Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Nuclear Powered Craft

  1. May 2, 2004 #1
    I've been reading (rather, re-reading) Robert Zubrin's book Entering Space, in which he makes some fairly damning accusations of Michio Kaku. I'd like to know how Dr. Kaku responded, or if he did. I'd also like to hear from anybody who could argue Dr. Kaku's case, and people thoughts in general about the accusations.

    All my information here is from Zubrin's book, so if it's wrong, blame him, not me. I'll simply state what Zubrin says Dr. Kaku has done as fact, to avoid having to begin every sentence with "According to Zubrin."

    Dr. Kaku has demonstrated and filed lawsuits in attempts to block the launch of every recent radioisotope-equipped probe. According to Dr. Kaku and other anti-nuclear activists, the launch of radioisotope thermoelectric generators (RTGs) poses an intolerable risk to the atmosphere because a launch failure could spread plutonium into the atmosphere and pollute the world. In a debate with NASA's ex-nuclear program director Dr. Gary Bennet, Dr. Kaku claimed that the Galileo space probe could perform just as well using batteries.

    An RTG contains about 100,000 Ci of Pu-238. According to Zubrin, if a launch of an RTG-powered probe were to fail, the RTG and all the plutonium it carried would stay intact and sink like a brick into the Atlantic subseebed dowrange of Cape Canaveral. But, if for some reason the plutonium was released and spread around in the Earth's biosphere, it would represent 1% of 1% of the radiation released by a typical nuclear bomb test. To put that in another perspective, it would represent a smaller fraction of the average person's daily radiation dose that the half-dozen or so sunken U.S. and Soviet submarines.

    There is no danger of some rogue nation or terrorist picking up the plutonium, either, as the Pu-238 used in RTGs is not the right kind for nuclear bomb, which use Pu-235. Plus, the Pu-238 is not used as-is in metallic form, but as plutonium oxide, a chemically inert substance which could never become chemically attached to anything and hence never rise from the seebed.

    "equally silly," says Zubrin, "is Professor Kaku's assertion that outer solar system probes could be powered by batteries." The Galileo spacecraft was powered by two 300 W RTGs and warmed by several hundered 1 W radioisotope haeting units (RHUs) for about 800 W of power in all. In Zubrin's discussion, he (for the purpose of argument) assumes this is overkill and that the probe needed only 200 W of power. (This makes his conclusion even more difficult to refute). Zubrin says in his book, "Good primary batteries can store about 300 W*hr/kg. Galileo left Earth in October 1989, and as of August 1998, or 70,000 hours later, was still functioning. At 300 W*hr/kg, that would be about 47,000 kg of batteries! (The two RTGs currently on board weigh about 60 kg; the RHU mass is neglible.) Of course, with this much battery mass, the power requirement would be much greater than 200 W, since the spacecraft would require additional power to keep the batteries from freezing. To keep 47,000 kg of batteries (about 5,000 gallons' worth) warm, we would probably need to expend at least 2000 W. But to supply that power, we would need 470,000 kg of batteries, which would need 20,000 W to keep warm, which would require 4,700,000 kg of batteries, and so on. The mission is clearly impossible on battery power."

    Zubrin goes on to advocate the use of a 30 kW nuclear fission reactor for interplanetary probes; the threat this would pose during a failed launch would obviously be significantly higher. But his point about RTGs and RHUs still stands. Has Dr. Kaku countered this argument? Can anybody here? Does anybody agree with Zubrin? Any thoughts at all?
    Last edited: May 2, 2004
  2. jcsd
  3. May 27, 2004 #2
    Sounds to me like all we need to do is improve the launch. If everyone is so scared of a failed launch, someone needs to stop screwing around. :D
  4. Jun 16, 2004 #3
    Amen Brother

    Another project that was killed for almost the exact same reason was project ORION. This actually used Thermonuclear explosions to propel itself through space at ridiculously fast speeds. These ANTI-NUC NAZIS have been using the same excuses for the past 30 yrs. It is about time for someone to tell them to shut their ugly faces.
  5. Jun 17, 2004 #4
    Project Orion, I must say, does scare me. If the fututre of spaceflight really does lie in the commercial sector as this coming Monday's launch of SpaceShipOne would seem to indicate, I'm not sure it's a great idea to mass produce nuclear bombs and distribute them to companies. Not to mention that the pusher-plate is wildly inefficient. Still, I agree with Zubrin about the nuke stuff.
  6. Jun 17, 2004 #5
    I agree that commercial launches are the future, but nasa could build a few orions to explore with. The pusher plate was efficent enough for all practical purposes.
  7. Jun 18, 2004 #6


    User Avatar
    Staff Emeritus
    Gold Member
    Dearly Missed

    Orion technology would be good for nudging dangerous asteroids into safer orbits. It could do the large delta-vee required, and all the nuclear explosions would be well away from the earth.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Nuclear Powered Craft
  1. Nuclear Power (Replies: 18)