Summary of fuel-carrying propulsion systems

I've looked around on the internet and found some statistics on existing and proposed propulsion systems for spaceships. At the bottom of the page is a discussion of the specific impulse we need for TEP.

I make no claim as to the accuracy of any of this stuff, beyond that it mostly came from NASA sites. Some of the electric-propulsion ideas came from "Plasma Propulsion in Space", Eric J. Lerner, The Industrial Physicist Oct 2000 pp. 16-19. Here are some definitions used in the table:

Existing

has been flown or will be flown soon

Theoretical

we could build one without any major technological breakthroughs

Wild

we could build one with major technological breakthroughs but no new physics

Isp

Specific impulse, which is for a mass m of fuel thrust * time maintained divided by acceleration of gravity at earth's surface. This is measure of the efficiency of a drive. It relates directly to the exhaust velocity: specific impulse is exhuast velocity / g (9.8 m/s^2).

Plume Temperature

This and the mass flow rate determine how far away you can see one of these drives firing. For many of these systems, the answer is "all the way across the solar system."

Here's more explanation of what the systems are:

Chemical rocket

These statisics are for the Space Shuttle Main Engine (SSME), "the most efficient liquid rocket ever flown" (says NASA). The plume temperatures given are for general big chemical rockets, not specifically for the SSMEs.

Ion engine

Ion engines, also called electrostatic engines, use an electric potential to accelerate the ions in a plasma, which are then shot out the back at high speeds. They characteristically produce very low thrust. The first row is for the Deep Space 1 (DS1) vehicle, which I think has either flown or is about to be flown. The second row is a claim I saw on a NASA site as an upper limit.

Hall-effect engine

Rather than using a static electric field to accelerate ions, they can be accelerated through the interactions of magnetic fields and currents. This has the advantage that it spits out a neutral plasma rather than a stream of same- charge ions, so the spacecraft doesn't accumulated charge.

Magnetoplasmadynamic engine

Uses the Lorentz force from a radially outward directed electric current and its self-induced magnetic field to accelerate a (net) neutral plasma. These are pretty high-thrust devices, and one is serious use would presumably be powered by nuclear fission. None have flown yet, but they are under consideration for some upcoming NASA missions.

Fission rocket

The first row is a gas core fission reactor, in which the fission reaction heats LH2 which is the reaction mass. This is also called "nuclear thermal propulsion." The second row is for the NERVA system, a less efficient version which was built in the 1970s. Other fission rockets have been built with I_sp as high as 1100 s.

Electric Fission

NASA calls this "nuclear electric propulsion"; it is simply using a fission reactor to power an ion engine. The numbers given are for the "Leaky Magnetic Mirror" engine concept, which NASA has been playing with for a while but currently can't be built.

External Fission

Throw small fission bombs out the back of your spaceship and let the shocks push you. NASA's Orion project back in the '60s was based on this, and it was very efficient at the time. This one has the emissions of a bunch of small fission bomb blasts. NASA built a prototype using dynamite bombs.

Fusion rocket

I rate this as very theoretical because we can't make fusion reactors that break even yet. It's just like a fission rocket but with fusion.

Electric fusion

There are many suggestions for how to do this; the numbers given are theoretical numbers for a design called a "plasma focus", which uses a capacitor bank to generate a pulsed sheet of current which runs down a barrel between coaxial electrodes, and is pinched to a narrow focus at the end. The focus produces enough compression to start fusing, and as they decay form focused beams of ions that shoot away, propelling the ship.

External Fusion

This works just like external fission, but uses fusion bombs. Actually most proposals use fuel pellets that are ignited with lasers, or something. I rate this as theoretical because we could use our existing nuclear arsenals to build one. NASA had one of these on paper only, called the Daedalus project.

What specific impulse do we need?