NavList:

   

Reply

While reading "Carrying the Fire", by 1960s astronaut Michael Collins, I
enjoyed his description of a navigational experiment on his rookie
flight on Gemini 10 in 1966. It was a "very cumbersome procedure,
whereby I was to use a portable sextant to measure the angle between a
star and the earth's horizon (repeating the process at carefully
precribed intervals with stars selected for their positions with respect
to our orbit) and feed the angles and times into Module VI [software in
a memory expansion module] of our computer. Combining Module VI data
with a variety of charts and graphs carried on board, we would be able
to determine our orbit and predict where we would be at a given future
time relative to our Agena target."

The objective was to rendezvous and dock with an Agena upper stage
(already in orbit), using Module VI and no help from the ground, then
use the Agena to boost themselves into a higher orbit Then they would
rendezvous with a second Agena (but not dock). Collins would spacewalk
to the second Agena and remove a micrometeoroid experiment from its
exterior, for return to Earth.

Collins and crewmate John Young practiced the rendezvous interminably in
the simulator with the Module VI engineers. It was a tough grind,
"pushing me to my limits of time and understanding... for once a mistake
was made, there was no way to cross-check it. Instead all computations
downstream of the mistake were poisoned, and the ultimate result was
invariably incorrect."

One problem didn't show up until they got into orbit and Collins shot
the first star, Schedar. "My first shock comes when I try to find the
horizon: somewhere in that homogeneous void black sky changes to black
water -- that I can see, grossly, by the fact that the stars stop at a
certain point, but they seem to ooze into oblivion without any sharp
line of demarcation... After some experimenting, I find I can watch the
image of the star through my sextant as it approaches the horizon. There
is a faint muddy band, the airglow, into which the star, descending,
almost disappears, but if I watch closely enough, it re-emerges into a
very narrow zone of visibility before being snuffed out by the
atmosphere. It is this instant of snuffing that I must capture, as
accurately as possible. When I do I yell MARK, and John pushes a button.
Then we must turn up the lights long enough to read the sextant angle,
and manually punch it into the computer, digit by digit. I am getting
the hang of it, but the process is slow, and we are running behind by
the time we have finished with Schedar and are ready for Hamal, our
second star... I finally get one measurement at the last possible
moment. Then a quick and sloppy try at Vega and Altair before the night
ends and we break into brilliant sunshine near the western coast of
Australia. John is jubilant. 'Isn't that beautiful!' Deep in Module VI
calculations, I can only grumble, 'Don't even tell me about it, babe.
I'll look tomorrow.'"

Collins has some results by the time they reach Hawaii. It's a mixed
bag. His predicted thruster firing times look fairly good compared to
Mission Control's numbers, but he's way off laterally and cannot figure
out where the error occurred. They decide to use the data from the
ground to fly the rendezvous.

Although the celestial navigation experiment was disappointing, the
mission overall was a success. Both rendezvous were accomplished and the
experiment was retrieved.

On Collins' next (and last) flight he was the command module pilot on
the Apollo 11 mission with Armstrong and Aldrin.

On that mission one of his duties was to take star shots to keep the
inertial navigation platform aligned. "I had made several trips to the
Massachusetts Institute of Technology near Boston, and had tried my
level best to suffer through a couple weeks of 'simple' explanations of
the system by their experts, but I always came away shaking my head.
They didn't speak my language and I didn't speak theirs."

--
I block messages that contain attachments or HTML.


--~--~---------~--~----~------------~-------~--~----~
Navigation List archive: www.fer3.com/arc
To post, email NavList@fer3.com
To , email NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---

   

Reply