Path: utzoo!linus!husc6!hao!scdpyr!djr
From: djr@scdpyr.UUCP (Dave Rowland)
Newsgroups: sci.space.shuttle
Subject: Re: General Question
Summary: SRBs produce 85% of the thrust.
Message-ID: <266@scdpyr.UUCP>
Date: 6 Feb 88 09:47:07 GMT
References: <3a106850.7011@apollo.uucp> <2954@cup.portal.com>
Organization: Natl Ctr Atmospheric Research, Boulder, CO
Lines: 50

In article <2954@cup.portal.com>, CaptainDave@cup.portal.com writes:
> Just a quick question to anyone who might have an answer.
> What is the thrust distribution in percent between the two SRBs
> and the shuttle's three engnes at the time they are all operating
> at maximum thrust. I know the shuttle can continue its launch
> with only two engines operating. I am only interested in percents
> but if you have the thrust values handy, I am sure others would be interested.


The SRBs produce roughly 85% of the thrust at liftoff.  The three SSMEs
produce 375,000 lbs. of thrust each and the two SRBs produce 3,300,000 lbs.
of thrust each for a total of 7,725,000 lbs. of thrust.  The SSMEs are not
operating at their maximum at liftoff.  The maximum used in flight is
104% of their rated thrust which is 393,800 lbs. of thrust.  At liftoff
the SSMEs are producing 100% of their rated thrust.


As far as engine failures are concerned, what happens depends upon
when the failure occurs.  If the the failure occurs before SRB ignition
they do a RSLS (Redundant Set Launch Sequencer) abort.  An RSLS abort
involves shutting down the engines and activating the fire suppression
system on the pad (basically). Good way to wash the orbiter ;-).
To my knowledge there has been one RSLS
abort, I think it was the Spacelab2 mission.  If the engine failure
occurs early on in the launch they perform a RTLS (Return To Launch
Site) abort.  Maybe someone else can furnish the details of this abort
all that I know is they jetison everything and land at the cape.
After RTLS comes a TLA abort (they land in Spain).  After TLA is no
longer an option, there is an AOA (Abort Once Around).  Again, I am
not sure of the specifics, but they make one orbit? and land at Edwards.
The last abort is ATO (Abort To Orbit).  During an ATO they do an OMS
dump and continue the mission at a lower than planned orbit.  The OMS
dump gets rid of some of the weight of the OMS fuel and adds an extra
12,000 lbs. of thrust.  Main Engine Cut Off is inhibited and the burn
time of the remaining two engines is extended until the fuel in the ET
is exhausted.  I think that there has been one ATO, and I think it
was the same mission as the RSLS abort.  The abort screwed up the
experiments on that mission because they were set up for a certain
orbit.  Two aborts on one mission!  I think someone was having a bad
day! :-)


(To any of you who have been to Space Camp:  Did they pull any of
these aborts on you?  When I went they did a RSLS abort and an ATO.
If any of you have Space Camp war stories, I would love to hear
them.   What went wrong during your missions?)
-- 
	"Hey laser lips, your momma was a snow blower!"
					  -- Number 5
	Dave Rowland  at NCAR Boulder, Colorado  djr@scdpyr.UUCP