Lunar impact - were the S-IVBs ever observed?

[ka9q]

This article in the Guardian

http://www.theguardian.com/science/2014/feb/24/meteorite-moon-largest-lunar-impact-recorded

gives the mass and velocity of an impact on the moon last fall as 400 kg and 61,000 km/h, respectively. By my calculation that's roughly the same (within a factor of 2) of the energy released by a spent S-IVB hitting the moon between Apollos 13 and 17. But I've never heard of any of those impacts being observed. Has anyone else?

I haven't checked, but it's possible that they all hit in the daytime.

[Allan F]

They were observed by the seismic equipment left on the moon, but I don't think they were visually observed. They are simply too small to be seen.

[ka9q]

But that's my point. The energy release was comparable to this impact from last fall, so it should have been visible. Maybe it didn't happen on the night side.

[Allan F]

The energy may be comparable, but the speed it impacted with was an order of magnitude lower.

[ka9q]

So? It was still a lot of energy deposited in a small place, so the temperatures would probably have gotten as high.

[Allan F]

Let's see - 9.600 kg impacting at 2580 m/s - that's 6.4x10e10 Joule. The meterorite was 1.1x10e11 joule. That's close to a factor 2, all right.
What I think you haven't taken into consideration is the structure of the S-VIb - it's primarely a hollow tube, with a much larger lenght/width than the meterorite. The S-IVb would have impacted much more like a collection of objects, not like a solid object. The rock with a 400 kg mass would have a volume of around 100-150 liters, which would give a footprint of around (a little less than) one square meter one third meter in diameter. The S-IVb would have a footprint from 34 to 117 m^2. From this follows the intensity of the heating would be much less. From 70-235 370-1300 times less.

[Allan F]

http://history.nasa.gov/SP-4029/Apollo_18-26_S-IVB_Lunar_Impact.htm

[Allan F]

From the table above it appears they all impacted at lunar night.

[Glom]

From the table above it appears they all impacted at lunar night.

Of course they did. That way noone could see that it never happened.

Also, since each mission was timed for morning at the landing site and since naturally the S-IVB would have impacted near the limb, it would of course been night time at the impact site.

[Chew]

If I'm reading this right, an object has to hit in excess of a certain velocity to generate visible radiation in our atmosphere. How would that translate to a vacuum?

On page 9:

http://impact.ese.ic.ac.uk/ImpactEffects/effects.pdf

[ka9q]

At these velocities I tend to doubt that the object's physical size has much effect. The craters were much larger than the objects themselves.

I haven't checked to see whether it was day or night at the S-IVB impact sites. It wouldn't necessarily be one or the other. The post-separation maneuver slowed the S-IVB down so that the moon had a chance to move into its path. The more you slow the S-IVB, the farther east it impacts. Before Apollo 13, they slowed the S-IVB down so much that it missed the moon entirely and flew around its eastern hemisphere to get the escape slingshot.

They probably picked the spots to give good geometry with the existing seismometers.

[Allan F]

The link I provided above gives both coordinates and time of the recorded impacts. Also the calculated and observed size of the impact craters. About 170 meters across.