tree hugging aside, is a nuclear launcher feasible?

[spacefire]

here's info on the NERVA program<br />http://en.wikipedia.org/wiki/Nuclear_thermal_rocket<br />can that be used for anything other than deep-space applications? <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[spacefire]

here's a nuclear-powered ICBM design!<br /><br />http://www.astronautix.com/lvs/yardicbm.htm <br /><br />and a Bona-fide nuclear launcher!<br />http://www.astronautix.com/lvs/ritac.htm<br /> <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[najab]

I wouldn't call opposition to a rocket design that spews raw radioisotopes into the atmosphere "tree hugging".

 

[jurgens]

The Gas-Core Reactors don't spew radioactive isotopes into the atmosphere, but then again they never built a Gas-Core Reactor.

 

[najab]

I know, that's the problem. I <b>really</b> like gas core designs, but they have never tried to build one. <img src="/images/icons/frown.gif" />

 

[spacefire]

what about NERVA? it wasn't spewing any radioactive stuff. <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[scottb50]

They would if they had a problem and broke up or crashed.<br /><br />The biggest problem I see is carrying enough fluid to keep the core cool for any length of time when you are expelling the coolant it to propel a vehicle. Just a guess but I would think the tank to contain the amount of Hydrogen needed would be rather large. <div class="Discussion_UserSignature"> </div>

 

[najab]

><i> it wasn't spewing any radioactive stuff.</i><p>In the NERVA design, the working fluid passes through the reactor core itself and then into the atmosphere. As it says in the Wiki article you linked to, in order to get high efficiency you want to run the reactor as hot as possible, but the higher the temperature the more susceptible the core is to errosion. Add to that the fact that hydrogen (the best working fluid) is highly errosive, and it's almost certain that the exhaust will be quite radioactive.</p>

 

[spacefire]

nevermind, you're right...it can be seen from the diagram as well.<br /><br />however, since no reactor fuel is discharged in the atmosphere, just how dangerous is it?<br /> <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[JonClarke]

If all goes well no reactor fuel is lost to the atmosphere. However there will be loss of volatile fission products - iodine, strontinm, cesium, sodium. These have short half lives and are really radioactive, being readily taken up in the food chain. <br /><br />Of course not everyting goes well all the time. Then you get burning reactor core ejected into the hot exhaust. This is not good and happened at least once in US tests. At least the Russians had the sense to test their NTRs underground.<br /><br />Most gas core reactor design have some loss of the core as well as fission products to the exhaust. Not good at all. The exception are the "light bulb" designs, but they require large amounts beryllium to make the "light bulb" In the event of an accident this will be even more toxic than the reactor core.<br /><br />Chemical rockets have launch success rates of the order of 99%, if you are lucky. Any NTR must have a demonstrated safety record orders of magnitude above this.<br /><br />Insisting on high environmental standards is not tree hugging, it is best practice. I am all for space flight and civil nuclear power but it is nuts to want to contaminate our own beautiful world to go to far less hospitable ones.<br /><br />As for Orion, while conceptually feasible I am very glad this never flew. Do you really want 50 atmospheric nuclear explosions to go to Mars? Definitely inadvisable rocket science, to use Mark Wade's description (in his case to the Soviet nuclear powered ICBMs).<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[najab]

><i>just how dangerous is it?</i><p>In the GSOT (Grand Scheme of Things), probably not <b>that</b> bad compared to open air nuclear tests and other nasty things done in the 1950's and 60s, but still enough of a worry that I wouldn't want to live down wind of the launch site.</p>

 

[rybanis]

I, myself, am all for using NERVA...in space. Besides, I think you would want to launch them up into space where they would be most efficent (at least thats how I understand it).<br /><br />Also for Orion, could you imagine the havoc that would cause even using one in Earth orbit? Electronic things on the surface would probably get fried. <div class="Discussion_UserSignature"> </div>

 

[henryhallam]

Indeed - a catastrophic launch failure would produce pretty widespread contamination. Perhaps you could mitigate this by launching from somewhere in the middle of the ocean, but in all honesty I don't think even that would get past the huge political hurdles.<br /><br />NTR engines can still be extremely useful even if not used for launch. The amount of dV required to go to the Moon or Mars is about 40% of that used to get to LEO, so using a nuclear rocket for translunar or trans-Mars injection will easily let you get nearly twice the payload (assuming dV=5000 for TLI, braking into lunar orbit and TEI, this is about what Apollo used) chem Isp = 421 (S-IVB), nuke Isp=810 (NERVA), rocket fueled mass = 150t, chem payload = 45t vs. nuke payload = 81t ) to your destination compared to using chemicals all the way.<br />The ratio of payload for nuclear vs. chemical is not affected by increasing the fuelled mass of the rocket, but it IS affected by the delta-V - the more delta-V, the better the nuclear performs). <br /><br />You get even bigger benefits by using the nuclear rocket to brake into lunar or martian orbit, and some of the designs also provide for the use of the engine as an electrical generator when not in use for propulsion.<br /><br />With a nuclear rocket, it MIGHT even make sense to brake back into LEO - particularly since the treehuggers wouldn't like the hot core to re-enter. Perhaps for safety and mass-efficiency the capsule could detach prior to perigee and use a small thruster to put itself on a re-entry trajectory, while the nuke propulsion stage could stay on an orbit with a perigee out of the atmosphere, then burn to brake into orbit ready for the next trip.<br /><br />As an aside, the rocket needed for TLI etc would be much smaller than one used as the first or second stage of a launch vehicle. In fact the NERVA program already tested engines of comparable size, so they are definitely feasible, and much cheaper to develop than a monster first stage. <b></b>

 

[jurgens]

anyone wanna do an anaylsis on this engine?<br /><br />http://www.nuclearspace.com/A_PWrussview_FINX.htm<br /><br />Im not sure what it's exact risks are? I mean, it's a nuclear thermal rocket so it can provide higher isp then chemical rockets for LEO-Moon/Mars. It also can provide electrical power when not in use for propulsion, and can provide electric thrust for when it requires really high isp, ie LEO-Mars/Jupiter/Saturn

 

[spacefire]

well this is a spaceborne engine, not to be used for a launcher. it will spew some radioactive stuff:<br /><br /><font color="purple">BB: What about fission gas release percentage?<br /><br />RJ: Fission gas release is a direct function of the atom percent burn up. And for the UO2 Tungsten cladded CERMET fuel form we are down below 1/10 of a percent of burn up over the whole mission life. That takes you down to where fission gas release percentage is less than a 1% and that's hard to even reliably predict until we do testing, it's considerably low. Personally, I don't want to be spewing out a lot of fission product even if it's out in space even if no one (human) is behind me or nor would I want to be putting it out near another planet. It's not a good thing to design or allow for high fission product in the exhaust. The other point is in terms of testing. I would like to have fission product retention high so I can retain it all. The way I want to test this with a small engine so that my total product production is so low anyway. It'll be easier to ****** release by exhausting into a duct and then cleaning the duct or to the point were it has no release. Basically I don't have problems with fission product release or major fuel swelling over time with the TRITON engine operating for hours during high-thrust and years at power mode levels producing less than 500 kW thermally.<br /><br />BB: Is there any value in designing 'Swirl vanes' placed inside nozzle chamber in an effort to create vortex toward skimmers for the purpose of cleaning radioactive material from plumes?<br /><br />RJ: Bruce, I really don't have a way to postulate on that. I know how we've used it to enhance combustion. The use of swirl for combustion purposes because of centrifugal force in terms of delineating the density of gas products. As an indirect consideration you would think it's a positive thing to swirl to help you capture any higher molecular weight or higher micron elements toward the outside so</font> <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[starfhury]

I'd like to see a nuclear launcher as well, but the past proposals will never fly. The main reason is because at some point radiation can get into the exhaust even if the vehicle did not get into an accident. Orion, is just such an insane concept its a wonder it was even thought of at all. Nerva had potential, but such an engine would basically be for space only use. The way to use nuclear power is indirectly, much like it is used in a nuclear powered U.S. navy ship. Bury the reactor deep with in the LV so that it's not directly in the propulsion system. This ofcourse is going to reduce the absolute efficiency of the propulsion system, but if we have one or two powerful reactors, we can channel that energy into other means to power an LV. <div class="Discussion_UserSignature"> </div>

 

[spacefire]

the Prometjheus probe will use a different kind of nuclear engine,one that generates electricty to power a ionic thruster:<br /><br />http://www.space4peace.org/articles/prometheus3.htm<br /><br /><br />considering nuclear reactors can generate lots of electricty, could an ionic thruster powered by a nucllear reactor lift a rocket to orbit? <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[nacnud]

No. <br /><br />A very simple form of ion propultion that works in atmosphere are often refered to as lifters. These barely can lift their own weight, there is no chance of lifting the power supply as well as a supply of working fluid for when the atmosphere gets too thin.<br /><br />They do look like great fun to play with though <img src="/images/icons/smile.gif" />.

 

[henryhallam]

There is a hard upper limit to the maximum thrust an ion engine of a given mass can provide, no matter how big a power supply you have. This is due to electrode erosion.<br /><br />This limit is a long way below the weight that the engine has on Earth. Therefore an ion-powered takeoff from the Earth's surface is a physical impossibility.<br /><br />In fact this limit also prevents it really being feasible for a manned trip anywhere closer than about Saturn - although the engine is much more efficient than chemical or NTR, so you need less fuel, the time to accelerate and decelerate is so long that it's always slower than chemical or NTR. Perhaps useful for getting cargo to Mars but this is debatable. Ions are promising for cheaper robotic science missions to the outer planets though.

 

[najab]

That's not to say that there aren't NEP concepts that do make sensef for inner Solar system exploration - VASMIR is one design that has the potential to make NEP the system of choice.

 

[henryhallam]

Yes - VASIMR looks pretty promsing but at the moment it's still a paper engine.

 

[spacefire]

what if we could accelerate gas particles to relativistic speeds? relativisticmomentum nears infinity at the speed of light,so, providing you have the energy to accelerate particles to such speeds -well, to extremely high speeds- , your ship would get a great kick forward!<br />once again, providing you can accelerate particles this fast, seems you could lift off your entire mass ejecting just one atom at a time. is this correct? (at least theoretically) <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[jurgens]

A Paper engine? AFAIK they actually built a test VASIMR engine.

 

[najab]

><i>Yes - VASIMR looks pretty promsing but at the moment it's still a paper engine.</i><p>Not entirely true, it's moved beyond the paper stage and has been 'bench' tested. What Dr. Diaz is trying to do is find some way to get it space tested, at one point there was a plan to fly it as an experiment on ISS, but we'll have to see if that ever happens.</p>

 

[spacefire]

<font color="yellow"> A plasma drive like VASIMR can develop one newton of thrust per 100 kilowatts. One newton equals about 0.225 pounds. A one thousand ton Mars/Venus clipper with a 100 ton VCR generating 200 MWe will get about 450 pounds of thrust from a VASIMR drive. This will allow an acceleration of 0.0022 meters per second per second. In one hour the ship will speed up by 7.94 meters per second. In one day 190.5 m/s and in one week 1333 m/s or 1.33 kps. In four weeks 5.33 kps and in eight weeks 10.66 kps. Constant low thrust can lead to high speeds. VASIMR can be operated at higher power levels than electrostatic ion drives.<br /><br /><br />but...<br /><br /><br />For instance, one space propulsion expert critical of VASIMR observed that for the thruster to be useful for a human mission to Mars it needs four to six megawatts of power. This amount of power can only come from a very large on-board nuclear reactor. That hardware does not exist, and probably will not exist for quite some time, the expert told SPACE.com.<br /> </font><br /><br />in order to get enough thrust they need a super-duper nuclear reactor, which doesn't exist yet. that's the main objection to VASIMR <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>