Lunar Flashlight collects can be used to understand how volatile molecules, such as water, move from place to place and where they can accumulate, forming a layer of ice in these cold traps.

“This is an exciting time for lunar exploration. The launch of Lunar Flashlight, along with the many small satellite missions aboard Artemis I, can form the basis for scientific discoveries as well as support future missions to the lunar surface,” said Roger Hunter, Small Spacecraft Technology Program Manager at NASA’s Ames Research Center in California’s Silicon Valley.