CaptainDave@cup.portal.com (02/05/88)
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.
djr@scdpyr.UUCP (Dave Rowland) (02/06/88)
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
henry@utzoo.uucp (Henry Spencer) (02/07/88)
> ... 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. Nothing happens until after the SRBs depart (essentially no abort is possible before then). Then they quite literally turn the whole assembly around and start decelerating. When they are heading back to the Cape at modest speed, they shut down main engines and jettison the tank. They then land at KSC. Probably the single biggest weather consideration for shuttle launches is whether the weather on the Cape is suitable for such a landing. (The Cape gets a lot of thunderstorms. The shuttle is nominally capable of a landing in essentially zero visibility, but nobody wants to try it.) As you might guess, this turn-around-and-decelerate business is something the astronauts aren't too enthusiastic about. -- Those who do not understand Unix are | Henry Spencer @ U of Toronto Zoology condemned to reinvent it, poorly. | {allegra,ihnp4,decvax,utai}!utzoo!henry
petej@phred.UUCP (Pete Jarvis) (02/11/88)
Henry, there is a procedure for SRB quick-disconnect from the stack. I'm told the sequence takes 3 seconds to actually disconnect them. Peter Jarvis.........Physio-Control......Redmond, Washington
marcus@illusion.UUCP (Marcus Hall) (02/13/88)
In article <2023@phred.UUCP> petej@phred.UUCP (Pete Jarvis) writes: >Henry, there is a procedure for SRB quick-disconnect from the stack. >I'm told the sequence takes 3 seconds to actually disconnect them. > >Peter Jarvis.........Physio-Control......Redmond, Washington You must be refering to the manual SRB separation control. This is supposed to fire the charges that separate the SRBs from the stack in case the automatic sequencer fails. Although I guess it is possible to hit this switch during SRB burn (there are precautions taken against doing this accidently!), such a separation is not in any of the abort sequences and would most likely result in one of both SRBs hitting the ET or orbiter on their own flight path (without guidance) as well as subject the ET to very high heat from their exhaust plumes. This is not considered to be a viable option. Marcus Hall ..!{ihnp4,mcdchg}!illusion!marcus
sheppard@convex.UUCP (02/14/88)
Yes, there is indeed a manual SRB separation switch in the shuttle. It's
actually two switches, one is an arm (enable) switch, the other is the
actual separation switch. Both are located on panel C3 (center, between
the commander/pilot seats), in a deeply recessed slot about where the
pilot's hand would be if he were resting it on the panel. It would be
quite difficult to perform a manual sep accidently.
Manual SRB sep is definitely NOT an option while the SRB's are still
burning. Since directional control for them comes from the shuttle itself,
once separated they could very likely cause the problem that we've already
seen. Of course, if the alternative is to lose an orbiter crew if it isn't
done, it probably can't hurt. What I don't know is if manual sep is locked
out until after SRB burnout...
Andy Sheppard
Convex Computer Corporation
{ihnp4,sun,uiucdcs}!convex!sheppardmjk@edison.GE.COM (Mark Kocher) (02/16/88)
In article <2954@cup.portal.com>, CaptainDave@cup.portal.com writes: > 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. "The Illustrated Encyclopedia of Space Technology" lists the SRBs at 5.3 Million pounds (combined) and the main engines at 1.41 Million pounds (combined).