NASA's Lunar Atmosphere Dust Environment Explorer will soon end its mission — but not before swooping close to the lunar surface and enduring the frigid darkness of a total lunar eclipse.
|Update: Ground controllers at NASA's Ames Research Center have confirmed that the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft impacted the farside of the Moon, as planned, sometime between 9:30 and 10:22 p.m. PDT on April 17th. For more details see NASA's press release.|
On or about April 21st, NASA's Lunar Atmosphere Dust Environment Explorer (LADEE) will crash into the far side of the Moon. Good thing LADEE's flight team is doing it on purpose.
LADEE was launched last year on September 6th on the first-ever use of the Minotaur rocket (full specs here), and the mission was never intended to last a long time. After settling into lunar orbit in mid-October and completing its checkout, the spacecraft started its observations of gas and dust hovering over the Moon.The craft's orbit was relatively snug, ranging from as close as 20 to 50 km at low point to as high as 75 to 150 km. Science observations were only expected to last 100 days, ending early in March. But flight controllers have been so frugal with fuel reserves that the mission got a month-long extension — and, with that, a chance to do some daring low-level passes over the lunar landscape.
"LADEE's science cup really overfloweth," said project scientist Rick Elphic (NASA Ames Research Center) during a teleconference with reporters on April 3rd. One discovery is that a veil of micron-size dust particles continually encases the Moon (created by a constant rain of meteoritic matter onto its surface). The spacecraft picked up the presence of helium, neon, and argon right away in the Moon's ultra-tenuous transient atmosphere (technically called an exosphere), and it's detected atoms of magnesium, aluminum, titanium, and oxygen — the remnants of rocky minerals blasted upward from the lunar surface.
Curiously, the spacecraft didn't detect any change in the exosphere's composition following the arrival of China's Chang'e 3 lander on December 14th. There was a spike in exospheric dust about that time, but mission scientists attribute that to surface impacts during mid-December's Geminid meteor shower.
Elphic says more research on LADEE's findings will be published in the coming months, but its science team already presented many preliminary results at the Lunar and Planetary Science Conference a few weeks ago.Every time LADEE has flown lower, Elphic says, it has discovered something new — a statement echoed by Butler Hine (NASA Ames Research Center), LADEE's project manager. So, given a perfectly functioning spacecraft, its primary science goals completed, and fortuitous timing, the mission team gets to pursue some bonus (and very daring) science objectives.
First, LADEE's close point is going to be dropped to a very low altitude — just 3 km (2 miles) up — to observe the lunar terrain and measure the dust distribution close to the ground. Those crater-skimming passes should start this weekend. Flying this close to the surface does not come without risks: the Moon's gravity is very uneven, and at such low altitudes there's a chance that an unforeseen perturbation will cause the spacecraft to plunge into a fatal trajectory.
"Our low point this weekend occurs as we pass over the Apennine Mountains," notes Elphic, at latitude 22°: north and longitude 0.9° east. "Our path will take us slightly north of the crater Conon, and north of an Apennine peak named Mons Bradley."
But the team is confident that LADEE won't clip a mountaintop or crater rim inadvertently. Regardless, comments Butler, the potential payoff of doing such low-altitude observing and data-gathering is worth the risk, especially since the primary mission is "in the bag."
Second, skywatchers and the LADEE team both have a keen interest in the total lunar eclipse that's coming on the night of April 14–15. This eclipse should offer a grand celestial spectacle as seen from Earth. But what does it mean for a spacecraft orbiting the moon? The answer is simple: darkness and deep cold. LADEE's systems weren't designed to be out of sunlight for long, so the eclipse offers NASA's engineers a way to test how the spacecraft and its instruments respond to extended darkness (about 4 hours' worth in this case, notes Hine).
LADEE will fire its engine for the last time on April 11th, redirecting it onto a sure-fire, but gradual collision course somewhere on the farside — well away from any historical landing sites — at 1.6 km per second (3,600 miles per hour). While LADEE makes its final descent on the lunar farside, the science team will lose radio contact.
So the precise time and location of the crash won't be known — at least initially. Afterward the team hopes to identify the impact site and reconstruct the craft's final moments using high-resolution images from NASA's Lunar Reconnaissance Orbiter.
To make the intentional, destructive crash of a $250-million space robot more interesting, NASA has set up what is essentially a massive betting pool, the Take the Plunge challenge, allowing the public to guess LADEE's exact crash time. The winner gets a certificate and bragging rights.
Any wagers from S&T.com's visitors?