Conference 7.286::space

Date:     Thu, 25 Oct 84 13:32:46 EDT
From:     Will Martin <[email protected]>
To:       [email protected]
Subject:  Satellite retrieval / gateway breakage

For those interested in the satellite-retrieval process, I recommend
you see if your local PBS station will broadcast the latest "Enterprise" 
program (this is a series of half-hour shows on various businesses).
This last one was on the insurors' and underwriters' efforts to recover
the two satellites lost from the shuttle flight a while back. An excellent
discussion, including more technical info on the causes of the failures
than I have seen anywhere else. Since many PBS stations repeat programs
or tape-delay them, I thought it was worthwhile to mention this on the
net. The program aired in St. Louis on Wednesday, 24 Oct.

Other topics -- it appears that the same gateway breakage that has
isolated the ARPA and USENET portions of many other lists has also 
affected SPACE. Hopefully this can be soon remedied. Until then,
submitters who have both ARPA and USENET access should send postings
to SPACE@MIT-MC AND post them to net.space.

Will Martin

USENET: seismo!brl-bmd!wmartin     or   ARPA/MILNET: [email protected]

Date: 26 Oct 84 10:59:40 PDT (Friday)
Subject: Re: Satellite retrieval mechanism
To: [email protected]
cc: [email protected]
From: Jerry <[email protected]>

The PBS "Enterprise show aired here in LA last wedensday (Oct.24) on
channel 24 and was EXCELLENT!. I hope they show it again.

I was interested in the "stinger" that the astronauts will use to
recover the satellites. For those not familiar with it, its an assembly
with a long rod that the spacewalker will insert into the satellite's
rocket exhaust and then throw a lever that causes prongs to pop out from
the shaft and keep the rod from being withdrawn from the satellite. It
is a rather nice idea but I was wondering if the prongs were
retractible? It would be a terrible mess if they weren't and something
went wrong. Anybody on this list familiar with the equipment?

Also aren't the satellites spinning? Do they intend to match the spin
before grabing the satellite or grab it and then de-spin? Can the MMU
handle such de-spin manuvers? Also the plan calls for the MMU to bring
the satillites back to the shuttle and then use the arm to put them in
the bay. Why not have the astronaut put it in the bay? Is this too
complex a manuver? Too little space in the bay for the MMU and
sattilite?

~ Jerry

Message-Id: <[email protected]>
Date: 27 Oct 84 14:52:24 EDT (Sat)
From: Nathaniel Mishkin <mfci!mishkin%[email protected]>
Subject: More on Satellite Retrieval
To: space@mit-mc

While we're all wondering about some details of the satellite recovery
schedule for the next shuttle mission, I'd like to add my own wonders:

What are the constraints on the rendezvous?  According to the PBS show,
the satellites are in quite an elliptical orbit.  I got the impression
that the apogee of the orbit is well higher than the maximum possible
shuttle apogee.  So presumably they have to time the rendezvous so
that the shuttle meets the satellite when the satellite is at a low
point in its orbit.  How long do the astronauts have before the 
satellite drifts too far away?  How elliptical can the shuttle's
orbit be made?  How much force needs to be applied to the satellite
to get it into the shuttle bay?  (After all, it DID fire an engine so
it does have some momentum that has to be overcome, right?  My physics
is, er, a bit rusty.)

How dangerous is all this?  I mean, in the most recent shuttle mission
during the refueling experiment people commented on the "danger" of
dealing with the fuel in that environment.  Mightn't there be some
unexpended fuel sitting in the satellite's booster?  Would you want
to be staring down the gullet of an engine that didn't behave as
expected in the first place?

                -- Nat

Date: 28 Oct 84 12:38:00 PST
From: WOO IL LEE <lee@su-star>
Subject: Re: satellite recovery
To: space%mit-mc <space%mit-mc@score>
Reply-To: WOO IL LEE <lee@su-star>

A question was raised recently about the remaining fuel in Palapa &
Westar. Please note that the fuel-transfer experiment in the last 
Shuttle mission used liquids. That is because the idea is to refill
the attitude control system tanks. Attitude control thrusters are
always, as far as I know, liquid systems. That's due to the need 
to switch them on and off, which can't be done with solids.
	The Thiokol engine is a solid. Its igniters,which are one-shot
affairs, have already been used  up. Furthermore, the failure mode,
as described in most reports, involves the structural failure of
the nozzle throat area. The nozzle portion downstream of this point
was blown away, so even if some other mechanism were to produce
ignition condition, chamber pressure conditions would make it
impossible to complete the ignition process and reach sustained
combustion.

	As for the orbital mismatch between the Shuttle and the
satellites, I understand that they are planning to use the attitude-
control thrusters to reduce and circularize their orbits. Maybe
they can use them to kill the spin too, as with the Orbiting Obsevatory?
	Does anybody have some accurate information?
					Emilio P. Calius
					Stanford Univ.

------------------------------

Date: 28 Oct 84 13:01:00 PST
From: WOO IL LEE <lee@su-star>
Subject: Reusing satellites
To: space%mit-mc <space%mit-mc@score>
Reply-To: WOO IL LEE <lee@su-star>

By the way, the followin thought just hit me!  If this mission is
succesful, this will be the FIRST TIME EVER that a spacecraft has bee
returned to Earth to prepare it to fly ANOTHER mission. And these satelli-
tes weren't even designed for orbital servicing (after all they were
supposed to go to GEO, and it will be a few years before we service that
one regularly).

I think we are going to learn all kinds of interesting things when the
Hughes engineers try to re- furbish them. For example, are they going to
replace the hydrazine tanks or try to refill them? Will they find some new
effects of the Earth environment on systems that have already been
operating in space?

	Any thoughts?
				Emilio P. Calius
				Stanford Univ.

Date:     Mon, 29 Oct 84 20:31:11 EST
From:     Joe Pistritto <[email protected]>
To:       [email protected]
Subject:  Palapa Recovery Techniques

	Yes, the attitude control thrusters will be used to de-spin
the Palapa satellite and its lost brother.  As a matter of fact, this
has already been accomplished, I believe.  The thrusters will be
of course, deactivated from performing ANY control functions when
the orbiter approaches the satellites.  The spin rate at contact will
be 1 RPM or less.  (IT can't be zero, or the satellites would start
pitching around, etc. and would require constant thruster firings to
maintain a stable attitude).  The remaining spin will be killed by
the astronaut after he has grappled the satellite.  Note that the
astronaut will approach from along the spin axis this time, inserting
an expandable probe into the solid rocket motor nozzle of the satellite.
(Yes, NASA DOES learn from its almost-mistakes, (ie. Solar Max))

							-JCP-

Date: 30 Oct 84  0107 PST
From: Robert Maas <[email protected]>
Subject: Retry - "first spacecraft to ..."?
To:   [email protected]
CC:   [email protected] 

[Retry, SU-Ethernet and/or SCORE mailbridge was down when I tried earlier]
Date: 29 Oct 1984 1823-PST
Reply-to:REM@MIT-MC
Subject: Returning spacecraft to fly again?
To:   lee%su-star@SCORE
cc:   space%mit-mc@SCORE

    Date: 28 Oct 84 13:01:00 PST
    From: WOO IL LEE <lee@su-star>
    By the way, the followin thought just hit me!  If this mission is
    succesful, this will be the FIRST TIME EVER that a spacecraft has bee
    returned to Earth to prepare it to fly ANOTHER mission.
You're forgetting the obvious!! The STS orbiters have been returned to
Earth to fly another mission. Perhaps you meant to say UNMANNED spacecraft?