T,D&E

I have a theory that I'd like one of you orbital dynamics geniuses to
think about...

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. After all,
you're in a relatively circular orbit, and even a few fps of delta-V in
any given vector will start you moving toward or away from your target
after only a few minutes.

Compare this to T,D&E done within an hour after TLI. Your trajectory
looks like a pretty straight line at that point -- certainly at this
point, the effect of the maneuvering required for T,D&E isn't nearly as
pronounced in relative motion between the two vehicles as it is in LEO.

At least, that's how it seems to this math-deficient brain... does this
theory have merit?

--

Do not meddle in the affairs of dragons, for | Doug Van Dorn
thou art crunchy and taste good with ketchup |

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.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

In article , says...
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.

So how come McDivitt and Young had such trouble with their rendezvous'
in Gemini?
--
Kevin Willoughby lid

Imagine that, a FROG ON-OFF switch, hardly the work
for test pilots. -- Mike Collins

On Thu, 11 Sep 2003 23:06:01 -0400, Kevin Willoughby wrote:

In article , says...
The counter-intuitive effects of orbital dynamics
are largely absent when ranges are short and relative speeds are low.

So how come McDivitt and Young had such trouble with their rendezvous'
in Gemini?

Because the ranges were longer and the relative speed were higher.

It's quite different achieving a rendezvous with a separately launched
vehicle than with a just undocked portion of the same vehicle as would be
the case in an Apollo transposition and docking between the CSM and LM.

In article ,
lid says...
In article , says...
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.

So how come McDivitt and Young had such trouble with their rendezvous'
in Gemini?

It was McDivitt and White, but yeah, that was one of the things I was
thinking of... 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, i.e., turn around and thrust straight back towards the
spent second stage. And yet, the thrusting McDivitt was doing --
straight-line closure just like an Apollo T,D&E -- sent the Gemini into a
sufficiently different orbit such that they couldn't manage to close.

What was the difference between GT-IV and Apollo 9? And yes, I have an
ulterior motive for asking, I'm taking on the project of helping to
develop the Apollo 9 Flight Journal, and this is one of the areas I'd
like to discuss a bit in it.

--

Do not meddle in the affairs of dragons, for | Doug Van Dorn
thou art crunchy and taste good with ketchup |

In article ,
says...
On Thu, 11 Sep 2003 23:06:01 -0400, Kevin Willoughby wrote:

In article , says...
The counter-intuitive effects of orbital dynamics
are largely absent when ranges are short and relative speeds are low.

So how come McDivitt and Young had such trouble with their rendezvous'
in Gemini?

Because the ranges were longer and the relative speed were higher.

It's quite different achieving a rendezvous with a separately launched
vehicle than with a just undocked portion of the same vehicle as would be
the case in an Apollo transposition and docking between the CSM and LM.

On GT-IV, the Gemini attempted to do a transposition demonstration by
turning around and closing with its spent second stage. It was a very
similar maneuver to an Apollo T,D&E. And it failed because straight-line
closure thrusting placed the Gemini into a different orbit which caused
it to separate from the booster.

--

Do not meddle in the affairs of dragons, for | Doug Van Dorn
thou art crunchy and taste good with ketchup |

In article ,
says...
In article ,
lid says...
So how come McDivitt and Young had such trouble with their rendezvous'
in Gemini?
It was McDivitt and White,

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

otoh: I hadn't realized the significant differences between
rendezvousing with your own Titan upper stage and a separately launched
Agena. Thanks for pointing that out.

Could part of the problem have been the personality of these two pilots?
The "engineer's engineer" kind of pilot (Armstrong/Gemini VIII,
Shirra/Gemini VI) didn't seem to have this kind of problem...
--
Kevin Willoughby lid

Imagine that, a FROG ON-OFF switch, hardly the work
for test pilots. -- Mike Collins

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

So how come McDivitt and Young had such trouble with their rendezvous'
in Gemini?

Because they were 200m away before they even started. Too far.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

In article ,
lid says...
In article ,
says...
In article ,
lid says...
So how come McDivitt and Young had such trouble with their rendezvous'
in Gemini?
It was McDivitt and White,

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

otoh: I hadn't realized the significant differences between
rendezvousing with your own Titan upper stage and a separately launched
Agena. Thanks for pointing that out.

Could part of the problem have been the personality of these two pilots?
The "engineer's engineer" kind of pilot (Armstrong/Gemini VIII,
Shirra/Gemini VI) didn't seem to have this kind of problem...

I don't think McDivitt's problem was in the same class as Young's.
Gemini X was launched with an out-of-plane error in its stable matrix, so
its rendezvous included an out-of-plane vector that resulted in its
tremendous whifferdill. McDivitt just thrusted line-of-sight toward the
Titan second stage and the particular vector he was pointing ended up
imparting out-of-plane velocity.

--

Do not meddle in the affairs of dragons, for | Doug Van Dorn
thou art crunchy and taste good with ketchup |

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.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |