Apollo Lunar Impact Sites

[Kiwi]

A while back someone asked about the lunar impact sites of Apollo SIVBs or some similar question. I can't find the question and don't recall the answers, but in case it's useful, have just come across the following document which gives coordinates of the LMs (landing and impact, where known), LRRRs and SIVBs. It also has some useful links at the bottom of the page.

nssdc.gsfc.nasa.gov/planetary/lunar/apollo_tables.html#lunar_sites

[ka9q]

Thank you!

I might have sent the message you saw. If you look at that list, you'll notice that the impact locations of two Apollo LM ascent stages are unknown: those for A11 and A16. Both were abandoned in lunar orbits that later decayed long after they went dead, so there was no tracking and no direct knowledge of their impact locations. But I am wondering if new data (LRO mapping and the improved gravity models from the Japanese Kaguya and the US GRAIL missions), plus a good collective eyeball effort, just might make it possible to discover one or both of those LM impact locations.

[PhantomWolf]

Feb 15, 2012 8:01:02 GMT -4 ka9q said:

Thank you!

I might have sent the message you saw. If you look at that list, you'll notice that the impact locations of two Apollo LM ascent stages are unknown: those for A11 and A16. Both were abandoned in lunar orbits that later decayed long after they went dead, so there was no tracking and no direct knowledge of their impact locations. But I am wondering if new data (LRO mapping and the improved gravity models from the Japanese Kaguya and the US GRAIL missions), plus a good collective eyeball effort, just might make it possible to discover one or both of those LM impact locations.

Best idea is to follow along a ground path based on their last known orbit and the rotation of the moon from then until estimated impact. It's unlikely that they would have strayed from that before impact. Then look for something that resembles the other known impact sites. Still a huge amount of ground to cover, but less than having to search the entire moon for them.

[ka9q]

Although the moon has no draggy atmosphere, nearly all lunar orbits are unstable due to the perturbations by the earth and sun and the moon's lumpy gravity field. Eventually they get perturbed so much that the orbital path intersects the surface.

The estimated orbital lifetimes of the abandoned LMs is usually said to be about a year. I don't know if that's just a guess or if it comes from actual orbital modeling. Once Eagle and Orion died after jettison nobody really cared what happened to them. (The other four were deorbited while still operating.) The subsatellite left in lunar orbit by Apollo 15 lasted about 15 months; the one left by Apollo 16 lasted only a month because of a non-optimal deployment orbit.

So without knowing exactly when they hit, we only know that their impact sites are somewhere in a latitude band centered on the equator and bounded north and south by their orbital inclinations. The news media uses this fact to play Chicken Little every time a large earth satellite is about to decay. They show the band on a map and proclaim that everyone and everything in it is subject to arbitrary instant death and destruction from above.

Apollo 11 landed within a degree of the equator from a very low inclination orbit, so Eagle's impact site should be the easier one to find. We only need search LRO photos for a narrow band around the equator. But I don't know if they have very high resolution photos of the moon's entire equatorial region; the narrow angle camera produces far too much data to map the entire moon.

Apollo 16's Orion landed at about 9 degrees south so its lunar orbit had an inclination of at least 9 degrees. We'd have to search the entire band between 9N and 9S to be sure of finding the site. But the moon rotates 30x slower than the earth, so if we can use an orbital model to approximate the time of the impact, say within a few days, we might only have to search the orbital path at that time.