Do you support a Nuclear Space Initiative? - Poll Results.

Josh Cryer · 2003-02-02 01:08:31

I support all forms as long as they are shown to be clean.

soph · 2003-02-02 10:22:42

josh, how clean is clean? the fuels from the colombia werent "clean." in such a situation, a properly designed reactor would have released little to no contaminants.

but i completely support nuclear options to space. i truly think they can be made clean, but lack of research for too long of a time has stopped any progress beyond the tremendous achievements of the early nuclear program.

Josh Cryer · 2003-02-02 11:38:58

I doubt there's exactly ?no? chance of contamination with NTRs. In fact, it could be argued that due to their complexity the odds of failure are greater. (Isn't that the whole reason NTRs were dropped from begin with? Back then the anti-nuke crowd didn't exist, so blaming them is no excuse.)

When you don't have zero emission systems, ?clean? has to be proportionate to the total pollution created by humans within the Earth's atmosphere (by virtue of how the ecosystem works, humans are the only beings which pollute or cause pollution). Otherwise you don't have a mesurable scale...

The Space Shuttle is clean, in that its total launches only leave a very small fraction of pollutants in the atmosphere (most in the form of steam). If we had five dozen Space Shuttle launches every year (which had SRBs), obviously it would not be clean.

I also agree that nuclear can be clean. Obviously I'm with you with regards to a Space Elevator (you should know that by now), but until one can be built, nuclear rockets are much more inticing, and also currently feasible. And even if they do leave a small ammount of radiation, which has a very short half life (as RobS, or RobertD said), I would consider it clean, since it would not be adding harmful pollution to the environment.

soph · 2003-02-02 12:13:49

Actually, the 70's saw the beginning of anti-nuclear, i believe.

however, i believe they were dropped because NASA saw them as a threat to the apollo program. this is the same reason NERVA was dropped. NASA has had a history of killing competing programs, such as the X program. i dont know why, but its sad to say.

NTR's really arent that complex. in fact, i would say they are less complex than a shuttle launch. at the exact moment of ignition thousands of gallons of water have to be loaded into a tank under the shuttle to absorb some of the shock. then the oxidizer has to be set. then the tanks have to fire, taking a huge shock. imagine if one of those tanks ruptured.

Josh Cryer · 2003-02-02 13:02:11

Hmm, why (or is?) is that behavior exclusive to the Space Shuttle? Wouldn't all very large payload rockets require some sort of shock absorption? Is it because the Space Shuttle is so fragile or what? I've always wondered this...

I read about the pros and cons of NTRs, don't have the link with me, but basically there are a lot of places where failure could occur in the engine alone.

I think I read it somewhere around here: http://www.fas.org/nuke/space/index.html

But I could be wrong. In any case, that's a really good site to read about the history of the nuclear program (and basic NTP concepts in general). We've had a fairly strong program from the 60s to the 70s, and it even continued into the 80s with SDI... (like always say, if the government wants, it can and will ignore the environmentalists).

soph · 2003-02-02 13:06:29

i really dont know about this shock to the space shuttle. someone with more expertise will have to answer that.

i really dont know what you mean about lots of places for failures. care to elaborate?

Josh Cryer · 2003-02-02 13:17:55

Nah, I should probably get going, that's what I linked that page. I believe I read it in there somewhere. I'll be back later tonight to discuss the design of NTRs... maybe we can get some people from NuclearSpace to discuss the complexity of the engines themselves, and where potential problems could occur.

I could be wrong. In fact, I hope I'm wrong. I hope NTRs can be simple. I like simple.

soph · 2003-02-02 13:20:08

yeah, we should. there are some really smart people over there. ill mention it. i didnt know you checked the site out

soph · 2003-02-02 21:14:42

Actually, the exhaust from a nuclear jet engine would not be radioactive. Neutron absoption requires a moderator, and I explained in another message that neutron absoption of 99.795% of oxygen would just transmute it into another naturally occuring, non-radioactive isotope. Neutron absorption of the 0.205% which is 18O would just turn into 19O, which would decay with a half-life of 26.9 seconds into 19F, which is the natural, non-radioactive form of fluorine. The decay releases beta radiation, which is an electron. You would get more beta radiation from sitting in front of your computer monitor reading this message. 99.9885% of hydrogen is 1H, normal hydrogen, which would turn into deuterium with neutron absorption. 2H is the other 0.0115%, and it is natural and non-radioactive. Neutron abosption by deuterium becomes tritium (3H), which has a half-life of 12.32 years to become 3He by beta decay. The incredibly tiny quantity of deuterium in moisture in the air would not produce significant quantities of tritium. 3He is a natural occuring isotope of helium, although only 0.000137% on Earth. With nitrogen gas, 99.632% is 14N which would transmute into 15N, the other naturally occuring isotope. 15N would transmute into 16N, which beta decays with a half-life of 7.13 seconds into 16O, the predominant natural isotope of oxygen.
Fission of 235U involves absorbing a moderated (slowed) neutron to become 236U. That breaks down in a fraction of a second into Krypton 89Kr, Barium 144Ba, and 3 high-speed neutrons. These byproducts are highly radioactive, but primarilly release beta readiation. Krypton 89Kr has a half-life of 3.15 minutes to become Rubidium 89Ru. 89Ru half-life is 15.15 minutes to become Strontium 89Sr. 89Sr half-life is 50.53 days to become yttrium 89Y, which is stable. The other product of uranium fission was barium 144Ba. 144Ba half-life is 11.5 seconds to become lanthanum 144La. 144La half-life is 40.8 seconds to become cerium 144Ce. 144Ce half-life is 284.893 days to become praseodymium 144Pr. 144Pr half-life is 17.28 minutes to become neodymium 144Nd. 144Nd half-life is 2.29 quadrillion years (10^15 years) to become cerium 140Ce, which is stable. All of these decay steps emit a beta particle (electron), except the last one. 144Nd emits an alpha particle (helium nucleus) to become 140Ce. The extremely long half-life means extremely low rate of radiation.
This means as long as you ensure the nuclear fuel and its byproducts are contained, the exhaust will not be radioactive. Just stay away from the engines themselves.

thats a Robert Dyck quote. I read over at nuclearspace that the NTR process is so hot you cant make radioactive hydrogen. i wonder if this means that there is nothing radiocactive to leak if an NTR hits the ground!

Josh Cryer · 2003-02-05 05:53:30

Hmm, that changes my understanding somewhat drastically. My thought was that the thrust was much much greater than that (the ISP numbers must have biased me or at least made me not question the thrust)...

soph · 2003-02-05 14:12:58

i think you could design for more thrust...the Saturn V was a behemoth. If you designed a complete heavy lift booster using nuclear rockets, i believe you can do better.

soph · 2003-02-05 14:36:11

Source

after doing some research, i found that those 250,000 lb. numbers are from the late 60s/early 70s. These were still experimental engines, and given time and more funding, i think we could have expected double that, and greater isp. With 2 or 3 of these reactors, we could outperform the shuttle.

In addition, NTR engines provide power, which chemical engines dont. So your engine does double duty. another point is that many of these nuclear concepts, including mars missions, would be launched via heavy booster, and turn on in orbit, so they cant go hiroshima before then. astronauts are big supporters of ntr missions, in fact, because of the flexibility and speed, which allows them shorter cosmic radiation exposure.

so by comparison, the chemical boosters on the shuttle produce about 400,000 lbs. each, and these have been developed for 30 years. NERVA was researched for less than a decade! Imagine what the results could be at this point had we continued. These engines would use 77 pounds of uranium for a round trip mission to mars. Imagine the possibility for SSTO flights! Surely, not now, but after further development to ensure full reliability, this could be a great option. I wonder how much the chemical fuels weigh, and how much less thrust you would need to get an orbiter into orbit with nuclear propulsion because of the decreased weight!

tim_perdue · 2003-02-05 22:14:15

so by comparison, the chemical boosters on the shuttle produce about 400,000 lbs. each, and these have been developed for 30 years. NERVA was researched for less than a decade! Imagine what the results could be at this point had we continued. These engines would use 77 pounds of uranium for a round trip mission to mars. Imagine the possibility for SSTO flights! Surely, not now, but after further development to ensure full reliability, this could be a great option. I wonder how much the chemical fuels weigh, and how much less thrust you would need to get an orbiter into orbit with nuclear propulsion because of the decreased weight!

Surely you don't think the military abandoned such promising technology? Just because it's not public doesn't mean it doesn't exist, doubly so when it is so superior to chemical rockets.

soph · 2003-02-06 05:32:45

i cant say. but i think it was killed, because the military would have no use for it without NASA having nuclear engines.

If it wasnt, all the better!

RobertDyck · 2003-02-06 09:58:13

DARPA did develop an updated NTR in the late 1980's and early 1990's. The Timberwind launch vehicle used 2 Titan solid rocket boosters and a NTR sustainer core stage. The Timberwind 250 engine had a thrust of 250,000 kg force in vacuum, but the total liftoff thrust was 1,396,380 kgf, and total mass of 884,478 kg. Astronautix does not list its lift capacity, but that site quotes an article from Asker, James R, Aviation Week and Space Technology, "Particle Bed Reactor Central to SDI Nuclear Rocket Project", 1991-04-08, page 18. This is a lot smaller than Saturn V, but is a reasonable size. As a comparison, the Titan 4B had a total liftoff thrust of 1,396,380 kgf, the Titan 4-1 core stage had a thrust of 247,619 kgf, and the total launch mass was 943,050 kg. The Timberwind launch vehicle was developed in 1992. Titan 4B included an upper stage, and the 4-1 core stage had 155,000kg propellant vs 125,000kg propellant for the Timberwind core stage, but Timberwind had a specific impulse of 780 seconds at sea level or 1000 seconds in vacuum, vs Titan 4-1 which had 250 seconds at sea level or 302 seconds in vacuum. That means Timberwind's fuel would last longer. All-in-all Timberwind sounds like a vehicle in the same class as Titan 4B.

Flat Tharsis · 2003-02-06 14:09:32

Personally I am really excited about the prospect of a renewed NASA nuclear program, especially if they are looking at using nuclear engines in launch vehicles. NTR power is the key to building SSTOs and getting cheap acess to space in the near term.

I was kicking around the idea of using a fission reactor to power a aray of laser for a pulse fusion engine. Would it be feasible for a fission reactor of launchable size to power the large lasers required to bring a pellet or deuterium/tritium to ignition?

soph · 2003-02-06 16:27:19

Robert: that engine doesnt seem up to NERVA's level...and it certainly doesnt seem to be much of an improvement. I wonder just how much more we can do with NTRs.

What new materials can we use today that they didnt have back in the 60s? What new fuels, and techniques? Im sure that there is plenty of improvements we could make that would get more thrust and isp out of NTRs, and lighten the reactor itself.

RobertDyck · 2003-02-07 10:17:49

Notice the total thrust at launch of the Timberwind launch vehicle is exactly the same as Titan 4B. I don't think it's a coincidence that the total liftoff thrust, core stage thrust, and diameter are exactly the same. In fact, the solid rocket boosters are the same ones. That means it could use the same launch facility, and be a direct replacement. Titan 4-1 stage had a gross mass (stage plus propellant) of 163,000kg and Titan 4-2 stage had a gross mass of 39,500kg for a total of 202,500kg. Timberwind had 170,000kg. That means if the Timberwind stage can provide thrust for as long as the 2 Titan stages combined, then it would provide 31,500kg more payload capacity. Titan 4B could lift 21,680kg to 150km orbit at 28.6? inclination. That more than doubles the lift capacity, and I suspect the increased specific impulse would provide thrust for even longer, providing even more lift to orbit.

In the 1990's an updated version of Nerva was proposed called Nerva 2. Instead of a 8.7 metre diameter core stage, Nerva 2 had 10.0 metres. It would have also used the Titan solid rocket boosters, but the core stage would have gross mass of 158,400kg, empty mass 27,000kg, thrust 34,000kg force, and specific impulse (Isp) 925 seconds in vacuum. That seems a lot less than Timberwind.

As for updating the design to this decade, you could use carbon fibre/epoxy composite cryogenic propellant tanks. X33 proved a hollow wall honey comb structure propellant tank does not work with cryogenic propellants, but DC-X proved a solid wall does work.

For the reactor itself, you could find a new ceramic to encase the nuclear fuel. The ceramic must withstand the heat of a nuclear reactor, and handle the impact of falling out of orbit and striking the ground without cracking open. Some of the waste product of nuclear fission is gas, so the ceramic capsule must be sealed and able to withstand the pressure build-up as krypton and barium gas are produced from uranium. At operation temperature, barium is a gas. Ground impact would occur with barium as liquid, but krypton would remain gas. That places stringent requirements on the ceramic.

Plutonium produces more energy per unit mass of nuclear fuel, but it is highly toxic. For safety reasons, you don't want to use plutonium for NTR. With a higher U235 enrichment, the reactor can operate without moderating neutrons to thermal energies. (For the purists, that is 235U.) Only U235 is useful fuel, so highly enriched uranium produces more heat with less mass. This not only eliminates U238 which is just dead mass, and eliminates the need for a moderator, it also reacts much faster. You don't need NTR fuel to last for months, it only takes minutes to achieve orbit. I believe Timberwind is a Pellet Bed Fast NTR.

soph · 2003-02-07 10:23:48

Do you need large boosters for a small NTR that is about the mass of the shuttle orbiter? How much would the mass be? And would they have to be expendable, or could they be built into the design?

RobertDyck · 2003-02-07 10:30:03

The Titan 4-1 stage had a burn time of 164 seconds, the Titan 4-2 stage had 223 seconds, for a total of 387 seconds. Timberwind had a burn time of 493 seconds. That would provide greater total lift than just the stage mass difference.

dickbill · 2003-02-07 10:39:59

basic question probably but just to be sure: a nuclear engine is designed to be used only once in space, right ? not for lift off.

soph · 2003-02-07 10:43:42

not for an SSTO, my idea is to lift off using the nuclear rocket, orbit, and shut the reactor down before reentry. There is minimal chance of meltdown in the launch phase, which is a few minutes, and the exhaust is clean. Once you shut it down for reentry, any chance of catastrophic nuclear accident is mitigated.

Robert, what about my booster questions?

New Mars Forums

Announcement

#1 2003-02-02 01:08:31

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#2 2003-02-02 10:22:42

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#3 2003-02-02 11:38:58

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#4 2003-02-02 12:13:49

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#5 2003-02-02 13:02:11

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#6 2003-02-02 13:06:29

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#7 2003-02-02 13:17:55

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#8 2003-02-02 13:20:08

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#9 2003-02-02 21:14:42

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#10 2003-02-05 05:53:30

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#11 2003-02-05 14:12:58

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#12 2003-02-05 14:36:11

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#13 2003-02-05 22:14:15

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#14 2003-02-06 05:32:45

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#15 2003-02-06 09:58:13

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#16 2003-02-06 14:09:32

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#17 2003-02-06 16:27:19

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#18 2003-02-07 10:17:49

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#19 2003-02-07 10:23:48

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#20 2003-02-07 10:30:03

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#21 2003-02-07 10:39:59

Re: Do you support a Nuclear Space Initiative? - Poll Results.

#22 2003-02-07 10:43:42

Re: Do you support a Nuclear Space Initiative? - Poll Results.

Board footer