The most interesting version of this that I've heard of is a "fusion candle", ie a pair of fusion rockets mated back-to-back and hovering in the atmosphere of a gas giant. One rocket thrusts downward towards the planet (ie. rocket plume going upwards), ejecting mass at greater than the planet's escape velocity. The other thrusts upward away from the planet, balancing both the planet's gravity and the thrust from the first rocket. Together they apply a net thrust on the planet, moving the entire thing along with any moons while the rocket exhaust provides heat and power for the inhabitants of the moons.<p><a href="https://worldbuilding.stackexchange.com/questions/36732/fusion-candle-getting-earth-to-jupiter" rel="nofollow">https://worldbuilding.stackexchange.com/questions/36732/fusi...</a>
I have never seen a combination of such interesting individual pages organized in such a horrific way. It's sort of like looking into an alternate universe where the principles of web design turned out totally different from our own.