Topic: Nuclear rockets to the moon?

[Nemesis]

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NASA could save billions of dollars in launch costs for its planned return to the Moon by using nuclear-powered rockets, a top scientist says

Carried out by university students funded by CSNR, the study examined the potential savings from incorporating nuclear power into NASA's Ares V, the launch vehicle being developed to haul heavy cargo, including parts for a lunar base, to the Moon.

Under this scenario, the Ares V would use ordinary chemical rockets to launch into Earth orbit, where it would dock with the Orion crew vehicle that would have launched on a separate Ares I rocket. In NASA's current plans, a second stage on the Ares V would then ignite to send the crew and cargo out of Earth orbit and towards the Moon. But in Howe's scenario, this Earth-departure stage would be nuclear-powered instead.

Howe envisions using a nuclear engine similar to one designed and tested in the 1960s called Nuclear Engine for Rocket Vehicle Application (NERVA). In the NASA-funded NERVA design, hydrogen gas is heated by nuclear reactions in a uranium reactor and expelled to produce thrust.

The higher efficiency of such an engine means almost 29 tonnes of cargo could be delivered to the Moon in a single Ares V launch, compared to 21 tonnes with the non-nuclear version. This would allow a 250-tonne lunar base to be constructed with only nine rather than 12 Ares V launches, Howe says.

NASA has not said how much each launch would cost, but Howe estimates it at $1.5 billion each. At this price, three fewer launches would save $4.5 billion. Previous work, including a NASA study, have suggested that it would cost only $2.5 to $3 billion to develop the nuclear rocket technology, so even with development costs, the nuclear option could still save NASA billions, Howe says.

One thing that I don't understand with this is why they wouldn't create a reusable engine module that stays in orbit.  A dockable fuel tank would seem much better than re launching a nuclear reactor for each of 9 trips. 

[Centurus]

One of these days we're gonna have to create an orbital manufacturing facility that can mass produce the parts we need for space stations.  But then that really wouldn't solve anything, cause the raw materials would still need to be shipped from the planet.

[Tus-XC]

One thing that I don't understand with this is why they wouldn't create a reusable engine module that stays in orbit.  A dockable fuel tank would seem much better than re launching a nuclear reactor for each of 9 trips. 

Probably due to the nature of the engine itself.  The temperatures in which a nerva reactor can reach are much higher than those of the materials we can make today.  While we do regulate this temperature when we pass the fuel through  (i think at around 3000k, though thats off the top of me head, don't have any books to check that atm), it still causes quite a bit of wear and tear on the parts, most notably the nozzle.  Even with liquid hydrogen being pumped through to ensure that the nozzle doesn't melt does not ensure that the nozzle won't take damage.  there are also other limitations, that may be related some of the mechanical parts (turbo pumps).  My best guess is that they are predicting a bit of wear and tear on the system, and don't want to risk using it when the final condition is unknown.  However with out a more accurate picture i'm not sure i can give you a more percise answer.