Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!rice!uw-beaver!zephyr.ens.tek.com!tekig5!philj
From: philj@tekig5.PEN.TEK.COM (Phil Jansen)
Newsgroups: sci.space.shuttle
Subject: Re: How do they get it pointing up?
Keywords: Shuttle, launch, SRB, main engine
Message-ID: <5103@tekig5.PEN.TEK.COM>
Date: 29 Nov 89 17:39:24 GMT
References: <1989Nov23.165606.27671@utzoo.uucp> <117.UUL1.3#5131@mvac23.UUCP>
Reply-To: philj@tekig5.PEN.TEK.COM (Phil Jansen)
Organization: Tektronix, Inc., Beaverton,  OR.
Lines: 49

Doug Krause:
> [H]ow is the shuttle supported at launch time?  It seems the tank
> would be too weak to support the weight of the whole rig.

Henry Spencer:
> No, the tank is strong enough.  It has to be.  From assembly to launch,
> the orbiter hangs on the side of the tank and the tank hangs between the
> two SRBs.  Only the bases of the SRBs are supported.  (In fact, the bases
> of the SRBs are bolted to the mobile pad, using pad-mounted bolts and great
> big explosive nuts.  The nuts are blown at the same instant that the SRB
> igniters fire.)

thomas%mcvac23@udel.edu (tom):
> I assume that one of the reasons that shuttle's engines start before the
> solid boosters is to help counteract the tendency of the whole thing to
> fall on the orbiter's back?

Phil Jansen:

Actually, they start the main engines first because they can turn them off if
there's a problem.  This happened with the first aborted launch of Columbia.
There was a problem with one of the engines (the turbine driving it wasn't
developing enough pressure or something).

Only when you know all the main engines work do you light the SRBs -- once
those are on you have to launch since they can't be turned off.  Both
boosters had better start at the same time.

The abbreviated schedule is (sorry I don't remember the real T numbers):

T-5	Start the main engines in sequence.  Bring them up to full power.

	The shuttle rocks forward (pitches down) as thrust builds. 
	Eventually the shuttle pitches back to vertical from the springiness
	of the boosters, booster mounts, etc.

T+0	At the moment the shuttle is pointing vertically again, fire the
	explosive bolts and start the boosters.  You're leaving.

I think one of the explosive bolts failed to blow on one launch; it
got pulled off instead (a little extra damage to the pad that time).

Everyone, I recommend Space Academy (in Huntsville)!  I had a wonderful time
and learned a lot!

-- 
                          If you repeat things often enough, they become true.
Phil Jansen               If you repeat things often enough, they become true.
philj@tekig5.pen.tek.com  If you repeat things often enough, they become true.