A tiny spacecraft is ready to head out for a big job: shining a light on water ice at the Moon’s south pole.
Lunar Flashlight is a cubesat about the size of a briefcase, set to launch on December 1 on a SpaceX Falcon 9 rocket, sharing a ride with the Hakuto-R Mission to the Moon.
The tiny 14 kg (30 lb) spacecraft will use near-infrared lasers and an onboard spectrometer to map the permanently shadowed regions near the Moon’s south pole, where there could be reservoirs of water ice.
“If we are going to have humans on the Moon,” said Barbara Cohen, Lunar Flashlight principal investigator, “they will need water for drinking, breathing, and rocket fuel. But it’s much cheaper to live off the land than to bring all that water with you.”
Several previous missions have found evidence of water ice at the Moon’s poles, including Lunar Prospector, the Lunar Crater Observation and Sensing Satellite (LCROSS) and the Lunar Reconnaissance Orbiter. Additionally, other observations have provided many lines of evidence for deep water ice deposits the permanently shadowed regions across both lunar poles.
Cohen told Universe Today that Lunar Flashlight will be looking for “operationally useful” quantities of ice, meaning enough water ice within the craters or embedded in the regolith that could be easily extracted by future rovers or lunar explorers.
Lunar Flashlight has just one instrument, a four-laser reflectometer that uses a low-power infrared beam to illuminate the permanently shadowed regions in polar craters. The spectrometer can distinguish between dry regolith and water ice, as the light reflected back from the lunar surface will allow the spacecraft to detect water ice absorption bands in the near infrared.
“Infrared wavelengths are absorbed by water,” Cohen explained, “so if water ice there, we’ll get fewer photons back than we what we sent.”
By repeating these measurements over multiple points and across multiple orbits, the Lunar Flashlight team will be able to create a map of surficial ice concentration. This method could allow NASA to not only find reservoirs of ice but potentially figure out how large they are, since more absorption could indicate more water. Cohen said the data they get can be correlated with data from previous missions to help guide future rovers and humans where to find the water ice.
That’s a big task for such a small spacecraft, and Cohen said having such a small footprint to work with was a challenge in constructing the spacecraft.
“Having a 14-kilogram spacecraft means you have to shrink a lot of things down,” Cohen said. “But it also means you must get innovative about what you’re including and what you’re not. That means we could only have one instrument, as we didn’t have room for more. But it’s a great instrument and it’s the first time that active laser spectroscopy will be done at the Moon.”
They also had to make their spacecraft require very low power, as there isn’t room for a lot of batteries.
“Our lasers have the intensity similar to that of a laser pointer,” Cohen explained. “Such low power means we need to be very close to the lunar surface, about 15-20 kilometers away.”
Even a full size satellite with a lot of fuel would have a hard time maintaining a that low of an orbit, so Lunar Flashlight will use an innovative orbit called a near rectilinear halo orbit. This is the same orbit currently being used by the microwave-oven-sized CAPSTONE (Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment), which is conduct tests to make sure this unique lunar orbit is actually stable. The same orbit has been proposed for the NASA’s future Lunar Gateway. This near-rectilinear halo orbit will take it 70,000 km (42,000 miles) from the Moon at its most distant point and, at its closest approach, the satellite will graze the surface of the Moon, coming within 15 km (9 miles) above the lunar South Pole.
“This orbit enables us to come very, very close to the surface when we want to make the measurements and then go very far away as an energy saving measure for the rest of the orbit,” Cohen said, adding that her team is definitely keeping an eye on how things are going for CAPSTONE.
For the primary mission, Lunar Flashlight will get approximately 10 passes of the Moon, depending on how much fuel they have.
“We have an eight-month primary mission, but it depends on fuel,” Cohen said. Roughly 50 minutes after launch, Lunar Flashlight will eject from the second stage of the Falcon 9 rocket. “When we are ejected, the spacecraft will tumble and we need to use fuel to get into the right orbit. With such a small fuel tank, we don’t have a huge amount of margin.”
Lunar Flashlight is considered a technology demonstration mission, as it is testing out several technological firsts, including the first use of the laser reflectometer to look for water ice and the first planetary CubeSat mission to use “green” propulsion – a propellant that is less toxic and safer than hydrazine, a common propellant used by spacecraft.
Another unique aspect is that the “mission control” for the spacecraft is housed at Georgia Tech and will be staffed by a group of 14 operators — eight graduate students and six undergraduates.
“These students helped put this spacecraft together, they wrote all the scripts, they’ll be doing the uplink and downlink – they’re the ones actually in control of the spacecraft. It’s been really gratifying to see such a really meaningful level of student involvement, and they’re going to know the ins and out of operating a spacecraft. You just know those students are going to go on to have amazing careers.”
There have been a few delays leading up to the launch of Lunar Flashlight and Japan’s Hakuto-R Mission, but the launch time is now set for Thursday, December 1 at 3:37 a.m. ET from Cape Canaveral Space Force Station in Florida.
For more details on the mission, see the Georgia Tech website and this article from JPL.