T,D&E

In article , says...
In article ,
Doug... wrote:
... after all, GT-IV was separated (IIRC) from the Titan
second stage at about the same velocity as the CSM was separated from the
S-IVB, and they were supposed to do pretty much the same thing that
Apollo crews did...

While it's hard to find numerical details on Gemini, the best picture I
can put together at the moment has Gemini 4 separating at 3m/s (vs. a
nominal 0.3m/s for Apollo 9) and starting maneuvering at about 200m (vs.
Apollo 9 nominally turning and halting separation at 15m). That is, they
went out an order of magnitude farther and faster. Big difference.

The combination of the pyro ring and the sep burn was a 10 fps separation
on GT-IV? Wow... that's a LOT faster than I thought the Gemini separated
from its booster.

--

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On Thu, 11 Sep 2003 22:19:54 GMT, (Henry Spencer)
wrote:

In article ,
Doug... wrote:
It seems to me that the most difficult T,D&E (transposition, docking @
extraction) in the Apollo program was on Apollo 9. This is because
Apollo 9 did it in LEO, where translation maneuvers almost immediately
cause non-intuitive relative motions between spacecraft...
At least, that's how it seems to this math-deficient brain... does this
theory have merit?

Alas, not very much. The counter-intuitive effects of orbital dynamics
are largely absent when ranges are short and relative speeds are low.

....And, for that matter, if TDE is done with the stack perpendicular
to the Earth at the start of the manouver, aren't the translational
effects diminished, or am I simply not drunk enough to grasp orbital
mechanics again?


OM

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Kevin Willoughby wrote:
No, I really meant McDivitt and Young. There were wifferdills on both
Gemini IV and Gemini X.

GT10's wifferdill was the result of a bad guidance load.

D.
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In article ,
Henry Spencer wrote:

In article ,
Doug... wrote:
... after all, GT-IV was separated (IIRC) from the Titan
second stage at about the same velocity as the CSM was separated from the
S-IVB, and they were supposed to do pretty much the same thing that
Apollo crews did...

While it's hard to find numerical details on Gemini, the best picture I
can put together at the moment has Gemini 4 separating at 3m/s (vs. a
nominal 0.3m/s for Apollo 9) and starting maneuvering at about 200m (vs.
Apollo 9 nominally turning and halting separation at 15m). That is, they
went out an order of magnitude farther and faster. Big difference.

Still, it seems to me that the real rule of thumb should be that "The
counter-intuitive effects of orbital dynamics are largely absent when the
whole maneuver takes only a small fraction of an orbit". That is,
although increased range increases the weirdness, increased speed
decreases the weirdness. If Gemini 4 had separated, moved out to 200m,
then instead of trying to rendezvous with their target, pulled out a
rifle and fired at it, they wouldn't have had to adjust their aim much
(if at all) for orbital-dynamic factors, since the travel of the bullet
between the two spacecraft would have occurred so quickly that, to a very
good approximation, both the spacecraft and the bullet would have been
moving in a constant, uniform gravitational field, in which ordinary
notions of dynamics would apply. On the other hand, when one thrusts a
tiny amount "forward" (starting from a circular orbit), then waits until
the orbit has traveled 90 degrees around the Earth, the direction of that
"forward" thrust will, in the new reference frame, be "up", not
"forward". And that is only the beginning of the complexity; when you
are farther up, the gravity is less, so the orbit is slower, and you fall
behind.


--
Norman Yarvin