You use a Prometheus generator to get to the asteroid or comet and do insertion, then use the electric power to fire a laser at it. The jet reaction caused by this provides your change in velocity.

Since you're using the asteroid or comet's own mass for fuel, it's more efficient than simply attaching the spacecraft to it and using its engine to do the job.

Why the f* Weiler didn't adopt planetary protection instead of a trip to Jupiter as a vehicle for the development of space nuclear electric power generators is beyond me. Maybe he could stick it on as a followup program to the Jupiter trip, then cancel Jupiter.

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