Any new development on Nuclear Thermal Rocket or Orion Project?

[Red Iron Crown]

Maybe. I certainly could be wrong about how the public would react, but there is definitely irrational fear of nuclear power around. For example, here in Canada we design and manufacture some of the safest nuclear reactors for power plants, but it is incredibly difficult to get approval for construction of new ones domestically.

[magnemoe]

Why would it be a problem? Unless the reactor's propellant passages have leaks in it, nothing radioactive should come out of the exhaust; just pure hot hydrogen in gaseous form. There'd be a big flame in atmospheric conditions, but people would expect that in rocket engine tests anyway.

I thought it was some uranium leaks coming out too however if the rods / pellets are covered it would be radiation free at least for some time.

And regardless that other posts, static tests of experimental engines are not announced.

Protests require that the activists know about the event, main issue is not protests who are irrelevant unless huge or an decent faction of an local populatiuon even if media love to report of them on slow news days.

The real problem is lawfare,

[kzauner]

Why would it be a problem? Unless the reactor's propellant passages have leaks in it, nothing radioactive should come out of the exhaust; just pure hot hydrogen in gaseous form. There'd be a big flame in atmospheric conditions, but people would expect that in rocket engine tests anyway.

We ar talking about the same concept (NERVA) here, in which the LH is the primary coolant of the reactor? Yes, brace yourself: Science has found out that releasing the primary coolant into the atmosphere is not such a clever idea as it might look. Even not for means of propulsion. Yes, no fissile material from the reactor will get outside (if there is no RUDE). But the irradiation will generate H-Isotope which will react with the O2 in the air to form a liquid substance, which is usually ingested by lifeforms on this planet.

[Kryten]

Protium has a very low neutron cross-section, production of significant amounts of tritium during as brief an exposure as a NERVA test would involve would be highly unlikely.

[shynung]

We ar talking about the same concept (NERVA) here, in which the LH is the primary coolant of the reactor? Yes, brace yourself: Science has found out that releasing the primary coolant into the atmosphere is not such a clever idea as it might look. Even not for means of propulsion. Yes, no fissile material from the reactor will get outside (if there is no RUDE). But the irradiation will generate H-Isotope which will react with the O2 in the air to form a liquid substance, which is usually ingested by lifeforms on this planet.

What, deuterium? Tritium? They're pretty harmless in the quantities produced during a NTR firing test. The propellant molecules only spends a few microseconds near the actual nuclear fuel itself, so the chances of any creature in the vicinity ingesting enough of it to visibly harm them is pretty much negligible.

The only thing dangerous about it is that it's very hot (some 2000 K) and is travelling at 8 km/sec. That alone would be the only thing harming anything near it.

[kzauner]

Protium has a very low neutron cross-section, production of significant amounts of tritium during as brief an exposure as a NERVA test would involve would be highly unlikely.

Well, it was an issue. And It could not have been that small, the NERVA 'lost' more then 10 gram of each fuel elements (there are >500 of them

in one engine) carbon per hour. This was rather high irradiated, totaling for more than 5 kg loss in moderator. I have no intention in digging around in the old historic stuff, but OTOH the 2H & 3H was clearly the second big concern. So sorry: no Bequerel numbers at hand.

Anyway - its irrelevant: The engine has a bad ISp if you compare it for instance to a VASIMR-Design, and the longer burn-times of the later not really be relevant given the overall trip-time to Mars or beyond.

Nerva looks like a bad idea, from many standpoints. Sorry - you need cooling that engine for a few hours after you have finished your burn (means: you need another power-source for the cooling system, capable handling a few 100 kW). You may not restart it for some time due to the buildup of Xenon-Isotopes and so on, and so on.

If you go with a small reactor & an electric propulsion system you get 2 cool things: a) power for your spacecraft (the reactor stays on) and propulsion.

[Kryten]

I'm sorry, I stopped reading the post when you implied that deuterium is dangerous. Come back when you've got some actual knowledge of what you're talking about, rather than just repeating buzzwords.

Edited December 1, 2014 by Kryten

[kzauner]

What, deuterium? Tritium? They're pretty harmless in the quantities produced during a NTR firing test. The propellant molecules only spends a few microseconds near the actual nuclear fuel itself, so the chances of any creature in the vicinity ingesting enough of it to visibly harm them is pretty much negligible.

Would you an Kryten please read up at least some basic Design principles of the engine we are discussing here? The Nerva used the LH-Tanks also as shielding against the Reactor-neutrons when the later was firing. You may be right, that the intake during core-passage is not really high, but the overall absorbtion-rate was more than just notable. OTOH the payloads n-fluxrate was around 50% higher when then tanks got empty.

The only thing dangerous about it is that it's very hot (some 2000 K) and is travelling at 8 km/sec. That alone would be the only thing harming anything near it.

Well, a lot of other people think a little bit different about these issues. But it's not really important, as its unlikely that a nerva-based design will play a significant role in space-travel in the near future. And the radioactive exhaust is not really the showstopper when one writes down a list of reasons-why (it would be somewhere way down the list, filed under 'one might also consider...').

[shynung]

Well, it was an issue. And It could not have been that small, the NERVA 'lost' more then 10 gram of each fuel elements (there are >500 of them

in one engine) carbon per hour. This was rather high irradiated, totaling for more than 5 kg loss in moderator. I have no intention in digging around in the old historic stuff, but OTOH the 2H & 3H was clearly the second big concern. So sorry: no Bequerel numbers at hand.

Anyway - its irrelevant: The engine has a bad ISp if you compare it for instance to a VASIMR-Design, and the longer burn-times of the later not really be relevant given the overall trip-time to Mars or beyond.

Nerva looks like a bad idea, from many standpoints. Sorry - you need cooling that engine for a few hours after you have finished your burn (means: you need another power-source for the cooling system, capable handling a few 100 kW). You may not restart it for some time due to the buildup of Xenon-Isotopes and so on, and so on.

If you go with a small reactor & an electric propulsion system you get 2 cool things: a) power for your spacecraft (the reactor stays on) and propulsion.

There's a nuclear engine concept called a Bimodal NTR. Instead of letting the reactor cool down completely on engine shutdown, it runs a small heat engine-radiator complex through secondary cooling passages to power the spacecraft. This way, the reactor never completely shuts down, and can be fired up much faster than a conventional NTR when a maneuver node is coming up.

Also, electric propulsion system, while have greater specific impulse (more than 4-digit seconds are typical), their thrust is abysmally small (about a few to a few hundred Newtons, compared to tens of Kilonewtons when using nuclear thermal), so travel time will take a significant hit. For a comparison, the SMART-1 probe launched by ESA in 2003, powered by a xenon Hall thruster, took a year just to reach the earth-moon L1 point, while NASA's Lunar Reconnaissance Orbiter, using a common chemical thruster, took about 4 1/2 days.

EDIT:

Would you an Kryten please read up at least some basic Design principles of the engine we are discussing here? The Nerva used the LH-Tanks also as shielding against the Reactor-neutrons when the later was firing. You may be right, that the intake during core-passage is not really high, but the overall absorbtion-rate was more than just notable. OTOH the payloads n-fluxrate was around 50% higher when then tanks got empty.

You want basic designs? Here they are.

Well, a lot of other people think a little bit different about these issues. But it's not really important, as its unlikely that a nerva-based design will play a significant role in space-travel in the near future. And the radioactive exhaust is not really the showstopper when one writes down a list of reasons-why (it would be somewhere way down the list, filed under 'one might also consider...').

You're right, NERVA designs won't play a significant role; they're from the 70s. Whatever future designs that would have flown would have been much safer, easier to manage, and has much better performance, and possibly at a cheaper overall cost.

The only significant barrier to nuclear thermal rocket developments are political. Nothing more.

Edited December 1, 2014 by shynung

[MBobrik]

The only significant barrier to nuclear thermal rocket developments are political. Nothing more.

So only the biggest, by orders of magnitude, showstopper remains ... encouraging...

[Red Iron Crown]

One scenario where an NTR might be better than a reactor+electric propulsion scheme is if ISRU is used for the planned return trip refueling (proposed for some manned Mars missions, possibly others, too). The propellant for an NTR can be much easier to manufacture than the noble gases needed for an electric drive system, and the NTR could be used for a landing/ascent engine while electric engines don't have the necessary TWR.

[magnemoe]

I'm sorry, I stopped reading the post when you implied that deuterium is dangerous. Come back when you've got some actual knowledge of what you're talking about, rather than just repeating buzzwords.

I thought he was talking about hydrogen dioxide, you know that chemical who is created then burning hydrogen and oxygen, who kills thousands of people every year

[kzauner]

You want basic designs? Here they are.

I know this page, but to be honest: It does not really provide a lot of background. But I'm a big fan of nowaydays old SciFi, in book, film and comic^W graphic novel form. In fact, the bimodal engine you posted was proposed in a NASA approach for a Mars-Mission.

You're right, NERVA designs won't play a significant role; they're from the 70s. Whatever future designs that would have flown would have been much safer, easier to manage, and has much better performance, and possibly at a cheaper overall cost.

Nah, the Nerva is at least 1 decade older. I think the test-firings were in the end of the sixties; In the 70's there were proposals to use the Nerva for a possible Mars-Mission (to get the idea back out of the shelfes).

The only significant barrier to nuclear thermal rocket developments are political. Nothing more.

Yeah, because the late 60's were so anti-nukular, weren't they? As were the 70's. Sorry, I think you are somehow making up some reasons ... In those times atmospheric nuclear tests were not uncommon. You really think people were concerned by the comparatively miniscule amounts of radiation from those engines? The shutdown of the program started around '69 and was finally dimissed '71 or '72 (or so). And as far as i know: not due to environmental concerns.

Russia hold on to their RD-0410 (or so) a little bit longer. 'till the eighties. Also shut down. definitely not due to environmental concerns.

The only significant barriers to the concept are:

* There is no real usecase requiring them and therefore there is

* no Money

And for all the Mars-Projects I've got a glance, there were some sporting nuclear Engines. But I don't remember any of them providing a real, plausible advantage especially when it comes to launch costs.

[kzauner]

I thought he was talking about hydrogen dioxide, you know that chemical who is created then burning hydrogen and oxygen, who kills thousands of people every year

This substance you are trying to referring to goes by the name Dihydrogenmonoxide (DHMO). At least I think thats what you are referring to by 'hydrogen dioxide' (sic!). Not that your substance is completly unheared of (but it goes by another name). And its not formed by burning hydrogen and oxygen.

You know, trying to make fun of sbdy using chemical formulas can really be dangerous if one does know chemistry ... be careful!

Edited December 1, 2014 by kzauner

[Jovus]

To be fair, 'hydrogen dioxide' is a deadly poison. We just don't usually think of it that way because we're rarely exposed to enough to do more than kill a few topical cells (and, more importantly, whatever bacteria may be in the area of application).

Edited December 2, 2014 by Jovus

[sgt_flyer]

Hehe yeh, hydrogen dioxide (HO2) would end up being an incomplete molecule (it would be missing one electronic pairing)

the complete molecule is hydrogen peroxide (H2O2) - at the temperatures and pressures of a NTR, having peroxyde inside it would quickly make a boom (as we already can't heat peroxyde to boiling point at 1 ATM without it going boom)

Edited December 1, 2014 by sgt_flyer

[Steambirds]

I think the reason why we don't use nuclear rockets is what do we do when the rocket explodes on the launchpad, spreading radioactive fuel everywhere?

[NERVAfan]

I think the reason why we don't use nuclear rockets is what do we do when the rocket explodes on the launchpad, spreading radioactive fuel everywhere?

That may be the political reason, but an inactive reactor almost certainly has less radioactivity than an RTG (which we do launch) since plutonium-239 (half life ~90 years) is many orders of magnitude more radioactive than uranium-235 (half life ~700 million years). The reactor becomes badly radioactive once it's operating... so you don't turn it on until you're safely in orbit.

[NERVAfan]

Yeah, because the late 60's were so anti-nukular, weren't they? As were the 70's. Sorry, I think you are somehow making up some reasons ... In those times atmospheric nuclear tests were not uncommon.

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

However, the lack of demand (as by then NASA budgets were going to be severely cut following Apollo thus no money for a Mars mission) was definitely a (maybe the) major factor in canceling NERVA. The anti-nuclear thing would definitely be a major factor in trying to use NTRs now though. (in the US anyway. I doubt Russia or China would have a problem.)

Edited December 2, 2014 by NERVAfan
fixed quote tag

[shynung]

I know this page, but to be honest: It does not really provide a lot of background. But I'm a big fan of nowaydays old SciFi, in book, film and comic^W graphic novel form. In fact, the bimodal engine you posted was proposed in a NASA approach for a Mars-Mission.

Enough to provide basic information about the engines themselves. If nothing goes wrong, NTRs emit only hydrogen (or whatever they used as propellant) out the nozzle. One can add many complexities to the engine itself, and this would still hold.

Yeah, because the late 60's were so anti-nukular, weren't they? As were the 70's. Sorry, I think you are somehow making up some reasons ... In those times atmospheric nuclear tests were not uncommon. You really think people were concerned by the comparatively miniscule amounts of radiation from those engines? The shutdown of the program started around '69 and was finally dimissed '71 or '72 (or so). And as far as i know: not due to environmental concerns.

Russia hold on to their RD-0410 (or so) a little bit longer. 'till the eighties. Also shut down. definitely not due to environmental concerns.

Since when did rocket scientists ever cared much about environmental concerns? Just before the NERVA project, they fired rockets burning anything from nitric acid, diborane, liquid fluorine, chlorine trifluoride, and even liquid mercury in some cases. These beasts are far more unpleasant than a typical NTR in terms of what goes out of the nozzle, not to mention the fuels themselves being horrifically corrosive, explosive, or a combination of both. You can read more about them here.

Oh, and the anti-nuclear sentiment is still with us. I'm not making it up; just trying to get building permit for a civilian nuclear power station is exceedingly hard these days. It's just that whenever someone says 'nuclear' stuff, all that came into the commoner's mind would be Hiroshima-Nagasaki bombs, the Chernobyl/Fukushima accidents, and stories of people getting hurt by the radiation.

The only significant barriers to the concept are:

* There is no real usecase requiring them and therefore there is

* no Money

And for all the Mars-Projects I've got a glance, there were some sporting nuclear Engines. But I don't remember any of them providing a real, plausible advantage especially when it comes to launch costs.

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.

[magnemoe]

This substance you are trying to referring to goes by the name Dihydrogenmonoxide (DHMO). At least I think thats what you are referring to by 'hydrogen dioxide' (sic!). Not that your substance is completly unheared of (but it goes by another name). And its not formed by burning hydrogen and oxygen.

You know, trying to make fun of sbdy using chemical formulas can really be dangerous if one does know chemistry ... be careful!

Yes, i messed up the name, but honestly it sound like he was pulling our legs then he talked about the hydrogen being dangerous.

The problem I was thinking of was was leaks from fuel cells and dust from irradiated parts.

No it would not be an health issue, an legal one.

[NERVAfan]

Since when did rocket scientists ever cared much about environmental concerns? Just before the NERVA project, they fired rockets burning anything from nitric acid, diborane, liquid fluorine, chlorine trifluoride, and even liquid mercury in some cases.

They actually considered dimethylmercury (which is vastly worse than elemental mercury as it passes through the skin vastly more effectively, and even passes through common glove materials like latex, gets into the brain and is horribly neurotoxic). That one didn't get to the test phase, though (thankfully) as sanity prevailed (or rather they couldn't get anyone to make it in the needed quantities).

EDIT: The nitric acid isn't nearly as crazy as the other things listed. Hazardous, yes, and there's a very good reason the US uses LOX instead these days, but the Russian Proton still uses massive quantities of N2O4. Strong oxidizers aren't really safe things.

(One of the crazier bits was "inhibiting" the nitric acid's corrosiveness by adding a bit of HF. So... yeah, still pretty extreme.)

Edited December 2, 2014 by NERVAfan

[kzauner]

Hehe yeh, hydrogen dioxide (HO2) would end up being an incomplete molecule (it would be missing one electronic pairing)

Jep, it was quite funny. Anyway, HO2 in fact really exists, Its somehow necessary in metabolism (don't remember the details); there were also some stuff going on with the Ozone-Layer. But wether biology nor meterology are fields I pay specific attention to...

the complete molecule is hydrogen peroxide (H2O2) - at the temperatures and pressures of a NTR, having peroxyde inside it would quickly make a boom (as we already can't heat peroxyde to boiling point at 1 ATM without it going boom)

Well, this is somehow OnT here: One can use the stuff as mono- or as bipropellant. But I bet that in times like ours if you try to buy a few litres 70% H2O2 a SWAT team enters right after, as for sure you must be some sort of terrorist, which has to be detained immediately. But maybe I'm nowadays too old for playing around with things which can easily lead to a loss of a finger or hand.

[kzauner]

I think the reason why we don't use nuclear rockets is what do we do when the rocket explodes on the launchpad, spreading radioactive fuel everywhere?

No, not really. Yes, there are safety-concerns, but they are not show-stoppers. One can build such a thing that it stays more-or-less intact. In case of a catastrophic launchpad-failure you will maybe have some reactor debris, but 'chunks' of Uranium are not very dangerous. Decontamination would be easy.

[kzauner]

Yes, i messed up the name, but honestly it sound like he was pulling our legs then he talked about the hydrogen being dangerous.

The problem I was thinking of was was leaks from fuel cells and dust from irradiated parts.

No it would not be an health issue, an legal one.

No, I was not pulling you legs. Point is: Nervas exhaust was radioactive. As a lot of the projects documents are declassified nowadays you can easily check this up yourself. It was usually summarized as 'acceptable' of 'neglibile'. But you know, they had other emission limits back then. You will not get a permit to conduct such a test now (with those emission values).

It would not be a problem for a 'real rocket', becaus an NPR will not be the Lifter stage. The whole discussion started because sbdy stated that they are harder to test (on the ground) that electric propulsion systems.

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. The irradiated C makes up the most of the problematic stuff (as I wrote, the loss was about 10 grams / hour and element - which should sum up to about 5 kG for the engine). I'm not completely sure with this figures (but I'm sure they a correct dimension-wise; so let it be a kilo plus or minus), but It should be easy to check that.

This is also the reason why later on there were exhaust scrubs invented, for testing (not the nerva, but for other designs). Which is problematic that tests get a way higher pricetag, making NPRs even more expensive in development.