From: strider@clotho.acm.rpi.edu (Greg Moore)
Newsgroups: sci.space
Subject: EVA troubles (Was Re: ground vs. flight
Date: 24 Dec 92 17:40:23 GMT
Organization: The Voice of Fate

In article <Bzr29K.5GB@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes:
>In article <=hv29vp@rpi.edu> strider@clotho.acm.rpi.edu (Greg Moore) writes:
>
>The platform being unstabilized actually had little to do with it, aside
>from dictating a relatively early end to the exercise when Collins's
>various forces exerted on it started complicating its motion to the
>point of unpredictability.  The problems were general issues of EVA,
>not particular to the nature of the Agena.  NASA hadn't fully realized
>the difficulties of free-fall maneuvering in spacesuits at the time.
>
	That's partly what I was refering to, the exertiion of forces
taht leads to unpredictability.  However, at that stage in the progrm
I'msure just general EVA problems were a bigger problem.

>>	Also, given that the bottom of the shuttle is covered with
>>tile, can the orbiter exert a Y+ (i.e. vertically up) translation?
>
>There aren't any RCS nozzles on the orbiter's belly, but both the forward
>and aft RCS systems have nozzles angled down so that they can (somewhat
>inefficiently) thrust upward.
>
	Ok, taht's what I thought.  So I'd assume you'd want to do as
little Y+ translations as possible.  Anyone know the approach path 
for the orbiter?  Will it approach cargo bay first, or will it attempt
to do a partial "flyby" where it approaches nose first (i.e X+ translation).
I'd assume the latter, to safe fuel, and to allow it to "float by' if 
something goes wrong.  With a Y+ translation if an 'up" thruster
(to stop the Y+ movement) fails, you risk running the shuttle into the
orbiter.  With the X+, if something fails, you just float on by.  If
it works, you simply stop 15'-20' away and let the arm pull oyu in the
rest of the way.

>>>As far as I know, the success rate for grapple fixtures is 100%.  They've
>>>sometimes had to proceed slowly and carefully, but I don't think they've
>>>ever had to abandon a grabbing attempt.
>>
>>	Didn't they ahve to manually slow down a rotating satellite
>>since the arm couldn't grapple the fixture fast enough? (Solar Max?)
>
>On Solar Max, originally Pinky Nelson's backpack was to take the spin
>off the satellite so it could be grabbed by the arm.  Didn't work because
>the fancy grappling gadget he was equipped with -- unrelated to the one
>on the arm -- didn't work.  He did try to do it manually, but that wasn't
>properly planned and it didn't work either.  Nobody really expected a
>direct grapple attempt with the arm to work, although they did try it.
>Eventually they decided to gamble, slowed the spin down a lot with the
>satellite's on-board systems, and *then* the arm got it.
>
	Ok, this may or may not have been what I was thinking of. Not sure.

>On the Palapa/Westar retrieval, the next generation of fancy gadgets didn't
>work either, but that time they had a manual backup plan, which was used.
>(Like Intelsat, these birds had no grapple fixtures, so the arm couldn't
>be used until *something* was grappled to them by other means.)  On the
>Leasat repair, the hardware was kept very simple and the astronauts'
>arms did almost all the work.  (How quickly they forgot these lessons...)

	I don't recall what Leasat was.  Could you give me some private email
sometime to jog my memory?
	It seems like a good argument for satellite manufacturers to include
a grapple point.  That way Shuttle, DC-? or whatever will be able to
effect a dock easily.
	I don't want to re-open the can of worms about this (since we
debated once before) but two points: Granted: it adds weight, and most of
the time would be a waste.  But, Is the weight loss that big of a deal.
And, sure, most of them will be in GEO which Shuttle can't make.  But,
if DC-1 works, we're more likely to have a OMV which CAN get to them.

>-- 
>"God willing... we shall return."       | Henry Spencer @ U of Toronto Zoology
>       -Gene Cernan, the Moon, Dec 1972 |  henry@zoo.toronto.edu  utzoo!henry