Any new development on Nuclear Thermal Rocket or Orion Project?

[kzauner]

US and Soviet atmospheric nuclear tests ended in 1963 with the Partial Test Ban Treaty.

Ah yes. You are right. But I think the French continued bombing around for another decade or so. Tempus fugit, tsk, tsk.

[Red Iron Crown]

Anyway - the whole discussion started when - i think Red Crown - stated that there will be only Hydrogen in the exhaust.

No. If you can't be bothered to check, don't name names.

[Kryten]

You have a lot of stuff in Nervas exhaust - D/T, as well as bleeded Moderator ©. And other radiating substances, as Xenon-Isotopes.

Again with this stuff! Deuterium isn't radioactive and is only dangerous in quantities of litres/day, this is very basic. As is how to use hyphens.

[rkman]

I certainly could be wrong about how the public would react,

You definitely are wrong about how people do react when craft with RTGs are launched.

[Red Iron Crown]

You definitely are wrong about how people do react when craft with RTGs are launched.

Are you saying no one protests RTGs being launched?

[shynung]

One of the fallacies is to conclude that there was no irradiation due to the fact it was within the 60's emission limits. Anyway - the whole discussion started when - i think Red Crown - stated that there will be only Hydrogen in the exhaust. A point which is just wrong, and i pointed that out. You have a lot of stuff in Nervas exhaust - D/T, as well as bleeded Moderator ©. And other radiating substances, as Xenon-Isotopes.

If you want to name names anyway, at least make sure you get it right: I said it.

First, D/T concentrations in a typical NTR nozzle is completely harmless to anyone or anything in the vicinity. By itself, deuterium has no radioactivity. 1 in every approximately 6000 hyrogen atoms has an extra neutron (deuterium) anyway, and has been shown to have little effect to life in general. Tritium is regularly used in self-illuminating equipment, and has been used for years without any major health complications arising from its use.

Second, an NTR's moderator is not designed to be bled away in normal operations. Typically, they are coated with a heat-resistant metal to keep it from being carried away by the propellant.

Third, unless the propellant mixture has xenon in it, there will be absolutely no Xenon isotopes in the exhaust. Even if xenon is used as a secondary coolant, the passages will be different, and there's no chance that the xenon goes out of the nozzle.

If you still do not agree with me, do yourself a favor and link a reliable source that proves me wrong. Otherwise, don't bother continuing this discussion.

[MBobrik]

Third, unless the propellant mixture has xenon in it, there will be absolutely no Xenon isotopes in the exhaust. Even if xenon is used as a secondary coolant, the passages will be different, and there's no chance that the xenon goes out of the nozzle.

What about the xenon produced by the reactor itself and other gaseous radioactive fission products ? Are they sufficiently immobilized inside the fuel ?

[shynung]

What about the xenon produced by the reactor itself and other gaseous radioactive fission products ? Are they sufficiently immobilized inside the fuel ?

Assuming an intact fuel containment, no, there shouldn't be any fission products in the exhaust.

[Kryten]

What about the xenon produced by the reactor itself and other gaseous radioactive fission products ? Are they sufficiently immobilized inside the fuel ?

Even if they aren't, the xenon isotopes involved aren't long-lived enough to be a threat at any great distance from a test site. Xe-135, by far the most common, has a half-life of only 9 hours.

[EzinX]

Changing subject : was any research done on some kind of hybrid NERVA-jet-scramjet design?

I thought of this when trying to work out a plausible method of exploring an earth-like planet. Suppose, just for the sake of argument, that warp drives like described here work and are even easier to make work than Dr. White and co think.

So in the near future (100 years), a manned spacecraft with a warp drive is assembled and launched and they find a planet that has gravity and atmosphere similar to earth's.

Assuming no other massive breakthroughs besides the warp drive itself, how would they land on the planet and reach orbit again?

Well, landing's easy, just need a heat shield and parachutes/a little rocket dV when the atmosphere is thick enough like on Earth. So you're on the ground, and you'd like to reach orbit again in 1 stage without a runway.

So say you have a huge fan, driven by a working fluid cycle that runs through part of the NERVA reactor. You compress oxygen or CO2 and inject it into the reactor instead of hydrogen. (a larger volume of the stuff would be needed). Assuming you can get a TWR larger than 1, your ascent vehicle lifts off and begins to pick up speed. At some time later, you divert air from the compressor fans to a straight ramjet intake that changes geometry in flight to become a scramjet intake...

This unholy hybrid of engineering then somehow reconfigures itself during scramjet flight to accept hydrogen as the propellant instead (I guess you gradually transition the internal state of the control rods in the NERVA reactor to the mode that is configured for hydrogen and gradually increase the percentage of hydrogen injected). It uses the stored hydrogen and a nice strong ISP of better than 1000 to reach orbit. At some point during this process you actually jettison the compressor fans and air intakes, they descend on a parachute and could in theory be recovered if you wanted to do this all over again a second time on the same planet.

The showstopper problem I can see here is that the internal structural of a NERVA optimized for hydrogen is probably hugely different than one designed to heat some mix of CO2 and oxygen, and in flight transitions might be unfeasible.

[kzauner]

Again with this stuff! Deuterium isn't radioactive and is only dangerous in quantities of litres/day, this is very basic. As is how to use hyphens.

Yes, But Tritium is. And the later is a quite common result of nuclear reactions.

[kzauner]

If you want to name names anyway, at least make sure you get it right: I said it.

First, D/T concentrations in a typical NTR nozzle is completely harmless to anyone or anything in the vicinity.

Because you said so?

Second, an NTR's moderator is not designed to be bled away in normal operations. Typically, they are coated with a heat-resistant metal to keep it from being carried away by the propellant.

Sorry, I just checked if the information is really that hard to find, But no .. just google 'Nerva moderator loss'.

First hit, for instance: <http://www.astronautix.com/engines/neralpha.htm>

... The fuel-element weight loss by diffusion of carbon through the coatings was assumed to be, based on calculations, 12.3 g/element/hour under these conditions ...

I stand corrected, the loss seems to be 12.3g, and with 564 element, not 500 as i had in the back of my head this gives you an overall loss of 6.9 kg per hr, not 5 as I assumed. And these are the design specification, so sorry: the NERVA was designed to bled the Moderator.

Third, unless the propellant mixture has xenon in it, there will be absolutely no Xenon isotopes in the exhaust. Even if xenon is used as a secondary coolant, the passages will be different, and there's no chance that the xenon goes out of the nozzle.

Well ... maybe, just maybe this is a result of the Uranium decay? Did that cross your mind (I think the way is U->Te->I->Xe, but can be wrong).

If you still do not agree with me, do yourself a favor and link a reliable source that proves me wrong. Otherwise, don't bother continuing this discussion.

Do you accept the austronautix? If not, then take the old docs (mostly scanned typewriter-things) like:

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19920001919.pdf

(NASA Technical Memorandum 105252)

... examination of the fuel elements showed an average mass loss of 10-13 grams per element ...

[kzauner]

Changing subject : was any research done on some kind of hybrid NERVA-jet-scramjet design?

It was called 'project pluto', some sort of nuclear-powered cruise-missile. It was a ram-jet design. Never took off and was canceled as reliant ICBMs were developed (providing easier means to deliver warheads across the atlantic ocean).

[EzinX]

It was called 'project pluto', some sort of nuclear-powered cruise-missile. It was a ram-jet design. Never took off and was canceled as reliant ICBMs were developed (providing easier means to deliver warheads across the atlantic ocean).

Project Pluto isn't a hybrid.

[shynung]

Sorry, I just checked if the information is really that hard to find, But no .. just google 'Nerva moderator loss'.

First hit, for instance: <http://www.astronautix.com/engines/neralpha.htm>

... The fuel-element weight loss by diffusion of carbon through the coatings was assumed to be, based on calculations, 12.3 g/element/hour under these conditions ...

I stand corrected, the loss seems to be 12.3g, and with 564 element, not 500 as i had in the back of my head this gives you an overall loss of 6.9 kg per hr, not 5 as I assumed. And these are the design specification, so sorry: the NERVA was designed to bled the Moderator.

If you haven't noticed, near that line is:

To provide for a two-hour duration, the fuel-element exit-gas temperature would be reduced by 60 K. This would result in a lower fuel-element mass loss rate (~ 9.2 g/element/hour) and would provide a wider margin between the operating temperature and the limit.

They are actively trying to conserve the fuel elements here. The reason there was still some that's bled off by the reactor is from improper design. From the NASA archived document you linked:

For NTP systems, the goal of fuel element design is to achieve the highest possible propellant exit temperature while maintaining structural integrity under design loads.

Their goal is maintaining integrity of the fuel elements. That means no leaks, no fuel element loss. The NERVA project didn't completely achieve this one bit.

If that still worries you, the same engine that leaks almost 7 kg of fuel element and fission products in an hour would have exhausted several tons of propellant in the same length of time. It's not negligible, but not enough to be of significant concern.

Well ... maybe, just maybe this is a result of the Uranium decay? Did that cross your mind (I think the way is U->Te->I->Xe, but can be wrong).

So what? NERVA project documents already stated that integrity of fuel element is to be maintained. A finished, service-ready engine would have eliminated the fuel loss down to negligible amounts. The NERVA project ended before this was achieved.

Also, consider the use-case for these engines. I'm not talking what missions it would serve in, but on where the engine was likely to be used. Would you think an NTR would be fired while close to the ground, enough for the 'radioactive' exhaust to have any visible effects? Most NTR proposal I've seen was for either upper stage work, or for deep-space operations. In the former case, the exhaust would have dispersed wide enough to have little effect on the environment; in the latter, it wouldn't matter where it will end up anyway. (By the same reasons, engines developed for space work in the 60s were occasionally designed to burn chlorine trifluoride; if burned with hydrogen, the exhaust would have been HF and HCl, both being poisonous and corrosive.) Why bother fussing around about how dangerous the exhaust is?

Edited December 3, 2014 by shynung

[rkman]

Are you saying no one protests RTGs being launched?

None that i heard off, and i follow both mainstream and fringe media. If there were/are any protests re RTGs (which is entirely possible), those are not substantial - as in: have no effect on actual launching of RTGs.

From where i'm sitting claims to the contrary look like victim playing by the pro-nuclear crowd.

[Red Iron Crown]

None that i heard off, and i follow both mainstream and fringe media. If there were/are any protests re RTGs (which is entirely possible), those are not substantial - as in: have no effect on actual launching of RTGs.

From where i'm sitting claims to the contrary look like victim playing by the pro-nuclear crowd.

Definitely agree they have had no effect on the launches. The point of my post about this was if people are silly enough to protest launches of RTGs, I would expect much greater protest to nuclear rocket testing on the surface (especially as the finer points of the dangers of NTR exhaust are likely to be misunderstood).

A couple of links for RTG protests:

Hundreds protest Cassini launch.

Dozens protest New Horizons launch.

Oddly, Curiosity's launch protest was cancelled for nebulous reasons.

[shynung]

Oddly, Curiosity's launch protest was cancelled for nebulous reasons.

It's not simply because it went to Mars, is it? What really happened?

[Red Iron Crown]

It's not simply because it went to Mars, is it? What really happened?

No idea. There were some pre-launch organization efforts but the protestors ended up not going without much in the way of explanation. *shrug*

[architeuthis]

In response to the OP, work on NTR propulsion at NASA did not entirely stop with NERVA.

The SLS DRM for manned missions to Mars still assumes NTR, and research into NTR at NASA was restarted in FY2012 under the NCPS (Nuclear Cryogenic Propulsion Stage) project.

Currently NASA is getting ready to start tests at NTREES (Nuclear Thermal Rocket Element Environmental Simulator, located at NASA Marshall) of advanced graphite composite, and cermet fuel elements that should have operating temperatures far in advance of anything tested for NERVA or Project Rover (upwards of 3000K). This corresponds with an isp of between 900-1000 seconds. These new fuel elements are also expected to resist release of fission products far more robustly than the old NERVA era ones.

By 2017 NASA should start breaking ground on the SAFE (Subsurface Active Filtration of Exhaust) NTR ground testing site in Nevada, with first hot-flow tests taking place sometime in the 2020's.

Edited December 6, 2014 by architeuthis

[kzauner]

Advantage against what? What are you comparing the NTR here against?

If chemicals, the advantage is clear: higher specific impulse, which means much lower propellant requirements, which means lower launch mass, and therefore launch cost. If electric engines, the advantage is travel time. Why would anyone want to take a decade-long trip to Mars when a chemical/NTR equivalent could do it in a year? Life support mass gets heavier the longer you the mission is, so that'll effectively eat into the final scientific payload.

I was not comparing 'nuclear' vs. 'chemical' versus electrical engines. I said, that - when it comes to mars-projects, nuclear engines are by far not a must-have. If you have a look at the concepts, you will quickly see that 'travel time' is a rather moot point. Due to orbital mechanics the missions usually have multiple-months at mars (the 'shortest stay' is a few weeks, AFAIR). So you gain nothing mission-wise, as the operative radius of the ground crew will be rather limited.

The trips are BTW by the way not decade-long, mission-times were between 400 to 800 days (OTOH). Flight times vary, typically between 120 and 180 days. By going nuclear you can in fact shorten flight times by using a higher energetic transfer, but using way more fuel. In fact electical systems may give you shorter travel-times (given 'constant thrust'). But as said, travel time is not really a concern.

So it boils down to 'fuel-requirements'. Lets say you need 1 extra launch for providing fuel (tanking in LEO) then your development of the NPR-engine must be lower than the cost for that 1 launch. Thats just not very plausible. But back to 'ISP' - even for chemical-rockets one would likely not use LH/LOX but other propellants, despite the worse ISP as for instance the LH boiloff is a real problem for such a mission. And never forget: dV requirement for mars is not that high. If you compare it with a flight to the moon (and the US pulled that off, some time ago using chemical propellants).

If you are interested in real mission plan, NASA has about 5 years ago published mission-profiles, about a half a dozend, older an newer ones. There is a lot of stuff to find in their archives.

Requirements concerning propulsion may change if you have multiple mission, maybe a real permanently manned outpost on mars (or in its orbit) and a lot of flights. But I don't see such an endeavor within the next few decades.

[kzauner]

If you haven't noticed, near that line is:

They are actively trying to conserve the fuel elements here. The reason there was still some that's bled off by the reactor is from improper design.

Na, the document gives not away what you are implying. The loss-rate is iherent, it was known from the very beginnig, in fact - if you go through the documets you will find, that they are very, very proud that they could maintain the rate even when the engine was used out of the design limits (for instance as a fuel-seal broke).

From the NASA archived document you linked:

Their goal is maintaining integrity of the fuel elements. That means no leaks, no fuel element loss. The NERVA project didn't completely achieve this one bit.

The elements kept their integrity. The loss was specified. The elements were not compromised, they operated within specifications. The results are an all go. There was no crack, or worse. The reason for the end of project rover was money, human resources and no real usecase.