Modular NTR/NERVA system

[zypofaeser]

I have this idea about a way to extend NASA's capabilities in space. The idea is to revive the NERVA and to make a single engine rocket stage. The stage should be made so that it can  be launched on both early versions of the SLS and scaled up versions so that it can use the capacity of the later versions of the SLS.

The LH2 tank could be based on the shuttle ET with solar panels and extra insulation (Maybe some kind of active cooling?).

It should be made in a way that allows multiple of these stages to be connected in space for use on missions such as the NASA design reference mission and such. Google: IMIS Spacecraft (May use a split mission approach instead of the all egg in one basket approach)

This rocket stage would allow for launches of bigger spaceprobes to the outer solar system and for manned missions to Mars, Venus and asteroids.

What are your thoughts?

[RanulfC]

Note that the NERVA engines were designed to be multi-stage engines in that some Mars missions used several "booster" NERVA stages and a central core NERVA which were stage at various points in the mission.

It's more than a bit of a waste even though the later NERVA's were only designed to be "used-once" reactors. Better would be to launch a tri-mode NERVA and have it capable of using attachable hydrogen tanks for reaction mass I'd think.

Randy

[zypofaeser]

The idea is to make the NTR system ready to fly with less launches required to make a spacecraft that is capable of doing a mission. Also, the NASA plan uses 3 reactors on the Mars Transit Vehicle while this only uses 2

[RanulfC]

The idea is to make the NTR system ready to fly with less launches required to make a spacecraft that is capable of doing a mission. Also, the NASA plan uses 3 reactors on the Mars Transit Vehicle while this only uses 2

My point was I'd only use ONE (1) or only one "set" on a single "core" vehicle. NERVAs can be "reusable" but you have to design that in from the start.

Propellant is still the limiting factor (the reactor will slowly "poision" itself over time and really should be rebuilt/replaced every couple of missions) for in-space use. You really want to launch mostly propellant and as few NTRs as possible. That's why one of the Mars DRM missions uses a "de-mountable" (read: drop-tank) LH2 tank for one version. Removing and replacing a tank of LH2 is much easier than trying to replace the whole reactor until you have to.
(Note also: A tri-mode NTR in generator mode {idle} would produce enough power to run a cryo-cooler system for the attached LH2 tanks as well as power the vehicle)

Randy

[JasonAW3]

Question;  Assuming that we CAN extract resources from asteroids or moon dust, are there others types of gasses than hydrogen that could be used in a NERVA reactor?  I understand that hydrogen was originally chosen as it is the lightest element that could be used as reaction mass,  but are there other, heavier gasses that could be used instead?  (Obviously not oxygen, as even at high tempertures internal components would start to oxidize internal components even at the high internal temperatures of the reactor vessel).

[zypofaeser]

Question;  Assuming that we CAN extract resources from asteroids or moon dust, are there others types of gasses than hydrogen that could be used in a NERVA reactor?

As far as i know water would work. Why shouldnt other gases work too?

[sghill]

Question;  Assuming that we CAN extract resources from asteroids or moon dust, are there others types of gasses than hydrogen that could be used in a NERVA reactor?

As far as i know water would work. Why shouldnt other gases work too?

Any gas will work.  The gas is just a medium for the reactor to heat and expand to create thrust.  The nuclear scram jets were VERY similar to NERVA rockets, but they scooped up normal air instead of using compressed gases.

[RanulfC]

Question;  Assuming that we CAN extract resources from asteroids or moon dust, are there others types of gasses than hydrogen that could be used in a NERVA reactor?

As far as i know water would work. Why shouldnt other gases work too?

There are problems running a NERVA on anything its not specifically designed to use as reaction mass because of reactor matrix materials interactions. For example water tends to disassociate at the temperature being considered which means you have very hot oxygen running through your reactor elements. Being graphite elements in the "baseline" NERVA this would mean a very neat but highly detrimental to your reactor fire (burning of the graphite) which would destroy the matrix and release all the fissile material into the exhaust

You can of course coat the elements to resist such issues but normally what will work for one (such as oxygen) is highly ineffective under other chemicals (such as hydrogen).

Water's ISP is very much less than Hydorgen, and if you split it and make hydrogen and oxygen you can use the hydrogen through the reactor and add performance by injecting the oxygen into the exhaust. "Local" resource use can be had in the outer planets if you design the NERVA to run on Ammonia and use local sources to provide reaction mass.

http://www.projectrho.com/public_html/rocket/atomicfuel.php

Randy

[RanulfC]

The nuclear scram jets were VERY similar to NERVA rockets, but they scooped up normal air instead of using compressed gases.

I know this is going to sound "nit-picky" as heck but its an important point for nuclear rocketry of any type

RAM-jet, NOT SCramjet because a nuclear reactor provides all the "heating" of the propllant, (reaction mass) there is in fact NO combustion, supersonic (SCramjet) or otherwise.

You'd be surprised at how many people "assume" hydrogen was used because it was easier for the reactor to burn as "fuel" to produce thrust. It makes explaining things like LOX-augmentation very much harder to explain

Because water is used in power reactors people tend to think that water should work fine in an NTR but in truth your basic NTR runs much hotter than any power reactor and due to flight-weight requirements normally ends up being "compatable" with only a small range of hot gasses with the core matrix materials.

Randy