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#160
by
TJL
on 19 Feb, 2007 19:45
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#161
by
Mark Dave
on 19 Feb, 2007 23:33
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Discovery's only remaining old look is on the inboard elevons. I don't even know how to reproduce that affect on the models I have.
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#162
by
hyper_snyper
on 20 Feb, 2007 14:36
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I have a kind of off the wall question. If you attach an SSME (or any engine for that matter) to a test stand and give it unlimited fuel and ox, how long can it last before it fails? What will fail first? I'm guessing overheating will get at it first. Thanks.
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#163
by
Jim
on 20 Feb, 2007 15:08
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pump bearings would wearout
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#164
by
joema
on 20 Feb, 2007 15:21
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All engines are different. By design, they have differing amounts of certified maximum firing time. They also differ in the amount of margin in each component between the certified maximum and ultimate failure point. Even a single engine -- the SSME -- varies based on the version of engine. The latest "block II" versions have improved turbopumps and other reliability enhancements.
http://www.pw.utc.com/vgn-ext-templating/v/index.jsp?vgnextrefresh=1&vgnextoid=75a0184c712de010VgnVCM100000c45a529fRCRDSince the SSME is designed for reuse it has a very long maximum total firing time. Normally the engine is inspected after each flight, so while the engine is certified for 20 or 50 flights, that assumes it's inspected and possibly refurbished after each 8.5 min firing.
In the hypothetical case of a ground test with unlimited propellant, the block II SSME enhancements would probably translate to a longer continuous firing time before ultimate failure (vs earlier SSME versions).
If run continuously to failure, it seems unlikely thermal or erosion problems in the engine itself would be the cause. Rather the turbopumps might fail in some way, as they normally require inspection and possibly some refurbishing (but not overhauling) after each flight. The turbopumps are highly stressed rotating turbomachinery spinning at 36,000 rpm, and producing about 75,000 shaft horsepower in the space of a trash can. My guess is a turbine blade would crack or a bearing fail before the engine combustion chamber, nozzle or associated plumbing would fail.
It's an interesting hypothetical exercise -- what if you took an F-1, RS-68, and SSME and ran them continuously to failure in a ground test. Which one would run the longest, and how long would that be? The SSME has the advantage of longest certified total running time, but it's not designed to run that long continuously, plus the chamber pressure and turbopumps are highly stressed relative to the other engines. While you're at it, may as well run a simple pressure-fed hypergolic engine like the OMS. Since it has no turbopumps, maybe it would win the "run 'till you blow" test.
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#165
by
Antares
on 22 Feb, 2007 04:57
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When the STA is out flying around as it was tonight, are controllers on console in Houston simming as well?
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#166
by
MKremer
on 22 Feb, 2007 06:10
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joema - 20/2/2007 10:21 AM
...-- what if you took an F-1, RS-68, and SSME and ran them continuously to failure in a ground test. Which one would run the longest, and how long would that be? The SSME has the advantage of longest certified total running time, but it's not designed to run that long continuously, plus the chamber pressure and turbopumps are highly stressed relative to the other engines. While you're at it, may as well run a simple pressure-fed hypergolic engine like the OMS. Since it has no turbopumps, maybe it would win the "run 'till you blow" test.
Sorry, but you can't make any firm conclusions that way - you'd have to run at least a dozen of each for their entire burn in your scenario to just get some baseline data - since each engine is more-or-less hand-built with dozens of sub-contractor parts, there's more than too-many factors to evaluate to even begin to disrespect one engine design/constrution over another.
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#167
by
C5C6
on 23 Feb, 2007 12:00
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just a question: all that "emergency egress" systems including the slidewire basket and the armored personnel carrier, are they useful? I mean, obviously they are but, what event would require them? by the way, how much time would take to the crew to leave the orbiter without assistance?
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#168
by
geminy007
on 23 Feb, 2007 12:10
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they are required in the event, that the crew needs to get away form the pad quickly. Those events can range from anything in your phantasy leading to exposion of the entire stack on the pad (Hydrogen in explosive measures, short circuits, fire somewhere,..)!
And timing: Depends, but asap might be a good idea, there are more than 2000t of propellant ready to explode,... so I would hurry;-)
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#169
by
Jim
on 23 Feb, 2007 12:16
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Antares - 22/2/2007 12:57 AM
When the STA is out flying around as it was tonight, are controllers on console in Houston simming as well?
Not for the STA flights
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#170
by
STS-500Cmdr
on 23 Feb, 2007 15:58
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Somewhat in the vein of C5C6's Q--and about the White Room--i see when the closeout crew breaks down the White Room and pulls back that retaining section with the dock seal and tie it down--i wonder why they do that?? I assume its to protect that seal thing from the blast. The other thing is when they pull that section back and tie it down--theres a gap between the White Room and the hatch and the closeout guys hook up to the harnesses so they dont fall down thru that gap. Hows the crew suppose to get out of the vehicle in a hurry without falling through that gap between the WR and the ship's hatch and falling to their death on the MLP??
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#171
by
Jim
on 23 Feb, 2007 16:12
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STS-500Cmdr - 23/2/2007 11:58 AM
Somewhat in the vein of C5C6's Q--and about the White Room--i see when the closeout crew breaks down the White Room and pulls back that retaining section with the dock seal and tie it down--i wonder why they do that?? I assume its to protect that seal thing from the blast. The other thing is when they pull that section back and tie it down--theres a gap between the White Room and the hatch and the closeout guys hook up to the harnesses so they dont fall down thru that gap. Hows the crew suppose to get out of the vehicle in a hurry without falling through that gap between the WR and the ship's hatch and falling to their death on the MLP??
The gap is not that big.
Two things get folded away: 1. the "back" wall with opening to the orbiter with the dock seal. 2. Part of the "left" wall is folded back. The reason is for if there was a emergency egress after the OAA is retracted. The OAA would swing back to the service position. If the astronauts were a little jumpy, they might have the hatch open before the OAA is in place. If it weren't for these walls folded away, the whiteroom would slam into the hatch and the crew couldn't get out. The reason for the harness is the opening on the left side once the walls are folded. For a crew egressing, the open hatch blocks the opening, protecting the crew
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#172
by
TJL
on 24 Feb, 2007 19:49
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I have a question related to STS-5.
Any reason why all 4 crew members did not sit on the flight deck for launch and landing, as did the STS-6 crew?
Thank you.
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#173
by
Jim
on 24 Feb, 2007 20:14
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TJL - 24/2/2007 3:49 PM
I have a question related to STS-5.
Any reason why all 4 crew members did not sit on the flight deck for launch and landing, as did the STS-6 crew?
Thank you.
With the ejection seats on Columbia (which were taken out later), there wasn't enough room
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#174
by
shuttlefan
on 26 Feb, 2007 12:33
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When NASA tanks and then has to go into a 24-hour scrub turnaround for whatever reason, is it the same fuel that is loaded into the ET the next day?
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#175
by
DaveS
on 26 Feb, 2007 12:38
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shuttlefan - 26/2/2007 2:33 PM
When NASA tanks and then has to go into a 24-hour scrub turnaround for whatever reason, is it the same fuel that is loaded into the ET the next day?
Yes, except for the amount that has boiled off during the countdown prior to the scrub and start of draining activties.
Also please note that both fuel(LH2) and oxidizer(LOX) is loaded into the ET and both are drained from the ET and reused on subsequent launch attempts.
So to be really technically correct, you want to use the term "propellents".
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#176
by
nathan.moeller
on 26 Feb, 2007 12:38
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Jim - 24/2/2007 3:14 PM
TJL - 24/2/2007 3:49 PM
I have a question related to STS-5.
Any reason why all 4 crew members did not sit on the flight deck for launch and landing, as did the STS-6 crew?
Thank you.
With the ejection seats on Columbia (which were taken out later), there wasn't enough room
Jim, could you elaborate on the ejection seats and how they would have worked. I've always been very curious about this.
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#177
by
Jim
on 26 Feb, 2007 12:47
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nathan.moeller - 26/2/2007 8:38 AM
Jim - 24/2/2007 3:14 PM
TJL - 24/2/2007 3:49 PM
I have a question related to STS-5.
Any reason why all 4 crew members did not sit on the flight deck for launch and landing, as did the STS-6 crew?
Thank you.
With the ejection seats on Columbia (which were taken out later), there wasn't enough room
Jim, could you elaborate on the ejection seats and how they would have worked. I've always been very curious about this.
They were similar to "standard" ejection seats for high speed aircraft. They were 'usable" on ascent until 140K ft (mkirk knows the number) and also on descent. There was debate whether the seats could have cleared the SRB plumes
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#178
by
joema
on 26 Feb, 2007 13:15
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nathan.moeller - 26/2/2007 7:38 AM
...could you elaborate on the ejection seats and how they would have worked. I've always been very curious about this...
Columbia was equipped with modified SR-71 ejection seats
http://www.ejectionsite.com/sr1seat.htm for the first four missions. The astronauts wore pressure suits, I believe also derived from the SR-71 suits.
The theoretical ejection envelope extended from on the pad to (very roughly) about 120,000-140,000 ft and Mach 3.5, which occurred at about T+110 seconds. The "negative seats" call which indicated they were above the ejection envelope happened at about 120k ft.
On ascent the seats would be used similar to those in fighter planes or the Gemini spacecraft -- pull the handle and go. On descent the seats would be usable below about 120k ft, or roughly the same envelope.
Doubt has been expressed concerning how effective the seats would have been. However essentially the same seats and pressure suits have been proven in several successful SR-71 ejections, some from high Mach numbers and altitudes.
A potential problem is clearing the hot SRB plume. This is a function of several factors, including atmospheric drag on the ejected astronaut at altitude, seat ejection G force and time, acceleration/orientation of the vehicle stack, and whether a forward component exists in the rocket catapult. In general the ejected astronaut would be moving laterally at high acceleration, probably about 12 Gs, decelerating longitudinally based on atmospheric drag at given altitude & speed, while the vehicle continued accelerating upward. This gives a time period over which the seat trajectory must clear the cone-shaped SRB exhaust. There are many unknowns but simple calculations show it's possible to clear the plume, at least for some conditions.
The problem with seats is they take a lot of space, aren't really feasible for the entire crew, plus cover only a small fraction of the vehicle operating envelope. They're also full of explosives, so there's a small but finite risk of uncommanded operation, fire or other hazards while on orbit.
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#179
by
Austin
on 26 Feb, 2007 14:05
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joema - 26/2/2007 6:15 AM
The problem with seats is they take a lot of space, aren't really feasible for the entire crew
Indeed...as Henry Hartsfield once said, how would it make you feel if the captain and copilot on your next airline flight were wearing parachutes?! If it isn't possible to include ejection seats for the entire crew -- you don't include them for anyone.