[X] My Assistant

[Bob Shaw]

Phil and Bruce;

David Harland's excellent 'Exploring the Moon: The Apollo Expeditions' (Springer-Praxis, 1999) quotes the Flamsteed site as ALS-6, and confirms that it *wasn't* the Surveyor 1 site. He then goes on, however, to say that the Flight Dynamics guys *did* push for Surveyor 1, but that because both it and the ALS-6 site were so far west it had no back-up site and was abandoned (p34). The Apollo 12 Surveyor 3 target site (ALS-7) had the advantage of offering orbital imagery of both Fra Mauro and the Davy crater chain. The site numbering is obviously a tad awry somewhere, but the song remains the same.

And no, I'm not on a retainer from Springer-Praxis - they just do fine books!

Bob Shaw

[Phil Stooke]

OK, here's the Apollo 12 backup story. I think this has never been told fully before. Don Wilhelms, if I recall, mentions that nine points in the Site 5 ellipse were identified but does not give further details.

Apollo Site 5 at about 40 west, 2 north was the Apollo 12 backup. But the goal was not 'land anywhere' as Apollo 11's had been, it was 'achieve a pinpoint landing'. So a specific target point had to be selected. ASSB asked USGS to identify interesting points. Newell Trask of USGS chose nine points in the ellipse. All were small fresh craters with a characteristic morphology discovered in Lunar Orbiter photos - very rocky, with a concentric inner ridge. Craters like this, about 100 or 200 m across, are common in the maria and are thought to show where the crater penetrated through the regolith into underlying bedrock.

Now the detective work begins! First I found Trask's letter in the history collection at Flagstaff. (ASSB minutes don't say anthing about this.) The nine points are listed, but only as measurements on individual framelets of the lunar orbiter photo. So then I had LPI copy the appropriate frames for me and made those measurements. Sure enough the nine points can be found. But which was the landing point? Trask's letter identifies it. The landing point is just north of and between two of these small fresh craters near the south edge of the ellipse, with a distinctive pattern of four larger shallow craters ('four crater cross') just to the east to serve as a landmark during descent.

I attach two images (one attachment) to illustrate this. In the first, 'B', the nine dark circles are the locations of the nine fresh craters. Of course you don't land on the crater, so the target is beside one of them.

Phil

[Bob Shaw]

Phil:

Fascinating!

Bob Shaw

[JRehling]

Phil:

OK, we're talking about a crater which is about 95km across, central peaks 1.2km (some sources) or 400m (other sources) high, greatest extent of the peaks about 15km.  If the moon's diameter is about 3,500km, then surely only the tops of any ring wall mountains will be visible?

Where's VistaPro when you need it!

Bob Shaw

The function of how far you can see to the horizon, as a function of your height above a perfect sphere, varies approximately with the square root function (a very good approximation until you start to get a significant fraction of the radius above the perfect sphere). It varies linearly with radius of the body. For Luna, the coefficients make it:

D = 0.97 sqrt(h)

Where h is height in meters, and D is horizontal distance to the horizon in *kilometers*. Yes, that coefficient is close to 1.0, so you can save on paper.

For two elevated bodies (like a distance mountaintop and an astronaut), you can add the two distances. Of course, this is to determine merely if you can see the tippytop of the mountaintop.

Basically, to see the top half of a 10km, you'd need to be able to see a "peak" 5 km up, which on Luna, is possible from:

D = 0.97 sqrt(5000)
D = 68.6 km

68 km away. Near the center of Copernicus, then, you would not only be able to see the "near" wall, you would be able to see all portions of the *far* wall that weren't obscured by yet-closer peaks! And 5 km of visible wall, at a distance of 60 km or so, would subtend about 5 vertical degrees of arc, which would be a nice vista. But 40 km away, you could see 8.5 km of a 10 km wall, and it would subtend over 10 vertical degrees of arc. 20 km away, it would subtend about 25 vertical degrees of arc, which would be almost dizzying, I think. With the vaccum-based illusion that distant objects appear to be in the immediate foreground, the astronauts might lean to compensate!

[Bob Shaw]

I located the proposed Apollo 18 landing site on the larger scale image - it's the red dot, surrounded by circles at 1km. I think I may have located it in the Lunar Orbiter 'Picture of the Century' shot, too (probably just hidden behind the central row of mountains).

Here's the big picture (the landing point is just right of centre, at 2 o'clock).

Attached thumbnail(s)

 

[Bob Shaw]

More Apollo 18 - 50% and 25% reductions of the last post.

Attached thumbnail(s)

 

[Bob Shaw]

Apollo 18, a rather closer view (actually a crop from the big file) - still with the circles etc.

Attached thumbnail(s)

 

[Bob Shaw]

And the location - I think - on the Lunar Orbiter oblique image.

Which means, if I'm right, that we actually *do* have a surprisingly good idea of what the guys on the ground would have been lookng at!

Attached thumbnail(s)

 

[Bob Shaw]

The function of how far you can see to the horizon...

Thanks! That's a keeper!

[Guest_BruceMoomaw_*]

Yes, I have an Alphonsus traverse map, though without sample stations etc.  Alphonsus was always popular as a second choice, but never made it to the top of the list.  One problem was that the later Apollo sites had to have multiple objectives - at Taurus-Littrow you had the valley floor basalts, the Serenitatis basin massifs, the supposed volcanic vent at Shorty (incorrect interpretation) and a young landslide.  Alphonsus had the dark halo craters, but the pre-Imbrian walls (such old material was a major objective of the last 2 missions) were likely covered with a thick layer of Imbrium ejecta.

Phil

Yeah, I know about that problem. My main reasons for suspecting that it would still likely have been chosen are that:

(1) Apollo 14 would have revealed Littrow to be a failure as a source of young volcanics (restoring interest in Alphonsus for that purpose); and

(2) There don't seem to have really been any other possible sites that were more promising as a source of highlands material uncontaminated by Imbrium ejecta (although that WAS the single most important science goal for Apollo 17). Taurus-Littrow, would, I imagine, have been ruled out as too close to the Apollo 14 site (as well as having no young volcanics), and other sites in the highlands between Mares Serenitatis and Crisium (according to the Apollo 17 postflight report) were ruled out on the grounds that there was a good chance the Soviets would sample them (which, in fact, they later did). By contrast, there was considered to be at least a fair chance that Alphonsus would have some non-Imbrium highlands material (which Gassendi, Copernicus, Davy Rill and the Marius Hills would definitely not have had), as well as those young volcanics.

Still, there's obviously a huge amount of guesswork in this conclusion of mine. After Apollo 14 had revealed Littrow not to have young volcanics as expected, it's hard to really predict where the last three missions would have been sent (except that Descartes strikes me as a certainty for one of them).

[dvandorn]

Still, there's obviously a huge amount of guesswork in this conclusion of mine.  After Apollo 14 had revealed Littrow not to have young volcanics as expected, it's hard to really predict where the last three missions would have been sent (except that Descartes strikes me as a certainty for one of them).

If 13 had landed at Fra Mauro and 14 at Littrow, I don't think that would have affected the selection of either Hadley or Descartes. Assuming the same eventual cancelation of the Apollo 15 H-mission and of Apollo 19, you would be looking at selecting sites for the J missions using the same requirements as were actually used -- multiple sampling opportunities, Imbrium and pre-Imbrium impact materials, lava features -- all of which drove the selection of Hadley-Appenine. And Descartes was going to get a J mission somewhere.

I will point out that Descartes was originally a prime site consideration for the *first* J mission, but was bumped to the second because of lack of good photography. When 13 aborted and was unable to get good Descartes pictures, it was left for Apollo 14 to get good coverage of Descartes so that it could be validated as a safe landing site. But since the good site photography wasn't available until after Apollo 14 (and after the site for 15 had to be selected), Descartes fell out of the running for 15. If 13 had gotten that good Descartes coverage, I think Apollo 15 *would* have flown to Descartes.

*Then* you can ask whether Hadley would have been the 16 or the 17 site. Without something like Taurus-Littrow beckoning (and I agree, if 14 had landed at the original Littrow site, Taurus-Littrow would never have been selected for a J mission), then I think it likely that 16 would have landed at Marius Hills and that 17 would have landed at Hadley.

-the other Doug

[Guest_BruceMoomaw_*]

Once again, however, they very badly wanted to get samples of highlands material uncontaminated by Imbrium ejecta -- in fact, that was officially listed as an even more important goal for Apollo 17 than the young volcanics were. And they would have had at least a chance of getting that at Alphonsus, but not at the Marius Hills.

While we're on the subject, Apollo 15 came close to being sent to the Marius Hills instead -- the final choice was made because they wanted a better spread pattern for the first three ALSEP seismometers and because David Scott said he thought a Marius landing would be somewhat harder. Apollo 16's choice was between Descartes and Alphonsus; they picked the former largely on the assumption that #17 would be sent to the latter. But by the time that they actually picked #17's site, both Taurus-Littrow and the center of Gassendi Crater had moved ahead of Alphonsus in the rankings, with the latter finally being rejected because of its lack of non-Imbrium highlands material and because the Gassendi floor looked rugged enough that the rover might have trouble reaching the central peak. (I have no doubt, though, that there are a lot of things that I don't yet know about in the Apollo landing site selections.)

[Phil Stooke]

One other factor was not in Alphonus's favor: the orbital remote sensing was not very different from that of Apollo 16. By the time the last site was actually being selected (so I don't mean earlier when lots of alternatives were being examined for the last few flights) they knew Apollo 16 was going to Descartes. The real contenders in those days were Gassendi, Alphonsus and a site in the general area they referred to as "SW of Crisium". They looked at several sites in that area, including Azout Domes (very close to the later Luna 24) and Proclus, but as Bruce said, rejected them because they were accessible to the Lunas. Gassendi was not ideal topographically or geologically (as Bruce said) but it offered fabulous remote sensing across northern Orientale. SW of Crisium gave the best chance of really old stuff not mantled by Imbrium ejecta, and reasonable remote sensing, though a bit too similar to Apollo 15. But Alphonsus lost out on both counts. Yet Alphonsus had those volcanic vents. But then somebody (I think Farouk el-Baz) found the 'cinder cones' in the Taurus-Littrow valley and that blew Alphonsus out of the water. I still think some of the cinder cones were probably real, further west, but they chose one that wasn't! - Shorty Crater. Oh well, can't win 'em all.

Phil

[Phil Stooke]

I just want to follow up on Bob's comment on Apollo site numbering.

After a long selection process there were five candidate sites for the first landing, ALS (Apollo Landing Site) 1 to 5, very close to the equator, numbers increasing to the west and all shown on the Nat. Geog. map of the time. As Bob said, ALS-6 was in Flamsteed, but it was NW of Surveyor 1 in the plains. ALS-7 was near Surveyor 3. Each was a roughly 5 by 8 km ellipse. But after the first landing they would need pinpoint targets (defined as within 1 km of an interesting feature), and so a set of those targets were also identified within or at least near the ellipses. The idea was, the autopilot system would bring the LM down into the ellipse and the Commander would then 'bias' (tweak) the trajectory towards the point of interest. So they were called 'biased sites' or 'redesignated sites', and numbered ALS-1R, ALS-2R and so on. ALS-6R was up against one of the hills surrounding Surveyor 1. ALS-7R was Surveyor 3. (for completeness, 1R was a hill, 2R was a secondary crater, 3R was a mare ridge near Surveyor 6, 4R was first a ridge, then a Tycho secondary, 5R... - can't remember!)

Phil

[Bob Shaw]

Phil and Bruce:

You've both said that the US mission planners were aware of the areas where the later Luna sample return missions could target. My reading of the Lunas is that yes, they were quite limited in latitude/longitude due to trajectory constraints (though, unlike Apollo, demonstrably not at all limited in terms of time of lunar day (other than presumably avoiding the depths of night-time cold or the noon heat)). That understanding, however, is based on both information from the memoirs of ex-Soviet space programme participants and the detective work of various western researchers, largely working backwards from the trajectories which were flown by the later Luna samplers and Lunokhod busses.

So: how did the Apollo-era planners know what the capabilities of the Luna system were before they flew? The unclassified CIA material which I've seen is actually quite vague in terms of payload weights, upper stages etc for Proton, and just a few percentages out would make a helluva difference in terms of actual capacity to change trajectory out at the Moon.

Bob Shaw