Shuttle Questions Q and A

• #160 by psloss on 19 Dec, 2005 12:26
• Another way of putting it:  throttle up is a normal event; engine-failures are not normal.  The throttle up call is a "when" call -- when it is done, the call is made (the "negative return" call is another example).  The press calls are "if" calls -- if an engine fails now, you can continue.
  
  Philip Sloss
  
• #161 by Chris Bergin on 19 Dec, 2005 12:38
• You yourself are a great example of this - and now you're thinking "What the heck is he talking about"
  
  STS-51F is the video you kindly allowed us to use. On that, the call is for Challenger to "Press to ATO", in case they need to, in preparation of.
  
  Then you hear they have the centre engine down, which Houston reacts with "Challenger, Houston. Abort ATO".
  
  Best example I can think of.
  
  http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=713&start=1
• #162 by RoadRunner on 19 Dec, 2005 14:48
• Thanks to everyone for the responses.
  
  To Philip Sloss:
  Yep, I've been reading the 'andyzone' document. Although informative, 'press' wasn't really explained (at least not from what I've read so far and I've read up to and including RTLS aborts - I've tried flying a few of them - heck !!!).
  
  My 'press to throttle up' comment was a bit tongue in cheek. I was trying to point out that this word 'press' doesn't seem to be an instruction to literally press a button.
  
  Now, just to be clear on something you've said here:
  the throttle up call is  "go at throttle up" and is made after the engines have throttled up.
  
  The initial ground-to-air call 'go at throttle up', is made AFTER the engines have throttled back up (out of the throttle bucket).
  There is then an air-to-ground acknowledgement - "Roger, go at throttle up".
  
  This is what I understood from your post.
  As opposed to the ground-to-air call being made as an instruction to the crew to throttle up. The crew then throttle up and acknowledge air-to-ground, 'Roger, go at throttle up.'
  
  The throttle is controlled by the on-board flight computers, yes ? There would be no need for the INSTRUCTION, from ground-to-air: 'Throttle up'.
  
  I'm sorry if this sounds disjointed, but I just want to make sure that I am clear on that point, and that there is no ambiguity in my mind as to what that call means and when/why it's given - Not that my initial query has anything at all to do with that call, it was purely about the use/meaning of the word 'press'.
  
  Knowing that the SRBs are kicked off when their pressure drops below 50psi and that NASA have been known to use the term 'press' to refer to 'pressurization' ('Cabin re-press valve' and other such terms I've heard here and there), I thought that maybe 'press' in the context of the abort calls meant pressure (I'm no rocket-scientist).
  
  Thus, single engine press to ATO (for example) would mean that there is still enough pressure for one engine to deliver enough delta-V to achieve Abort-To-Orbit.
  
  I'd pretty much worked out that 'press' wasn't an instruction to press a button (although I had not totally ruled out the possibility that it may be) and besides the 'pressure' theory, I could not determine what else this word might mean.
  
  To RedSky:
  Aha. The added connotation... Yes, now that really does make sense... I should have realised that much sooner. Pressing on is just that little bit more than 'continuing' and does imply adversity.
  
  You had me hunting about in my previous posts..... and..... you are correct. When I wrote : Single engine press (on) to 104
  I should have written: Single engine press (on to) 104.
  I wasn't paying proper attention to what I was typing.
  The implication of 'to MECO' which has been dropped to abbreviate the call, makes sense.
  
  To Chris:
  I've downloaded the video to which you posted the link and I shall get stuck into that between making this post and my next job (it's now dark enough for me to fly (virtual) Discovery home ) .
  
  ----
  
  I'm sorry if I've caused some confusion as to exactly the point of my question, but it seems that the general concensus of opinion is that 'press' in the context of our abort calls means 'to press on' rather than 'press a button' or 'you have enough pressure'.
  
  I've heard those calls time and time again but was never quite sure what 'press' meant.
  
  So, unless anyone else contests this explanation and offers another explanation and/or reference, I'll consider my question answered and thank you all very much for your efforts.
  
  Thanks again, peeps.
  
  The RoadRunner..
  
• #163 by Flightstar on 19 Dec, 2005 15:06
• Quote

  RoadRunner - 19/12/2005  9:48 AM
  
  Now, just to be clear on something you've said here:
  the throttle up call is  "go at throttle up" and is made after the engines have throttled up.
  
  The initial ground-to-air call 'go at throttle up', is made AFTER the engines have throttled back up (out of the throttle bucket).
  There is then an air-to-ground acknowledgement - "Roger, go at throttle up".
  
  This is what I understood from your post.
  As opposed to the ground-to-air call being made as an instruction to the crew to throttle up. The crew then throttle up and acknowledge air-to-ground, 'Roger, go at throttle up.'
  
  The throttle is controlled by the on-board flight computers, yes ? There would be no need for the INSTRUCTION, from ground-to-air: 'Throttle up'.
  
  

  
  Yes. The Shuttle is flying herself. The Flight Computers are controllings the SSMEs telling them what they want, with the SSMEs then talking back to the flight computers, who chat and vote amongst themselves on how it's all going. It's all very clever, but I'm not a computer man. But imagine each SSME is a company employee of Shuttle Inc, and the Flight computers are a company board of Shuttle Inc. Each SSME person has to continually report to the Board, who hold the ultimate decision. If an SSME employee has a problem, they report to the board immediatly, who then vote amoungst themselves to make an instant decesion and order that SSME employee to do as they say.
  
  SSME employees can vote too, but I don't want to complicate this.
  
  The Pilot and Commander are literally sitting there reading those conversations through the readouts. Mission Control at JSC are seeing the same conversations via their readouts via the downlink.
  
  So the flight computers order the SSMEs to throttle down, and then throttle up. No one else is involved. What you hear is the astronaunts comfirming what they are reading and feeling. JSC see their readouts and call the Shuttle "Go" at Throttle Up is JSC confirming they are seeing it go to plan, and visa versa for the Crew confirming "Roger, Go at Throttle" (I confirm, we have throttled up).
  
  No buttons are pressed.
  
  Pre-Press is pre-pressurization.
  
  Press to ATO for example is the same as "Prepare....." and that does involve potential pressing of buttons, moving of switches. I will try and find you an image of the abort switche.
• #164 by psloss on 19 Dec, 2005 15:24
• Quote

  RoadRunner - 19/12/2005  10:48 AM
  
  The initial ground-to-air call 'go at throttle up', is made AFTER the engines have throttled back up (out of the throttle bucket).
  There is then an air-to-ground acknowledgement - "Roger, go at throttle up".
  
  This is what I understood from your post.
  As opposed to the ground-to-air call being made as an instruction to the crew to throttle up. The crew then throttle up and acknowledge air-to-ground, 'Roger, go at throttle up.'
  
  The throttle is controlled by the on-board flight computers, yes ? There would be no need for the INSTRUCTION, from ground-to-air: 'Throttle up'.
  
  I'm sorry if this sounds disjointed, but I just want to make sure that I am clear on that point, and that there is no ambiguity in my mind as to what that call means and when/why it's given - Not that my initial query has anything at all to do with that call, it was purely about the use/meaning of the word 'press'.

  The purpose for some of the calls differs and some calls have been added/deleted over the years.
  
  The "go at throttle up" call seems to me to be an informational call as well as a way to do a quick communications check -- similar to the crew-initiated "roll program" call after liftoff.  Assuming everything is working, both the crew and the ground are already aware that these things are happening or have happened.  At the same time everybody is busy, so I don't think anyone wants to be "chatty" during ascent.
  
  (During the first few test flights, there was an additional call -- "go at 40" [seconds].)
  
  Regarding "Pc < 50", that doesn't separate the boosters, it starts the separation sequence in the orbiter computers; from the Andy Zone reference:
  http://www.theandyzone.com/launchzone/stsasct1.htm
  
  

  Quote

  After load relief is complete, the shuttle flies the rest of the first stage guidance table...velocity, pitch, roll, yaw...over and over again until SRB Separation occurs, controlled by the SRB SEPARATION SEQUENCER.
  
  The SRB SEPARATION SEQUENCER runs during all of first stage. This software monitors pressure inside the solid rocket boosters. When the pressures on both SRB's fall below 50 psi, it initiates the SRB SEPARATION SEQUENCE that kicks the solids off the vehicle.  In case both chamber pressures don't come down (as they might not if sensors had failed), the software blows the solids loose anyway at 129.8 seconds mission elapsed time since the solids cannot physically burn that long.

  
  (During the first few flights, the crew made a "Pc < 50" call to the ground.)
  
  Philip Sloss
  
• #165 by RedSky on 19 Dec, 2005 16:15
• There's another informational call that I remember hearing shortly after SRB Sep:  "First stage performance: Nominal".
  Basically saying that as of SRB sep, the expected velocity is what is should be.  I  remember on one flight, however, hearing a "First stage performance: Low" call.  Apparently the SRB performance wasn't as good as expected.  Then hearing something like "expect future calls to be late".  Thus, becuse it wasn't quite as fast as is should have been going, the main engines would be firing longer, and the expected timings for the abort calls would not occur on time since they are also a function of velocity as well as altitude and location.
  
  
• #166 by Flightstar on 19 Dec, 2005 16:51
• Can you remember which launch that was? My mind isn't what it used to be in my old age. The SSMEs can only fire for as long as the ET allows prior to a MECO deterimed by the ECO sensors. APU assist helps. If it was too low a performance then an abort would be called.
• #167 by RedSky on 19 Dec, 2005 17:34
• Quote

  Flightstar - 19/12/2005  11:51 AM
  
  Can you remember which launch that was? My mind isn't what it used to be in my old age. The SSMEs can only fire for as long as the ET allows prior to a MECO deterimed by the ECO sensors. APU assist helps. If it was too low a performance then an abort would be called.

  
  Sorry, can't recall.  It was probably fairly early... before the Challenger accident.  I just recall hearing it and thinking... Oh?  Then the (CNN) former astronaut / commentator just mentioned casually that it must have been a slight underperformance in the SRBs., but wasn't anything that the main engines couldn't make up the difference  (obviously, or there would have been some form of notice of a possible abort call).  It wasn't the  "Abort ATO" of 51F.
  
• #168 by psloss on 19 Dec, 2005 17:38
• The first stage performance call has been made multiple times, though I can't recall it on a recent flight.  I'll see if I can find a couple for reference...
  
• #169 by psloss on 19 Dec, 2005 19:35
• The call itself has been shortened over time to just "performance nominal" or "performance low."  In reviewing a few launches -- which have PAO voice-over that might mute the sound -- I don't hear the call much after the ISS assembly flights start, though STS-88 itself did have it, as did others with the OMS assist, which I see referenced as being incorporated into the OI-26 flight software. (OI = "operational increment")
  
  In the handful of launches I quickly reviewed (most of which were after 1995), all I heard was "performance nominal," though it was a small sampling.
  
  Philip Sloss
  
• #170 by Stardust9906 on 19 Dec, 2005 20:44
• Quote

  Flightstar - 19/12/2005  5:51 PM
  
  Can you remember which launch that was? My mind isn't what it used to be in my old age. The SSMEs can only fire for as long as the ET allows prior to a MECO deterimed by the ECO sensors. APU assist helps. If it was too low a performance then an abort would be called.

  
  I happen to have a video of this one.  It was STS-41C
• #171 by Flightstar on 19 Dec, 2005 21:34
• Thanks I'll look for history. I'd also like to say I've no idea why I wrote APU assist!!!!! Explains why I'm on part-time work as I near retirement!
• #172 by psloss on 19 Dec, 2005 22:23
• Quote

  Flightstar - 19/12/2005  5:34 PM
  
  Thanks I'll look for history. I'd also like to say I've no idea why I wrote APU assist!!!!! Explains why I'm on part-time work as I near retirement!

  Well, I'll take "APU assist" for the mains over hydraulic lockup any day.
  
  Actually did a little more digging and found this relatively loquacious exchange on STS-5:
  
  Capcom (Bob Stewart): "Columbia, this is Houston, your first stage was low on performance this morning."
  CDR (Vance Brand): "OK, fine."
  
  Philip Sloss
  
• #173 by Shuttle Man on 19 Dec, 2005 22:55
• Vance Brand, now there's a name I'll instantly remember. That man was born to fly, I don't think there was a plane he couldn't master. That comment is a-typical of him. Missed out on Apollo, back up a number of times. Finally got the Apollo-Soyuz and then found his true space wings with the Shuttle. I know he commanded Columbia twice and he truely loved her. I remember him calling her "his mistress".
  
  Thanks for bringing back a warm memory.
• #174 by psloss on 19 Dec, 2005 23:34
• Hasten to add another FAQ reference is one for the sci.space.shuttle Usenet group (it's a bit old and predates the Columbia disaster):
  http://www.geocities.com/spaceshot2000/sss-faq.htm
  
  Also, this is a good "inside the MCC" article by Mr. Grabois:
  http://www.geocities.com/spaceshot2000/mcc.htm
  
  (Apologies again if I'm duplicating other posts here.)
  
  Philip Sloss
  
• #175 by NASA_Twix_JSC on 19 Dec, 2005 23:54
• Inside the MCC is dated, but a fantastic read, well worth reading for anyone interested. There is another FDO who's produced his own site, I'll ask to find out the URL.
• #176 by psloss on 19 Dec, 2005 23:58
• Not sure this is the person you're referring to, but Roger Balettie was also a regular s.s.s. contributor before STS-107...
  http://space.balettie.com/
  
• #177 by Chris Bergin on 20 Dec, 2005 00:09
• Did he stop because of Columbia? I ask as I've been meaning to mail him for a long long time, but wouldn't want to intrude if this is the case?
  
  This is also worth a mention: http://space.balettie.com/LastDay.html
  
  Says it all really.
• #178 by psloss on 20 Dec, 2005 00:25
• Quote

  Chris Bergin - 19/12/2005  8:09 PM
  
  Did he stop because of Columbia? I ask as I've been meaning to mail him for a long long time, but wouldn't want to intrude if this is the case?
  
  This is also worth a mention: http://space.balettie.com/LastDay.html
  
  Says it all really.

  I don't know; I stopped lurking in s.s.s. for a long time after 1 February 2003.  (It was bad enough the loonies in there before we lost Columbia; I thought the newsgroup was almost worthless for a while after that, with few exceptions.)  
  
  It should be fairly easy to search for his posts, though...
  
  Philip Sloss
  
• #179 by Mark Max Q on 20 Dec, 2005 01:26
• These are great links! I'm going to have square eyes by tonight.