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Project Bifrost: (Fission) Rockets of the Future?

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  • 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.

  • 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.

  • Re:legal? (Score:5, Informative)

    by cbhacking (979169) <been_out_cruising-slashdot&yahoo,com> 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.

  • 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.

  • 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...

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