LM/CSM Rendezvous

[Dave.B]

Hello, first of all, I'm not a hoax believer. Very, very far from it. I've participated in this forum a few times, but it was many years ago. I Just lurk here nowadays, mainly due to overwhelming pig-headedness of HBers. I don't know how you guys have the patience.
Anyway - my question, which is entirely genuine:
In photos of the LM ascent stage and CSM docking after lift off from the Lunar surface, why do so many photos from the LM show the CSM with the moon behind it? (Example from A10 here: http://history.nasa.gov/SP-350/ch-10-7.html)
Surely it was a waste of fuel if the LM lifted off and then attained a higher orbit than the CSM? Having said that, I have only an extremely basic understanding of orbital mechanics.
I am happy to be educated.

[LunarOrbit]

This is just a guess based on my time playing Kerbal Space Program, but it might be because the orbits of the two spacecraft weren't perfectly circular, but more elliptical. If that's the case then over time the two spacecraft could alternate between being higher or lower than the other.

[ka9q]

I can't speak to rendezvous; the mission reports for A10 and A11 don't say anything special about the final docking sequence. But I do know that after undocking prior to descent the CSM generally made a radially-downward separation maneuver. Such a maneuver only changes the orbital eccentricity; the period remains the same. I think the CSM made this maneuver to conserve fuel on the LM, which was generally more fuel-limited.

[bknight]

I can't speak to rendezvous; the mission reports for A10 and A11 don't say anything special about the final docking sequence. But I do know that after undocking prior to descent the CSM generally made a radially-downward separation maneuver. Such a maneuver only changes the orbital eccentricity; the period remains the same. I think the CSM made this maneuver to conserve fuel on the LM, which was generally more fuel-limited.

In that case whatever the orbit the LM achieved then the CSM would necessarily have to meet  the LM  where it was,to conserve fuel.

[ka9q]

In that case whatever the orbit the LM achieved then the CSM would necessarily have to meet  the LM  where it was,to conserve fuel.

Not necessarily. The LM mass was far less after its return to orbit while the CSM's mass was almost unchanged. The LM could therefore make orbital maneuvers more efficiently than the CSM.

[onebigmonkey]

Do you have any other examples?

This was briefly discussed elsewhere on the forum -  after separation in lunar orbit the LM would position itself above the CSM for inspection against the dark background of space, but I'm not sure if it was done during post-landing rendezous?

[ka9q]

I do know that the LM approached the CSM from below (how could it not?) but once they were in the station-keeping phase it made very little difference who was above and who was below. In orbital mechanics, altitude is not nearly as important as velocity, and for all practical purposes they were at the same velocity. So the exact relative positions prior to docking had more to do with visibility and astronaut convenience than anything else.

[Kiwi]

In photos of the LM ascent stage and CSM docking after lift off from the Lunar surface, why do so many photos from the LM show the CSM with the moon behind it? (Example from A10 here: http://history.nasa.gov/SP-350/ch-10-7.html)

Look carefully at the reflections in the shiny tape on the command module in that photo. There is more moon reflected than dark sky, so I don't believe the CSM is pointing vertically down toward the moon and therefore the LM isn't substantially above it, although it might be a little higher than the CSM.

It may just be one of those optical illusions for which the moon is famous because of not much to give us scale. It's hard to tell exactly where the sun is, but I'd guess at about 11:30 o'clock from the centre of the docking probe, as the photo is oriented.

[Kiwi]

Go to Kip Teague's Apollo Image Gallery
http://www.apolloarchive.com/apollo_gallery.html
and click on Apollo 10, where there are four photos in a row which show the effect of CSM tilt (relative to the moon) on the amount of moon reflected in the front of the CM. Note that HiRes copies can be downloaded of all but the first, and the fourth photo is similar to the one on the page linked in post 1. In the fourth, the angle of the camera's lens axis to the CM might have a bearing on how much moon is reflected -- I've never experimented with reflections off a cone.

Click on the frame number at far left to get the thumbnail at upper centre, then click on that to get a medium-sized photo, or on the Hi-Res button to get the biggest:--

AS10-27-3856 – CSM tilted down – more moon reflected
AS10-27-3872 – CSM tilted up – less moon reflected
AS10-27-3873 – CSM tilted up – less moon reflected
AS10-27-3881 – CSM tilted down – more moon reflected

One intriguing thing about that gallery is a new section of scans from entire rolls of film, and apparently taken from the original films, with both medium and hi-res. Sixty-four films have been done so far, but none for Apollo 10.

On looking at the translunar film for Apollo 11, there's no evidence of the "searing radiation hell" of the Van Halen belts,  but it's easy to see the result of the spacecraft moving around and away from Earth. I wonder what hoax-believers will have to say about that.

[bknight]

...
On looking at the translunar film for Apollo 11, there's no evidence of the "searing radiation hell" of the Van Halen belts,  but it's easy to see the result of the spacecraft moving around and away from Earth. I wonder what hoax-believers will have to say about that.

From my brief encounters with them they will claim:
1. Never left LEO, so they were always protected.
2. Never left Earth, "somehow" gotten out of the capsule rather like Capricorn One
I know what you are thinking that all can be debunked and both have many times.  But they don't see it our way.

[bknight]

Not necessarily. The LM mass was far less after its return to orbit while the CSM's mass was almost unchanged. The LM could therefore make orbital maneuvers more efficiently than the CSM.

I was on mobile and didn't check this out.  From what I read the CSM was the stationary object with the LM doing all the rendezvous movements.  The CSM would have been used in an emergency only.