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| Scifor Refugee |
 Posted: Thu Apr 10, 2008 12:09 pm Post subject: One-piece lunar ship launched from the space shuttle? |
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Forum Ph.D.
Joined: 02 May 2005
Posts: 947
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I've been reading lately about the new nuclear thermal engines that have been developed in the last 10 years or so. They have a specific impulse of around 980, and can be made to produce a thrust of around 14kN. Best of all, they only mass a few hundred kg, including the reactor housing and control systems. Google "MITEE nuclear engine" for cool details. With something like that, could you build a ship that's carried up in the shuttle, launched with a crew to the moon, lands, and then returns to low earth orbit?
The shuttle has a cargo capacity of about 24 tons. You need a velocity change of about 11km/sec to go from LEO to the moon's surface and back. With the kind of high specific impulse that these engines provide, you would only need a mass ratio of around 3.7, so our ship could be 7.5 tons empty and 24 tons full of fuel. You would only need two engines to lift off from the moon, but assume three so that you have a backup if one fails. All three together would probably be less than 1 ton. You would also need fuel tanks for your 16.5 tons of fuel, so call that another 1.5 tons. This leaves you with about 5 tons for the rest of the ship+crew+cargo. Not a lot, but the empty LEM from the Apollo missions was only something like 4.5 tons empty, and that included the mass of the engines and fuel tanks, so it seems doable. As a bonus, the engines can also provide electrical power during the flight.
It could be launched from the space shuttle and sent to the moon and back. The crew would need to transfer to some sort of earth-return vehicle for the trip back, probably by docking with the ISS. The ship stays in LEO, and if you want to make another trip you just send up another shuttle with 16.5 tons of fuel and some new crew, gas the thing back up, and make the trip again. You could imagine it being cycled with each shuttle trip bringing up a new crew+fuel and picking up the crew from the previous mission to bring them back to earth. |
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| kojax |
| Posted: Thu Apr 10, 2008 10:38 pm Post subject: |
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Forum Ph.D.
Joined: 27 Mar 2007
Posts: 713
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| I wonder what they use as propellant. I'm assuming the energy that throws out the propellant is generated by the nuclear process. You think they could scoop up some moon dust and use it as propellant? |
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| Scifor Refugee |
| Posted: Fri Apr 11, 2008 6:55 am Post subject: |
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Forum Ph.D.
Joined: 02 May 2005
Posts: 947
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| kojax wrote: |
| I wonder what they use as propellant. I'm assuming the energy that throws out the propellant is generated by the nuclear process. You think they could scoop up some moon dust and use it as propellant? |
Hydrogen is usually used because it gives the most change in velocity/mass of fuel. But you can use any gas - oxygen, CO2, whatever. |
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| UKDutyPaid |
| Posted: Sun Apr 13, 2008 8:42 am Post subject: |
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Forum Freshman
Joined: 13 Nov 2007
Posts: 77
Location: London
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This is an interesting idea, but what are you gaining by using the shuttle? surely firing a 24t ship into orbit on a rocket is a much more efficient way of doing it. As the shuttle itself would be surplus to requirement in such a mission, plus you limit yourself in size and weight. Hence why NASA are engineering the ares.
so what is your thinking behind using the shuttle? |
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| Scifor Refugee |
| Posted: Sun Apr 13, 2008 3:15 pm Post subject: |
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Forum Ph.D.
Joined: 02 May 2005
Posts: 947
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| UKDutyPaid wrote: |
This is an interesting idea, but what are you gaining by using the shuttle? surely firing a 24t ship into orbit on a rocket is a much more efficient way of doing it. As the shuttle itself would be surplus to requirement in such a mission, plus you limit yourself in size and weight. Hence why NASA are engineering the ares.
so what is your thinking behind using the shuttle? |
I'm assuming it's going to be reused. For each new mission you need to launch 16.5 tons of fuel (plus tankage), send up a new crew, and bring the old crew back down. The shuttle can do all that in one trip. If you used regular rockets, you would need to send up at least two - one with the fuel and one to launch some sort of manned vehicle to bring a new crew up/bring the old crew back down. This also leaves you with a few tons of leftover cargo space on the shuttle, so it could also bring supplies to the space station (where I assume the refueling and crew swap takes place). |
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| UKDutyPaid |
| Posted: Sun Apr 13, 2008 3:25 pm Post subject: |
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Forum Freshman
Joined: 13 Nov 2007
Posts: 77
Location: London
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| Your argument makes sense. Except for the fact the shuttle is dated and very expensive to operate. It is the basic reason it is coming to the end of it's lifetime. Things like the Jules Verne and Apolloa style re-entry capsules will replace it. Because these are cheaper and safer, yet equally effective. |
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