psloss - 31/3/2006 8:55 PMOK, the ET diffuser "what ifs" have me wondering about elaborating on some countdown terms I've heard over the years, but never seen much discussion.First question: what's the difference between a Redundant Set Launch Sequencer (RSLS) hold and an RSLS abort? Is it the difference between a hold by the RSLS before or after main engine start? Or is there more to it than that?And second question has to do with the terms used in some of these cases over the years...for holds inside of T-31 seconds but prior to main engine start, I've heard the word "breakout" used in at least one case and "cutoff" used more often...is there any distinction between the two given the context? Or do they mean different things?Thanks,Philip Sloss
mkirk - 1/4/2006 10:33 AMI would have to know the context of your second question about "Brakeouts". I think you are referring to the GLS breakout points after T-31 seconds and these are just points where a specified GLS sequence would occur if the countdown is stopped. These are based on the vehicle's configuration at the "Cutoff" point.Mark Kirkman
Launch was delayed on Saturday, July 24, due to a problem with the right hand solid rocket booster (SRB). The ground launch sequencer detected an unacceptably slow speed rate of a hydraulic power unit located inside the shuttle's right hand solid rocket booster. The hydraulic power unit (HPU) was replaced and retested.
Jim - 1/4/2006 11:32 AMI have been on console and have heard the NTD request "GLS give cutoff". I don't remember all the details. What would happen after T-31sec that it would have to be a manual cutoff. It wasn't the range.
psloss - 1/4/2006 10:46 PMThat occurred memorably on STS-93 -- the 20 July 1999 attempt was stopped by manual call just before main engine start; in the background one can hear a call to "give cutoff," almost overlapped by the same request from the NTD. It was amazing, even considering all the practice, how quickly that happened, since it sounds like the initial call came in right around T-10 seconds.(Not sure what console, but it had to be MPS-related, since that was a spike in the hydrogen concentration in the aft compartment -- subsequently attributed to a sensor misreading.)
Mark Max Q - 1/4/2006 1:23 PMHow does the hand off to the orbiter for Auto Sequence Start happen?Does the orbiter pick up the count after the T-9:00 hold and thus be in alignment, ready for the T-31?
Chris Bergin - 1/4/2006 5:01 PMQuotepsloss - 1/4/2006 10:46 PMThat occurred memorably on STS-93 -- the 20 July 1999 attempt was stopped by manual call just before main engine start; in the background one can hear a call to "give cutoff," almost overlapped by the same request from the NTD. It was amazing, even considering all the practice, how quickly that happened, since it sounds like the initial call came in right around T-10 seconds.(Not sure what console, but it had to be MPS-related, since that was a spike in the hydrogen concentration in the aft compartment -- subsequently attributed to a sensor misreading.)And here's the video for that (first link)http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=442&start=1From the audio, you can hear something being said at T-9.5 seconds, with the "Cutoff, give cutoff....cutoff is given" through to T-7 seconds.
mkirk - 2/4/2006 1:05 PMThe proper call for a Cutoff is "CGLS, Give Cutoff". Both the GLS console operator and the NTD are spring loaded to respond to those words immediately. For that particular scrub the CHGD (hazardous gas detection system console) operator made a call "CGLS, Give Cutoff" and I believe what you here after that is the NTD echoing the command. CHGD had noticed a spike of 640 ppm in the Hydorgen concentration in the orbiter's aft compartment. This could be indicative of a fuel leack...as it turned out I believe they decided that it was bad data from the sensors and we could have launched with no problem...I will get into the problems on the actual launch when I have more time to review my notes and tapes.
mkirk - 2/4/2006 1:05 PMOne of the more recent times that I can recall would have been the STS-88 launch attempt. MCC and LCC were both looking at APU hydraulics data and while MCC cosidered it to be within limits the LCC needed more time to reach that conclusion. Holding at T-31, a go was finally given to pick up the count but by that time the short launch window had elapsed...by a couple of seconds as I recall. This meant we had used up our performance margin of availabel fuel in the external tank. MCC tracks this and immediately John Shannon the Flight Director called "NTD, Houston Flight, WE ARE NO GO FOR LAUNCH"...NTD responded with a Cutoff request. This was not an automatic cutoff because the hold time constraint of "LOX performace margin" is not a parameter that the GLS or RSLS would track.As I said in another thread...that launch scrub frightened us a little bit...you just don't want to run around with your hair on fire that late in a countdown. There were a lot of lesssons learned from the STS-88 launch attempt.
Davie OPF - 10/4/2006 5:26 PMI think that's Discovery, with her KU Band Antenna in OPF3.