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Noclevername
2012-Nov-08, 12:45 AM
As far as I know (from 5 minutes of Wikipedia research), the NERVA rocket was cancelled, not because there was a problem with the concept, but because of politics. Will it be possible for a NERVA-derived rocket, such as TRITON, to see any actual use in space?

WARNING: This subject may lead to political speculation, so kindly watch your posts and, please, keep it space-related, keep it impartial and keep it within the rules.

EDIT: For those unsure about the rules I'll provide a handy link (http://cosmoquest.org/forum/showthread.php/32864-**-Rules-For-Posting-To-This-Board-**). Please note in particular rule 12a and the subsequent emphasis on focussed and polite discussion. I don't want to bring the Wrath Of Mod down on this thread.

Van Rijn
2012-Nov-08, 02:24 AM
As far as I know (from 5 minutes of Wikipedia research), the NERVA rocket was cancelled, not because there was a problem with the concept, but because of politics.


Although NERVA worked, there were only certain types of missions where it would be useful, so I'd say that it wasn't just politics.



Will it be possible for a NERVA-derived rocket, such as TRITON, to see any actual use in space?


I don't recall TRITON. Presumably it's another solid core nuclear thermal rocket. Do you have a reference?

Anyway, sure, it's possible NERVA might be used at some point. But you'd need an application where the advantages would outweigh the disadvantages. In the case of NERVA, you first have to get it into space on chemical rockets (there were some other concepts that might have been able to get themselves off the surface of Earth, in theory at least, like DUMBO, but you would have big political issues there). Then you're dealing with a lot of reactor mass, so to provide a useful advantage over a chemical rocket for interplanetary flight, you are probably going to need a pretty large rocket. And a NERVA just isn't going to be a game changer - it will have a somewhat higher exhaust velocity over good chemical rockets, but it isn't that huge a difference.

I think it's more likely that other nuclear concepts would be used for interplanetary flight: Nuclear electric would be a good bet, perhaps gas core fission if somebody can ever develop a practical design, some type of fusion pulse, or antimatter/fusion hybrid (for instance, firing very small amounts of antimatter at small deuterium pellots).

Noclevername
2012-Nov-08, 02:54 AM
TRITON is a Pratt & Whitney solid core NTR under development now. It is basically bimodal (warm power source or hot rocket), with a LANTR oxy "kicker" that gives it a third mode, making it "trimodal".

http://mailman.mcmaster.ca/mailman/private/cdn-nucl-l/0410/msg00044.html

http://www.physicsforums.com/showthread.php?t=505391-- This page has a link to a PDF file about TRITON in post #2. EDIT: Google link to PDF, warning: It's a PDF. http://www.google.com/url?sa=t&rct=j&q=pratt%20%26%20whitney%20triton&source=web&cd=3&cad=rja&ved=0CD0QFjAC&url=http%3A%2F%2Fwww.pwrengineering.com%2Fdatareso urces%2FAIAA-2004-3863.pdf&ei=viWbUKjjAdLOyAHbp4HoBg&usg=AFQjCNFwyUCFeSme9G-1m6ylsDvO8Ch9TA

http://www.projectrho.com/public_html/rocket/enginelist.php#id--Solid_Core_Nuclear_Thermal_Rocket--NTR-SOLID/NERVA A simplified diagram of TRITON is available here.

Noclevername
2012-Nov-08, 03:03 AM
Maybe that bimodal effect could make a hybrid thermal-electric possible-- electric drive for long slow parts of the voyage or minor orbital changes, NTR for higher thrust/larger changes.

Noclevername
2012-Nov-08, 04:47 AM
But you'd need an application where the advantages would outweigh the disadvantages. In the case of NERVA, you first have to get it into space on chemical rockets (there were some other concepts that might have been able to get themselves off the surface of Earth, in theory at least, like DUMBO, but you would have big political issues there). Then you're dealing with a lot of reactor mass, so to provide a useful advantage over a chemical rocket for interplanetary flight, you are probably going to need a pretty large rocket. And a NERVA just isn't going to be a game changer - it will have a somewhat higher exhaust velocity over good chemical rockets, but it isn't that huge a difference.


For a mission where the craft already had to be big, such as a manned Mars mission (which NERVA was originally developed for) a relatively larger reactor could be workable. And it would have considerable thrust, possibly enough to take off from Mars (I haven't done the math on that) and certainly enough to land and take off from the Moon or similar bodies. With slight modifications it could be designed to make use of local materials for reaction mass. Upon landing it would provide a power source for the explorers, and if it can't take off directly it could be used to make methane/O2 fuel for a return trip. For a mission to a body with ice, it could crack water for hydrogen, assuming it isn't designed to use water directly as steam (I know it can't use both kinds of matter, they have different chemical properties and would corrode systems designed to resist other materials).

Could it be used for braking, without the dangers of aerocapture?

Noclevername
2012-Nov-08, 10:18 AM
For smaller craft MITEE is a possibility: http://web.archive.org/web/20050307163826/http://www.newworlds.com/mitee.html (Takes you to the Wayback Machine, which then takes you to the MITEE page.)
The mass of the MITEE reactor is very low, ~100 kg, and the weight of the complete engine only about 140 kg. This order of magnitude reduction in mass over previous engines like NERVA makes MITEE very attractive for planetary science missions where high V performance and very low engine mass are critically important to mission success, and to keeping mission cost within acceptable limits.

kzb
2012-Nov-08, 01:01 PM
To go back to the political angle, I remember reading NERVA got cancelled because of nuclear weapons treaties. In other words, a nuclear engine in space could be interpreted as a nuclear weapon in space, which is forbidden by the terms of the treaty.

Don't know if it's the truth, but I certainly read this somewhere.

Also, NERVA was intended as a high thrust upper stage to a chemical rocket, i.e. to achieve orbit and/or escape velocity. The power levels were extremely high, with all the weight penalties etc that would involve. I think these days we would go for low power for extended periods instead.

Noclevername
2012-Nov-08, 02:15 PM
To go back to the political angle, I remember reading NERVA got cancelled because of nuclear weapons treaties. In other words, a nuclear engine in space could be interpreted as a nuclear weapon in space, which is forbidden by the terms of the treaty.

Don't know if it's the truth, but I certainly read this somewhere.


The angle on it that I've been given to understand was that NERVA was meant for an expensive Mars mission that Nixon et al weren't willing to pay for-- it was an extension of the Apollo program that was also cancelled. We've used nuclear materials in space since then, so I don't think it's because of the treaty ban. 'Twas money killed the beast.

NEOWatcher
2012-Nov-08, 02:26 PM
Don't know if it's the truth, but I certainly read this somewhere.
Here's the pertinent passage (http://www.oosa.unvienna.org/oosa/en/SpaceLaw/gares/html/gares_21_2222.html): (if I got the right document)

States Parties to the Treaty undertake not to place in orbit around the earth any objects carrying nuclear weapons or any other kinds of weapons of mass destruction, install such weapons on celestial bodies, or station such weapons in outer space in any other manner.
The moon and other celestial bodies shall be used by all States Parties to the Treaty exclusively for peaceful purposes. The establishment of military bases, installations and fortifications, the testing of any type of weapons and the conduct of military manoeuvres on celestial bodies shall be forbidden. The use of military personnel for scientific research or for any other peaceful purposes shall not be prohibited. The use of any equipment or facility necessary for peaceful exploration of the moon and other celestial bodies shall also not be prohibited.
I'm sure that you can interpret "weapon" however you want, but that last sentence seems to allow it as long as the mission is clear.

galacsi
2012-Nov-08, 02:57 PM
WARNING: This subject may lead to political speculation, so kindly watch your posts and, please, keep it space-related, keep it impartial and keep it within the rules.


Great :I did not know you have been promoted "Moderator".

Noclevername
2012-Nov-08, 03:06 PM
Great :I did not know you have been promoted "Moderator".

Sorry. I just had a thread closed because some participants didn't do the above, so I may have overreacted. Mods, I apologize, I wasn't trying to do your job. My intent was a suggestion, not a demand.

Swift
2012-Nov-08, 04:24 PM
Sorry. I just had a thread closed because some participants didn't do the above, so I may have overreacted. Mods, I apologize, I wasn't trying to do your job. My intent was a suggestion, not a demand.
While I appreciate the concern, we would prefer that members not post "moderator-style" comments. A better method is just to promptly Report posts that may be straying into bad areas.

We would also appreciate it if members did not try to moderator the self-moderators, especially if they have already Reported the post.

Now back to the nuclear rocket discussion, before you all get on my NERVAs. :D

Ara Pacis
2012-Nov-09, 08:34 AM
IIRC, NERVA's exhaust was radioactive. The supersonic cruise missile in Project Pluto was similarly powered and after dropping nuclear bombs could continue to fly around irradiating the countryside and knocking things down with it's sonic boom.

I don't think a nuclear thermal core is comparable to the RTGs we use today in terms of danger, militarization, proliferation or weaponization if lost and found.

Van Rijn
2012-Nov-09, 11:02 AM
IIRC, NERVA's exhaust was radioactive.

Radioactive exhaust wasn't a big problem for a NERVA rocket (barring damage). The hydrogen essentially was coolant for the solid core reactor, and there wasn't much radioactive material that would get loose. A nuclear jet would be a bigger issue (easier to induce radioactivity with all the stuff in air). Now, if you were talking about a gas core nuclear reactor, that would have a nasty exhaust (one of the reasons they never got very far with those, though they potentially had a much higher exhaust velocity).

Anyway, with NERVA the plan was to launch them on a chemical rocket and start them in orbit. NERVA wouldn't have had the thrust for Earth launch, and in any event, the big concern would be for a running reactor with lots of short lived fission products crashing somewhere. An unstarted, clean reactor crashing would be a much smaller issue.

In space, you'd either have a crewed section trailing behind the reactor/rocket attached by cable, or have it in front like 2001's Discovery. That would provide distance from the reactor so less shielding would be needed while it was running.

Van Rijn
2012-Nov-09, 11:10 AM
For a mission where the craft already had to be big, such as a manned Mars mission (which NERVA was originally developed for) a relatively larger reactor could be workable. And it would have considerable thrust, possibly enough to take off from Mars (I haven't done the math on that) and certainly enough to land and take off from the Moon or similar bodies.


I don't think it would be very practical for landing or launch for Mars or the Moon. One of the issues (mentioned in earlier post) is that you wanted distance from the running reactor. Given the mass, I don't see what the advantage would be.


Upon landing it would provide a power source for the explorers, and if it can't take off directly it could be used to make methane/O2 fuel for a return trip.


For a power reactor, it would almost certainly be easiest to use a reactor designed for the purpose, and kept cold until placed where you want it. That way you don't need special remote control equipment to move it around. Once placed, they might well cover it in sand bags for shielding (or just run a long power line and have it in a small crater away from the habitat).

Nick Theodorakis
2012-Nov-09, 11:50 AM
To go back to the political angle, I remember reading NERVA got cancelled because of nuclear weapons treaties. In other words, a nuclear engine in space could be interpreted as a nuclear weapon in space, which is forbidden by the terms of the treaty.

Don't know if it's the truth, but I certainly read this somewhere.
...

I had heard that a Project Orion (the concept for a nuclear bomb-powered pulse rocket, not the current re-etnry capsule). although I don't know if it was ever considered "alive" enough to be "killed."

Nick

Noclevername
2012-Nov-09, 11:59 AM
I don't think it would be very practical for landing or launch for Mars or the Moon. One of the issues (mentioned in earlier post) is that you wanted distance from the running reactor. Given the mass, I don't see what the advantage would be.


Dang. And of course a "retractable" reactor would be an untenable engineering and maintainance nightmare.