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Post by ka9q on Jan 7, 2011 2:13:23 GMT -4
Yeah, with an ISP of 1000 sec you could easily do this with a single stage.
Would there be any advantage to staging with an unobtanium engine? What's the thrust-to-weight ratio of the engine itself? If I can't throttle them, can I have several smaller engines rather than one big one so I can shut some down early to limit g's?
The real fun is taking dynamic loading into account. What's the rocket's diameter and drag coefficient?
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Post by Glom on Jan 7, 2011 13:03:48 GMT -4
Oh yes forgot about that. Diameter is 6m and the drag coefficient is 1 (it's a pig!).
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Jan 7, 2011 14:11:57 GMT -4
I think a more interesting question is: can a SSTO 1000 ISP vehicle go all the way the way to Moon, land, and return? Here’s my estimate of the delta-v budget, based on Apollo, in m/s: Launch 9,000 TLI 3,150 LOI 900 Descent 2,050 Ascent 1,850 TEI 1,000 MCC 50 Total 18,000 I’m assuming the vehicle would make a Shuttle-like unpowered gliding landing. Based on the delta-v, the required mass ratio is 6.27, which is well within reach of a single-stage vehicle. In Glom’s scenario, we have a dry mass of 105,000 kg, so we require 553,350 kg of propellant, giving a total launch mass of 658,350 kg. For a Moon landing the engines would have to be throttleable, but even if they weren’t, this vehicle could still fly and meet Glom’s criteria. If the acceleration at burnout were the maximum 8g, than the thrust is 840,000 kgf (8,238 kN). This makes the liftoff thrust-to-weight ratio 1.28, which is adequate for launch. In reality, we’d probably have multiple engines, with some being shut down as propellant is consumed to reduce acceleration. There would also have to be some sort of throttleable engine(s) for fine control during the Moon landing.
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Post by ka9q on Jan 9, 2011 11:47:36 GMT -4
Wow. That's a pretty good illustration of the importance of Isp!
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Post by Kiwi on Jan 10, 2011 7:44:56 GMT -4
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Jan 15, 2011 17:07:40 GMT -4
I just uploaded the second installment to my web page: Part 2 – Technology. www.braeunig.us/space/race/part2.htmI’ve also decided to add a new part titled “Procedures”, which was originally going to be included in the technology section. The technology part now deals strictly with the hardware. The procedures part will describe an entire lunar landing mission from launch to recovery. The technology section intentionally omits any description of science experiments and cameras, as these items will be discussed in the “Science” and “Imagery” parts.
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Post by Ginnie on Jan 15, 2011 20:32:41 GMT -4
Nice work, Bob. I like how clean your layout is, and good illustrations.
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Post by theteacher on Jan 16, 2011 18:48:29 GMT -4
An amazing wealth of details. The Service Module..as it name implies... it -> its Thermal control...rejected to space by process of sublimation. Is it due to my lack of proficiency in English that I miss a "the" or an "a" before "process"? A "yes!" is ok :-) Propulsion systemAerozine 50 is explained here, but the name has been used previously. Reaction controlWouldn't it be appropriate to mention the propellant for the RCS? This is really great!
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Jan 16, 2011 19:36:13 GMT -4
An amazing wealth of details. I actually had a really hard time limiting my words to fit on a single slide - I could have easily written much more if I didn't constrain myself. Sometimes I had to split what was planned to be a single slide into two slides. I also kept thinking of new things to add, which was a pain because I had to renumber the slides and revise all the links. The words used are as they appear in NASA documents. I'll probably leave it as is (unless gillianren advises me otherwise ). Aerozine 50 was developed by Aerojet for the Titan missile. I'll try to add something about it in the Titan II slide. DONE - I also defined "hypergolic" I thought about that but not all the RCS used the same fuel (CM used MMH and SM & LM used Aerozine 50), and I was starting to running out of the room needed to explain it. Maybe I could just say something like "The RCS used hypergolic bi-propellant engines" without getting into specifics. DONE
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Post by theteacher on Jan 16, 2011 21:33:29 GMT -4
I actually had a really hard time limiting my words to fit on a single slide - I could have easily written much more if I didn't constrain myself. Yes. It must be a tough one. On the other hand it is a brilliant concept, as it guarantees the readability of the individual subjects. One gets an overview at a certain level. It's really interesting to follow your work. :-)
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Post by gillianren on Jan 17, 2011 2:02:52 GMT -4
I would leave the "a" out. "By a process of sublimation" is, frankly, unnecessary. There's only one, I thought. "The process of sublimation" is workable, but it isn't strictly necessary in technical documents. I'm doing my standard "try to think of a similar example with different words," but I've had a rough day. How about "by way of example"?
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Post by theteacher on Jan 17, 2011 12:25:46 GMT -4
I would leave the "a" out. "By a process of sublimation" is, frankly, unnecessary. There's only one, I thought. "The process of sublimation" is workable, but it isn't strictly necessary in technical documents. I'm doing my standard "try to think of a similar example with different words," but I've had a rough day. How about "by way of example"? Example accepted. Thank you :-) Edited for spelling!
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Jan 17, 2011 12:32:27 GMT -4
After weighing my options, I've decide by process of elimination to leave the wording as is.
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Post by gillianren on Jan 17, 2011 15:26:12 GMT -4
Thank you, Bob. That's a perfect example. And you're quite welcome, Theteacher.
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Post by theteacher on Jan 17, 2011 18:19:12 GMT -4
Thank you, Bob. That's a perfect example. And you're quite welcome, Theteacher. Damn! For this once I omitted the Spell Check. It looked kind of wrong, but I chose to ignore it. Thanks! :-)
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