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#2060
by
Specifically-Impulsive
on 14 Jul, 2011 20:33
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Sorry if this is the wrong place to post this, but I have a question about the net mass of the MPLM cargo on this mission. The Flight Operations and Integration PDF on L2 lists the mass of the MPLM as 25,478 lbs up, and this page indicates that the empty mass of an MPLM is 9000 lbs, so the cargo should be 16,478 lbs. However this article says that the MPLM cargo came to 9,403 lbs. Where is the discrepancy?
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My documentation shows 26700 lbm total, 16008 cargo + packing material, 10692 net cargo.
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#2061
by
spacecane
on 14 Jul, 2011 22:09
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Why is the "neutral" thrust vector of the SSMEs angled relative to the stack? I've always wondered why they were set up to where they are sort of pushing the orbiter towards the ET. I assume that because of this the stack doesn't travel exactly in the direction the nose is pointing?
they are pointed at the CG of the stack.
So in that case is the direction of travel of the stack offset by an angle from the direction the nose is pointing? If so are the wings creating "lift" pulling the orbiter away from the ET (although definitly not nearly as strong as the engines are pushing towards the ET)?
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#2062
by
Specifically-Impulsive
on 15 Jul, 2011 01:32
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[/quote]
So in that case is the direction of travel of the stack offset by an angle from the direction the nose is pointing? If so are the wings creating "lift" pulling the orbiter away from the ET (although definitly not nearly as strong as the engines are pushing towards the ET)?
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If memory serves, the orbiter flies at a negative angle of attack during first stage specifically to keep the wings from generating lift. All steering and trajectory control comes from the SSME and SRB thrust vector control.
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#2063
by
elmarko
on 15 Jul, 2011 08:35
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Duh, of course.
I think I was getting confused with OMS, thanks
What happens after SRB and ET separation? It changes and so the orbiter has to make burns at a weird orientation?
Why is the "neutral" thrust vector of the SSMEs angled relative to the stack? I've always wondered why they were set up to where they are sort of pushing the orbiter towards the ET. I assume that because of this the stack doesn't travel exactly in the direction the nose is pointing?
they are pointed at the CG of the stack.
The SSMEs gimbal to handle the transient at SRB sep. If you watch the ET camera you can see that it's small and controllable, not a "weird orientation" at all.
ET sep is not an issue since MECO occurs before then.
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#2064
by
Mark Dave
on 15 Jul, 2011 19:23
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#2065
by
Zpoxy
on 20 Jul, 2011 02:00
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What is that tiny hole for on the Forward RCS? You see it in this photo http://upload.wikimedia.org/wikipedia/commons/8/8a/STS-135_Atlantis_port_side_view.jpg
And here with rectangular cover over it. Look to the upper left of the green access panel cover. http://upload.wikimedia.org/wikipedia/commons/3/38/STS-135_Atlantis_Ready_to_Roll.jpg
You see it between the edge of the FRCS module and the thruster nozzles.
It's a helium relief valve/burst disk overboard dump port for the FRCS fuel tank pressurization system. There is a mirror image port on the starboard side of the FRCS for the oxidizer tank system. And each OMS pod has two ports on the base heat shield arranged around the OMS engine cover. Again, one port for the fuel system and one for the oxidizer. The relief valve/burst disk assembly protects their systems from an overpressure caused by a failed pressure regulator.
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#2066
by
mgfitter
on 20 Jul, 2011 11:43
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I've got a strange question and wonder if anyone knows: As the ET drains during the flight, the forward sections of the tanks are no longer in direct contact with the cryogenic fluids. So how much of a temperature difference do those forward sections see by the time the vehicle reaches MECO? I would imagine that a significant temperature change might cause quite a bit of thermal stress on the fwd sections.
-MG
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#2067
by
DMeader
on 20 Jul, 2011 13:34
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I've got a strange question and wonder if anyone knows: As the ET drains during the flight, the forward sections of the tanks are no longer in direct contact with the cryogenic fluids. So how much of a temperature difference do those forward sections see by the time the vehicle reaches MECO? I would imagine that a significant temperature change might cause quite a bit of thermal stress on the fwd sections.
-MG
Not to mention the fact that, after main engine start, the ET tanks are pressurized with oxygen and hydrogen gas tapped off from the main engines. The hydrogen to pressurize the hydrogen tank comes from the flow that drives the LPFT turbopump which comes from the main combustion chamber cooling jacket. The oxygen tank is pressurized with gas from the heat exchanger in the HPOT turbine exhaust which comes from the oxidizer pre-burner. My point is, both of those sources produce what is probably pretty hot gas.
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#2068
by
Specifically-Impulsive
on 20 Jul, 2011 22:04
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I would imagine that a significant temperature change might cause quite a bit of thermal stress on the fwd sections.
-MG
It does and is suspected to contribute to the foam loss issues. Liquid air which collects in cracks or voids expands rapidly when the underlying aluminum heats up, and blows off chunks of foam - this is 'cryopumping'. Charts were shown at one of the MMTs during this mission with graphs of the fluid interface position vs time and how it correlated to foam loss.
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#2069
by
Mark Dave
on 20 Jul, 2011 22:38
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Does this helium dump port have a door to cover it? As it looks like a place heat could enter.
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#2070
by
Danny Dot
on 21 Jul, 2011 13:37
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So in that case is the direction of travel of the stack offset by an angle from the direction the nose is pointing? If so are the wings creating "lift" pulling the orbiter away from the ET (although definitly not nearly as strong as the engines are pushing towards the ET)?
[/quote]
If memory serves, the orbiter flies at a negative angle of attack during first stage specifically to keep the wings from generating lift. All steering and trajectory control comes from the SSME and SRB thrust vector control.
[/quote]
You are correct. It flies at about minus 4 degrees.
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#2071
by
padrat
on 21 Jul, 2011 14:37
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Here's a bit of perspective for you. During fueling, when the ECO sensors in the bottom of the LH2 tank go wet, it's still reading 70-80 degrees at the top of the LH2 tank. Quite a bit of distance between the two.
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#2072
by
iskyfly
on 22 Jul, 2011 14:21
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What will become of the sims?
Is the source code for the GPC's PASS available to the public? My limited knowledge of the GPC's is that their memory and storage space is significantly less than today's PC's (and that isn't to knock how great they are / specialized for flight) and that compared to today's software out there I'd imagine the source code wouldnt be as big. Also, since this isn't private sector (ala microsoft) and was paid for by tax dollars and not a national security secret (or is it?) I would think that it should be available?
Thanks
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#2073
by
JayP
on 22 Jul, 2011 14:28
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What will become of the sims?
Is the source code for the GPC's PASS available to the public? My limited knowledge of the GPC's is that their memory and storage space is significantly less than today's PC's (and that isn't to knock how great they are / specialized for flight) and that compared to today's software out there I'd imagine the source code wouldnt be as big. Also, since this isn't private sector (ala microsoft) and was paid for by tax dollars and not a national security secret (or is it?) I would think that it should be available?
Thanks
First, It very much is a national security secret. Any goverment sponsered sofware dealing with the guidence of rockets in flight is by definition.
Second, Even if the code was available, It's written in a unique language called HAL/S. You'd need a special compiler just to read it.
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#2074
by
Malderi
on 22 Jul, 2011 14:34
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The HAL/S source code is, if you're a programmer, not too difficult to figure out (at a high level, anyway). It was designed to be a readable language, for the 60's anyway, so that non-programmers like GNC guys can go read GNC code and make sure it does what they want it to.
But, you're absolutely correct that it will almost certainly never be released. The Apollo LM code is out there, though, all in assembly, just released a few years ago. If you ever see the PASS source code in public, it'll likely be a long time from now.
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#2075
by
iskyfly
on 22 Jul, 2011 17:54
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First, It very much is a national security secret. Any goverment sponsered sofware dealing with the guidence of rockets in flight is by definition.
Second, Even if the code was available, It's written in a unique language called HAL/S. You'd need a special compiler just to read it.
Just so I understand.
The shuttle launches, and goes through the roll program.
In all the documentation / resources on here- we don't know how the gimballing is commanded and how the computers maintain control? Thats the secret?
Ok, so redact anything to do with guidance. Or just leave out the launch and ascent. I'd be happy with re-entry and landing.
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#2076
by
Jim
on 22 Jul, 2011 18:12
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In all the documentation / resources on here- we don't know how the gimballing is commanded and how the computers maintain control? Thats the secret?
Ok, so redact anything to do with guidance. Or just leave out the launch and ascent. I'd be happy with re-entry and landing.
The issue is knowing what it does but how it does it.
Entry and landing is also guidance driven.
Entry control is also ITAR material.
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#2077
by
iskyfly
on 23 Jul, 2011 15:13
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#2078
by
DansSLK
on 23 Jul, 2011 20:22
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What will become of the sims?
Is the source code for the GPC's PASS available to the public? My limited knowledge of the GPC's is that their memory and storage space is significantly less than today's PC's (and that isn't to knock how great they are / specialized for flight) and that compared to today's software out there I'd imagine the source code wouldnt be as big. Also, since this isn't private sector (ala microsoft) and was paid for by tax dollars and not a national security secret (or is it?) I would think that it should be available?
Thanks
You'll find a plethora of HAL/S specifications online along with the entry guidance and PEG algorithms, including from NASA direct.
As for the source code itself, ITAR i'm afriad, illogical huh!
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#2079
by
Sesquipedalian
on 26 Jul, 2011 01:37
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Sorry if this is the wrong place to post this, but I have a question about the net mass of the MPLM cargo on this mission. The Flight Operations and Integration PDF on L2 lists the mass of the MPLM as 25,478 lbs up, and this page indicates that the empty mass of an MPLM is 9000 lbs, so the cargo should be 16,478 lbs. However this article says that the MPLM cargo came to 9,403 lbs. Where is the discrepancy?
My documentation shows 26700 lbm total, 16008 cargo + packing material, 10692 net cargo.
Thanks for the response and sorry for the delayed follow-up. This comes close, but it doesn't resolve the entire discrepancy, as there is still 1,289 pounds of difference between 10,692 and 9,403.
