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9:58 pm
January 18, 2010
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Luke Maurits
| | Adelaide, Australia | |
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Something we seem to have overlooked:
All our propellant mass calculations to date have suggested that the only way to get the lunar landing CLLARE stack on top of a Falcon 9 is to use LOX/LH2 to keep propellant mass down.
However, as far as I can ascertain, these propellants aren't self pressurising at all. If we want to avoid using turbopumps (which I fear would be the Kiss of Death for our low-tech low-cost approach) I think we are going to have to use an inert pressurant like helium to drive the LOX/LH2 into the combustion chamber. This means we need to take into account the mass of the pressurant and its tank(s), which we have not been doing.
I wouldn't even know where to begin on calculating how much pressurant we need for these purposes.
Is there another way around this? If we need a lot of pressurant this could really spoil things with regards to our Falcon 9 mass limit.
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Starting a new TA job next week, might be busy for a while! Main CLLARE workgroups: Mission Planning, Navigation and Guidance. I do maths, physics, C, Python and Java.
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11:46 pm
January 18, 2010
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brmj
| | Rochester, New York, United States | |
| Member | posts 352 |
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As far as I can tell, Hellium pressurant may be our only good option. Fortunately, it is pretty light and we won't need all that much of it. Here's a diagram of the Apollo LEM decent stage to give you an idea of just how little is needed. The helium tanks that are visible appear to be the only ones it had.
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Main work groups: Propulsion (booster), Spacecraft Engineering, Computer Systems, Navigation and Guidance (software)
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11:51 pm
January 18, 2010
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Luke Maurits
| | Adelaide, Australia | |
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Post edited 5:53 am – January 19, 2010 by Luke Maurits
Ah, good to know. I was a little worried that we'd overlooked what could be a significant source of mass.
I notice the tank is labelled "supercritical helium". I'm quite rusty on my thermodynamics / kinetic theory of matter. What's a supercritical state again? Is it difficult to get helium in this state and are there considerations with the tank?
EDIT: The Apollo LM used hypergolic propellants, not LOX or LH2, of course. Is there any reason to think this might change the required quantity of pressurant?
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Starting a new TA job next week, might be busy for a while! Main CLLARE workgroups: Mission Planning, Navigation and Guidance. I do maths, physics, C, Python and Java.
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12:07 am
January 19, 2010
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Luke Maurits
| | Adelaide, Australia | |
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This is actually quite relevant to our plan of using the PM's tank body as part of the PM structure. If there has to be helium stored behind the propellants then we'd need some kind of additional structure to house the tanks for it. Or could we have a second bulkhead in the tank, separating helium from one of the other propellants?
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Starting a new TA job next week, might be busy for a while! Main CLLARE workgroups: Mission Planning, Navigation and Guidance. I do maths, physics, C, Python and Java.
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12:40 am
January 19, 2010
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brmj
| | Rochester, New York, United States | |
| Member | posts 352 |
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Luke Maurits said:This is actually quite relevant to our plan of using the PM's tank body as part of the PM structure. If there has to be helium stored behind the propellants then we'd need some kind of additional structure to house the tanks for it. Or could we have a second bulkhead in the tank, separating helium from one of the other propellants?
I think having an additional bulkhead may be a bad idea. We might not even need enough helium for the bulkhead to be kept in a reasonable place. The additional tank(s) could be quite small, so it probably wouldn't be too hard to find a spot for them.
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Main work groups: Propulsion (booster), Spacecraft Engineering, Computer Systems, Navigation and Guidance (software)
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1:00 am
January 19, 2010
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brmj
| | Rochester, New York, United States | |
| Member | posts 352 |
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Luke Maurits said:
Ah, good to know. I was a little worried that we'd overlooked what could be a significant source of mass.
I notice the tank is labelled "supercritical helium". I'm quite rusty on my thermodynamics / kinetic theory of matter. What's a supercritical state again? Is it difficult to get helium in this state and are there considerations with the tank?
http://en.wikipedia.org/wiki/S…..ical_fluid
EDIT: The Apollo LM used hypergolic propellants, not LOX or LH2, of course. Is there any reason to think this might change the required quantity of pressurant?
I have no idea how this would affect that, but I do know that it is potentially feasible. This is what NASA intends to do for the decent stage of their next lander. http://en.wikipedia.org/wiki/A…..pacecraft)
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Main work groups: Propulsion (booster), Spacecraft Engineering, Computer Systems, Navigation and Guidance (software)
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1:04 am
January 19, 2010
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Luke Maurits
| | Adelaide, Australia | |
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| posts 1089 |
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"Both the cryogenic and hypergolic systems, like that of the Apollo LM, will be forced-fed using high-pressure helium, eliminating the need for malfunction-prone pumps utilized in most rocket technology."
Well, at least we know for sure it is feasible to use high-pressure helium for a LOX/LH2 engine. If the small, spherical tanks at the top of Altair are where they're storing it, then it looks like not a lot is needed.
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Starting a new TA job next week, might be busy for a while! Main CLLARE workgroups: Mission Planning, Navigation and Guidance. I do maths, physics, C, Python and Java.
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1:28 am
January 19, 2010
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brmj
| | Rochester, New York, United States | |
| Member | posts 352 |
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I suspect the tanks on the top are the fuel and oxidize tanks for the assent stage. I can't seem to find good information or diagrams for their design, unfortunately.
Thus far, I have been unable to turn up anything that indicates how much helium is necessary, but it shouldn't be all that much. Gases expand to fill all available space, so as long as we can establish enough pressure to force the liquids where they go, it will be fine. The helium isn't expended, just used to keep the tank filled, so it ought not to require too much. I'd do some quick calculations using values from Wolfram Alpha, but I'm just about dead tired right now. Maybe tomorrow morning.
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Main work groups: Propulsion (booster), Spacecraft Engineering, Computer Systems, Navigation and Guidance (software)
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1:34 am
January 19, 2010
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Luke Maurits
| | Adelaide, Australia | |
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| posts 1089 |
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No worries, it's not urgent. Get some sleep, we've already had a productive night with the back and forth on your new lander design elsewhere.
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Starting a new TA job next week, might be busy for a while! Main CLLARE workgroups: Mission Planning, Navigation and Guidance. I do maths, physics, C, Python and Java.
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