Shuttle Questions Q & A (Part 4)

• #540 by nathan.moeller on 10 Feb, 2008 21:21
• Quote

  Jim - 10/2/2008  4:06 PM
  
  

  Quote

  ntschke - 10/2/2008  4:56 PM
  
  That is what I thought...but found it hard to believe.  Basically we're talking about something the size of a passenger plane mounted to one side of a stack.  Are those bolts and SRBs THAT stable to be able to overcome that imbalance alone?

  Obviously yes, but still amazing.  Especially when considering it moves 3+ miles and up a ramp (which the MLP comepensates for)...

  
  Think harder (not being snotty).  What happens from T-6 sec to T-0?

  
  Ntschke - Jim's referring to main engine start and the ensuing twang that occurs.  The entire stack leans forward due to the 1.2 million lbs. of thrust being generated by the shuttle's main engines, so the bolts have to hold the stack down and keep it from tipping over.
• #541 by Lee Jay on 10 Feb, 2008 21:30
• Quote

  ntschke - 10/2/2008  2:56 PM
  
  

  Quote

  triddirt - 10/2/2008 3:50 PM

  Quote

  janmb - 10/2/2008 3:43 PM sorry if this as been covered before, but couldn't find anything like it... When standing on the pad, what is actually holding the shuttle stack (carrying the weight and keeping it stable)? Or put even more clearly, at which points is the shuttle components attached to the pad... Of all the thousands of great pad images I've seen, I've yet to see anything really covering this... The large gray clamps holding the shuttle are fairly apparent, but there's gotta be more weight transfer points than that?

  I'm sure this is in the Q/A somewhere.. The entire weight of the stack (including orbiter) is carried by the SRBs. What you have called clamps are in fact the tail service masts and do not carry any weight.. The SRB bolts are holding it all.

  That is what I thought...but found it hard to believe.  Basically we're talking about something the size of a passenger plane mounted to one side of a stack.  Are those bolts and SRBs THAT stable to be able to overcome that imbalance alone?

  Obviously yes, but still amazing.  Especially when considering it moves 3+ miles and up a ramp (which the MLP comepensates for)...

  
  Let's do a small amount of math, shall we?
  
  Look at this image (the large version will work best):
  
  http://mediaarchive.ksc.nasa.gov/detail.cfm?mediaid=34867
  
  Okay, look at the SRB aft skirt at the lower-left of the image.  You can see three of the four hold down posts (one is behind the SRB).  There are four on each, of course.
  
  A bolt is not designed to be a rigid element.  Rather, it's a spring, that applies a force between two surfaces.  In this case, that spring is a 3.5" diameter steel bolt.
  
  The following is all guesses since I don't know the real numbers.  Let's assume the distance between the bolts on the opposite side from the orbiter to the ones on the orbiter side is 4 meters.  Let's also assume these are good bolts and are pre-tentioned to 100,000psi.
  
  pi*(3.5/2)^2 * 100,000 = 962,000 pounds of clamp.  To be conservative, lets say they're each at 750,000 pounds.
  
  There are four of them on the side opposite the orbiter, two on each SRB.  So that's 4*750,000 pounds of force, or 3 million pounds holding them down, with a lever arm of 4 meters (I hate mixing units so this ends here).  That's 53.5 million N-m of resistance against overturning.
  
  Let's say the orbiter weighs 125,000kg and it's center-of-gravity is, say, 7 meters (remember, I'm making up these numbers so don't assume it's correct) from the center of the tank.  That's 8.6 million N-m of moment trying to tip over the stack - a mere 16% of the capability of the bolts!  (This explains why it doesn't really matter if my numbers are perfectly accurate - whether it's 10% or 25%, it's still way less that the bolts can take).
  
  In fact, as Jim points out, these have to take the bending applied by the SSME's lighting up, but I suspect that the driving load is a hurricane wind load against the stack (these things tend to happen in Florida).
  
  Bottom line - bolts are strong, and when they are widely-spaced they can take a MASSIVE moment.
• #542 by ntschke on 10 Feb, 2008 21:45
• Quote

  Jim - 10/2/2008 5:06 PM

  Quote

  ntschke - 10/2/2008 4:56 PM That is what I thought...but found it hard to believe. Basically we're talking about something the size of a passenger plane mounted to one side of a stack. Are those bolts and SRBs THAT stable to be able to overcome that imbalance alone?

   

  Obviously yes, but still amazing. Especially when considering it moves 3+ miles and up a ramp (which the MLP comepensates for)...

  Think harder (not being snotty). What happens from T-6 sec to T-0?

  Thanks Jim, I appreaciate that.  But up until T-6 sec the stack has been the same since the shuttle was mounted on there in the VAB right?  I know the twang tilts the stack forward and then back to verticle...THEN the bolts are blown and the SRBs ignite.

  The forward/backward push happens for 6 seconds, where as the stack remains the same from the VAB til launch. 

• #543 by ntschke on 10 Feb, 2008 21:51
• Quote

  Lee Jay - 10/2/2008 5:30 PM

  Quote

  ntschke - 10/2/2008 2:56 PM

  Quote

  triddirt - 10/2/2008 3:50 PM

  Quote

  janmb - 10/2/2008 3:43 PM sorry if this as been covered before, but couldn't find anything like it... When standing on the pad, what is actually holding the shuttle stack (carrying the weight and keeping it stable)? Or put even more clearly, at which points is the shuttle components attached to the pad... Of all the thousands of great pad images I've seen, I've yet to see anything really covering this... The large gray clamps holding the shuttle are fairly apparent, but there's gotta be more weight transfer points than that?

  I'm sure this is in the Q/A somewhere.. The entire weight of the stack (including orbiter) is carried by the SRBs. What you have called clamps are in fact the tail service masts and do not carry any weight.. The SRB bolts are holding it all.

  That is what I thought...but found it hard to believe. Basically we're talking about something the size of a passenger plane mounted to one side of a stack. Are those bolts and SRBs THAT stable to be able to overcome that imbalance alone?

  Obviously yes, but still amazing. Especially when considering it moves 3+ miles and up a ramp (which the MLP comepensates for)...

  Let's do a small amount of math, shall we? Look at this image (the large version will work best): http://mediaarchive.ksc.nasa.gov/detail.cfm?mediaid=34867 Okay, look at the SRB aft skirt at the lower-left of the image. You can see three of the four hold down posts (one is behind the SRB). There are four on each, of course. A bolt is not designed to be a rigid element. Rather, it's a spring, that applies a force between two surfaces. In this case, that spring is a 3.5" diameter steel bolt. The following is all guesses since I don't know the real numbers. Let's assume the distance between the bolts on the opposite side from the orbiter to the ones on the orbiter side is 4 meters. Let's also assume these are good bolts and are pre-tentioned to 100,000psi. pi*(3.5/2)^2 * 100,000 = 962,000 pounds of clamp. To be conservative, lets say they're each at 750,000 pounds. There are four of them on the side opposite the orbiter, two on each SRB. So that's 4*750,000 pounds of force, or 3 million pounds holding them down, with a lever arm of 4 meters (I hate mixing units so this ends here). That's 53.5 million N-m of resistance against overturning. Let's say the orbiter weighs 125,000kg and it's center-of-gravity is, say, 7 meters (remember, I'm making up these numbers so don't assume it's correct) from the center of the tank. That's 8.6 million N-m of moment trying to tip over the stack - a mere 16% of the capability of the bolts! (This explains why it doesn't really matter if my numbers are perfectly accurate - whether it's 10% or 25%, it's still way less that the bolts can take). In fact, as Jim points out, these have to take the bending applied by the SSME's lighting up, but I suspect that the driving load is a hurricane wind load against the stack (these things tend to happen in Florida). Bottom line - bolts are strong, and when they are widely-spaced they can take a MASSIVE moment.

  Thanks Lee Jay, I remember moments from a "while back" in structural engineering courses.   Makes sense,  still just seems LOOK like it should fall over, but after looking at your example I can see your point-especially since one has never fallen over.

  edit: One more thing, I take it these bolts aren't made in taiwan or available at Home Depot are they?  Cuz I could used them right NOW...lthe DC area is under a wind warning tonight, up to 60mph gusts.

  20 minutes ago my Directv Dish literally blew off the roof.  Serioulsly,  No NTV til I can get them to fix it or climb up there myself.  Dammit.

• #544 by Jim on 10 Feb, 2008 21:57
• Quote

  ntschke - 10/2/2008  5:45 PM
  
  

  Quote

  Jim - 10/2/2008 5:06 PM

  Quote

  ntschke - 10/2/2008 4:56 PM That is what I thought...but found it hard to believe. Basically we're talking about something the size of a passenger plane mounted to one side of a stack. Are those bolts and SRBs THAT stable to be able to overcome that imbalance alone?

  Obviously yes, but still amazing. Especially when considering it moves 3+ miles and up a ramp (which the MLP comepensates for)...

  Think harder (not being snotty). What happens from T-6 sec to T-0?

  Thanks Jim, I appreaciate that.  But up until T-6 sec the stack has been the same since the shuttle was mounted on there in the VAB right?  I know the twang tilts the stack forward and then back to verticle...THEN the bolts are blown and the SRBs ignite.

  The forward/backward push happens for 6 seconds, where as the stack remains the same from the VAB til launch.  

  
  But the moment on the SRB skirts is greater during the firing.   The duration the orbiter is cantilevered really doesn't matter  (1 hour or 1 year) that much especially in comparison to those 6 seconds
  
• #545 by Lee Jay on 10 Feb, 2008 21:58
• I suspect the pedigree of those bolts can be traced all the way back to where the iron was extracted from the ore.  Space-qualified bolts (and most everything else) are ridiculously expensive, mostly because every single step in the production process is tracked, and each process is tightly controlled and validated.  I don't know what they are, but it wouldn't surprise me if they are double vacuum-arc-remelted 10.9s or some such very high performance material.
• #546 by ntschke on 10 Feb, 2008 22:04
• Quote

  Jim - 10/2/2008 5:57 PM

  Quote

  ntschke - 10/2/2008 5:45 PM

  Quote

  Jim - 10/2/2008 5:06 PM

  Quote

  ntschke - 10/2/2008 4:56 PM That is what I thought...but found it hard to believe. Basically we're talking about something the size of a passenger plane mounted to one side of a stack. Are those bolts and SRBs THAT stable to be able to overcome that imbalance alone?

   

  Obviously yes, but still amazing. Especially when considering it moves 3+ miles and up a ramp (which the MLP comepensates for)...

  Think harder (not being snotty). What happens from T-6 sec to T-0?

  Thanks Jim, I appreaciate that. But up until T-6 sec the stack has been the same since the shuttle was mounted on there in the VAB right? I know the twang tilts the stack forward and then back to verticle...THEN the bolts are blown and the SRBs ignite.

  The forward/backward push happens for 6 seconds, where as the stack remains the same from the VAB til launch.

  But the moment on the SRB skirts is greater during the firing. The duration the orbiter is cantilevered really doesn't matter (1 hour or 1 year) that much especially in comparison to those 6 seconds

  Gotcha, now I see your point.  And thanks again.  Keep forgetting that the boosters are 12+ ft in dia (prob closer to 14 at the skirts between front and rear bolts?).

   

• #547 by MKremer on 11 Feb, 2008 05:52
• Quote

  ntschke - 10/2/2008  5:04 PM
  

  Gotcha, now I see your point.  And thanks again.  Keep forgetting that the boosters are 12+ ft in dia (prob closer to 14 at the skirts between front and rear bolts?).

  
  And they are large, thick flanges, with big 3" dia. bolts (and even larger nuts) at each aft skirt corner.
  
• #548 by janmb on 11 Feb, 2008 16:04
• Quote

  Jim - 3/11/2007  5:32 PM
  
  ZOE is not a generic term for loss of Ku coverage.  ZOE is a gap in Ku coverage that always resides over the Indian Ocean, where TDRS spacecraft are out of view of the ISS.  ZOE does not describe outages for the rest of the orbit.  
  
  KU coverage is not always available during orbits due to blockages from the ISS structure while the orbiter docked

  
  Small follow-up on this one...
  
  How come we have gaps in the ku coverage anymore at all, given the number of geo stationary satellites operational in this system? Fair enough, low earth orbit is quite low and produces line of sight issues, but still, the number of satellites considered I have a hard time seeing how gaps exist anymore at all...
• #549 by bobthemonkey on 11 Feb, 2008 16:10
• Some of it is structual issue blocking LOS. The TDRSS birds aren't just used for ISS/Shuttle - they support other missions as well, and there are only 8 active sats (well 9 if you count TDRS1 which is mostly for polar support now I believe)
• #550 by Jim on 11 Feb, 2008 16:26
• Quote

  janmb - 11/2/2008  12:04 PM
  
  

  Quote

  Jim - 3/11/2007  5:32 PM
  
  ZOE is not a generic term for loss of Ku coverage.  ZOE is a gap in Ku coverage that always resides over the Indian Ocean, where TDRS spacecraft are out of view of the ISS.  ZOE does not describe outages for the rest of the orbit.  
  
  KU coverage is not always available during orbits due to blockages from the ISS structure while the orbiter docked

  
  Small follow-up on this one...
  
  How come we have gaps in the ku coverage anymore at all, given the number of geo stationary satellites operational in this system? Fair enough, low earth orbit is quite low and produces line of sight issues, but still, the number of satellites considered I have a hard time seeing how gaps exist anymore at all...

  
  Also, not every satellite is assigned to the shuttle/ISS, only 3 or so.
  
  Structure still applies
• #551 by Danderman on 11 Feb, 2008 16:41
• The current Shuttle crew is conserving power to allow extension of the mission by an extra day or two. Whatever happened to the ISS to Shuttle power adapter? Why can't the crew simply hook up an  extension cord (or equivalent) from ISS to the Shuttle?
  
• #552 by Lee Jay on 11 Feb, 2008 16:43
• Quote

  Danderman - 11/2/2008  10:41 AM
  
  The current Shuttle crew is conserving power to allow extension of the mission by an extra day or two. Whatever happened to the ISS to Shuttle power adapter? Why can't the crew simply hook up an  extension cord (or equivalent) from ISS to the Shuttle?
  

  
  Atlantis doesn't have it.
• #553 by SpikeSpiegel on 11 Feb, 2008 20:55
• Since the OBSS has to be left on the ISS after Atlantis undocks, has it been modified to receive power from the SSRM?  I remember from STS-120 that there was some discussion about looseing heaters after the OBSS was handed off from the shuttle arm to the SSRM.
• #554 by psloss on 11 Feb, 2008 21:01
• Quote

  SpikeSpiegel - 11/2/2008  4:55 PM
  
  Since the OBSS has to be left on the ISS after Atlantis undocks, has it been modified to receive power from the SSRM?  I remember from STS-120 that there was some discussion about looseing heaters after the OBSS was handed off from the shuttle arm to the SSRM.

  This unit won't be left on the station; the one on the next flight (ISS-1J/A, STS-123, orbiter Endeavour) will be.
  
  Edit -- don't know if Chris has written an article on this yet.
  
• #555 by SpikeSpiegel on 11 Feb, 2008 22:27
• Probably found on L2. another reason for me to beg the wife to let me sign up!  (paying off all our debts in a year,  so we  don't blow alot of  extra money)
• #556 by JayJay on 12 Feb, 2008 13:33
• I've been meaning to ask this question since STS-118 landed and all those people were underneath inspecting the TPS.
  
  How hot are the various spots on the shuttle when it actually lands?  Its easy to find the max temps during entry.  I am more interested in the actual temps when the shuttle is sitting on the runway being safed and the astronauts do their walk-around.
  
  Thanks in advance!
• #557 by ntschke on 12 Feb, 2008 13:45

• Quote

  JayJay - 12/2/2008 9:33 AM I've been meaning to ask this question since STS-118 landed and all those people were underneath inspecting the TPS. How hot are the various spots on the shuttle when it actually lands? Its easy to find the max temps during entry. I am more interested in the actual temps when the shuttle is sitting on the runway being safed and the astronauts do their walk-around. Thanks in advance!

  I'd wait for one of the guys that really knows for a more accurate answer...

  But from my own experiments with a tile sample, I heated it to glowing red hot and was able to touch it in just a few seconds.  I'd imagine the tiles on the shuttle retain heat longer depending on thickness, location etc, but I think by walk-around time they're probably cool to the touch. 

  Experts?

• #558 by Jim on 12 Feb, 2008 13:49
• Quote

  JayJay - 12/2/2008  9:33 AM
  
  I've been meaning to ask this question since STS-118 landed and all those people were underneath inspecting the TPS.
  
  How hot are the various spots on the shuttle when it actually lands?  Its easy to find the max temps during entry.  I am more interested in the actual temps when the shuttle is sitting on the runway being safed and the astronauts do their walk-around.
  
  Thanks in advance!

  
  It isn't hot to the touch
• #559 by Lawntonlookirs on 12 Feb, 2008 14:21
• I know this question has been answered before, but I am not able to find it in the search.  How do you copy a picture from NASA TV and post it in the forum?  
  
  Another item, for someone new on the forum, the question and answere section is so big that it is hard to find a specific item although the information is very informative.