Sunday August 3, 2003
Book 3: Under New Management — Part III: Board of Accidental Tourism
Building a gas-giant colony ship is not as difficult as it looks.
  1. Build a fusion candle. It's called a "candle" because you're going to burn it at both ends. The center section houses a set of intakes that slurp up gas giant atmosphere and funnel it to the fusion reactors at each end.
  2. Shove one end deep down inside the gas giant, and light it up. It keeps the candle aloft, hovering on a pillar of flame.
  3. Light up the other end, which now spits thrusting fire to the sky.
  4. Steer with small lateral thrusters that move the candle from one place to another on the gas giant. Steer very carefully, and signal your turns well in advance. This is a big vehicle.
  5. Balance your thrusting ends with exactness. You don't want to crash your candle into the core of the giant, or send it careening off into a burningly elliptical orbit.
  6. When the giant leaves your system, it will take its moons with it. This is gravity working for you. Put your colonists on the moons.
For safety's sake, the moons should orbit perpendicular to the direction of travel. Otherwise your candle burns them up. They should also rotate in the same plane, with one pole always illuminated by your candle (think "portable sunlight"), and the other pole absorbing the impact of whatever interstellar debris you should hit (think "don't build houses on this side")

Whether or not your gas giant heats up to the point that it ignites and turns into a small star depends largely on how much acceleration you're trying to get out of your candle. Remember, slow and steady wins the race!

Addendum to Note: Larry Niven suggested that such an arrangement could be used to move rocky worlds from one orbit to another, and he wrote a novel entitled A World Out of Time in which the Earth was moved with the help of giant candle they'd shoved up Uranus. I'm not making this up.

Transcript

Ennesby: These robots are a menace to themselves and anyone around them.
Narrator: Under the sands of an unnamed world, Ennesby-Mind of the mercenary ship Serial Peacemaker-Reports on the true nature of an interloping sail ship.
Ennesby: The debris-ring around this star is the result of their failed attempt to colonize this system. They crashed a gas giant.
Tagon: You mean they crashed into a gas giant?
Ennesby: They did that, too. They crashed one gas giant into another. Apparently the lifting end of the engine choked on some unexpected chemistry, and the thrusting end shoved the engine clear into the diamond core of the gas giant they were piloting.
Ennesby: By the time the crew got it repaired, they were going too fast to slow down. My guess is that they tried to shed velocity with a series of close passes on other giants in the system, and screwed up that operation, as well.
Ennesby: It's a miracle any worlds in this system survived.
Jevee Ceeta: I bet our primitive friends up on the beach were embarking on true civilization when they got knocked back into the stone age.
Ennesby: Heh. No bet. The fossil record is likely full of pointers to that smoking gun.
Tagon: Smoking gun... That reminds me - I really, really want to shoot them, and then blow smoke out of the barrel of the gun.
Ennesby: Terapedoes don't smoke that way, sir.
Ennesby: I'm sure Kevyn could arrange for a smoking barrel, though.