Shuttle Q&A Part 5

• #1660 by chriswaterrockets on 26 Feb, 2011 11:42
• Hi all,
  
  Before the launch of every shuttle there is some kind of gas exiting at the base of the main engines. (see picture) I wanted to know what exactly that is. I read somewhere that it is gaseous oxygen that is vented. Is that correct? If yes, what's the purpose?
  
  Thanks for your answers.
  
  chris

  ---

  
• #1661 by Jim on 26 Feb, 2011 11:45
•  It is to chill down the engines
• #1662 by chriswaterrockets on 26 Feb, 2011 11:51
• Ok, thanks, but isn't oxygen awfully corrosive, at least when liquid? Why don't they use the liquid hydrogen?
• #1663 by dsmillman on 26 Feb, 2011 12:16
• Quote from: chriswaterrockets on 26 Feb, 2011 11:51

  Ok, thanks, but isn't oxygen awfully corrosive, at least when liquid? Why don't they use the liquid hydrogen?
  

  They don't want hydrogen around the engines at SSME ignition.  If you watch a shuttle countdown you see the gaseous hydrogen around the SSME's is deliberately burned off just before the SSME's are ignited.
• #1664 by chriswaterrockets on 26 Feb, 2011 12:22
• Okay, thanks very much.
• #1665 by Jim on 26 Feb, 2011 12:26
• Quote from: chriswaterrockets on 26 Feb, 2011 11:51

  Ok, thanks, but isn't oxygen awfully corrosive, at least when liquid? Why don't they use the liquid hydrogen?
  

  
  flammable
• #1666 by sivodave on 26 Feb, 2011 22:26
• hi all.
  
  few questions about the TPS.
  
  1. in which way tiles, gap fillers and filler bars are removed?
  2. in which way tiles are repaired if there is for instance damage like scratches or gouges?
  
  thanks
  
  Davide
• #1667 by rbfnet on 27 Feb, 2011 03:10
• During the STS-133 countdown, I thought I heard that the limiting factor in how long the T-5 hold (for the range issue) could last was LOX drainback (rather than the end of the full 10 minute launch window) ... and that ultimately they got the count restarted with only 2 seconds of hold time left (again, LOX drainback limited).  But LOX replenish doesn't terminate until T-4:55, so they would have been replenishing during the hold ... so I would have expected a T-5 hold to be able to last up until the point where the resulting T-0 would be out of the 10 minute launch window.  Am I missing something?
• #1668 by wally on 27 Feb, 2011 09:56
• During STS-133 hatch closing
  Isn't there a No Step sign?
• #1669 by subisnack on 27 Feb, 2011 11:05
• Quote from: rbfnet on 27 Feb, 2011 03:10

  During the STS-133 countdown, I thought I heard that the limiting factor in how long the T-5 hold (for the range issue) could last was LOX drainback (rather than the end of the full 10 minute launch window) ... and that ultimately they got the count restarted with only 2 seconds of hold time left (again, LOX drainback limited).  But LOX replenish doesn't terminate until T-4:55, so they would have been replenishing during the hold ... so I would have expected a T-5 hold to be able to last up until the point where the resulting T-0 would be out of the 10 minute launch window.  Am I missing something?
  

  
  A few posts back there was a long conversation about this, starting here: http://forum.nasaspaceflight.com/index.php?topic=17437.msg697651#msg697651
  
  Also see here: http://forum.nasaspaceflight.com/index.php?topic=625.msg23596#msg23596
• #1670 by glanmor05 on 27 Feb, 2011 16:39
• Today the SSMRS had to get the OBSS out of the payload bay and hand it off to the Shuttle Arm.  Before docking the Shuttle Arm could get its own OBSS.  Was today just about clearance issues?
• #1671 by DaveS on 27 Feb, 2011 17:08
• Quote from: glanmor05 on 27 Feb, 2011 16:39

  Today the SSMRS had to get the OBSS out of the payload bay and hand it off to the Shuttle Arm.  Before docking the Shuttle Arm could get its own OBSS.  Was today just about clearance issues?
  

  More like interference issues. The SRMS can't reach the forward OBSS grapple fixture due PMA2/Node2 being in the way.
• #1672 by Jorge on 27 Feb, 2011 17:09
• Quote from: glanmor05 on 27 Feb, 2011 16:39

  Today the SSMRS had to get the OBSS out of the payload bay and hand it off to the Shuttle Arm.  Before docking the Shuttle Arm could get its own OBSS.  Was today just about clearance issues?
  

  
  Yes, specifically between the shuttle RMS and the JEM.
• #1673 by glanmor05 on 27 Feb, 2011 17:44
• Thank you!
• #1674 by sivodave on 27 Feb, 2011 17:55
• Quote from: sivodave

  hi all.
  
  few questions about the TPS.
  
  1. in which way tiles, gap fillers and filler bars are removed?
  2. in which way tiles are repaired if there is for instance damage like scratches or gouges?
  
  thanks

  
  Hi guys...nobody of you has any answer to my questions? I'm doing a research work about this subject and I'm curious to know the answers to these questions.
  
  thanks
  
  Davide
• #1675 by Gary on 27 Feb, 2011 19:22
• What's the difference between air to ground & space to ground and how does the 'big loop' actually work?
  
  Thanks.
• #1676 by Jorge on 27 Feb, 2011 19:34
• Quote from: Gary on 27 Feb, 2011 19:22

  What's the difference between air to ground & space to ground

  
  Terminology. A/G is used for shuttle and S/G is used for ISS.
  
  

  Quote

  and how does the 'big loop' actually work?
  

  
  Loops A/G 1 and S/G 1 are tied together so that transmissions on one loop are heard on the other. During free-flight the loops are tied using the UHF radios (SSOR on the shuttle and SSSR on ISS). During docked ops there is a hardline connection.
• #1677 by subisnack on 27 Feb, 2011 19:55
• Quote from: sivodave on 27 Feb, 2011 17:55

  Quote from: sivodave

  hi all.
  
  few questions about the TPS.
  
  1. in which way tiles, gap fillers and filler bars are removed?
  2. in which way tiles are repaired if there is for instance damage like scratches or gouges?
  
  thanks

  
  Hi guys...nobody of you has any answer to my questions? I'm doing a research work about this subject and I'm curious to know the answers to these questions.
  
  thanks
  
  Davide
  

  
  Don't give up. It's a weekend, and some of the folks who could accuratly answer are probably busy working STS-133.
• #1678 by JayP on 27 Feb, 2011 22:15
• Quote from: subisnack on 27 Feb, 2011 19:55

  Quote from: sivodave on 27 Feb, 2011 17:55

  Quote from: sivodave

  hi all.
  
  few questions about the TPS.
  
  1. in which way tiles, gap fillers and filler bars are removed?
  2. in which way tiles are repaired if there is for instance damage like scratches or gouges?
  
  thanks

  
  Hi guys...nobody of you has any answer to my questions? I'm doing a research work about this subject and I'm curious to know the answers to these questions.
  
  thanks
  
  Davide
  

  
  Don't give up. It's a weekend, and some of the folks who could accuratly answer are probably busy working STS-133.
  

  
  I basically asked the same as your question 1 a couple of weeks ago with no results. I have never seen any PR photos of the process either, so it may be somthing NASA feels is sensative and the people around here are respecting that.
  
  As far as your question 2, small dings and chips in the borosilicate glass coating of the tiles is repaired with a putty compound. That is what they did the other day durring Discovery's launch when they got a chip in one of the tiles when removing the protective sheets after closing the hatch. Normally they would coat the repair with a water-proofing compound (similar to 3M's scotchguard but a different formula), but they waived that this time.
  
  Good luck with your research.
• #1679 by jeff122670 on 27 Feb, 2011 23:52
• Saw the explanation of LOX drainback from Mark.
  
  Is there a document that explains that and other functions we routinely hear about?
  
  I looked around L2 and no luck.....
  
  thanks!!
  
  Jeff