Whifferdills & Rendezvous

[banjomd]

In reading one of Michael Collins' books, he talks about getting into a whifferdill and wasting a LOAD of fuel to rendezvous. Is it safe to say that whifferdills are of historical significance and do not occur anymore? If so, when did they stop being a threat to rendezvous?

[PhantomWolf]

So assuming he wasn't meaning that he was really a shape-changing alien from Xenon, I'm suspecting he mean a multi-axis movement that cost him fuel to get out of. If so, I'm suspect that they are not historical, and can still occur with the shuttle or more likely the Soyuz craft, and that they are still a threat to any rendezvous where there is a need to do a multi axis change, such as an orbital plan shift.

[PhantomWolf]

In fact, in a stunning coincidence check out the bottom quite in this post made just today.

[banjomd]

I saw that!
from, "Carrying The Fire"; Michael Collins. p209-210
"good Lord, we are doing a whifferdill around the Agena, an out-of-plane whifferdill...John and I both know what has to be done now. We have sinned. We have somehow wandered off our prescribed path of righteousness, albeit only a tiny little meander, but now we must pay the penalty, and that means fuel...John has no choice but to hose out whatever fuel is necessary to cut short our helix-shaped circumnavigation of the Agena, driving us right up to it and stopping next to it."
Gemini 10 had 36% fuel remaining instead of the 60% that it should have had. (BTW- Collins' books are an excellent read!)

[banjomd]

"Whifferdills are caused by allowing the target to move relative to the stars (failing to null the inertial line of sight rate, as the experts would describe it) and not making large enough corrections early enough to completely stop this unwanted motion.)
"Carrying The Fire" Michael Collins P188

[Bob B.]

From How NASA Learned To Fly In Space by David Harland:

As would be determined following splashdown, when Gemini 10's inertial platform was initialized, it had been slightly misaligned with the result that the spacecraft was not flying in quite the plane that its platform indicated, and instead of reducing both the range and range-rate to zero simultaneously the 'closed loop' solution had brought the vehicle to a halt some 600 feet to the left of the target, and as the vehicles had pursued their slightly inclined orbits the range had varied as their trajectory traced a helical arc (or as Collins later describe it, a "whifferdill") in to the target. They had seen such a situation in simulations when they had been out-of-plane, but this time their instruments had misled them into thinking that they were in-plane. The additional propellant had been consumed in eliminating this out-of-plane error. This was galling to Young, because in the astronaut corps efficient use of fuel was the primary indicator of having what author Tom Wolfe would later immortalize by the term "the Right Stuff". In the post-flight debriefing, Young regretted not splitting the difference between their own and Houston's TPI solutions. "That was my first error of judgment," he admitted. "I should have applied 37 feet per second forward, as near as I can figure, and let it go at that, and seen what developed." Since they had arrived early, they had had to brake in darkness. Furthermore, although he had observed that the target was drifting with respect to the stars, he had not tried to correct this because he was rehearsing the braking profile that he intended to use with the inert Agena. "I think it was an error to try to do more than one thing at a time. You've got to worry about one rendezvous at a time." The situation was complicated by the out-of-plane error - it was this that had caused the target to drift against the stars towards to end of the transfer. "With all that out-of-plane, I just couldn't hack it," he concluded.

[banjomd]

Thanks, Bob B.
Looks like I'll be ordering another book! ;D

[Bob B.]

Mar 7, 2010 19:59:08 GMT -4 banjomd said:

Thanks, Bob B.
Looks like I'll be ordering another book! ;D

I enjoyed reading it. Of course, I’ve always had a particular fondness for the Gemini missions. Those flights are often overlooked and not given the recognition they deserve.

[banjomd]

Agreed. They were absolutely essential for Apollo to be successful.

[echnaton]

It's a great read. Detailed but not overly technical.

[clipperride]

"How NASA Learned To Fly In Space" by David Harland - looks like I will be adding another title to my wish list. I do enjoy David Harlands writing. Is there a "Book Review" thread on the forum? I've tried the search function, but there seems to be a problem with it at the moment, or a problem with my connection.

Regards

Mark

PS Search is working now and it seems that there isn't an Apollo Book Review thread. Wonder if it is worth having one as a sticky?

[Ginnie]

Apr 3, 2010 14:46:29 GMT -4 clipperride said:

"How NASA Learned To Fly In Space" by David Harland - looks like I will be adding another title to my wish list. I do enjoy David Harlands writing. Is there a "Book Review" thread on the forum? I've tried the search function, but there seems to be a problem with it at the moment, or a problem with my connection.

Regards

Mark

PS Search is working now and it seems that there isn't an Apollo Book Review thread. Wonder if it is worth having one as a sticky?

The proboards search engine sucks anyway....
We should get Kiwi to put together some sort of database!