Shuttle Questions Q & A (Part 4)

• #220 by Jorge on 07 Dec, 2007 16:44
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  pr1268 - 7/12/2007  11:37 AM
  
  

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  mkirk - 7/12/2007  11:27 AM  

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  SiameseCat - 7/12/2007  8:03 AM  If the launch has to be flown manually, will ET Sep and the -Z translation occur automatically, or will those also have to be manually commanded?

   If you happen to be flying CSS (control stick steering) on Ascent then you also have to take manual throttles which means you also have to manually command MECO.  ET Sep and the Minus Z Translation are automatic as long as the “MECO CONFIRMED” flag has been set in the software.  In other words the GPCs (General Purpose Computers) must recognize the fact that all of the main engines have been shut down.    In the case of a manual MECO the pressing of the three main engine pushbuttons located on the center console should be enough for this.  If the buttons aren’t working correctly (i.e. comm faulted) there are other options to “mode guidance” and set “MECO Confirmed” such as manually transitioning the flight software to OPS 104 by typing that in on the keyboards.  To answer your question they SHOULD occur automatically depending on the nature of the failure that caused you to take over manual flying in the first place.  Mark Kirkman

  I gather that controlling the Shuttle manually during ascent is very difficult, given the sheer speed of which events occur.  Can this be done?  Or has it been done on any previous mission?

  
  It is possible after T+90 seconds. Prior to that, wind shear can change too rapidly for the CDR to keep up. It has never been performed in flight but has been done frequently in sims.
  
  

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  A scene from the Ron Howard movie Apollo 13 where the astronauts perform a course correction maneuver without the computer's assistance seems to resonate in my mind right now... Any comments from the more-enlightened STS folks??
  

  
  The scene from the Apollo 13 movie grossly exaggerated the motion of the CSM/LM during the manual burn.
• #221 by Jim on 07 Dec, 2007 16:57
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  Jorge - 7/12/2007  12:44 PM
  
  
  It is possible after T+90 seconds. Prior to that, wind shear can change too rapidly for the CDR to keep up. It has never been performed in flight but has been done frequently in sims.
  
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  Doubtful that orbit still could be achieved.  Sims are one thing.
• #222 by pr1268 on 07 Dec, 2007 17:09
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  Jorge - 7/12/2007 11:44 AM The scene from the Apollo 13 movie grossly exaggerated the motion of the CSM/LM during the manual burn.

  
  Well, I suppose Ron Howard did need to spread out the drama evenly throughout the movie  Did that course correction actually take place?
  
  Slightly different topic:  I read somewhere a few months back that there was one STS mission whose entire re-entry and landing were done manually.  Any good links / pointers / info on that?  Thanks for satisfying my curiousity.
  
• #223 by mkirk on 07 Dec, 2007 17:39
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  pr1268 - 7/12/2007  11:37 AM
  
  I gather that controlling the Shuttle manually during ascent is very difficult, given the sheer speed of which events occur.  Can this be done?  Or has it been done on any previous mission?

  A scene from the Ron Howard movie Apollo 13 where the astronauts perform a course correction maneuver without the computer's assistance seems to resonate in my mind right now... Any comments from the more-enlightened STS folks??
  

  
  This answer is based solely on my personal experience in the SMS (shuttle mission simulator), training material, discussions with flown CDRs and PLTs, and word of mouth around the office.  I should also point out no-one has ever flown ascent manually.
  
  My Opinion:  The shuttle’s fight control system is very precise and I would characterize the manual flying task (i.e. with good guidance and no systems failure) as a piece of cake.  For ascent, on orbit, and entry it is very easy to get the orbiter to do what you want it to do.
  
  Generally I like to say that the orbiter pitches like a fighter (i.e. it is relatively sensitive in pitch) and rolls like a heavy airplane.
  
  Training Techniques and Flight Rules dictate that manual take over will not occur prior liftoff + 90 seconds.  This is because there is no mechanism or feedback within CSS to fly the shuttle through the “load relief“ region.  Load relief is when the flight controls are deflected in a manner that minimizes aerodynamic loading.  However, in the SMS, flying manually to MECO is no problem – you just follow the guidance needles and Trajectory Displays.
  
  Now having said that I should point out that any situation that is going to put you in a manual flying scenario on ascent is probably going to mean you have degraded performance, bad guidance, or worse and therefor the flying task will be much more complicated.
  
  Mark Kirkman
  
  
  
• #224 by SpikeSpiegel on 07 Dec, 2007 17:48
• The talk here has been all about the ECO sensors, and the problems with running out of fuel before MECO.  (thrashed turbos, loss of orbitor, ect)  Have they tested any of the SSME to see how lost of LOX or LH would damage the engines?  Pictures would be interesting.
  
  ~spike
• #225 by Jim on 07 Dec, 2007 18:14
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  SpikeSpiegel - 7/12/2007  1:48 PM
  
  The talk here has been all about the ECO sensors, and the problems with running out of fuel before MECO.  (thrashed turbos, loss of orbitor, ect)  Have they tested any of the SSME to see how lost of LOX or LH would damage the engines?  Pictures would be interesting.
  
  ~spike

  
  No speculation.  Fuel or Ox depletion shutdowns are bad for turbopump type of rocket engines
  
  A engine on a test stand in Santa Susana had a LH2 duct rupture.  One second there was an engine and the next it was gone.
  
• #226 by psloss on 07 Dec, 2007 18:19
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  Jim - 7/12/2007  2:14 PM
  
  No speculation.  Fuel or Ox depletion shutdowns are bad for turbopump type of rocket engines
  
  A engine on a test stand in Santa Susana had a LH2 duct rupture.  One second there was an engine and the next it was gone.
  

  What about the test stand?
  
• #227 by GLS on 07 Dec, 2007 18:38
• I've seen a pic of that in a PDF file... the engine (from the LPTPs discharge ducts down) ended up on the flame deflector/stone valey below the stand...
  If you run out of LH2, you won't have much of an engine afterwards because a LOX rich shutdown just *eats* the metal! It melts it like butter in a oven!
  LH2 rich shutdowns probably aren't that bad, but like Jim said TPs don't like to cavitate...
• #228 by Bejowawo on 07 Dec, 2007 19:00
• I knew that TPs don't really like cavitation - but how do the engines perform a nominal shutdown during MECO? I imagined they would just coast to a full stop after the LH2 and LOX vents are closed after throttling down the engines!
  
  Does anyone know how this really works?
• #229 by mainengine on 07 Dec, 2007 19:08
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  Bejowawo - 7/12/2007  9:00 PM
  
  I knew that TPs don't really like cavitation - but how do the engines perform a nominal shutdown during MECO? I imagined they would just coast to a full stop after the LH2 and LOX vents are closed after throttling down the engines!
  
  Does anyone know how this really works?

  
  You my have a look at the website of enginehistory.com and search for Mr. Bigg's article on the Main Engines. There is the explanation how it works.
  
  O.K. it is enginehistory.org
  see below
  
  Start and Shutdown sequence @ http://www.enginehistory.org/SSME/SSME3.pdf
• #230 by SpikeSpiegel on 07 Dec, 2007 19:38
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  mainengine - 7/12/2007  3:08 PM
  
  You my have a look at the website of enginehistory.com and search for Mr. Bigg's article on the Main Engines. There is the explanation how it works.

  
  Are you sure it isn't http://www.enginehistory.org ?
  
  specifically, this http://www.enginehistory.org/ssme.htm
  
  Very interesting stuff. thanks everyone.
• #231 by j2_ on 08 Dec, 2007 00:12
• Why are the LH2 ECO sensors in the tank, but the LOX sensors are in the in the orbiter feedline?
• #232 by Jim on 08 Dec, 2007 00:19
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  j2_ - 7/12/2007  8:12 PM
  
  Why are the LH2 ECO sensors in the tank, but the LOX sensors are in the in the orbiter feedline?

  
  The LOX tank is up on top and the feedline has some good LOX in it.  The LH2 tank is on the bottom and had no feedline so to speak
• #233 by j2_ on 08 Dec, 2007 01:10
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  Jim - 7/12/2007  5:19 PM
  
  

  Quote

  j2_ - 7/12/2007  8:12 PM
  
  Why are the LH2 ECO sensors in the tank, but the LOX sensors are in the in the orbiter feedline?

  
  The LOX tank is up on top and the feedline has some good LOX in it.  The LH2 tank is on the bottom and had no feedline so to speak

  
  The diagrams show the LOX ECO sensors on the orbiter side of the feedline, so why couldn't the LH2 sensors be put on the orbiter side as well. There's propellent in both of the orbiter side feedlines after tanking right? Why does the length of the tankside feedlines matter?
  
  It seems like there has to be a good reason for the LH2 ECO sensor to be in the tank, considering the added complexity of the interface between the orbiter in the tank makes this sensor more prone to failure.
• #234 by mkirk on 08 Dec, 2007 01:16
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  j2_ - 7/12/2007  8:10 PM
  
  

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  Jim - 7/12/2007  5:19 PM
  
  

  Quote

  j2_ - 7/12/2007  8:12 PM
  
  Why are the LH2 ECO sensors in the tank, but the LOX sensors are in the in the orbiter feedline?

  
  The LOX tank is up on top and the feedline has some good LOX in it.  The LH2 tank is on the bottom and had no feedline so to speak

  
  The diagrams show the LOX ECO sensors on the orbiter side of the feedline, so why couldn't the LH2 sensors be put on the orbiter side as well. There's propellent in both of the orbiter side feedlines after tanking right? Why does the length of the tankside feedlines matter?
  
  It seems like there has to be a good reason for the LH2 ECO sensor to be in the tank, considering the added complexity of the interface between the orbiter in the tank makes this sensor more prone to failure.

  
  Location is a function of relative density and flow rate for the propellants.
  
  Mark Kirkman
• #235 by cantuezel on 08 Dec, 2007 11:17
• Hi,
  
  on many landing videos at L2 - when the orbiter has come to a complete stop - CAPCOM says "No post landing DELTA required". What does that mean?
  
  Thanks in advance!
  
  Greetings
  
  Can
  
• #236 by DaveS on 08 Dec, 2007 11:23
• Actually the call is "we have not post-landing deltas, we'll meet on on page 5-3"
  Delta means change. In this case, they don't have any changes to the post-landing procedures portion of the ENTRY checklist.
• #237 by cantuezel on 08 Dec, 2007 13:49
• What could those changes (delta) might be for instance (examples, e.g. blown-tire/bad tiles etc.?)
• #238 by cantuezel on 08 Dec, 2007 13:53
• The shuttle communicates the most time of the flight via TDRS-technics.
  
  Is it nevertheless correct that at at the pre-launch countdown and even shortly after launch(?) communication runs via UHF?
  
  If so at which exact points (MET) the voice-communication switches from UHF to TDRS at launch and backward, during entry/approach procedure, from TDRS to UHF?
  
  Thanks!
  
  Greetings
  
  Can
  
• #239 by Jim on 08 Dec, 2007 14:09
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  cantuezel - 8/12/2007  9:49 AM
  
  What could those changes (delta) might be for instance (examples, e.g. blown-tire/bad tiles etc.?)

  
  It is for changes to deactivation procedures for turnaround etc