[X] My Assistant

[Bob Shaw]

I have the (in)famous Ranger issue of National Geographic, but it's somewhere in storage right now and I don't have it at hand.

What I don't recall is how the hard-lander "ball" was to be controlled in attitude during the retro-rocket firing.  Was it spin stabilized?  I sure don't remember it having anything like a sophisticated RCS.  Perhaps a control-moment gyro system?  A CMG wouldn't have to be all that heavy, since the ball was fairly light.

But I do recall that the lander only really had the one-axis seismometer, a transmitter and a battery.  No camera, no other particles and fields sensors that I recall off the top of my head.

-the other Doug

Yup, spin-stabilised. I think via a 'thread' in the motor, like one V-2 vane...

[Guest_BruceMoomaw_*]

It had a smaller solid motor inside the big conical nozzle of the main retrorocket, with (I think) two little nozzles pointed along the inside tangents of the nozzle's wall. It ignited 1 second before the main engine ignited, at which point the little spin-stabilizing motor was blown out of the nozzle and became the very first part of the craft to hit the Moon. (Similarly, the Altitude Marking Radar package that ignited the solid retromotor on the Surveyors was inside that motor's nozzle and was blasted out of the nozzle straight into the Moon.)

By the way, the hard-lander capsule was designed to be tough enough to have a good chance of surviving even if the retromotor failed to separate from it after burnout -- although, as I've said before, there were serious doubts (at least as of the launch of Ranger 3) on whether the drop tests had been rigorous enough to provide confidence that the capsule actually would survive even normal impact.

And, yep, the one-axis seismometer was the only instrument; its fluctuating signal output was directly hooked to the analog-channel radio transmitter. However, it would also double as a penetrometer to provide a profile of landing shock and thus of surface hardness.

[edstrick]

...."on whether the drop tests had been rigorous enough to provide confidence that the capsule actually would survive even normal impact."

Considering that candidate landing tartet materials probably included bare lava flows or pumice-like rock, the almost universal meter-plus thick regolith layer on the moon would have greatly improved a "marginal" design's chances of surviving impact.

[dvandorn]

The lunar regolith compacts very, very quickly into a material with some cohesiveness and pretty good bearing strength. The surface is only "soft" for the first inch or two (a little more on crater rims).

Yes, that first inch or so gives you a tiny advantage -- but not that much.

-the other Doug

[Bob Shaw]

The lunar regolith compacts very, very quickly into a material with some cohesiveness and pretty good bearing strength.  The surface is only "soft" for the first inch or two (a little more on crater rims).

Yes, that first inch or so gives you a tiny advantage -- but not that much.

-the other Doug

I wonder what the difference between a 90 degree angle of impact and a much more oblique one is, in terms of effect on a hard-lander (or, say, a redundant LM ascent stage). Or is the instantaneous shock still so utterly enormous as to provide explosive vapourisation of the projectile, as with typical rocky impacts?

And what sort of debris field will have resulted from the LM impacts (and the S-IVB stages)? If the Apollo 12 S-IVB stage was identified spectroscopically (thanks to the titanium oxide paint, not a normal constituent of Earth-crossing asteroids!) then will spacecraft debris fields also be identifiable?

Answers on a postcard, please!

[edstrick]

The LM impacts were extremely oblique... 80 degrees off vertical or more.

The SIV-B impacts were more or less vertical. Later Apollo missions were able to get images of some of the earlier impact points. I don't recall about Clementine.

The Ranger impacts were pretty easily identified, except for 8's, which was looking off impact target to get more pictures of terrain, accepting motion blur and non-contiguous last images. The surprise which hindered identification for a while was that the Ranger impact ejecta was DARK, like scuffed up lunar dirt disturbed by the astronauts.

The reason is a mix of the Rangers not pulverizing bedrock, just re-distrubuting regolith, and the non-hyper-velocity speed of the impacts, compared with natural impacts.

[Bob Shaw]

The LM impacts were extremely oblique... 80 degrees off vertical or more.

*Really* oblique natural impacts produce craters with oddly shaped ejecta, often as a 'fan' shape. Presumably the LM impacts would have been somewhat similar, then...

[Phil Stooke]

The best reference for artificial impact craters on the Moon is Ewen Whitaker's short article in the Apollo 16 Preliminary Science Report - should be easy to track down in any good university or big city library. He saw the craters made by Ranger 7 and 9 in Apollo 16 pan camera frames, and Ranger 8's was seen by a Lunar Orbiter. Then he found the SIVB impact craters from Apollo 13 and Apollo 14, and the Apollo 14 LM ascent stage impact ejecta (not crater). A few of these can be seen in Clementine LWIR images - I have Ranger 7 and Apollo 14 SIVB at least. No other impacts were found at that time. The later Apollo impacts were in areas not phtographed at high resolution at that time.

I have a tentative ID of Ranger 6's impact ejecta. It was on LOPD (LPOD is still on hiatus alas...):

http://www.lpod.org/LPOD-2004-08-05.htm

It's an odd triangular patch, dark in Clementine LWIR images, so bright in albedo. Unfortunately the Consolidated Atlas frame of the area was taken after Ranger 6, so I have not been able to see if the bright spot is new. But the resolution would be marginal. The triangle opens to the east as Ranger 6's trajectory would suggest it should.

LRO will allow a search for all impact craters - including, presumably, Ranger 4, Lunas 2, 5, 7 and 8, Hiten... quite a few.

Speaking of impacts... It was commonly said that Luna 2's upper stage rocket hit the Moon 30 minutes after Luna 2 itself. But where? If it followed the same trajectory but a bit slower (assuming separation slowed it and speeded up Luna 2), it would be displaced by the Moon's orbital motion, which would put it near the east limb. I never came across any mention of this.


Phil

[AndyG]

*Really* oblique natural impacts produce craters with oddly shaped ejecta, often as a 'fan' shape. Presumably the LM impacts would have been somewhat similar, then...

...but still probably quite small.

A LM ascent stage, massing about 2000kg once empty, hitting the surface at around 1680m/s (i.e. Lunar low orbital speed) would make for an impact energy of 2.8GJ - say about 2/3rds of a tonne of TNT.

The resultant crater size for a vertical impactor with that energy would be in the "few tens of metres' diameter" range, perhaps disturbing up to 200 tonnes of regolith. A shallower impact would, as you suggest, spray debris further downrange - probably up to several kilometres if my back of an envelope is to be believed - but the bulk of the material would be landing within a couple of hundreds of metres.

It should be easily visible from orbit: is there any photography (from Clementine?) which depicts the results of LM and SRB impacts? A quick google only raises endless Moon-Hoax rubbish.

Andy G

[ljk4-1]

The best reference for artificial impact craters on the Moon is Ewen Whitaker's short article in the Apollo 16 Preliminary Science Report - should be easy to track down in any good university or big city library. 

The Apollo 16 Preliminary Science Report may be found online here:

http://history.nasa.gov/alsj/a16/as16psr.pdf


Also, if you go to this Web page:

http://www.geocities.com/bobandrepont/apollopdf.htm

Scroll down to the Apollo 16 section, where you will find links to other relevant documents regarding the geology of the landing site and even a brief report on the impact of an upper Saturn stage just 10 km from the landing area.

[ljk4-1]

The Apollo 16 Preliminary Science Report may be found online here:

http://history.nasa.gov/alsj/a16/as16psr.pdf
Also, if you go to this Web page:

http://www.geocities.com/bobandrepont/apollopdf.htm

Scroll down to the Apollo 16 section, where you will find links to other relevant documents regarding the geology of the landing site and even a brief report on the impact of an upper Saturn stage just 10 km from the landing area.

And the 1968 NASA book, Exploring Space with a Camera, has an image of the Ranger 8 impact crater from Lunar Orbiter 2 and the famous image of Surveyor 1 on the lunar surface from Lunar Orbiter 3.

Starting here:

http://history.nasa.gov/SP-168/section2b.htm#94

[edstrick]

Phil said: LRO will allow a search for all impact craters - including, presumably, Ranger 4, Lunas 2, 5, 7 and 8, Hiten... quite a few... Also the Lunar Orbiters, at mostly utterly unknown locations. Orbiter 1 was intentionally impacted to "open" radio channel space for Orbiter 2.

I hope we get good coverage of the Luna 9 and 13 landing sites. Precise locations not known, to maybe a degree or somewhat better in lat and long. Luna 9 is supposedly on the edge of mare at the west edge of Procellarum, but the panoramic images show a hummocky rolling terrain very much like subdued parts of Fra Mauro, and I'm convinced it's in the adjacent very subdued highland patch by the nominal landing site. Luna 13 is totally unambiguously on mare.

Note the Luna landers ejected two instrument compartments before retrofire, then jettisoned the hard lander sphere at retro burnout while the main spacecraft went *CRUNCH-TINKLE* (well.. no tinkle in vaccuum...) nearby. I was a bit surprised I never could recognize the wreckage in post-landing panoramas, but it may have simply been out of view for both missions.

[ljk4-1]

Phil said: LRO will allow a search for all impact craters - including, presumably, Ranger 4, Lunas 2, 5, 7 and 8, Hiten... quite a few... Also the Lunar Orbiters, at mostly utterly unknown locations.  Orbiter 1 was intentionally impacted to "open" radio channel space for Orbiter 2.

I hope we get good coverage of the Luna 9 and 13 landing sites.  Precise locations not known, to maybe a degree or somewhat better in lat and long.  Luna 9 is supposedly on the edge of mare at the west edge of Procellarum, but the panoramic images show a hummocky rolling terrain very much like subdued parts of Fra Mauro, and I'm convinced it's in the adjacent very subdued highland patch by the nominal landing site.  Luna 13 is totally unambiguously on mare.

Note the Luna landers ejected two instrument compartments before retrofire, then jettisoned the hard lander sphere at retro burnout while the main spacecraft went *CRUNCH-TINKLE*  (well.. no tinkle in vaccuum...) nearby.  I was a bit surprised I never could recognize the wreckage in post-landing panoramas, but it may have simply been out of view for both missions.

Do not forget the later Lunas like 23 and 24, which should be even more visible as they are larger. How well do we know their landing sites?

And the famous Luna 15, which tried to beat Apollo 11 back with regoltih samples.

And Ranger 4 - I'd like to know if the balsa wood sphere survived.

And of course Surveyor 4 - did it land okay or did it crash? Lunar Orbiter 3 could essentially tell the difference with Surveyor 1.

One more - Luna 2 supposedly spread shiny USSR Coat of Arms all over the place of its impact site. Could those be seen from orbit, especially if the sunlight hits them just right?

[edstrick]

"And of course Surveyor 4 - did it land okay or did it crash? "

Surveyor 4 went from "nominal" to zero signal essentially instantaneously, right about the time of maximum thrust from the solid retro-rocket, a second or so before burnout. The failure review found no smoking gun in preflight documentation and absolutely nothing in the telemetry. They concluded that the retro may have exploded, or that there was a sudden and total power failure to two separate transmitter systems at the same time <as I recall>, which could include the entire spacecraft's power, of course.

Either it scattered shredded metal bits over a square kilometer plus of moonscape, hit the surface at the some 500 miles/hr remaining at retro burnout and lined a crater with shiny metal bits, or it more or less successfully landed or did a low speed impact after continuing a descent in the blind.

Sinus Meridiani contains the shiny-metal-bit lined crater of Surveyor 2, the remains of 4, and successfully landed Surveyor 6. As a very old mare with very deep.. estimated 10 meter thick.. regolith, the site has very few large loose rocks and is a generally good place to look for geologically fresh disturbances, though as old mare, the medium size crater population is large.

[Phil Stooke]

Meridiani? Yikes, it was off course!

Phil