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Dr. Phil Metzger @DrPhiltill
, 21 tweets, 7 min read Read on Twitter
I'll reply to this tweet with some Scanning Electron Microscope pictures of Surveyor 3's surface before and after sandblasting by the lunar soil blown from the Apollo 12 landing. It's extremely interesting!
2/ This is a super-magnified view of Surveyor 3's white paint where it was NOT sandblasted with lunar soil. The round balls are the normal way the paint dries, though our unaided eyes can't detect it. Cool, right? Next, what lunar soil does to the paint...
3/ Now here is the same paint in an area where it got sandblasted by lunar soil blown from the Apollo 12 Lunar Module landing. The paint's natural texture got crushed, and lunar soil particles are mixed in the surface.
4/ This is magnified 5× more than the prior two. One large paint pigment ball escaped destruction from the sandblasting. Note there are at least two small, perfectly spherical particles. These are glass beads that exist in lunar soil - a strong clue that you're seeing lunar dust.
5/ Here again is one of the coupons from Surveyor 3 returned from the Moon by Apollo 12. Note it's a lighter color on the left & right edges, darker in the middle. That's because a cable on Surveyor 3 hung in front of the middle part, shadowing it from the full sandblasting.
6/ We used Energy-Dispersive X-Ray Spectroscopy to determine what elements are where across that surface. We especially looked for four elements known to be in lunar soil that are NOT in that paint. This plot shows those elements on a path across the coupon.
7/ What we found is that everywhere the surface of the paint is darker, there is more lunar soil. Everywhere it is lighter, there is less lunar soil. But the lighter areas are where it got sandblasted by lunar soil. Blasting lunar soil made less lunar soil? NOT what we expected!
8/ But this makes sense when we think about the physics. In the vacuum of the Moon, high-velocity dust bounces. It traveled so fast it wasn't able to cling and stick. It rammed into dust that was already on the surface and knocked that off, too, producing a net reduction in dust.
9/ That might sound like a good thing: it cleaned the surface, right? But remember it also crushed the surface material and damaged it. Also, note the mud-cracking pattern in the paint in the lower left corner where sandblasting was heaviest.
10/ We used a laser-scanner to map and measure the depths of all these cracks in the paint. We used the same laser scanner that was used for the Space Shuttle's windshield between every flight to measure the micrometeoroid impact damage on the glass.
11/ We found there are not just cracks, but also tiny pinholes. This map is an example of the cracks with gray circles as the pinholes. Most of the pinholes are on the cracks, and far too many are at the juncture where the cracks meet. So there's some relationship to explain!
12/ This is a highly magnified inside-out/upside-down 3D map of one of the cracks (in yellow) cutting across one of the pinholes (in blue). We found the pinholes are much deeper, reaching the bottom of the layer of paint. So the pinholes caused the cracks, rather than vice versa.
13/ And with the Scanning Electron Microscope, a member of our team peered into the bottoms of at least one of the pinholes, and what did he discover there? A single sand-sized grain of lunar soil.
14/ So we concluded that larger soil grains (the sand-sized ones) punctured the paint, and cracks radiated away from the punctures. Dust-sized particles were far more numerous, but they didn't puncture the paint. Instead they crushed and scoured the surface. Two types of damage.
15/ We counted the number of punctures per square centimeter and used it to help calibrate how much soil was blown by the Lunar Module landing. (In the tons.) We used many other methods to determine that, too. We need to know so we can protect hardware at future lunar outposts.
16/ And we have been developing technologies to prevent the blowing of soil at future lunar outposts. One summer @paulvans spent a summer with me at @NASAKennedy building lunar landing pads and blasting them with a rocket motor. That was a fun way to spend a summer!
17/ And @Ryan_N_Watkins spent two summers with me studying lunar soil then she went on to analyze the lunar landing blast "scars" that are still visible on the Moon from space.
18/ And @CaseyQL spent a summer with me doing rocket blast experiments to solve the physics and calibrate high-fidelity simulation software NASA developed via several contracts, to better predict blast effects on the Moon and Mars.
19/ Then we wrote guidelines for how to land on the Moon without excessively damaging the historic sites on its surface. I wrote the blast protection sections informed by the Surveyor 3 hardware brought back from the Moon by Apollo 12.
20/ This brief review barely scratches the surface of all the work done on this topic. There were reduced gravity flights, firing rockets on a volcano, 3D printing lunar landing pads, testing inflatable blast barriers, blasting materials on the @mastenspace launch pad, etc.
21/21 But what the world needs now (besides love sweet love) is measurements ON THE MOON during the upcoming commercial lunar landings. That's another thing that there's just too little of. But we can fix that, and soon!
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