Re: Energy and momentum conservation in space propulsion

Centrillium wrote:

A question: what is the power requirement of a reactionless drive,
where a reactionless drive is a box upon which a net force acts when it
is supplied with power?

Does this question have a sensible answer, or is the concept inherently
unphysical? Would the result you derived above indicate that the power
requirement of the reactionless drive should increase with time, as the
spacecraft gains velocity?

As we've already discussed, the amount of kinetic energy required to accelerate something is frame dependent, so this means that the energy-momentum converter has some bizarre properties.

Really, once you've broken something as fundamental as conservation of momentum it's probably hard to come up with a coherent situation where you reformulate the rest of the laws into something consistent about that one's absence. It's the equivalent of creating a new set of physics laws.

To put this into context, consider the following. You wish to create
the biggest possible bang upon the surface of some planet, and you have
an amount of antimatter, a device to convert this antimatter to useful
energy, and a reactionless drive. Intuitively, the following would
seem to be obvious: annihilating the antimatter and using the energy
produced to run the reactionless drive to accelerate an object to some
velocity, and allowing it to impact the planet, should not create as
big a bang as simply placing the antimatter in contact with the planet.
Assuming everything is 100% efficient, the power requirement of the
drive should be such that the kinetic energy of the spacecraft once all
the antimatter is used up is equal to the energy equivalent to twice
the mass of the antimatter, or so it seems to me. What power
requirement can be placed upon a reactionless drive, such that this is
satisfied?

Why do you need a reactionless drive here? A conventional drive to accelerate your antimatter bottle toward the surface of a planet is just fine. The planet is made of matter, and so when the ship hits it, the antimatter bottle is ruptured and antimatter leaks out, annihilates with the surrounding matter, which releases huge amounts of energy, which vaporizes the ship, which releases all the antimatter, which then all annihilates in short order.

--
Erik Max Francis && max@xxxxxxxxxxx && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
Maybe this world is another planet's Hell.
-- Aldous Huxley
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