Path: utzoo!attcan!uunet!husc6!bloom-beacon!tut.cis.ohio-state.edu!mailrus!ames!pasteur!ucbvax!hplabs!hplabsb!dsmith
From: dsmith@hplabsb.UUCP (David Smith)
Newsgroups: sci.space.shuttle
Subject: Re: Orbiter/SRB separation
Message-ID: <4741@hplabsb.UUCP>
Date: 31 May 88 18:39:42 GMT
References: <1869@bigtex.uucp> <4706@hplabsb.UUCP> <1934@ssc-vax.UUCP> <478@uniq.UUCP>
Organization: Hewlett-Packard Laboratories
Lines: 45

In article <478@uniq.UUCP>, rjnoe@uniq.UUCP (Roger J. Noe) writes:
> In article <4712@hplabsb.UUCP>, dsmith@hplabsb.UUCP (David Smith) writes:
> > Thank you for the weight of the core (orbiter+ET).  Now let's look at
> > weights of the SRB's.  According to AW&ST, each SRB weighs 1.82 million
> > pounds empty, and is loaded with 1.11 million pounds of propellant (note 1).
> > Each SRB produces 3.3 million pounds of thrust at liftoff, "throttles" down
> 
> AW&ST said this?  My figures (which I admit are somewhat old, but at least
> they're ballpark correct) are 181000 lbs. for an inert SRB.  The amount of
> reactant looks about right; I show a gross liftoff weight of 1.287e6 lbs.
> But can that thrust be right?  I've got 2.67e6 lbs. sea-level thrust per
> SRB.

AW&ST said this in their coverage of Challenger's problem with the SRB,
Feb. 10, 1986, p.55.  If they messed up and slipped a decimal point on
the weight, it wasn't in final printing, as they spelled out "million".
Actually, I'd prefer to believe AW&ST made a mistake (it wouldn't be the
first) than that the SRB is such a stupid design (ahh, well, ...)

I'm less willing to believe they made a mistake on the thrust, since they
made a point about performance improvements introduced on the 8th shuttle
flight that raised liftoff thrust by 200,000 lb. from 3.1e6 to 3.3e6.

> Now back to the original question:
> > > In article <4706@hplabsb.UUCP>, dsmith@hplabsb.UUCP (David Smith) writes:
> > > > True, but since the orbiter is pushing forward on the tank, and not
> > > > vice-versa, might it be feasible to throttle down the SSME's to the
> > > > point that the loads are manageable?
> 
> The fact that the OV is exerting a net force on the ET is not the problem.
> Consider what would happen if you tried separating the orbiter vehicle
> from the rest of the system while everything's running.  First you have to 
> shut down the SSME's and disconnect the OV from the ET propellant lines.
> In that time, all the thrust is from the SRB's and both the ET and the OV
> are dead weight.

I had in mind chopping the attachments and fuel lines while the engines
were still running:  just let them shut down when the propellant in the
pipes runs out in a few seconds.

I have continued this topic as the devil's advocate, but will probably
not say more.

		David Smith
		HP Labs