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6:47 pm
January 11, 2010
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Rocket-To-The-Moon
| | Grand Forks, North Dakota, USA | |
| Member | posts 666 |
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Rocket-To-The-Moon said:
A brief tangent (related to the cabin atmosphere); I ran into an environmental systems engineer in some YouTube comments. I had him checkout the forums and he sounded interested, but so far it doesn't look like he has joined.
He just joined the forums, his username is maciejm.
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Main Workgroups: Propulsion & Spacecraft Engineering
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6:50 pm
January 11, 2010
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brmj
| | Rochester, New York, United States | |
| Member | posts 386 |
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Post edited 12:52 am – January 12, 2010 by brmj
Rocket-To-The-Moon said:
If the LMM tank(s) are sufficiently strong then they could be used as a structural component. My idea would be to have the tanks support compressive loads and then have tensioned cables to provide lateral and longitudinal support. Depending on the internal pressure of the tanks they should be quite sturdy.
You may be on to something. I'm not sure we'd even need the tensioned cables. A big, pressurized metal tank ought to be strong enough for the sort of accelerations our engines and RCS system could create. It might have a little more trouble with the launch acceleration, though, but there's no reason we couldn't have a frame to brace everything during launch so that we don't need to take that kind of structure to the moon and back.
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Main work groups: Propulsion (booster), Spacecraft Engineering, Computer Systems, Navigation and Guidance (software)
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8:06 pm
January 11, 2010
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Luke Maurits
| | Adelaide, Australia | |
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That's a really promising idea and we should investigate it (i.e. try to get the opinions of some real mechanical/structural engineers).
My only concerns would be:
- If the tank was insulated with something like foam, that would be quite vulnerable to micrometeoroid and spacjeunk impact.
- One side of the tank would catch a lot of sun, which is bad for cryogenic storage. We may have to line the foam insulation with something very light weight but highly reflective and preferable with poor thermal conductivity – such a material shouldn't be too hard to find, though.
Good idea, we are definitely starting to show the kind of creative and innovative thinking we will need to get the stack down to Falcon 9 mass!
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Main CLLARE workgroups: Mission Planning, Navigation and Guidance. I do maths, physics, C, Python and Java.
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7:04 am
January 12, 2010
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Luke Maurits
| | Adelaide, Australia | |
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Post edited 1:28 pm – January 12, 2010 by Luke Maurits
Another thought on reducing fuel requirements and hence total mass: Our lander delta-v budget has been copied exactly from Apollo, we may actually be able to decrease it. The bare minimum requirement (difference between 100km orbital velocity and zero) is around 1700 m/s, so total budget for ascent and descent is 3400 m/s. We have been banking so far on 4690 m/s, which is putting aside over 1000 m/s extra for maneuvering around to find a landing site, etc. If we plan our landing site and descent plan well enough we may be able to cut down on this considerably.
EDIT: Cutting our amount of "bonus" delta-v above the absolute minimum in half decreases our total stack mass by over 500kg, which is not to be sneezed at (although it's less than I expected).
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Main CLLARE workgroups: Mission Planning, Navigation and Guidance. I do maths, physics, C, Python and Java.
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8:38 am
January 12, 2010
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Luke Maurits
| | Adelaide, Australia | |
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| posts 1409 |
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Luke Maurits said:If we can get our…unfuelled PM down to 500 kg then we could just do this with a LOX/LCH4 engine and a Falcon 9.
Even this may be feasible! I've been reading up on the shuttle's Super Light Weight external tank. It stores 553,358 L of LOX and 1,497,440 L of hydrogen (side note: this is a LOX:H2 volume ratio of 0.3695, which is very close to the value of 0.3722 for the figures I calculated above, which is excellent! It suggests that a 6:1 ratio is good and that the Air Liquide gas encyclopedia is giving us usable values). This is about 100 times times more fuel than our LOX/H2 plans for and it has an empty mass of 26,500 kg. Gary Snyder has said to me in an email that, to a first approximation, a tank's mass if proportional to its volume, so a tank based on the shuttle tank design but carrying 1% of the propellant should have an empty mass of about 265 kg. Of course, that uses a few materials which may be a little exotic for us (Aluminium-Lithium alloys – not sure how much more these cost than plain old aluminium) but even if our tank is almost twice this figure we come in at under 500 kg. Of course, if we were to use methane (which is what we need an empty tank < 500 kg for) the tank would be even smaller (due to methane's much higher density) and hence lighter.
Maybe methane will be an option afterall!
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Main CLLARE workgroups: Mission Planning, Navigation and Guidance. I do maths, physics, C, Python and Java.
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4:19 pm
January 12, 2010
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Rocket-To-The-Moon
| | Grand Forks, North Dakota, USA | |
| Member | posts 666 |
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I'm not sure how well it would be able to hold cryogenic liquids, but a carbon fiber tank should be able to give us mass savings over pretty much any metal tank. There are plenty of aerospace companies that have the machines and autoclaves necessary to build carbon fiber aircraft fuselage sections so I would think that they could just as easily build a thick tank.
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Main Workgroups: Propulsion & Spacecraft Engineering
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4:38 pm
January 12, 2010
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Luke Maurits
| | Adelaide, Australia | |
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I have done a little reading on this. Right now, the general consensus seems to be that composite materials tanks are no good for cryo storage. There are a few companies working on special composites which will work but this is fairly new technology that is still being tested and is probably quite expensive. The technology may be mature enough for us to use by the time we are ready, but today it's probably not an option.
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Main CLLARE workgroups: Mission Planning, Navigation and Guidance. I do maths, physics, C, Python and Java.
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4:32 am
January 18, 2010
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Luke Maurits
| | Adelaide, Australia | |
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Getting back to the idea of the PM's tank being its own support structure: would we do this by making the tank cylindrical, or would we use a tank with hemispheres on the ends and then use some kind of light support frame at the ends to allow attachment to the OSM or the engine assembly?
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Main CLLARE workgroups: Mission Planning, Navigation and Guidance. I do maths, physics, C, Python and Java.
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9:37 am
January 19, 2010
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brmj
| | Rochester, New York, United States | |
| Member | posts 386 |
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I suspect we'd be best served by using hemispherical ends and a light frame, both because it would probably be less massive and because it is better for holding pressure.
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Main work groups: Propulsion (booster), Spacecraft Engineering, Computer Systems, Navigation and Guidance (software)
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7:38 pm
January 19, 2010
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Luke Maurits
| | Adelaide, Australia | |
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| posts 1409 |
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brmj said:I suspect we'd be best served by using hemispherical ends and a light frame, both because it would probably be less massive and because it is better for holding pressure.
Something like what can be seen in this Soviet lander? That looks more like a spherical tank than a "bullet" shaped tank, but the same concept applies.
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Main CLLARE workgroups: Mission Planning, Navigation and Guidance. I do maths, physics, C, Python and Java.
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1:56 pm
January 20, 2010
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brmj
| | Rochester, New York, United States | |
| Member | posts 386 |
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Main work groups: Propulsion (booster), Spacecraft Engineering, Computer Systems, Navigation and Guidance (software)
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7:09 pm
January 20, 2010
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Luke Maurits
| | Adelaide, Australia | |
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This approach is growing on me. If we had two "adaptors" (each a set of two rings with criss-crossing support beams between them, or something similar), each of which goes on one end of the tank (with one adaptor connecting to the CM-OSM and another to the engine block of the PM), with high tension cables between the inner rings of each adaptor holding the whole thing together then we can make arbitrarily long tanks and use otherwise identical components to make PM's of arbitrary delta-v capacity (we'll probably only need two, though – a TLI only version for circumlunar flights, and a TLI+LOI+TEI version for landing flights) – all that would have to change would be the cable lengths.
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Main CLLARE workgroups: Mission Planning, Navigation and Guidance. I do maths, physics, C, Python and Java.
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