[X] My Assistant

[jamescanvin]

Just read this interesting article about LRO

http://science.nasa.gov/headlines/y2005/28apr_lro.htm

"This is the first in a string of missions," says Gordon Chin, project scientist for LRO at NASA's Goddard Space Flight Center. "More robots will follow, about one per year, leading up to manned flight" no later than 2020."

One per Year? Is this just wishful thinking or have any tentitve plans been mentioned for follow up missions after LRO? If the next one is going to be 2009/10 then I guess some desisions about it will have to be made fairly soon.

James

[dvandorn]

In fact, Bob, the footprints and wheel tracks near the LMs were not at all darker than the general soil at the landing sites. The LM DPS exhaust would sweep the top layer of dust grains from the regolith during landing, resulting in a temporary brightening of the soil around the LMs. "Darkened" footprints and wheel tracks were simply *restoring* the soil's natural albedo within the splash of brightened soil.

There is some question, I guess, as to whether or not the local soil brightening around the LMs still exists. I don't believe any of the Clementine or SMART-1 or Lunar Prospector images were able to answer that question -- though Phil probably knows the answer to that better than I do.

-the other Doug

[Bob Shaw]

In fact, Bob, the footprints and wheel tracks near the LMs were not at all darker than the general soil at the landing sites.  The LM DPS exhaust would sweep the top layer of dust grains from the regolith during landing, resulting in a temporary brightening of the soil around the LMs.  "Darkened" footprints and wheel tracks were simply *restoring* the soil's natural albedo within the splash of brightened soil.

There is some question, I guess, as to whether or not the local soil brightening around the LMs still exists.  I don't believe any of the Clementine or SMART-1 or Lunar Prospector images were able to answer that question -- though Phil probably knows the answer to that better than I do.

-the other Doug

oDoug:

Yes, I had the mechanism 'backwards' - and, taking the DPS plume notion one step further, presumably the ascent engine firing again scoured the surface, as well as blasting bits of foil around the area. Apollo 12 was the dustiest landing site, AIRC, so were any pre-landing vs post-landing vs post-liftoff images taken from the CSM? Over a few hours the shadows wouldn't have changed much for the first two, but there's be quite a change between first and last, and that would obviously mask any effect.

Bob Shaw

[dvandorn]

...Apollo 12 was the dustiest landing site, AIRC, so were any pre-landing vs post-landing vs post-liftoff images taken from the CSM? Over a few hours the shadows wouldn't have changed much for the first two, but there's be quite a change between first and last, and that would obviously mask any effect.

Let's see -- the Apollo 12 CSM didn't have any cameras with enough "throw" to get the kind of resolution you'd need to observe that effect. I think the longest lens they carried for the CSM's Hasselblad was a 250mm. Dick Gordon did try to capture the view through the CSM's optics on his 16mm movie camera, and suceeded in getting an overexposed, washed-out image in which you can sort of recognize Surveyor Crater, but you can't really resolve the actual LM landing point. And the image was so overexposed that any local brightening was washed out.

The only other way to have documented the "bright splash" of the LM's landing site would have been the 16mm movie of the LM liftoff from inside the cabin.... except that the camera malfunctioned and there is no film of the Apollo 12 lunar ascent.

In fact, though, the Apollo 12 landing site probably wasn't all that much dustier than any of the other mare landing sites. Pete brought his LM down by curving along the north rim of the Surveyor Crater, and dropped pretty much straight down from about 200 feet directly over the northwest rim. Crater rims on the Moon seem to display less consolidation in their regolith -- the slope keeps the surficial layer from "firming up" as much as it does on more level ground. At least, all of the Apollo moonwalkers reported that the dust on relatively "flat" ground let them sink in less than an inch, but that crater rims were "soft" and that they sank in several inches on most crater rims. This was pretty ubiquitous at all of the landing sites, as I recall.

So, Pete's Intrepid blew up so much dust because 1) it kept blowing over the same spot for the final 200 feet of descent, and 2) it was blowing down on a crater rim that, by its nature, was composed of looser and less consolidated dust than they would have encountered on the adjacent plains.

To back this up, I'll point out that the second dustiest landing was Apollo 15's, during which the LM made a near-vertical final descent from about 150 feet, with the engine plume impinging directly on the rim of a 10-meter shallow crater. (The engine bell even got whacked by this small crater's rim, since the LM landed directly astride its western rim.) So, dustiness of landing seems to have been controlled by whether or not the exhaust was plowing up a crater rim during an extended near-vertical descent.

-the other Doug