Space Travel

Space Travel

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Maneuver Drives

Reaction Drives

Speculative Rocket Types

Fusion rocket

As with a fission rocket, the fusion rocket involves heating reaction mass with a controlled nuclear reaction, then expelling it as hot exhaust. A fusion rocket might offer performance nearly as good as a nuclear pulse drive, without the expense of specialized fuel pellets or the danger of carrying around hundreds of A-bombs.

Reactionless Drives

A reactionless drive is one that produces acceleration without discarding reaction mass. A reactionless drive requires power, and fuel for the power plant, but is not limited by needing to carry around vast amounts of reaction mass. A reactionless drive starship can be extremely efficient, carrying a large payload. Unless the physical principles behind the drive stop working at high velocity, a reactionless drive ship can easily approach lightspeed.

All reactionless drives are superscience, since they violate the known laws of physics. If reactionless drives are available in a setting, the GM should define their performance. The most important factor to consider is the thrust-to-mass ratio. If one ton of reactionless drives can deliver only one-tenth of a ton of thrust, then starships will only be able to manage acceleration up to about 0.1 G (with almost no payload). If one ton of drives can deliver two to five tons of thrust, then accelerations of two to five Gs can be obtained.

Dean Drives

A Dean drive is a class of reactionless drive that (somehow) converts rotary movement into linear movement. The ship's onboard engine includes a big flywheel that is driven by a power plant; the angular momentum of the flywheel can be tapped to accelerate the ship forward.

The Dean drive was "invented" in the 1950s, and was taken seriously by a few people in the SF community. Unfortunately, it was never demonstrated for or duplicated by reputable scientists, and was almost certainly a hoax. In fact, the Dean drive violates several known laws of physics. "Dean drive" can be used as a generic term for any reactionless drive that works by breaking the laws of motion as we currently understand them.

Diametric Drives

Another form of reactionless drive is the diametric drive. Such a drive creates an asymmetrical field of force around itself. The side of the force field that exerts more force on the ship will "push" the ship forward without any need for reaction mass.

Most diametric drive concepts involve manipulating gravity, since that force operates equally on all matter and can provide smooth acceleration.

A bias drive or gravity drive is a diametric drive that alters the force of gravity ahead of and behind the ship. In effect, the ship exists inside a bubble of space-time with its own arbitrary gravity. The ship is in free fall and doesn't feel acceleration, so it can safely pull hundreds of Gs (the speed of light is still an absolute limit).

Diametric drives are completely speculative; at present, we have no idea how to create the kind of force fields they require. They are similar in function to warp drives and may be a spinoff of that technology if it exists in the setting. Meanwhile, bias drives depend on fine control of gravity; they may be associated with artificial gravity or contragravity technologies.

Reactionless Drive (Thruster)

Earth 2100 campaign uses these. I don't care how they work, they just do. Inertia is not negated and gravity doesn't change; a 0.5 G thrust provides 0.5 G of acceleration. Reactionless drives are at TL9.

The reactionless drive, or "thruster", requires power but no reaction mass. This violates physical law as it is understood below TL9. But it is the only way to make lengthy high-G maneuvers possible without incredible amounts of power.

Thrusters are built in standard sizes, for different applications; a ship may carry several thrusters to get to the right total thrust. Standard sizes are 1, 5, 10, 100, and 500 tons, 1,000 tons (1 kiloton), 5, 10, and 20 kilotons.

At TL9, a reactionless drive produces 1 ton of thrust per MW. For each MW consumed, the drive masses 1 ton, takes 4 cy, and costs $50,000. When used in atmosphere, TL9 thrusters produce a great deal of waste heat, making a takeoff as fiery as a rocket's.

At TL10, a reactionless drive produces 1 ton of thrust per MW. For each MW consumed, the drive masses 0.5 tons, takes 2 cy, and costs $20,000. There is much less waste heat; thrusters tend to slag the landing spot but don't incinerate the surroundings.

At TL11+, a reactionless drive produces 10 tons of thrust per MW. For each MW consumed, the drive masses 0.5 tons, takes 2 cy, and costs $20,000. There is no waste heat problem.

Speeds with Maneuver Drives

The fastest way to get anywhere is to accelerate halfway there, turn the ship around, and decelerate the rest of the way. This uses fuel for the whole trip. One can always save fuel by traveling more slowly, or by accelerating only part of the way. Some travel times for constant-acceleration trips:

Distance	0.0001G	0.001G	0.01G	0.1G	0.5G	1G	2G
0.2 AU	4.5 mon	5.7 wks	1.8 wks	4 days	2.5 days	31 h	2 h
0.5 AU	7 mon	9 wks	2.9 wks	6.3 days	5 days	2 days	34 h
1 AU	10 mon	13 wks	1 mon	9 days	7 days	2.8 days	2 days
2 AU	14 mon	4.5 mon	6 wks	13 days	8.5 days	4.1 days	2.8 days
5 AU	23 mon	7 mon	9 wks	2.9 wks	2 wks	6.3 days	4.5 days
10 AU	32 mon	10 mon	13 wks	1 mon	20 days	9 days	6.3 days
50 AU	5.5 yrs	23 mon	7 mon	9 wks	6 wks	2.9 wks	2 wks
100 AU	7.8 yrs	32 mon	10 mon	13 wks	8.5 wks	1 mon	2.9 wks
271,000 AU	2K yrs	723 yrs	226 yrs	68 yrs	44 yrs	23 yrs	15 yrs

2 AU = Earth to Mars, very approximately

271,000 AU = Sol to Proxima Centauri