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#660
by
Chris Bergin
on 28 Jul, 2007 17:49
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And to add on to Jorge's post, we have a thread specific to STS-93, with videos and information pertaining to the ascent:
http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=442&start=1Attached is a short clip from the L2 video of the whole ride to MECO (with the LOX low level cut off and resulting underspeed), showing the faults being relayed on the MCC loop video.
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#661
by
Danny Dot
on 28 Jul, 2007 17:50
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Jorge - 28/7/2007 12:35 PM
snip
Jim is partially right and partially wrong. JURe is a real capability and there are flight rules and procedures governing it. However, whether it will be used (and whether it can save the crew) depends on circumstances. There is an internationally agreed-to minimum survivable altitude for ISS (150 n.mi., or 278 km), and under no circumstances would ISS be deboosted below that altitude in order to complete a JURe. So the answer to the survivability question depends on just how bad the shuttle's underperformance was (in other words, how early during the ascent did the SSME fail). In some cases, the magnitude of the OMS dump required to make up for the MPS underspeed may make it impossible for the orbiter to reach even 150 n.mi. In other cases, it may still be possible to reach 150 n.mi. but at the cost of giving up deorbit capability - and that means NASA would have to carefully weigh the risks of standalone repair/compromised entry vs JURe/CSCS/LON.
Does station carry anywhere close to enough fuel to drop to 150 NM and not deorbit due to drag -- before more fuel can be brought up? It must deorbit in a few days from 150 NM.
Danny Deger
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#662
by
Jorge
on 28 Jul, 2007 17:54
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spacemuppet - 28/7/2007 12:03 PM
What would happen if say before the shuttle even cleared the tower the entire autopilot system went down and the CDR had to assume manual control all the way to orbit? Is this theoretically possible and would he have anything to reference, anything to "aim for"? What about the roll? Is there an actual throttle lever in the cockpit? I assume that even if this is all possible the chances of living through it are slim and the chances of reaching a mission orbit are probably close to zero...(?)
It depends on what you mean by "entire". If all four PASS computers go down, the CDR engages the BFS and the BFS flies to orbit. If both PASS and BFS go down (highly remote, but then again I thought the same of the Russian computers on ISS until recently), the vehicle is lost. The CDR's stick inputs always go through the flight control software and if there is no flight software running, either PASS or BFS, then there is nothing to connect the stick inputs with the gimbal outputs needed to control flight.
If only PASS navigation and/or guidance is lost, but PASS flight control is still GO, a manual ascent is possible, but only after T+90 seconds. Flight Rules forbid manual control prior to T+90 seconds since it is thought to be impossible to manually fly the "load relief" portion of ascent - the CDR cannot react quickly enough to high-altitude wind shears. After T+90, the CDR can fly manually using cue cards. They are best-available pre-flight estimates and are a bit crude. Like Danny says, they will probably get the crew to a safe orbit but ISS rendezvous may not be possible.
BFS supports only automatic flight control during ascent.
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#663
by
Jorge
on 28 Jul, 2007 17:58
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Danny Dot - 28/7/2007 12:50 PM
Jorge - 28/7/2007 12:35 PM
snip
Jim is partially right and partially wrong. JURe is a real capability and there are flight rules and procedures governing it. However, whether it will be used (and whether it can save the crew) depends on circumstances. There is an internationally agreed-to minimum survivable altitude for ISS (150 n.mi., or 278 km), and under no circumstances would ISS be deboosted below that altitude in order to complete a JURe. So the answer to the survivability question depends on just how bad the shuttle's underperformance was (in other words, how early during the ascent did the SSME fail). In some cases, the magnitude of the OMS dump required to make up for the MPS underspeed may make it impossible for the orbiter to reach even 150 n.mi. In other cases, it may still be possible to reach 150 n.mi. but at the cost of giving up deorbit capability - and that means NASA would have to carefully weigh the risks of standalone repair/compromised entry vs JURe/CSCS/LON.
Does station carry anywhere close to enough fuel to drop to 150 NM and not deorbit due to drag -- before more fuel can be brought up? It must deorbit in a few days from 150 NM.
Danny Deger
Station has a truly prodigious fuel reserve right now - the FGB tanks are topped off by each Progress. It can survive at 150 n.mi. for about 90 days, I believe. Getting it back to nominal operating altitude would require a salvo of Progress launches (or one ATV launch).
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#664
by
Danny Dot
on 28 Jul, 2007 18:08
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Jorge - 28/7/2007 12:58 PM
snip
Station has a truly prodigious fuel reserve right now - the FGB tanks are topped off by each Progress. It can survive at 150 n.mi. for about 90 days, I believe. Getting it back to nominal operating altitude would require a salvo of Progress launches (or one ATV launch).
Is that 90 days AFTER it lowers its orbit to 150 to meet up with shuttle? It costs just a much to lower an orbit by 1NM as it costs to raise an orbit by 1NM.
Danny Deger
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#665
by
Jorge
on 28 Jul, 2007 18:24
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Danny Dot - 28/7/2007 1:08 PM
Jorge - 28/7/2007 12:58 PM
snip
Station has a truly prodigious fuel reserve right now - the FGB tanks are topped off by each Progress. It can survive at 150 n.mi. for about 90 days, I believe. Getting it back to nominal operating altitude would require a salvo of Progress launches (or one ATV launch).
Is that 90 days AFTER it lowers its orbit to 150 to meet up with shuttle?
That is my understanding.
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#666
by
spacemuppet
on 29 Jul, 2007 01:15
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How far can the shuttle translate in orbit with its OMS fuel? Meaning, how much of an altitude change can it do or how many orbit changes can it do before it reaches whatever NASA calls "bingo" "fuel?
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#667
by
mkirk
on 29 Jul, 2007 14:36
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spacemuppet - 28/7/2007 8:15 PM
How far can the shuttle translate in orbit with its OMS fuel? Meaning, how much of an altitude change can it do or how many orbit changes can it do before it reaches whatever NASA calls "bingo" "fuel?
Well as always it depends on the timing, weight (mass), and the situation. Typically by the time you get to flight day 2 with a space station flight (after all the ascent burns and an initial rendezvous burn such as the NC1) you generally have in the neighborhood of 450 to 500+ feet per second of delta V with the OMS engines. By the time you are in the space station orbit you have about 330 feet per second left in OMS delta V capability. These numbers do not take into account RCS capability.
A general rule of thumb is that 2 feet per second equates to a 1 nautical mile change in altitude for Hp (height/altitude of perigee). So you can do the math from there but remember you have to leave enough gas to come back down and de-orbit.
FYI: 1 nautical mile = 1.15 statute miles or 1.85 kilometers
Mark Kirkman
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#668
by
spacemuppet
on 30 Jul, 2007 02:31
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How "deep" into space could the shuttle go if the entire payload bay was loaded with a huge OMS fuel tank? I know this would never happen, just a question for fum.
I do know there were at one point before 1986 plans for an upper stage, I believe they called it "Centaur" or something of the like.
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#669
by
Danny Dot
on 30 Jul, 2007 02:42
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spacemuppet - 29/7/2007 9:31 PM
How "deep" into space could the shuttle go if the entire payload bay was loaded with a huge OMS fuel tank? I know this would never happen, just a question for fum.
I do know there were at one point before 1986 plans for an upper stage, I believe they called it "Centaur" or something of the like.
If you put additional 50,000 lbs of OMS propellant, the shuttle might make it up to about a 650 NM orbit. Not that high.
Danny Deger
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#670
by
SpaceNutz SA
on 30 Jul, 2007 10:29
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In the context of the current leak problem on Endeavours crew compartment:
How relevant is a leak check done at sea level (1atm) to the conditions in space (pratically 0 atm)? If the compartment is simply pressurised to 2atm to give the same pressure difference it would have the same mathematical difference (1atm) but the differential would only be 2x (2atm/1atm) as opposed to space (1atm/0atm = inf).
I know from scuba diving that the pressure differential from surface to 10m is 1atm but 2x. From surface to 20m is 2atm but 3x ie for every 10m descent the ambient pressure rises by 1atm but the differential for each 10m descent becomes less noticeable the deep you go. This is why the most equalising of ears etc occurs in the forst 10m. Working this backwards - going into space is like the ascent in scuba diving - moving to a lower ambient pressure with the differential becoming more pronounced as you ascend - the last 10m being the highest pressure change.
Just wondering how all of this ties up with the pressure changes on the vehicle?
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#671
by
SpaceNutz SA
on 30 Jul, 2007 11:19
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Let me put my question in a less confusing manner:
A container filled to 2atm at sea level has double the pressure inside than outside.
A container filled to 1atm at an outside pressure of 0.5 atm is double the outside pressure.
A container filled to 1atm at an outside pressure of 0.25 atm is 4x the outside pressure.
A container filled to 1atm at an outside pressure of 0.01 atm is 100x the outside pressure - this is approaching (but not nearly close to) the condition of the orbiter in orbit.
How much pressure must the orbiter be exposed to at sea level for the leak check test to be relevant to conditions on orbit? What pressure is actually used for theleak check?
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#672
by
Jim
on 30 Jul, 2007 11:28
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spacemuppet - 29/7/2007 10:31 PM
How "deep" into space could the shuttle go if the entire payload bay was loaded with a huge OMS fuel tank? I know this would never happen, just a question for fum.
I do know there were at one point before 1986 plans for an upper stage, I believe they called it "Centaur" or something of the like.
Centaur was for spacecraft, not shuttle. There were other upperstages: IUS, TOS, PAM-D, PAM-D2,
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#673
by
Jim
on 30 Jul, 2007 11:30
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SpaceNutz SA - 30/7/2007 6:29 AM
Just wondering how all of this ties up with the pressure changes on the vehicle?
The cabin leak check doesn't use more than a few psi above ambient. It is not pressurized to 2 atm.
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#674
by
SpaceNutz SA
on 30 Jul, 2007 11:55
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Jim - 30/7/2007 1:30 PM SpaceNutz SA - 30/7/2007 6:29 AM Just wondering how all of this ties up with the pressure changes on the vehicle?
The cabin leak check doesn't use more than a few psi above ambient. It is not pressurized to 2 atm.
That doesn't seem to be a very good test IMHO. A capsule containing humans going into a virtually 0atm environment where the inside pressure is 100's if not 1000's of times greater which hasn't been tested at even 2x? Am I missing something here?
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#675
by
Jim
on 30 Jul, 2007 12:03
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SpaceNutz SA - 30/7/2007 7:55 AM
Jim - 30/7/2007 1:30 PM SpaceNutz SA - 30/7/2007 6:29 AM Just wondering how all of this ties up with the pressure changes on the vehicle?
The cabin leak check doesn't use more than a few psi above ambient. It is not pressurized to 2 atm.
That doesn't seem to be a very good test IMHO. A capsule containing humans going into a virtually 0atm environment where the inside pressure is 100's if not 1000's of times greater which hasn't been tested at even 2x? Am I missing something here?
leak testing is not a ratio, only a difference. This is not pressure testing
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#676
by
pippin
on 30 Jul, 2007 12:06
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Pressure testing is something different than a leak check, pressure testing checks whether the cabin can stand the pressure difference, leak checks test for (small) leaks.
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#677
by
henrycheck
on 30 Jul, 2007 13:14
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SpaceNutz SA - 30/7/2007 7:19 AM
Let me put my question in a less confusing manner:
A container filled to 2atm at sea level has double the pressure inside than outside.
A container filled to 1atm at an outside pressure of 0.5 atm is double the outside pressure.
A container filled to 1atm at an outside pressure of 0.25 atm is 4x the outside pressure.
A container filled to 1atm at an outside pressure of 0.01 atm is 100x the outside pressure - this is approaching (but not nearly close to) the condition of the orbiter in orbit.
How much pressure must the orbiter be exposed to at sea level for the leak check test to be relevant to conditions on orbit? What pressure is actually used for theleak check?
Presumably the on-orbit pressure differential is factored into the determination of the allowable sea level leak rate. On orbit the allowable crew cabin leak rate is likely greater than 0.022 psi per 4 hours, which is really a tiny leak rate.
1 / (0.022/4) = 182 hours to drop one psi.
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#678
by
Danny Dot
on 30 Jul, 2007 15:37
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Jim - 30/7/2007 6:28 AM
spacemuppet - 29/7/2007 10:31 PM
How "deep" into space could the shuttle go if the entire payload bay was loaded with a huge OMS fuel tank? I know this would never happen, just a question for fum.
I do know there were at one point before 1986 plans for an upper stage, I believe they called it "Centaur" or something of the like.
Centaur was for spacecraft, not shuttle. There were other upperstages: IUS, TOS, PAM-D, PAM-D2,
And it was canceled post Challenger for safety reasons. NASA thought a LOX/LH2 payload was too dangerous. If the shuttle had gone RTLS or TAL with a Centaur in the payload, it would have dumped the Centaur's fuel overboard while flying the abort. I used to work with a guy that was working the Centaur abort modes. He was VERY happy when they canceled Centaur on shuttle.
Danny Deger
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#679
by
brihath
on 30 Jul, 2007 16:14
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Danny Dot - 30/7/2007 11:37 AM
Jim - 30/7/2007 6:28 AM
spacemuppet - 29/7/2007 10:31 PM
How "deep" into space could the shuttle go if the entire payload bay was loaded with a huge OMS fuel tank? I know this would never happen, just a question for fum.
I do know there were at one point before 1986 plans for an upper stage, I believe they called it "Centaur" or something of the like.
Centaur was for spacecraft, not shuttle. There were other upperstages: IUS, TOS, PAM-D, PAM-D2,
And it was canceled post Challenger for safety reasons. NASA thought a LOX/LH2 payload was too dangerous. If the shuttle had gone RTLS or TAL with a Centaur in the payload, it would have dumped the Centaur's fuel overboard while flying the abort. I used to work with a guy that was working the Centaur abort modes. He was VERY happy when they canceled Centaur on shuttle.
Danny Deger
Yes, I remember that. I think the Centaur servicing arm to the fixed service structure was actually built. It was sitting near some other old tower components in the Industrial Area at the Cape. There were several Centaur missions manifested on shuttle. I think Galileo, ISPM were originally manifested for Centaur, then switched to IUS post Challenger. I wonder how the astronauts at the time felt about THAT idea- putting a potential bomb in the payload bay.