Shuttle Questions Q and A

• #460 by Ender0319 on 02 Mar, 2006 03:07
• On top of what was already mentioned, they had thought about going to more of a glass cockpit approach to the A8 panel where we operate the RMS but of course money ran out so we use the same old panel.  It works great but it is a bit dated.
  
  

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  Martin FL - 1/3/2006  7:52 PM
  
  Did the RMS area get an upgrade like the flight deck area with the glass cockpit?
• #461 by Crispy on 02 Mar, 2006 08:44
• If you to positively, absolutely have to be sure that you've given power to something, nothing tells it like actually moving a bit of metal with your fingers. Tapping a touch screen and having "abort system a-ok!" flash up wouldn't fill me with as much confidence as a nice big switch and a soothing green light (A heavy clunk and hum of power would be good too)
• #462 by Justin Space on 02 Mar, 2006 14:23
• There's a question in there somewhere!
  
  If the orbiter lost power to the computers, could she still be flown, like in the movie Space Cowboys?
• #463 by mkirk on 02 Mar, 2006 14:39
• Quote

  Justin Space - 2/3/2006  9:23 AM
  
  There's a question in there somewhere!
  
  If the orbiter lost power to the computers, could she still be flown, like in the movie Space Cowboys?

  
  
  Absolutely not...No way...it is not possible!
  
  Without the GPCs (genral purpose computers) there is no way to command thruster firings, or flight control movements, manage control system gains.  There is no way to calculate and interperate data from the Inertial Measurment Units, the rate gyros, accelerameters and about a couple dozen other major problems.  There would be no way for the movements of the control stick to be interpreted and acted upon by the flight control system.
  
  Here is a simple rule of thumb, if you don't have electrons from the fuel cells, or commanding/data from the GPCs, or hydrualics from the Auxlliary Power Units...you are going to have a really bad day.  That is why all of these systems have redundancy and fault tolerance built in...they are critical to flight.
  
  I saw that movie with a bunch of my NASA freinds...they filmed it at JSC/KSC in fact a couple of my freinds were extras in it...but we all had a good laugh at the no GPC landing that they managed to walk away from.
  
  Without the GPCs you might as well be riding in an empty soda can...they would both have about the same amount of flight control...just a useless hunk of aluminum.
  
  Mark
• #464 by Jim on 02 Mar, 2006 14:51
• Quote

  Justin Space - 2/3/2006  9:23 AMThere's a question in there somewhere!If the orbiter lost power to the computers, could she still be flown, like in the movie Space Cowboys?

  
  Never!!!  The shuttle requires the computers to translate the astronauts control inputs into control surface movements (there is a lot more going on that I am leaving out).  Also the shuttle is aerodynamically unstable in certain regimes and the computers keep it under control
  
• #465 by Jonesy STS on 02 Mar, 2006 14:58
• So much for what Clint Eastwood did in that film then. One OMS out, so a short de-orbit burn. Flips her over manually, then fires the front RCS to slow down enough for entry-interface. Then, holding on to the stick, he battles her (with TPS falling off in all directions) through re-entry.
  
  Thought that was, how does Wayne Hale say it? Undesirable, to say the least!
• #466 by mkirk on 02 Mar, 2006 15:08
• Quote

  Jonesy STS - 2/3/2006  9:58 AM
  
  So much for what Clint Eastwood did in that film then. One OMS out, so a short de-orbit burn. Flips her over manually, then fires the front RCS to slow down enough for entry-interface. Then, holding on to the stick, he battles her (with TPS falling off in all directions) through re-entry.
  
  Thought that was, how does Wayne Hale say it? Undesirable, to say the least!

  
  Actually there is a flip procedure that is trained for extensively.  So that part is actually possible.  De-orbit capablity is obviously critical so there are several options such as using only a single OMS engine, crossfeeding tanks/pods, using aft RCS, aft and forward RCS, and Pre-Bank (i.e. roll the shuttle to decrease lift to get down to the atmosphere quicker and thus build up drag to slow you down).
  
  Mark Kirkman
• #467 by psloss on 02 Mar, 2006 17:20
• This just randomly reminds me that (although it's not that unusual) they went to single engine OMS burns on STS-113 due to a leak that was indicated at the end of the OMS assist during the second stage of ascent; so the OMS-2 burn was done with one engine as I recall, which naturally just about doubled the duration of the burn.  I guess the flight rules were such that the only two-engine OMS burn they would do after that was for de-orbit -- but perhaps that was only given no further problems...
  
• #468 by Ben E on 02 Mar, 2006 20:21
• If the re-entry is primarily computer-controlled, do the astronauts have to worry about the old "too steep - burn up/too shallow - bounce off" problem demonstrated in the movie "Apollo 13"? Or is this exclusively governed by the computers?
• #469 by mkirk on 02 Mar, 2006 20:31
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  Ben E - 2/3/2006  3:21 PM
  
  If the re-entry is primarily computer-controlled, do the astronauts have to worry about the old "too steep - burn up/too shallow - bounce off" problem demonstrated in the movie "Apollo 13"? Or is this exclusively governed by the computers?

  
  
  If the deorbit burn goes as targeted and the orbiter is in the proper attitude then it won't be a problem.  If you do anything different then yes it could be an issue.
  
  Mark
• #470 by Jim on 02 Mar, 2006 20:38
• Quote

  Ben E - 2/3/2006  3:21 PMIf the re-entry is primarily computer-controlled, do the astronauts have to worry about the old "too steep - burn up/too shallow - bounce off" problem demonstrated in the movie "Apollo 13"? Or is this exclusively governed by the computers?

  
  Duration of the deorbit burn determines the angle.  Crew has some control over this (manual shut off or additional burn).   Can't bounce off since any burn is going to reduce the energy to less than orbital speed (Apollo was coming from the moon faster than orbital speed).   The main issue is maintaining the proper attitude and back angles to bleed off energy, yet keeping the vehicle within thermal limits.  Thrusters are used early in the entry when the dynamic pressure is low.  As q increases the RCS is used less and the aero surfaces more. 
  
  Hate to say it, but any loss of the critical systems mentioned earlier in the thread would result in some similar to what we have already seen.
  
• #471 by mkirk on 02 Mar, 2006 21:01
• Maybe I should expand on what I said a little more in light of what Jim just said.
  
  We have basically two categories of deobit burn targets, shallow and steep.  These are tradeoffs between the amount of velocity you can get rid of during the burn (i.e. Delta V) and how much you will have to loose during atmospheric flight thru aerodynamic drag.  A steep trajectory is hotter but for a shorter duration...shallow targets will result in less thermally severe trajectory intitially but you are exposed to high heat for a longer duration (slowly baking the orbiter).
  
  The burn itself can be flown in auto or manual.  For auto the crew configures the propellant valves to feed from the desired tanks (straightfeed, crossfeed, etc...) checks that the burn targets are correct, arms the engines, and maneuvers the orbiter to the correct burn attitude.  Burn attitude and duration will determine the entry trajectory.  At T-15 seconds to the burn, they press the EXEC (execute) button on the computer keyboard.  If EXEC is pressed then at T-0 the engines will fire.  The burn can be stopped if needed or a "downmode" can occur if the burn needs to be completed with the RCS for example.  There is a point in the burn called Safe HP (perigee altitude usually 80 to 85 nautical miles) where if you have a malfunction above this altitude then you can stop and evaluate the situation and try again later.  If you are below this altitude then you are commited to re-entry and your only alternatative is to manage RCS usage, flight controls, and ROLL/PITCH attitude in an effort to control drag.
  
  During the Burn the commander is responsible for monitoring attitude and flying manually if needed and the pilot monitors the health of the engines.
  
  Mark Kirkman
• #472 by Shuttle Scapegoat on 02 Mar, 2006 21:23
• How long does it take for the orbiter to start feeling gravity after the de-orbit burn and does it make you feel really sick when you've had no gravity for a couple of weeks?
  
  Something about them drinking salt water beforehand?
• #473 by mkirk on 02 Mar, 2006 21:34
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  Shuttle Scapegoat - 2/3/2006  4:23 PM
  
  How long does it take for the orbiter to start feeling gravity after the de-orbit burn and does it make you feel really sick when you've had no gravity for a couple of weeks?
  
  Something about them drinking salt water beforehand?

  
  The crew does fluid loading (with a salt water solution) prior to the deorbit burn in order to reduce the effects of gravity on blood pressure and heart rate.  They are supposed to drink a total of 16 ounces and 4 salt tablets in the hour before deorbit.  Tastes awful!
  
  The forces gradually start to build just after entry interface which occurs roughly 30+ minutes after the burn , they will increase to about 1.3 G and stay there for most of the entry.  Crews have said that a 1/4th G after being in zero G feels like pulling two Gs in a T-38.  So yes they do find it a little harder to do there job.
  
  Mark
• #474 by braddock on 03 Mar, 2006 11:29
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  mkirk - 2/3/2006  5:34 PM
  They are supposed to drink a total of 16 ounces and 4 salt tablets in the hour before deorbit.
  

  
  There must be an anticdote about that in the annals of STS history, but I'm afraid to ask.
  How long from deorbit to reentry to landing?
• #475 by Jim on 03 Mar, 2006 11:36
• Quote

  braddock - 3/3/2006  6:29 AM

  Quote

  mkirk - 2/3/2006  5:34 PMThey are supposed to drink a total of 16 ounces and 4 salt tablets in the hour before deorbit.

  There must be an anticdote about that in the annals of STS history, but I'm afraid to ask.How long from deorbit to reentry to landing?

  
  There are many, especially when the shuttle gets waved off a rev and they have to fluid load again. 
  
• #476 by Hotol on 03 Mar, 2006 12:49
• The idea of loading such horrible fluids takes some of the glamour out of it!
• #477 by Ben E on 03 Mar, 2006 14:51
• It's often been said that the deorbit burn is "irreversible". At what point does it become so? If an OMS deorbit burn is terminated partway through - perhaps due to some unforeseen problem - what are the chances that the orbiter could still remain in space?
• #478 by mkirk on 03 Mar, 2006 18:36
• Quote

  Ben E - 3/3/2006  9:51 AM
  
  It's often been said that the deorbit burn is "irreversible". At what point does it become so? If an OMS deorbit burn is terminated partway through - perhaps due to some unforeseen problem - what are the chances that the orbiter could still remain in space?

  
  During the Deorbit burn itself the crew checks the progress of the burn by looking at a display called "DEORBIT MANEUVER EXECUTE" which shows among other things the current orbit of the shuttle and the desired orbit after the burn (the burn target).  As the engines are firing the appogee altitude (highest point of the orbit) and perigee altitude (lowest point of the orbit) will change.  Since the deorbit burn is retrograde, meaning the engines are firing in the direction of flight, the velocity of the orbiter is decreased and the HP (perigee altitude) will decrease.
  
  Flight rules designate "Safe HP" as the point of no return for an orbiter during a burn.  Safe HP is defined as the lowest altitude that assures a safe orbit for the shuttle for at least 24 hours.  This is usually set at 80 to 85 nautical miles.  The orbiter theoretically could go lower and still be considered "in orbit" but aerodynamic and orbital mechanics factors would cause the orbit to decay.  So "Safe HP" is set at a value that gaurenties at least 24 hours so that trouble shooting can occur.
  
  So if a failure occurs prior to descending below "Safe HP" then the burn will be stopped and the crew and mission control will trouble shoot and come up with a new deorbit plan.  If the failure occurs after "Safe HP" then the crew will "downmode" to another configuration.  Options consist of trying to continue the burn on one engine, cross feeding propellants between the OMS tanks and/or using OMS propellant for the RCS engines, using the AFT RCS jets, using the AFT RCS and then "Flipping" the orbiter to use the Forward RCS jets, rolling the orbiter to a "Pre-Bank" attitude to minimize lift and get down into the atmosphere quicker, or redesignating to another landing site.  
  
  The redesignation option is only available for Edwards landings...for instance if you couldn't slow down quick enough to make Edwards you would "RE-DES" to Northrup at White Sands New Mexico.  Redesignating from a Kennedy landing is not an option since there is nothing farther down range except water.
  
  During the burn you will hear the call "Safe HP" on the loops and PAO usually points this out because it is a major milestone.
  
  Mark
• #479 by Seattle Dave on 03 Mar, 2006 21:14
• Excellent thread.
  
  Q) Why do they keep powering up and down the Orbiters even out of OMM periods. Such as Atlantis is powered down on the latest status report. Is Atlantis completely turned off and when on, is it a case of her computer screen displays all being on etc?