SMART Probe to Crash Into the Moon

cyberbian writes "Amateur astronomers will be excited to note that they can witness the impact of the SMART-1 probe crashing into the moon. The impact is scheduled for the morning of September 2nd (PDT). From the article: 'There's nothing wrong with the spacecraft, which is wrapping up a successful 3-year mission to the Moon. SMART-1's main job was to test a European-built ion engine. It worked beautifully, propelling the craft in 2003 on a unique spiral path from Earth to the Moon. From lunar orbit, SMART-1 took thousands of high-resolution pictures and made mineral maps of the Moon's terrain. One of its most important discoveries was a "Peak of Eternal Light," a mountaintop near the Moon's north pole in constant, year-round sunlight. Peaks of Eternal Light are prime real estate for solar-powered Moon bases."

Re:Silly question

[RsG]

Couldn't the orbit decay and finally crash on the far side of the moon?

Not totally sure about the rest of your post, but I the answer here is "no".

Orbital decay only occurs when a satelite is within the atmosphere of the body it orbits. It's caused by air resistance sapping the satelite's orbital velocity.

Since the moon is essentially airless, this won't happen. You could (at least in theory) orbit as close to the moon as you like as long as your path doesn't smack into the side of a mountain. In practice, I'm not sure I'd want to risk it, but it's certainly not against the laws governing orbital mechanics.

Over extremely long time periods, you'd run into problems, since "essentially airless" is not quite the same as "totally airless" (even in deep space there is no true vacuum), but I suspect we'd be talking about decades at a minimum here.

Better ways to observe this

[midori_yamari]

Even if you can't see the explosion, you can either wait for the plume of ejecta to rise up into the sunlight (soon afterwards) or reflect earthshine, which may then be visible here on earth. Or, if you have the equipment, tune your radio gear to 2235.1 MHz and watch as the signal from SMART-1 goes from on (alive) to off (dead) - several radio telescopes in Australia and Chile will be watching as the probe hits.

Re:A DUMB probe would have crashed into the Earth

[AJWM]

I wonder if any of the Apollo ASLEP packages are still up and running and whether they would detect the impact?

The ALSEP packages were turned off remotely when the budget for collecting data ran out. That was Sep 30, 1977. Although the Apollo 14 ALSEP had failed a year and a half earlier, the others (A12, A15-17) were still going strong -- and still would be, the RTG power source having about a 90-year half life. (Well, barring hardware failure.)

Their seismometers did detect the impact of the S-IVB upper stages and LM ascent stages that were targeted at the Moon's surface. The SMART probe is much smaller so it would depend on how close it hit.

Re:So, can you really see it crash

[jakev]

the article says it could be possible to see the crash with a "backyard telescope", but also says that it might be too dim to be seen by a professional observatory:

"How bright will it be? No one knows. Estimates range from 7th to 15th magnitude. In other words, it might be bright enough for backyard telescopes--or so dim that even big professional observatories won't see a thing. The only way to find out is to look."

secondly..

"The nominal impact time [esa.int] favors observers in western parts of North America and across the Pacific Ocean. Depending on when SMART-1 hits, however, almost anyone could catch the flash."

Actually it's a very smart mission

[YA_Python_dev]

I know that yours was a joke, but FYI crashing into the moon is the end of every mission in lunar orbit (yes, this includes the ascent stages of the Apollo Lunar Modules); those orbits are not stable due to the gravity of the sun, the Earth and irregularities in the moon itself.

And, considering that this is an ESA mission, why the summary has only a link to the NASA site? ESA has a lot of good information about the mission and the impact:

• the SMART-1 divulgation site [esa.int], which includes a "vodcast" (H.264+AAC encoding, plays fine with mplayer and VLC)
• the SMART-1 science site [esa.int]
• and the impact site [esa.int]

IMHO the most important results from this mission (beside a lot of nice detailed images) are the successful use of a ion engine with a very complicated low-power path (that thing passed through the L1 Lagrangian Point, switching seamlessly from earth orbit to lunar orbit) and the extensive mapping of the moon surface chemical composition using X-ray and infrared instruments.

Re:This is all a test

[YA_Python_dev]

FYI there are no stable orbits around the moon: the perilune becomes smaller and smaller with time, so unless you periodically re-raise it using on-board fuel anything that orbits the moon will eventually crash on it.

See question 5 from the ESA's SMART-1 FAQs [esa.int] for more details.

Re:A DUMB probe would have crashed into the Earth

[DerekLyons]

The ALSEP packages were turned off remotely when the budget for collecting data ran out. That was Sep 30, 1977. Although the Apollo 14 ALSEP had failed a year and a half earlier, the others (A12, A15-17) were still going strong -- and still would be, the RTG power source having about a 90-year half life. (Well, barring hardware failure.)

It's not the half life that matters - it's when the output voltage drops below a useable value. The half life of the RTG's on the Voyager probes is comparable - but they had to start turning off instruments years ago, and the RTG is expected to stop producing sufficient power to operate anything in the next five years or so. Furthermore, the environment on the Lunar surface is extremely harsh, much harsher than that the Voyagers are exposed to. (Mostly due to the large temperature swings on the Moon. The Voyagers are colder, but the temperature is steady.)