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Project Bifrost: (Fission) Rockets of the Future?

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  • Good luck (Score:5, Insightful)

    by jonwil (467024) on Saturday January 21, 2012 @05:35AM (#38772748)

    Anytime anyone even thinks about mixing "nuclear" and outer-space (even radioisotope generators as used on many space probes) all the anti-nuclear groups kick up a huge fuss.

    Unless this mob has something different they can use to convince the anti-nuclear mob that its safe, they will have a hard time actually launching anything without massive protest.

    • Re:Good luck (Score:4, Insightful)

      by donscarletti (569232) on Saturday January 21, 2012 @06:10AM (#38772874)

      My opinion is if this thing blows up, it will kill the crew and pollute an area of space millions of kilometres from anything I personally give a shit about. This is pretty much the same end result as if a chemical rocket blows up. Sounds like a fantastic application for nuclear, makes good use of what nuclear is good at (fuel energy density) while minimising what it is bad at.

      I figure, presumably after the engine actually works and has been tested etc. we put this thing in orbit without any fuel, make sure it's an orbit that will stay stable for at least 20 years if something screws up. We then send up the fuel in small amounts, so if anything goes wrong, the amount of poisonous uranium or plutonium or whatever released is not going to kill whatever forest or reef or city etc it lands on.

      Then if something goes like really bad, we fire up the partially fueled engine and fly it into the sun. If not, we complete the mission.

      • by Bill Currie (487)

        Then if something goes like really bad, we fire up the partially fueled engine and fly it into the sun. If not, we complete the mission.

        Flying something into the sun is rediculously difficult (compared to Earth's orbit, the sun is pretty small). Much easier to just send the thing on its way and forget about it. If it's got enough delta-V to get it out of the solar system, we need not worry about it ever again.

        • Re: (Score:3, Insightful)

          by donscarletti (569232)

          From Wikipedia:

          Earth orbital speed: 29.78 km/s

          Sun's escape velocity at Earth (42.1 km/s)

          Thus, the delta V to completely de-orbit from Earth's orbit is far lower than to escape the solar system. After de-orbiting, hitting the sun is quite easy, it just will tend to fall in.

          • Re:Good luck (Score:4, Interesting)

            by Bill Currie (487) on Saturday January 21, 2012 @07:41AM (#38773176) Homepage

            Yes, the escape velocity is 42.1km/s. But anything in Earth's orbit already has a velocity of 29.78km/s (+/- a bit if in orbit around the Earth). This means that the delta-V required to escape the solar system from Earth's orbit is 12.32km/s. Less than half that required to de-orbit and fall into the sun.

            This is actually a mistake that I make quite often (forgetting to factor in the current orbital velocity).

            • who says that you have to hit the sun? Just let it fall slowly to the sun. Ideally, it can transmit information for a LONG LONG TIME as it heads there. Nothing better than allowing it to be a long life sat while on its way to oblivion.
              • I don't think you understand how "falling" works.

                Earth is moving at about 30 km/s relative to the Sun. That happens to be just the right velocity to keep it in an orbit at a distance of about 150 M km.

                Apply thrust along that same vector, and you go into a higher orbit. Apply thrust against that same vector, and you go into a lower orbit. Apply enough thrust against your vector long enough -- long enough to change your velocity by about 30 km/s, which is a heck of a lot -- and you eventually intersect the Su

            • by sjames (1099)

              You don't have to apply the entire 29.78km/s, just enough that the thing passes through the corona at some point in it's orbit.

          • Re:Good luck (Score:4, Informative)

            by Anonymous Coward on Saturday January 21, 2012 @07:55AM (#38773206)

            From Wikipedia:

            Earth orbital speed: 29.78 km/s

            Sun's escape velocity at Earth (42.1 km/s)

            Thus, the delta V to completely de-orbit from Earth's orbit is far lower than to escape the solar system. After de-orbiting, hitting the sun is quite easy, it just will tend to fall in.

            Hogwash. You do not know your stuff. Think before quoting Wikipedia.

            As you have Earth's velocity of 29+ km/s already for free when departing from Earth in its orbit around the Sun, you are virtually "halfway to anywhere" (Robert A. Heinlein) when making it into Low Earth Orbit (LEO). Thus, the delta v needed for going from Earth surface to escape velocity out of the solar system is *much less* (~12.9 km/s) than for going to the Sun. In order to do the latter, you first need to get into LEO and then you need to decelerate from Earth's orbital velocity of 29.8 km/s to 0. So, your total delta v is around 40 km/s (!!!). More than three times than for going to infinity (and beyond ...). Good luck.

            Hitting the Sun is anything but being "quite easy" (your words). That is the reason why it has never been done before.

            • by expatriot (903070)

              You are right. It's very hard to hit the sun. You could do it with less energy than the 40km/s delta implies by doing multiple slingshots, starting with the moon.

              • by donscarletti (569232) on Saturday January 21, 2012 @10:45AM (#38773776)

                I like your style.

                I'd be like the half-qualified director of NASA and would make this rousing as hell speech "do you want to be remembered as just some ordinary guy, or as the hero who flew a nuclear powered spaceship into the sun" and all of these cynical know it all guys would be like "you dumbass, you forgot to subtract Earth's orbital velocity from the Sun's escape velocity". And you'd be the promising young mathematician would would run to the front of mission control with a stack of paper and diagrams and be like "no, we need to launch this deadly broken nuclear spaceship at the moon first", then I'd smile and puff my cigar, knowing that everything would be awesome in the end.

                I'd pay my $8 to see that movie, I really would.

                • by jamstar7 (694492)
                  I'm thinkin the mission director will tell them to land at night when it's not so hot.
            • Re: (Score:2, Interesting)

              by donscarletti (569232)
              So, I mention de-orbiting (WRT the Sun) something already IN earth orbit, then you add in the delta V to get into LEO _again_, clearly distorting the number to prove your point. Also, you suggest needing to go to zero, which is untrue, if something enters the corona it will be decelerated, the corona takes about 2 degrees of arc in the sky meaning an elliptical orbit will be just as good, which does not require zero orbital velocity.
              • Re:Good luck (Score:4, Informative)

                by CrimsonAvenger (580665) on Saturday January 21, 2012 @09:43AM (#38773490)

                Also, you suggest needing to go to zero, which is untrue, if something enters the corona it will be decelerated, the corona takes about 2 degrees of arc in the sky meaning an elliptical orbit will be just as good, which does not require zero orbital velocity.

                Dropping something into the corona of the sun from LEO....

                Okay, assume that that requires us to get down to ~3,000,000 km (about four times the radius of the sun).

                orbital speed up at this end of the hohmann ellipse is ~5900 m/s.

                If we assume our orbital speed in LEO is about 7100 m/s (corresponding to an escape speed of about 10 km/s), then a single burn of about 18800 m/s is required to reach the corona of the sun.

                Note, for reference, that from the same LEO, solar escape speed requires ab out 8800 m/s deltaV.

                No matter how you slice it, it's easier to just toss something out of the solar system than it is to toss it into the sun...

                • OK, that all checks out, in truth I _had_ forgotten that I could subtract the earth's orbital velocity from the sun's escape velocity (also the spacecraft's orbital velocity, but that would work for both escape and de-orbit). So, I would like to change my position ever so slightly to say: "throwing something hazardous into the sun is awesome and _worth_ the extra deltaV".
        • You have to be kidding. Far easier to point it at the sun and go in, or simply point it retrograde, slow down speed relative to earth and allow the sun to pull it in to either venus, mercury or itself.
          • by Patch86 (1465427)

            I won't answer it again (siblings posts have done a far better job of it than I could), but to sum up- no. That isn't how space works.

          • by tempest69 (572798)
            the speed of the earth has you moving fast enough that getting enough speed to retrograde to a lower orbit (venus) is substantially more than the fuel needed to crash into jupiter.
            Really we just steer it into a comet, and let her take it into the sun for us ;)
      • "My opinion is if this thing blows up, it will kill the crew and pollute an area of space millions of kilometres from anything I personally give a shit about. This is pretty much the same end result as if a chemical rocket blows up. "

        You mean like the Challenger and Columbia? Except with nuclear fallout. I know the reactors in spaceships are usually much smaller than a nuclear plant, but this is definitely bigger risk than a chemical rocket.

        • Re:Good luck (Score:5, Interesting)

          by BlueStrat (756137) on Saturday January 21, 2012 @09:17AM (#38773408)

          You mean like the Challenger and Columbia? Except with nuclear fallout.

          What, are you a Flash Gordon fan!?

          Nobody designs even a chemical-powered interplanetary spaceship to land it's main mass (including it's main propulsion system) on a planet surface. That's what landers are for. Even Apollo used a Lunar Module to land on the moon and a small Command Module for Earth re-entry.

          This thing would be assembled in orbit and would never land on a planet. For something like a nuclear-powered interstellar spaceship, I imagine most of the construction would be done in low Earth orbit and then moved to a parking orbit at a La Grange point for final departure preparations, including loading the nuclear fuel.

          I think you understand this, but are allowing your nuclear fears to cause you to post ridiculous and unrealistic scenarios in an effort to fight the idea of nuclear-powered space propulsion systems.

          Strat

          • Does using a nuclear engine to power the vehicle through the atmosphere increase the risk of a nuclear spill, or will it inherently spew radioactive material into the air? If not, why not use a nuclear engine to get off the surface?
            • by BlueStrat (756137)

              If not, why not use a nuclear engine to get off the surface?

              Short answer: Shit happens.

              Longer answer:

              Why tempt Murphy's Law and/or an unlucky turn of the odds? Seems to me to just be smart risk management if you choose NOT to have critical fission piles screaming through the atmosphere of an inhabited planet at thousands of miles per hour if it's not necessary, even if the tech itself is very mature.

              Besides, the mass of shielding and armoring/hardening for the reactor core necessary to make it reasonably safe and resilient in a crash on the Earth's surface or in the

            • by tragedy (27079)

              Usually because you won't get enough thrust out of the engine. At an unachievable optimum efficiency, you need a theoretical 48 watts of power per kilogram just for the thrust to counteract gravity at the surface of the earth. This is ignoring aerodynamic effects entirely, of course, but it's just illustrative. So, if you want to actually go up, you need more power than that. So, the absolute maximum that 1 MW could lift would be a bit more than 20 tons. With an imaginary efficiency of 25 % (still unrealist

          • I'm talking about accidents, obviously. Space rockets are more fragile and less reliable than our usual nuclear power plants. That's what I'm talking about. Assembling the thing in the orbit doesn't really change the fact that space rockets are prone to fail.

            • by BlueStrat (756137)

              I'm talking about accidents, obviously. Space rockets are more fragile and less reliable than our usual nuclear power plants. That's what I'm talking about. Assembling the thing in the orbit doesn't really change the fact that space rockets are prone to fail.

              What kind of "accidents" do you mean here? We're talking about an interstellar spaceship that stays in space and doesn't ever land. If you're worried about a meltdown or explosion in space, then I hate to break it to you, but there are a whole lot of extremely dangerous, deadly-radiation-emitting, and lethal things in space. One of the most dangerous is a titanic ongoing thermonuclear reaction millions of times the size of Earth only about 93 million miles away, which is practically in our laps.

              Assuming the

        • but this is definitely bigger risk than a chemical rocket.

          You'd rather get showered in hydrazine than plutonium?

      • by petes_PoV (912422)

        pollute an area of space millions of kilometres from anything I personally give a shit about.

        Though in space things don't stay where you put them - they have an annoying habit of forming closed orbits (unless they're going fast enough). So the area of space that you personally don't give a shit about could soon find itself on an intersecting path with a person, place or planet that you do have some small gravitational attachment to.

        Added to which, if the engine does go <bang> then it's hard to say which pieces will go in which directions, and at what speed - so making any predictions about w

      • And what, exactly, can blow up on a nuclear rocket?
      • I call BS.

        To the uninitiated, I agree it sounds bad. "OMGWTFBBQ we're putting NUKES in SPACE!!1!"

        But it's not actually that bad. The fact is, uranium is not that radioactive before it has been in a nuclear reactor. I have held kilogram-quantities of uranium in my hands -- and still have all 10 fingers to show for it. Plutonium is more radioactive -- half a kilogram is warm to the touch -- but it's not deadly as long as it stays external to your system.

        The nastiness starts coming in after the re

        • by a_hanso (1891616)

          I have held kilogram-quantities of uranium in my hands -- and still have all 10 fingers to show for it. Plutonium is more radioactive -- half a kilogram is warm to the touch

          Just out of curiosity, have you ever tried to figure out what went down in between all those times when you got angry and those times you woke up somewhere in torn pants?

    • by symbolset (646467) *
      Indirect Toynbee tile reference. +1 for the reference, +1 for subtlety. I don't get mod points any more for some obsure reason, so this is what I can do.
    • Re:Good luck (Score:5, Informative)

      by dkf (304284) <donal.k.fellows@manchester.ac.uk> on Saturday January 21, 2012 @06:47AM (#38773010) Homepage

      Anytime anyone even thinks about mixing "nuclear" and outer-space (even radioisotope generators as used on many space probes) all the anti-nuclear groups kick up a huge fuss.

      Sucks to be them, then. Any time you push beyond the inner solar system, you need some sort of nuclear power to get electricity, as you can't burn things or use hydroelectric or wind-power. You can use solar panels in the inner solar system, but the further out you go the less practical that becomes. IIRC, solar is a no-go much beyond about the orbit of Mars, even for relatively low-power applications. High thrust engines are not low-power!

      What's more, as long as you're outside the Earth's magnetosphere, any nuclear explosion is exceptionally unlikely to contaminate Earth (or the Moon) as the solar wind will push all of the small particles out to interstellar space. Yes, you could be hit by a large piece even so, but that would be amazing bad luck; space is damn big.

    • Anytime anyone even thinks about mixing "nuclear" and outer-space (even radioisotope generators as used on many space probes) all the anti-nuclear groups kick up a huge fuss.

      Yes, look at the fuss kicked up over New Horizons and Curiosity... Oh, wait there wasn't any.

      Seriously, this myth (about anti-nuclear activists) needs to die in a fire. Over time, the protests have gotten quieter and quieter and come from ever further out on the lunatic fringe - until, over the last few years, they've become es

      • Yes, look at the fuss kicked up over New Horizons and Curiosity... Oh, wait there wasn't any.

        Probably because noone told them there were RTG's on those spacecraft. It's not like they glow from radiation, after all (and I suspect that many of the anti-nuke whackjobs really do believe that "nuclear" power plants/etc GLOW)....

      • Derek,
        Sending up small amounts is now accepted. Sending up the amount needed for NERVA would drive the same group that objected to the IFR batty. ANd yes, they would protest.

        But there is a simple solution. Send up a small processing/breeder unit to space, and then send up safe uranium. At that point, it gets bred to plutonium and allowed to be used.

        I wonder if a NERVA can be used to land on the moon? If so, that would become a truck. I noticed that Japan found Uranium on the surface, though quantity
        • I don't believe NERVA can be throttled that deeply... if that's true, it can't be used as a lander engine.

    • Re:Good luck (Score:5, Insightful)

      by BoRegardless (721219) on Saturday January 21, 2012 @09:59AM (#38773548)

      Nearest Star = 4.2 light years. At the moderate speeds we would be able to generate to accelerate, but then an equal amount of fuel to decelerate to enter orbit around such a star in time measured in something larger than 10s of thousands of years at survivable speeds that don't erode the probe down from "plasma erosion" like you have with a plasma jet cutting machine.

      Helium, Hydrogen and Protons and electrons hitting any metal or ceramic surface at huge speeds eventually cut through, even if only in thousands or tens of thousands of years.

      A signal back from the probe would then take 4.2 light years to reach back to earth......if it didn't hit the smallest little rock or ice chunk along the way, which is a real undetectable possibility, and at the high speeds it takes, those would be fatal.

      I understand the thrill of the thought process and the income if you are on the program and getting paid.

      As a taxpayer, it leaves me as cold as intersteller space.

      • As a taxpayer, it leaves me as cold as intersteller space.

        It leaves me with a warmer feeling than most of the things we spend our money on. Er, excuse me, we spend our kid's and grand kid's money on.

        Your cold hearted appraisal of the issues certainly has validity, but stuff like that hasn't stopped us in the past.

      • by 0111 1110 (518466)

        Where are you getting your data from? The hydrogen in interstellar space is very sparse and what little there is might be scooped up and used for fuel with a magnetic scoop. A super-Orion sized craft could reach speeds of up to about 0.1c. At that speed Alpha Centauri is only 44 years away. The chances of hitting a macro sized object in interstellar space are low. The vast majority of matter in the galaxy has already clumped into solar systems.

      • by Patch86 (1465427)

        Citation needed, on the travel time aspect.

        Project Orion (the 1970's attempt at a thermonuclear rocket) would have take 44 years to reach Alpha Centauri (assuming a fly-by with no deceleration time, and excluding 36 days worth of acceleration to it's top speed). A long time by human standards, but a very very long way short of "10s of thousands of years". If you launched one today, you could get your first pictures back in almost the same amount of time as between Apollo 11 and today. That's travelling abou

        • by the gnat (153162)

          Project Orion (the 1970's attempt at a thermonuclear rocket) would have take 44 years to reach Alpha Centauri (assuming a fly-by with no deceleration time, and excluding 36 days worth of acceleration to it's top speed).

          That was Freeman Dyson's calculation of what sort of extreme the technology could be pushed to; it's by no means a sure thing. However, the Orion drive was vastly more complicated (and expensive) than the nuclear thermal rockets they're talking about in the article, which would never be able

          • by jamstar7 (694492)

            Also, an NTR is something that a private company could theoretically build,

            Yeah, they can build it, they just won't be able to fuel the reactor. Governments get nervous at the thought of plutonium in private hands that can leave an easily monitored site.

            I'm thinking recalculate for http://www.thorium.tv/en/thorium_reactor/thorium_reactor_1.php [thorium.tv]thorium reactors. Thorium reactors don't go 'boom'.

          • by EdZ (755139)

            However, the Orion drive was vastly more complicated (and expensive) than the nuclear thermal rockets they're talking about in the article

            Not really, no. Ol' put-put is a dirt simple device: a gun to fire bombs a short distance, and a big honking pusher-plate on heavy suspension. A NTR needs some pretty esoteric construction materials to maintain integrity at the very high operating temperatures used (and some rather creative layout of the fuel elements to allow good hypersonic flow), whereas the Orion drive just needs to be big and heavy. The bigger the better, in fact; it scales up better than it scales down.

      • by khallow (566160)

        Nearest Star = 4.2 light years. At the moderate speeds we would be able to generate to accelerate, but then an equal amount of fuel to decelerate to enter orbit around such a star in time measured in something larger than 10s of thousands of years at survivable speeds that don't erode the probe down from "plasma erosion" like you have with a plasma jet cutting machine.

        [...]

        As a taxpayer, it leaves me as cold as intersteller space.

        Well, it's a good thing then that you aren't paying for it. I imagine people who live much longer than we do, would have a different take on the value and cost of such things. But they'll get to use their own money for that. Nuclear-powered propulsion has more practical uses within the Solar System than without.

  • Car analogies (Score:2, Insightful)

    by Anonymous Coward

    Brad Appel of General Propulsion Sciences frames the situation in more familiar terms: "To look at it another way, imagine you are planning a road trip from New York to Los Angeles and back. Except, there are no gas stations along the way -- you need to pack all of the fuel along with you. Using a chemical rocket to send humans to Mars would be like making the road trip in a cement truck. You might barely make it, but it would be one enormous, inefficient, and expensive voyage. Using an NTR, however, would

  • legal? (Score:4, Interesting)

    by kaspar_silas (1891448) on Saturday January 21, 2012 @06:03AM (#38772842)
    Sounds exactly like 1955s project Orion. And similarily to it I don't think they can actually legally work on this idea due to international nuclear regulation. In particular the comprehensive test ban treaty. Because after all what you are designing is something very like an icbm with a "dirty" warhead. I god damn guarantee if Iran openly worked on this the US would bust itself to attack ASAP.
    • Re:legal? (Score:5, Informative)

      by Anonymous Coward on Saturday January 21, 2012 @06:25AM (#38772932)

      Nothing at all like Orion. This is using hydrogen as the reaction mass, heating it with a fission reactor. Orion uses nuclear bombs set off repeatedly behind a fscking huge steel plate.

      You're right about there being international nuclear regulation that may stop it, though - if I recall correctly, there are legal hurdles to even test-flying nuclear reactors up to orbit and all kinds of international agreements following near-misses with both soviet and american test reactors in the 60s.

      • nope. Not from a treaty POV. We send up reactors all the time. NERVA has ZERO issue going. Orion is a different matter. Those are technically bombs on there. The treaties prevent that from going to space, though I suspect that if we got ALL of the signatories to agree to it, we could do it. And I have serious doubt that we could get that, except when an asteroid or some other major threat were in-bound to earth (and in light of how America's CONgress is acting, I would guess that even with a massive alien i
    • Re:legal? (Score:5, Informative)

      by cbhacking (979169) <[moc.oohay] [ta] ... isiurc_tuo_neeb]> on Saturday January 21, 2012 @06:53AM (#38773036) Homepage Journal

      Nuclear thermal rocket != nuclear pulse rocket. The latter is the classic "Project Orion" engine, utilizing super-critical explosions for propulsive force. The former is actually more akin to a traditional chemical rocket, in that it works by expelling reaction mass from thruster nozzles. However, the energy of the reaction mass is imparted by heat generated in critical or sub-critical (but not super-critical) nuclear reactions. You can use any number of materials for this reaction mass, though the popular ones are hydrogen and water. Neither is inherently harmful, nor is there any reason they would need to pick up radioactivity from the reactor (any more than the cooling water which cycles through the heat exchangers of nuclear electrical plants or naval vessels becomes radioactive).

      The test ban treaty has nothing to do with this. Nuclear pulse rockets are certianly forbidden by the test ban treaty - after all, they are literally exploding nuclear bombs as part of the engine's normal operation - but there's no reason nuclear thermal rockets would be that I can see. The argument about a "dirty warhead" is potentially valid (in that some would claim it, not in that it would be a plausible danger when you consider we already have nuclear-tipped ICBMs). However, there's no law or treaty against launching radioactive material into space. In fact, quite a few of our space probes and planetary rovers use radioactive thermal generators.

      Compared to chamical rockets, nuclear thermal rockets have a vastly higher specific impulse, which is to say that a given quantity of reaction mass (rocket fuel or hydrogen flowing past a reactor) can produce a greater thrust (simply put, higher efficiency). This is due to their (much) higher exhaust velocity. Remember, E (in Joules) = mass (in kg) * velocity (in meters/second) squared. If you divide both sides by kilos (fuel or reaction mass), your energy per unit of reaction mass becomes a function of v^2. In other words, doubling the speed of the reaction mass will get you four times as much energy for a given unit of reaction mass.

      Since the amount of thrust you can get out of the quantity of reaction mass that can be placed on a spaceship is the current limit on spacecraft range, speed, and payload, increasing that efficiency has the potential to revolutionize space travel.

      • oops. I should have read yours first. You are correct.
    • by jamstar7 (694492)
      Orion was the one you set off nuclear bombs under a heavy plate as a thrust mechanism. BiFrost is basically an upgraded NERVA system, from what little I can gleam from the article. Not a lot of hard science in it.

      NERVA basically pumps liquid hydrogen through a fission reactor core. The core heats up the hydrogen, it expands, escapes through the bottom of the reactor and the nozzle providing thrust. Think 'tea kettle'. It'll help you visualise it.

      The best reaction mass for this concept is stabilized m
    • by gatkinso (15975)

      Clearly you are either unfamiliar with Project Orion, or you didn't read the article.

  • Credibility (Score:4, Insightful)

    by Extremus (1043274) on Saturday January 21, 2012 @06:14AM (#38772894)

    It would be easier to believe in these guys if they provide more technical details in how they pretend to achieve fission propulsion. As it is mentioned in the article, this is not a new idea. Is there any new development that could cast new light on the problem of fission propulsion?

    • by 0123456 (636235)

      Is there any new development that could cast new light on the problem of fission propulsion?

      What problem? We've built and tested fission rockets; the only problem is getting them into space when politicos would prefer to listen to the anti-nuclear luddites.

  • Nothing new (Score:4, Interesting)

    by tsotha (720379) on Saturday January 21, 2012 @07:17AM (#38773118)

    There's nothing new here. It's another "study" rehashing technology that's been rehashed over and over for at least sixty years. And anyway nuclear thermal rockets don't address the biggest problem we have with space exploration, which is getting to orbit in the first place. Heinlein famously observed "Get to low-Earth orbit and you're halfway to anywhere in the solar system." But the converse is also true - no matter how good your deep space rocket is you're only half way to where you want to be.

    Nuclear thermal rockets have a wonderful ISP, but they don't have as much thrust as chemical rockets, and they're heavy. Even assuming you wanted to use one for the first stage it probably wouldn't have enough thrust to do the job. And you wouldn't want to start one up on earth, either. They never did figure out how to keep bits of the radioactive core from breaking off and entering the exhaust stream,

    • by Hentes (2461350)

      You could build the ship in orbit thus circumventing those problems.

      • by tsotha (720379)

        Well, yes, you could. But now you'll have to send up a bunch of extra kg into orbit, and the whole point of having an engine with high ISP is to get really good performance from your fuel because you didn't want to send a bunch of extra kg to orbit.

  • I was under the impression that the new Vasimir or Ion drives were WAY more efficient than this old tech. The only limiting factor is the size we currently them at.
    Imagine an ion drive with 8 or ten modules, all powered by a fission reactor, it would start slow, but by the time it got halfway through the solar system would be cooking along at good clip. How fast is the potential ? No one seems to know, but a constant acceleration sustained for years would get you to a nice portion of C.
    • If we wanted to go to another star system far in the future would it be possible to build an electromagnetic ramscoop [wikipedia.org] ship or is that still in the realms of fantasy? Such a ship could get to the centre of the Milky Way galaxy in 25 years ship time, although 50,000 years would have passed by on Earth. The only question is what would the Earth look like politics wise in 100,000 years?

      Would they have forgotten about you? What sort of technology do you really need to construct a ship to constantly accelerate at

      • by gatkinso (15975)

        I have read rebuttals to the ramscoop concept. Not sure if they are valid or not. One thing however that seems right: the amount of radiation produced by such a system is thought to be deadly to life. So such ships would have to be unmanned.

        • by drinkypoo (153816)

          At the point where we can actually do it, perhaps we can create an inverse field to protect crew. But they're theoretically plenty useful for unmanned probes, anyway.

      • This was already shown that the drag from the magnetic scoop was more than the energy that was derived from the particles. IOW, no.
      • by stevelinton (4044)

        Ramscoops, as described in the literature have basically two problems:

        1. Getting protons (as opposed to deuterium or something heavier) to fuse at a decent rate requires conditions substantially hotter and denser than found in the cores of even quite large stars. Something more like the conditions met in shockwaves in exploding supernovae. Without this your ramscoop isn't much use.

        2. The interstellar medium is very unevenly distributed. The sun is deep inside the bubble created by an ancient supernova, so t

    • by Oidhche (1244906)
      Ion engines have wonderful Isp, but very low thrust. And it's not just that a journey with such an engine would be longer - low-thrust transfers are inherently less efficient than Hohmann transfers, negating some of the Isp advantage. Moreover, you couldn't reach a nice portion of c with current ion engines: their Isp is good, but not that good. Most of them only have at most a few hundred km/s of effective exhaust velocity, limiting the maximum delta-v to like 0.3%-0.5%c under any design with realistic ma
    • Sigh.
      Ok, a VASIMR (a type of an ion engine) can drive an ion out at high speeds. HOWEVER, where does it get the energy to accelerate the ion from? Obviously from a generator or a solar collector. The problem with the solar collector is that not only does it add drag, it does not work as you get further and further from the sun. So, that leaves a nuke reactor. How much does it weigh? A lot. The real problem is one of efficiency and the fact that it will break down. To get electricity, you had to convert
      • This type of problem is why fusion is also considered an ideal propulsion system - because the fusion reaction itself is an electrically responsive plasma, so you can go more or less directly from energy generation -> propulsion.

      • by drwho (4190)

        Regarding the weight of nuclear reactors - I don't know exactly what 'a lot' means, in terms of weight, to WindBourne. I can mention that newer designs of nuclear (fission) power plants are smaller. The steam turbine will be replaced by a helium turbine. One of the advantages of space (when away from stars) is that heat loss due to radiation is high, so cooling is easier, so the difference in gas pressure between helium heated by a fission reaction and that at the other end of the turbine, cool be radiation

    • Basic physics tells you that total delta-V for any kind of rocket comes down to just two things: how much of the ship you can throw away to get thrust (mass ratio) and how fast you can throw it (exhaust velocity). For mass ratios of less than say 1000 (ie ship at launch no more than 99.9% reaction mass at launch), and non-relativistic exhaust velocities, total delta-V is no more than 8-10 times the exhaust velocity. Exhaust velocity of chemical rockets tops out at about 3-5 km/s, nuclear thermal rockets g

    • by jamstar7 (694492)
      Ion drives are more efficient, but they don't have enough thrust to take off in a gravity field. You need something with high thrust like a NERVA or a conventional rocket to pull that off. Otherwise, all us space cadets would have built ion rockets and left already.
  • What we need is a reusable and reliable system to get objects out of earth's orbit. I would think the nuclear energy would be better utilized in a magnetic launch system. After that is established, then building an ORION/NERVA powered vehicle in space would be practicle. Using an ORION/NERVA powered launch rocket isn't my idea of a good start, so to speech.

  • "Mass ejection" propulsion is so last century. Where are the darn warp drives? I say: "Go FTL or go home."

  • The problem is that we have so many left wingers that are gaga over the idea of nukes being launched into space. Yet, we could easily put up a small processing plant on either the moon or even in space, and simply send a safe form of Uranium up there to be processed and bred.
  • I thought this was banned by international treaty.

  • by Patch86 (1465427) on Saturday January 21, 2012 @01:22PM (#38774812)

    Reminds me of one of my favourite geek-out websites:

    www.projectrho.com/rocket/

    If only more writers of science fiction television trash would spend just one afternoon of their life skimming that website...

  • Too bad they won't name it "The Queller Drive" (cf. http://en.wikipedia.org/wiki/Voyager_One_(Space:_1999) [wikipedia.org] ) a fun scifi plot device being that there's this space drive system that gets you there really fast, but unfortunately kills everything that's in its wake.
  • Anyone who has any knowledge of space travel knows the issues raised in the referenced article. If you didn't care about space, you wouldn't read the article. Please, can we have reference to more scientific articles which advance the knowledge of geeks (that's what slashdot is for, remember)? I feel dumber just for having read that article.

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