-
#400 by Variable on 15 Aug, 2009 20:54
-
How many successive scrubs can the system handle?
Are these driven by the ET fill/drain cycles (limited number?) or something else?
2 when the ET is filled for both launch crew rest and MPS inspections.
ty Jim -
#401 by Aobrien on 16 Aug, 2009 14:23
-
Wow I just found out today that there had been launch aborts after Main Engine ignition. I was pretty amazed. I never hear about today.
Why were they having so many problems with the Main Engines cutting off? -
#402 by Jim on 16 Aug, 2009 14:25
-
Wow I just found out today that there had been launch aborts after Main Engine ignition. I was pretty amazed. I never hear about today.
Why were they having so many problems with the Main Engines cutting off?
Valves that weren't responding according to plans -
#403 by ChrisGebhardt on 16 Aug, 2009 17:20
-
Wow I just found out today that there had been launch aborts after Main Engine ignition. I was pretty amazed. I never hear about today.
Why were they having so many problems with the Main Engines cutting off?
Valves that weren't responding according to plans
And there have only been FIVE post-SSME ignition RSLS aborts in the 127 flight history of the Shuttle program.
And they weren't really having "so many problems." They just encountered times when one of the three engines on each of those five flights did not perform as it should in the initial fire-up and testing period. The system worked exactly as it should by initiating the aborts and safing the vehicle.
For what it's worth:
STS-41D (Discovery): 12th Shuttle Mission. 1st Flight OV-103 (Discovery). Launch attempt on June 26, 1984 aborted at T-6 seconds when the GPCs detected an anomaly in the orbiter's number three main engine. The abort marked the first time since Gemini 6A that a Manned Spacecraft experienced a shutdown of its engines just prior to launch.
STS-51F (Challenger): STS-51F was the 50th U.S. manned spaceflight. On July 12, 1985 the countdown was halted at T-3 seconds after main engine ignition when a malfunction of number two SSME coolant valve caused shutdown of all three main engines. Launch took place at July 29, 1985 at 5:00:00 p.m. EDT. Five minutes and 45 seconds into ascent, the number one main engine shut down prematurely due to a faulty high temperature sensor. To date, this has been the only in-flight main engine failure of the shuttle program. At about the same time, a second main engine almost shut down because of a similar problem, but this was observed and inhibited by a fast acting flight controller in Houston. The failed SSME resulted in an ATO trajectory.
STS-55 (Columbia): The launch attempt on March 22, 1993 was aborted automatically at T-3 seconds when computers detected an incomplete ignition of the number three SSME. The problem was traced to a leak in the liquid oxygen preburner check valve.
STS-51 (Discovery): On August 12, 1993, the count reached the T−3 second mark, at which point a shutdown was then triggered because of a faulty fuel flow sensor in one of the SSMEs.
STS-68 (Endeavour): Launch on August 18, 1994 was halted by a RSLS abort at T-1.9 seconds. The automatic abort was initiated by the onboard General Purpose Computers when the discharge temperature on MPS SSME Main Engine #3 High Pressure Oxidizer Turbopump (HPOT) exceeded its redline value. The HPOT typically operates at 28,120 rpm and boosts the liquid oxygen pressure from 422 to 4,300 psi (2.91 to 29.6 MPa). There are two sensor channels measuring temperature on the HPOT. The B channel indicated a redline condition while the other was near redline conditions. The temperature at shutdown was at 1563 degrees Rankine (868 K), while a normal HPOT discharge temperature is around 1403 °R (779 K). The readline limit to initiate a shutdown is at 1560 °R (867 K). This limit increases to 1760 °R (980 K) at T-1.3 seconds. -
#404 by SpaceCat on 17 Aug, 2009 04:36
-
When does an SRM become an SRB?
Is it a function of overall thrust percentage or a function of size of the unit... or something else? -
#405 by DaveS on 17 Aug, 2009 05:36
-
When does an SRM become an SRB?
Something else. SRM refers to the motor components only. SRB is the whole deal, both motor components and the non-motor components.
Is it a function of overall thrust percentage or a function of size of the unit... or something else? -
#406 by Longhorn John on 17 Aug, 2009 16:06
-
What would happen if the shuttle did not throttle down for MaxQ? LOV/C, or survivable, but part of the launch profile to ensure against problems?
-
#407 by Jorge on 17 Aug, 2009 17:21
-
What would happen if the shuttle did not throttle down for MaxQ? LOV/C, or survivable, but part of the launch profile to ensure against problems?
What's the failure mode that could cause all three engines to fail to throttle? If just one, I think you can continue. If all three, must be due to PASS software problem so the action would be to engage BFS.
Not an ascent expert, mkirk or Danny can fill in. -
#408 by Jim on 17 Aug, 2009 20:39
-
What would happen if the shuttle did not throttle down for MaxQ? LOV/C, or survivable, but part of the launch profile to ensure against problems?
The structure would be over stressed. -
#409 by Antares on 18 Aug, 2009 02:23
-
Yeah, but the wondrous FS=1.4 would solve that, right?
-
#410 by SpaceCat on 18 Aug, 2009 17:29
-
Thanks, Dave
What confused the nomenclature- to me anyway- is that the 'little guys' on Deltas & Atlases are typically referred to as SRM's; while the larger stacks on Shuttle & the big Titans (until phase out) were always called SRB's. -
#411 by Jim on 18 Aug, 2009 20:25
-
Thanks, Dave
What confused the nomenclature- to me anyway- is that the 'little guys' on Deltas & Atlases are typically referred to as SRM's; while the larger stacks on Shuttle & the big Titans (until phase out) were always called SRB's.
Titans used SRM's. SRB is an incorrect term for them -
#412 by edkyle99 on 18 Aug, 2009 20:50
-
When does an SRM become an SRB?
Is it a function of overall thrust percentage or a function of size of the unit... or something else?
"Something else" is probably the best answer!
A motor is a motor, no doubt about that, but try to find a precise definition of "booster".
In the old days of the space age, "booster" could have meant the entire rocket! (The "Booster" controllers at JSC were in charge of all of the Saturn propulsion stages, for example. Atlas was a "booster" for Mercury, etc.) Over the years, the meaning shifted toward describing the propulsive unit or units that initially lifted the rocket from the pad. During the Shuttle era, "booster" more commonly described strap-on units, because NASA named its STS solids "Boosters".
Calling a strap on solid motor a "motor" is always correct. But spin-stabilized third stage solid motors are also "motors". So are solid motors used to separate stages, etc. "Booster" is not as clearly defined and is, as a result, only assuredly correct when the name is called out by the vehicle creator. Space Shuttle Solid Rocket Boosters may be the only "Solid Rocket Boosters", though other solid rocket motors can be said to "boost". The Titan Stage Zero motors were not called Boosters (upper case), but it may have been correct to call them boosters (lower case).
I have a headache now ...
- Ed Kyle -
#413 by Jim on 18 Aug, 2009 20:55
-
The nomenclature for the shuttle is as the following:
The SRM is component that ATK produces, the motor with the nozzle. It becomes a SRB when the aft skirt, IEA, aft attach hardware, forward attachment, recovery systems, jettison motors and nose cone are added.
Edit: Typo fixed -
#414 by jcm on 19 Aug, 2009 04:54
-
The nomenclature for the shuttle is as the following:
The SRM is component that ATK produces, the motor with the nozzle. It becomes a SRM when the aft skirt, IEA, aft attach hardware, forward attachment, recovery systems, jettison motors and nose cone are added
Typo there Jim - you meant to write "it becomes an SRB when...".
-
#415 by SpaceCat on 19 Aug, 2009 18:50
-
I have a headache now ...
I'm with you, Ed!
See, I wouldn't have asked this if a 12-year-old had not asked me first.
Thanks, guys- I see what you're saying;
I'll pass all this along to the 12-yr-old.
-
#416 by Longhorn John on 19 Aug, 2009 22:04
-
Thanks Jorge, Jim. Curveball question that seems better placed here than another thread, is John Shannon NASA or USA?
-
#417 by DaveS on 19 Aug, 2009 22:11
-
Thanks Jorge, Jim. Curveball question that seems better placed here than another thread, is John Shannon NASA or USA?
NASA. He's a former Flight Director and the FDs have always been NASA employees and not contractor engineers. So Leroy Cain is NASA as well. -
#418 by Danny Dot on 19 Aug, 2009 22:46
-
Thanks Jorge, Jim. Curveball question that seems better placed here than another thread, is John Shannon NASA or USA?
NASA. He's a former Flight Director and the FDs have always been NASA employees and not contractor engineers. So Leroy Cain is NASA as well.
Not to mention he is currently Head of the Shuttle Program Office. This is a very, very big Civil Servant job at NASA. NASA is blessed to have him and Leroy working there.
Danny Deger -
#419 by C5C6 on 20 Aug, 2009 16:00
-
what's the ascent witch list performed at T-11H & hold???
