Spacecraft propulsion
From Wikinfo
There are many different ways to accelerate spacecraft. Below is a summary of some of the more popular, proven technologies, followed by increasingly speculative methods.
Three numbers are shown. The first is the specific impulse which is the amount of thrust that can be produced using a unit of fuel. This is the most important characteristic of the propulsion method as it determines the top speed available for the propulsion method.
The second and third are the typical amounts of thrust and the typical burn times of the method. One interesting and somewhat counterinituitive physics result is that outside a gravity well, the total energy provided by a propulsion mechanism is equal to the thrust times the time the thrust is applied. Hence, outside a gravitational potential small amounts of thrust applied over a long period will give the same effect as large amounts of thrust over a short period.
This result does not apply when the object is influenced by gravity.
| Method | Specific Impulse (seconds) | Thrust (Newtons) | Duration |
|---|---|---|---|
| Conventional propulsion methods | |||
| Solid rocket | 100-400 | 103- 107 | minutes |
| Hybrid rocket | 150-420 | minutes | |
| Monopropellant rocket | 100-300 | 0.1-100 | milliseconds - minutes |
| Momentum wheel (attitude control only) | n/a | 0.001-100 | indefinite |
| Bipropellant rocket | 100-400 | 0.1-107 | minutes |
| Tripropellant rocket | 250-450 | minutes | |
| Dual mode propulsion rocket | |||
| Air-augmented rocket | 500-600 | seconds-minutes | Liquid air cycle engine | 450 | seconds-minutes |
| Resistojet rocket | 200-600 | 10-2-10 | minutes |
| Arcjet rocket | 400-1200 | 10-2-10 | minutes |
| Hall effect thruster (HET) | 800-5000 | 10-3-10 | months |
| Ion thruster | 1500-8000 | 10-3-10 | months |
| FEEP (Field Emission Electric Propulsion) | 10000-13000 | 10-6-10-3 | weeks |
| Magnetoplasmadynamic thruster (MPD) | 2000-10000 | 100 | weeks |
| Pulsed plasma thruster (PPT) | |||
| Pulsed inductive thruster (PIT) | 5000 | 20 | months |
| Variable specific impulse magnetoplasma rocket (VASIMR) | 1000-30000 | 40-1200 | days - months |
| Solar thermal rocket | 700-1200 | 1-100 | weeks |
| Nuclear thermal rocket | 900 | 105 | minutes |
| Nuclear electric rocket | As electric propulsion method used | ||
| Solar sails | N/A | 9 per km2 (at 1 AU) | Indefinite |
| Mass drivers | N/A | Indefinite | seconds |
| Tether propulsion | N/A | 1-1012 | minutes |
| Technologies requiring more engineering development | |||
| Magnetic sails | N/A | Indefinite | Indefinite |
| Mini-magnetospheric plasma propulsion | N/A | Indefinite | Indefinite |
| Gaseous fission reactor | 1000-2000 | 103-106 | |
| Nuclear pulse propulsion (Orion drive) | 2000-100,000 | 109-1012 | half hour | Antimatter catalyzed nuclear pulse propulsion | 2000-40,000 | days-weeks |
| Nuclear salt-water rocket | 10,000 | 103-107 | half hour |
| Beam-powered propulsion | As propulsion method powered by beam | ||
| Nuclear photonic rocket | 5x106 | 1-105 | years |
| Biefeld-Brown effect (see also Lifter) | N/A | 0.01-1 (currently) | weeks, probably months |
| Significantly beyond current engineering | |||
| Fusion rocket | |||
| Bussard ramjet | |||
| Antimatter rocket | |||
| Redshift rocket | |||
| Requires new principles of physics | |||
| Alcubierre drive (Warp drive) | Not Applicable | ||
| Wormholes | |||
| Differential sail | |||
| Disjunction drive | |||
| Diametric drive | |||
| Pitch drive | |||
| Bias drive | |||
| Time machines | RS Model Warp Drives | ||
Launch mechanisms
The launch of a spacecraft from the surface of a planet into space places special requirements on the methods of propulsion used. Generally speaking high thrust is of vital importance for launch, and many of the propulsion methods above do not provide sufficient thrust to be used in this capacity. Exhaust toxicity or other side effects can also have detrimental effects on the environment the spacecraft is launching from, ruling out other propulsion methods. Currently, only chemical rockets are used for the launch of spacecraft from Earth's surface.
One advantage that spacecraft have in launch is the availability of infrastructure on the ground to assist them. Proposed ground-assisted launch mechanisms include:
- Space elevator
- Hypersonic skyhook
- Electromagnetic catapult (rail gun, coil gun)
- Laser propulsion (Lightcraft)
References
- Adapted from the Wikipedia article, "Spacecraft_propulsion" http://en.wikipedia.org/wiki/Spacecraft_propulsion, used under the GNU Free Documentation License
