From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: ground vs. flight
Date: Thu, 24 Dec 1992 06:05:43 GMT
Organization: U of Toronto Zoology

In article <=hv29vp@rpi.edu> strider@clotho.acm.rpi.edu (Greg Moore) writes:
>>>	... What did Michael Collins do while on the Agena?
>>Apart from just generally evaluating how easy it was to do -- not very --
>>he retrieved a micrometeorite experiment package...
>>
>	Actually Henry, that supports my original point, that EVA to and
>on and unstabilized platform isn't easy.

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.

>	However, I do find that this was sone very interesting.  Any
>idea how much if any tumbling the Agena was doing?

It was pretty steady when the exercise started, but the situation did
deteriorate.

>>[shuttle arm]
>>It's not rated for the full mass of an orbiter, which is why the station
>>arm will eventually take over the capture-for-docking job.
>>
>	I meant to ask about this earlier.  I thought at one point I
>saw a diagram for a special "arm" to do this...

I don't recall seeing anything like that, and I'm fairly sure it's not
planned now.  It may well have been proposed.

>	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.

>>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.

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