582. Newtonian Nukes

Everybody who read the last generation of science fiction juveniles before Apollo knew Newton’s third law:

For every action, there is an equal and opposite reaction.

The demonstrations in popular science books of that same era usually went something like this: imagine a person on a frozen pond wearing ice skates, throwing bricks. Every brick he throws will move him backward. If we could ignore the friction of skates on ice, it would be proportional. That is, if a hundred pound man  . . .

Okay, side issue. Most Americans back then, and even today, don’t think in kilograms or kilometers, nor distinguish mass from weight in everyday thought, so . . .

If a hundred pound man throws a one pound brick at ten miles per hour, it will propel him backward at one tenth of a mile per hour. 1 times 10 = 0.1 times 100. We are ignoring friction from the ice, the atmosphere, and probably a bunch of other things.

So, if you want to go faster, throw more bricks, right? If you throw a thousand bricks, you should be able to go pretty fast, right? Wrong, because the first brick your throw in the new scenario will have to move not only the hundred pound man, but also the other 999 pounds of bricks.

Increasing the amount of fuel carried quickly brings about diminishing returns. More fuel alone is not the answer.

In a Newtonian scenario, the faster the propellant leaves the rocket engine, and the more propellant you use, the faster you can go. LOX and LH are probably near the practical  maximum for propellant speed by chemical reaction. The logical next step would be to use a non-chemical energy source to activate our propellants, such as a nuclear powered rocket. Even that won’t get us to the stars, but it makes sense for travel inside the solar system.

Before Apollo, everyone who read science fiction knew that, which is why the Scorpius and her sisters in the Rip Foster book are nuclear powered. So were the ships in Bullard of the Space Patrol, a marvelous fix-up novel by Malcolm Jameson that no one remembers today. So were the ships in the Dig Allen series (1959 – 1962), six great but forgotten novels, and the ships of the Tom Corbett books, which were not so great and are not completely forgotten.

Star Trek put all these early concepts out of business. Warp speed was a necessity for roaming the galaxy, but it made nuclear rockets look old fashioned. I think that’s too bad. There is still room for them in science fiction, and certainly in real life.

I haven’t mentioned Heinlein yet. The Rolling Stone was nuclear, but he quickly moved on to torch ships, which had the capacity of total annihilation of matter. He never explained how that could be done, but the result would be “propellant” moving at essentially lightspeed. You can’t get faster than that without warp drive. His torch ships roamed the solar system and went on to explore nearby stars.

I stole that schtick for my coreships in Cyan, with a twist. See 23. Star Drives.

In a rational world — which we will probably never inhabit, but we can still write stories about — you would might use chemical rockets to get to LEO (low Earth orbit), nuclear powered rockets to zip around the solar system (fission powered if you were writing in the sixties, fusion powered if you were writing today), and “torch ships” to reach nearby stars. Beyond that, you would need FTL (faster than light) vehicles which, by our present understanding of the universe, are impossible.

Too bad about FTL, but why are we still using chemical propellants in the real world fifty years after Apollo? Fear of nukes, of course. There will be more to say about that on Wednesday.

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2 thoughts on “582. Newtonian Nukes

  1. sydlogsdon Post author

    Actually, it works this way as a general rule. Probes operating near sun use solar panels. Probes working far out use some kind of crude nuclear power. In both cases, these only provide power for the electronics. They get their velocity (delta V) at launch via chemical rockets.

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