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#500
by
Danny Dot
on 31 Aug, 2009 23:39
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Didn't we do this topic a few weeks ago? I was whining about how you'd cope with an underburn if you'd already targetted for a prebank or something like that.
It just came to me though it might have great utility in the remaining flights to help fill station to the brim with supplies. I am sure it gives about 800 pounds per flight -- for free. Why not do it?
Danny Deger
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#501
by
ChrisGebhardt
on 01 Sep, 2009 00:16
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Thank you all for your answers as to what a prebank is.
Now, just so I'm understanding this, what you're asking Danny is why not launch with 800 additional lbs of cargo that's not provided for under standard mission rules, burn extra OMS propellant during ascent to get you to orbit -- leaving you with insificiant fuel to do a standard OMS deorbit, then, at the end fo the mission (or AOA) you intentionally perform a D/O burn with an underburn and the prebank to get the Orbiter to E/I faster?
Wouldn't that carry a lot more risks than potential benefits?
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#502
by
Danny Dot
on 01 Sep, 2009 00:24
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Thank you all for your answers as to what a prebank is.
Now, just so I'm understanding this, what you're asking Danny is why not launch with 800 additional lbs of cargo that's not provided for under standard mission rules, burn extra OMS propellant during ascent to get you to orbit -- leaving you with insificiant fuel to do a standard OMS deorbit, then, at the end fo the mission (or AOA) you intentionally perform a D/O burn with an underburn and the prebank to get the Orbiter to E/I faster?
Wouldn't that carry a lot more risks than potential benefits?
You just don't carry the OMS prop up in the first place. The flight rules have lots of protection for reserves without the hip pocket reserves a planned pre-bank. For example you would probably still cover for both OMS engines failing and having to do the deorbit with RCS. Loss of an OMS tank while at station is probably loss of crew anyway. The scenario that extra 800 pounds would matter is basically nil.
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#503
by
Hungry4info3
on 01 Sep, 2009 14:01
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Loss of an OMS tank while at station is probably loss of crew anyway.
Why? Sudden thrust on the shuttle tearing it from the PMA resulting in ISS/STS depressurization?
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#504
by
Danny Dot
on 01 Sep, 2009 14:12
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Loss of an OMS tank while at station is probably loss of crew anyway.
Why? Sudden thrust on the shuttle tearing it from the PMA resulting in ISS/STS depressurization?
Not enough Delta V to do a survivable deoribit burn at station altitudes. Most shuttle missions are loss of crew for loss of OMS tank. And by loss of tank, I just mean the loss of ability to get the prop from a tank to either of the OMS engines or the 4 aft RCS jets. The shuttle is well designed to protect for this failure. About the only thing that could do this would be a design or manufacturing flaw in a tank weld. Even for a leak, you would burn it retrograde before it all leaked out.
Danny Deger
Edit, OMS tank leaks is one of the most fun things to throw at the control team during training an EVA session. Nothing like a potential loss of crew to wake them up. Just about everyone would get involved in the complex trade offs of when and how to burn. It is not just fun, it is great training for the team.
BTW, a flight ready mission control team is in my opinion one of the best examples of a finally tuned, ready for anything, group of people in the history of the world. This complement is coming from someone that use to train to fight WWIII for a living and has studied military history extensively. I used to consider it an honor to train them to the high state of readiness they
always achieved.
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#505
by
D.A.
on 01 Sep, 2009 19:02
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Been wondering this for a while:
Does the shuttle have the largest (by dimensions) payload capacity of all launch systems in use today? Wikipedia says it's 4.6m by 18m in size, how much of that can be used for a single payload?
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#506
by
Jim
on 01 Sep, 2009 19:10
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Been wondering this for a while:
Does the shuttle have the largest (by dimensions) payload capacity of all launch systems in use today? Wikipedia says it's 4.6m by 18m in size, how much of that can be used for a single payload?
No. It is 60 feet by 15 feet in diameter. All of it can used by a single payload.
Delta IV can have a longer fairing. Atlas V has a wider fairing.
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#507
by
Hungry4info3
on 01 Sep, 2009 21:33
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But if STS looses an OMS tank while at ISS, the crew can remain aboard ISS until the LON arrives. No LOC, right?
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#508
by
nooneofconsequence
on 01 Sep, 2009 21:37
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Ok. Danny's been talking of 60 degree alpha entry by the Shuttle.
I assume this means a rapid deceleration, instability, and low cross range entry profile.
1. Would it have made a difference to Columbia? Downsides?
2. Earlier Shuttle concepts had high angle entry with "belly flop" manuver. What were the limits of this high drag approach on TPS that caused it to go away?
3. RCC leading edge certainly takes more thermal load than the foamed glass bricks on the underside. But what about the heat capacity/ thermal distribution? Or do we still just melt aluminum too quickly, regardless of RCC hole size?
Thank you.
edit:
Anyone? Anyone? Bueller?
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#509
by
Jorge
on 01 Sep, 2009 21:39
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But if STS looses an OMS tank while at ISS, the crew can remain aboard ISS until the LON arrives. No LOC, right?
Not only is it not an LOC case, it is not even necessarily a CSCS/LON case. Prop fail will most likely start as a leak, not instantaneous failure of the tank. There is highly likely to be sufficient time for a joint expedited undocking/sep, followed by an orbit adjust burn using the leaking tank to lower perigee and decrease the prop cost of deorbit to within the capability of the good tank.
At least, that is how this case usually plays out when we sim it.
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#510
by
elmarko
on 01 Sep, 2009 23:11
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Re my whining about prebanks and underburn.
My point was that you use prebank as a backup option in case of an underburn. So if you've already targeted for a prebank scenario, and then you suffer an underburn, what do you do then? You can't prebank, because you've already targetted for an prebank.
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#511
by
Hobbs
on 01 Sep, 2009 23:20
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What is the whirring noise heard usually at about T-15 seconds? it sounds like what you'd expect the high-pressure turbos to sound like but this is much too early for them, so I can only guess its air being forced through the pipes and out of the nozzles as water runs through the sound suppresion system?
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#512
by
ChrisGebhardt
on 01 Sep, 2009 23:21
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What is the whirring noise heard usually at about T-15 seconds? it sounds like what you'd expect the high-pressure turbos to sound like but this is much too early for them, so I can only guess its air being forced through the pipes and out of the nozzles as water runs through the sound suppresion system?
The ROFI systems powering up.
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#513
by
ChrisGebhardt
on 01 Sep, 2009 23:23
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Re my whining about prebanks and underburn.
My point was that you use prebank as a backup option in case of an underburn. So if you've already targeted for a prebank scenario, and then you suffer an underburn, what do you do then? You can't prebank, because you've already targetted for an prebank.
That's what I'm thinking too. I know Danny's question was hypothetical, but I wouldn't expect NASA to plan for a pre-bank.
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#514
by
Hobbs
on 02 Sep, 2009 00:16
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Hmmm, what part of the ROFI's makes that noise?, from what I understand they are roman-candle type affairs which would be lit in the same way a model rocket would be (with a glow plug at the end of a wire), I cant see how this would make the distinct "revving" noise
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#515
by
Danny Dot
on 02 Sep, 2009 00:29
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What is the whirring noise heard usually at about T-15 seconds? it sounds like what you'd expect the high-pressure turbos to sound like but this is much too early for them, so I can only guess its air being forced through the pipes and out of the nozzles as water runs through the sound suppresion system?
The ROFI systems powering up.
I think it is the SRB's Aux Power Units powering up. And they are turbines.
Danny Deger
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#516
by
ChrisGebhardt
on 02 Sep, 2009 00:32
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What is the whirring noise heard usually at about T-15 seconds? it sounds like what you'd expect the high-pressure turbos to sound like but this is much too early for them, so I can only guess its air being forced through the pipes and out of the nozzles as water runs through the sound suppresion system?
The ROFI systems powering up.
I think it is the SRB's Aux Power Units powering up. And they are turbines.
Danny Deger
SRB HPU start is T-27secs with SRB nozzle steering checks at T-21secs
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#517
by
Danny Dot
on 02 Sep, 2009 00:36
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Re my whining about prebanks and underburn.
My point was that you use prebank as a backup option in case of an underburn. So if you've already targeted for a prebank scenario, and then you suffer an underburn, what do you do then? You can't prebank, because you've already targetted for an prebank.
That's what I'm thinking too. I know Danny's question was hypothetical, but I wouldn't expect NASA to plan for a pre-bank.
An underburn requires a failure of OMS propellant, not OMS engines. The shuttle routinely flies without protection for OMS propellant failures.
And if you plan for 90 and underburn, you recover with 180. And a targeted 90, with a recovery to 180 is the same temp profile as we have today with a 90 recovery.
It is fully allowed by the current flight rules and was approved without hesitation by Mr. Entry himself, Jon Harpold.
In my opinion the almost nil risk is very much worth getting several tons of supplies up to station. The current plan does not support ops without shuttle.
This extra upmass might make the difference between 6 and 3 man crew in the not too distant future.
Danny Deger
And I am not hypothetical. I recommend it be done for all remaining flights to station to get more supplies up there.
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#518
by
HarryM
on 02 Sep, 2009 00:57
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Ok. Danny's been talking of 60 degree alpha entry by the Shuttle.
I assume this means a rapid deceleration, instability, and low cross range entry profile.
1. Would it have made a difference to Columbia? Downsides?
2. Earlier Shuttle concepts had high angle entry with "belly flop" manuver. What were the limits of this high drag approach on TPS that caused it to go away?
3. RCC leading edge certainly takes more thermal load than the foamed glass bricks on the underside. But what about the heat capacity/ thermal distribution? Or do we still just melt aluminum too quickly, regardless of RCC hole size?
Thank you.
edit:
Anyone? Anyone? Bueller?
According to "The Space Shuttle Decision" it was the Air Force who really didn't like the belly-flop entry of the early Max Faget straight wing proposal, more to do with controllability than TPS.
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#519
by
Danny Dot
on 02 Sep, 2009 02:32
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Ok. Danny's been talking of 60 degree alpha entry by the Shuttle.
I assume this means a rapid deceleration, instability, and low cross range entry profile.
1. Would it have made a difference to Columbia? Downsides?
No change in deceleration. The shuttle would fly at a higher altitude to get the same amount of drag -- that is the whole point. The auto pilot is fully certified to fly at 60 alpha so no stability problems.
Cross range is reduced, but easily compensated for by landing opportunity selection, especially if you have days to plan the entry.
2. Earlier Shuttle concepts had high angle entry with "belly flop" manuver. What were the limits of this high drag approach on TPS that caused it to go away?
I don't understand the question exactly, but I hope this answers your question.
Maximum Lift over Drag is best cross range. For shuttle this is alpha 20. But the leading edge temperature is too high at alpha 20. Minimum heating is a maximum lift. This is 60 for the shuttle, but lift over drag is much less at 60 than 20. Alpha 40 is the lowest alpha to not over temp the RCC on the leading edge of the wings, so it was picked. But the autopilot was certified to 60 just in case this high alpha was ever needed for any reason.
3. RCC leading edge certainly takes more thermal load than the foamed glass bricks on the underside. But what about the heat capacity/ thermal distribution? Or do we still just melt aluminum too quickly, regardless of RCC hole size?
An alpha 60 entry certainly reduces both heat rate and total heat load a lot. But, in my opinion Columbia was probably hurt to bad to have been saved by this technique. But remember, NASA didn't know how bad Columbia was hurt. Given they didn't know, an alpha 60 entry should have been done in my opinion.
I learned all this when I trained astronauts how to do an approved "High Energy TAL", which is done at alpha 50. I would put the failure in to get the correct entry condition and have the crew do the procedure. The orbiter bug on the display showed us WAYYY past the max temp line on the entry display. I was concerned we were actually burning up, but the sim doesn't model heating anyway. I took a screen shot of the display and talked to the flight design guys about this. They confirmed I put the crew where they belonged, but because they were alpha 50 instead of 40 -- all was well. The reduction of heat at 50 was huge. 60 is even better.
As I said the shuttle is designed an certified to fly an alpha 60 entry. It only limits your landing opportunities.
Danny Deger