Re: SLA question

On Thu, 14 Aug 2008 21:18:19 +0000 (UTC), Rick Jones
<rick.jones2@xxxxxx> wrote:

Scott Stevenson <almostfm.AMSPAY@xxxxxxxxxxxxxxxxxx> wrote:
On Wed, 13 Aug 2008 17:37:52 GMT, "Alan Erskine"
<alan.erskine@xxxxxxxxxxx> wrote:

During all the Lunar Apollo missions, the panels of the SLA
(Spacecraft Lunar module Adaptor) were jettisoned from the S-IVb
during the T&D (Transposition and Docking); but, as the panels were
travelling along the same trajectory as the rest of the spacecraft,
did any of the panels crash into the moon?

That's an interesting question. I don't know, but I would guess
not. On most (all?) of the missions, the S-IVb required a maneuver
(usually, I think, a propellant dump) to put it on a collision course.

When the panels were released, they had some "lateral" motion to
them. If that was only 1 fps, they would be about 45 miles from the
original trajectory 65 hours later, about when the spacecraft was
getting ready to go into orbit.

That would be a "ring" (if four? panels constitutes a ring) round the
path of the spacecraft right?

Right. Each of the four panels took up 90 degrees of the
circumference. Assuming they all separated with equal energy exactly
perpendicular to the path of the spacecraft, you should get a steadily
expanding ring.

I don't think that was a big enough difference to put them on a
collision course...

How high was lunar orbit? I found one reference that suggested 60
miles. So if it was a bit more than 1fps there would be a chance? Or
was the LOI burn such that had it not happened, the spacecraft would
have been more than 60 miles altitude as it passed the moon?

60 nm is a good "ballpark" figure for an Apollo pericynthion, but when
they first went into orbit, I believe that occured on the far side.
Figuring out if the panels would collide is more complicated than it
first appears...

To get that 60 nm pericynthion you have to be in the right place at
the right time. Change the speed that you travel, and you change
where you need to aim. They used mid-course corrections to make sure
the spacecraft was on exactly the right heading and the right speed to
get to the proper place at the right time. But the SLA panels were
stuck on whatever trajectory they were on when the TLI burn ended
(plus whatever lateral motion they were given when they separated.)

Roll the stack a little before TLI, and the panels are no longer
flying purely "right, left, up, and down" compared to the original
trajectory (I know there's no up or down in zero G, but if you try and
picture it, it makes sense).

It gets really complex in a hurry...

take care,
Scott
.

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