NASA has confirmed it will crash its Lunar Atmosphere and Dust Environment Explorer (LADEE) probe into the Moon's surface on April 21 after the successful completion of its missions.
LADEE has been operating around the Moon since November, analyzing its scant atmosphere to solve one of the odder mysteries of our natural satellite – the early morning glow on the planetoid's surface observed by the Apollo 17 mission. The probe's primary mission is to discover if dust in the Moon's tenuous atmosphere is to blame for the phenomenon.
The vending-machine-sized probe has also been testing out NASA's homegrown space broadband system – the Lunar Laser Communication Demonstration (LLCD). The craft has been firing back information to Earth via laser, rather than traditional low-bandwidth radio communications, and has achieved connection speeds faster than 600Mbps with receiving stations on Earth.
At a press conference, NASA revealed the preliminary results of LADEE's efforts, and reported that the Moon is much dustier than first thought. The probe – which swoops 20 to 60 kilometres over the Moon's surface – has an onboard sensor that detects dust particles in the atmosphere, and has given scientists the best view yet of how the dust is distributed.
“We have beautiful data,” said CU-Boulder physics Professor Mihaly Horanyi of the Laboratory for Atmospheric and Space Physics, principal investigator for the Lunar Dust Experiment, or LDEX, onboard LADEE. “We discovered that a cloud of dust permanently engulfs the Moon, and that the dust density dramatically increases toward its surface."
The LADEE probe firing its space broadband ... as imagined by a graphic artist
Without an atmosphere to abate incoming meteorites, the Moon is peppered with thousands of space pebbles each year, and a gram of material hitting at 14 miles per second throws up an enormous amount of dust, Horanyi explained.
It's that dust that causes the glow on the surface as the Sun rises, as its light is diffracted by the particles. LADEE's findings suggest that similar orbital bodies in the Solar System with little or no atmosphere will have similar dust problems, something that's going to be a challenge in future exploration.
The dust is a problem because it's electrostatically charged, so it clings to anything it comes into contact with – including solar panels. It's also highly abrasive, which is bad news for machinery operating on the surface.
When NASA designed the Spirit and Opportunity Mars probes, it worked on the assumption that similar dust conditions existed on the Red Planet, which is one of the main reasons the probes were only expected to last 90 days before conking out. Thankfully the winds of Mars keep solar panels relatively clean, and Opportunity is still powered up more than ten years after its mission start date.
Death dive competition
The LADEE probe was designed for 100 days of observations, and NASA will shortly use the last of its fuel to send the probe into a kamikaze dive into the lunar regolith to avoid cluttering orbital paths around the Moon.
With its eccentric orbit, the craft needs constant adjustments to stay safe. The control team will complete the last maneuver on April 11 that will lower the spacecraft's orbit to just three kilometers above the surface to take a really low-altitude reading on dust levels.
On April 15 the Moon will be eclipsed by the Earth for four hours and the cold temperatures, in the lonely darkness, will be at the limit of what LADEE is engineered to withstand. If it survives, the team will then watch as its orbit decays.
"The Moon's gravity field is so lumpy, and the terrain is so highly variable with crater ridges and valleys that frequent maneuvers are required or the LADEE spacecraft will impact the moon’s surface," said Butler Hine, the probe's project manager at NASA Ames.
"Even if we perform all maneuvers perfectly, there's still a chance LADEE could impact the moon sometime before April 21, which is when we expect LADEE's orbit to naturally decay after using all the fuel onboard."
As a bit of fun, NASA is asking members of the public to log when they think the probe will touch down on the LADEE website, and the closest guess will receive a signed certificate from the team in commemoration – not much, but budgets are tight at the agency these days.
Sadly, we won’t be able to see the crash landing itself, since it is planned to take place on the "dark side" of the Moon (really the far side of the Moon).
The landing site may be picked up by cameras on NASA's Lunar Reconnaissance Orbiter, and its impact will raise a little more dust into the Moon's atmosphere, which seems a fitting end considering its mission. ®