Non-rocket spacelaunch
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Non-rocket spacelaunch is the idea of reaching outer space mainly without the use of rockets, which today is the only method in use. Transportation to orbit is often the limiting factor in space endeavours. Present-day launch costs are very high — $3,000 to $25,000 per kilogram from Earth to Low Earth Orbit (LEO). To settle space, e.g. space exploration and space colonization, much cheaper launch methods are required, as well as a way to avoid serious damage to the atmosphere from the thousands, perhaps millions, of launches required.
Many alternatives to conventional rockets have been proposed:
- A space tower is simply a conventional tower all the way up to outer space
- A conventional space elevator is a tether spanning from the surface to a point beyond geosynchronous orbit
- A space fountain is an elevator variant held up by a constant particle stream
- An orbital ring is an elevator variant spanning from the surface to a cable rotating around the planet
- A mass driver is a very long vacuum pumped accelerator
- A launch loop is a cable held at high altitude by magnetic levitation
- A space gun is a cannon with a very long gun barrel
- A spaceplane is a plane designed to reach outer space
Contents |
[edit] Comparison
| Method | Estimated building cost in billion dollars |
Estimated cost/kg put in GSO |
Capacity metric tons per year |
Possible with current technology |
|---|---|---|---|---|
| (Conventional rocket) | 3,000 to 25,000 | yes | ||
| Space tower | (impossible with modern technology) | no | ||
| conventional Space elevator | (impossible with modern technology) | no | ||
| Space fountain | ||||
| Orbital ring | 15 [1] | 0.05[1] | ||
| Mass driver | yes | |||
| Launch loop | 10 [2] | 300[2] | 40,000[2] | yes |
| 30[2] | 3[2] | 6,000,000[2] | yes | |
| Space gun | yes | |||
| Spaceplane | yes |
[edit] Space tower
A space tower is a tower that would reach outer space. To fully replace rocket-power in leaving the planet, it would not only have to reach the Kármán line at 100km height, which is a common definition of outer space, but have to reach the geosynchronous orbit at approximately 36.000 km, since any object released at this height could drift away with minimal power. The concept of a structure reaching to geosynchronous orbit was first conceived by Konstantin Tsiolkovsky,[3] who proposed a compression structure, or "Tsiolkovsky tower."
However, made of brick and stone, it could impossibly reach more than 7000 feet or 2 kilometres before the bricks at the bottom were crushed by the weight[4] With more advanced materials it may reach substantially higher, but far from any height of practical use, unless combined with any other method. The latter include being the base station of a space elevator, a pillar for the distal part of a mass driver or the "gun barrel" of a space gun.
[edit] Space elevator
A space elevator focuses on tensile structures (tethers) reaching from geosynchronous orbit to the ground.
The most common proposal is a tether, usually in the form of a cable or ribbon, spanning from the surface near the equator to a point beyond geosynchronous orbit. As the planet rotates, the inertia at the end of the tether counteracts gravity, and also keeps the cable taut. Vehicles can then climb the tether and reach orbit without the use of rocket propulsion. Such a structure could hypothetically permit delivery of cargo and people to orbit at a fraction of the cost of launching payloads by rocket.
Current technology is not capable of manufacturing materials that are sufficiently strong and light enough to build an Earth based space elevator as the total mass of conventional materials needed to construct such a structure would be far too great. Recent proposals for a space elevator are notable in their plans to use carbon nanotube-based materials as the tensile element in the tether design, since the theoretical strength of carbon nanotubes appears great enough to make this practical. Current technology may be able to support elevators in other locations in the solar system however, and other designs for space elevators exist that use current materials.
[edit] Space fountain
A space fountain is a proposed form of space elevator that does not require the structure to be in geosynchronous orbit, and does not rely on tensile strength for support. In contrast to the original space elevator design (a tethered satellite), a space fountain is a tremendously tall tower extending up from the ground. Since such a tall tower could not support its own weight using traditional materials, massive pellets are projected upward from the bottom of the tower and redirected back down once they reach the top, so that the force of redirection holds the top of the tower aloft. Satellite payloads ascend or descend by coupling with this stream of pellets or by climbing up the side of the tower. The space fountain has several key advantages over a space elevator in that it doesn't require materials with extreme strength, can be located at any point on a planet's surface instead of just the equator, and can be raised to any height required. Its major disadvantage is that it is an active structure, and so requires constant power input to remain aloft.
[edit] Orbital ring
An Orbital Ring is a concept for a space elevator that consists of a ring in low earth orbit that rotates at slightly above orbital speed, that has fixed tethers hanging down to the ground.
In the Paul Birch design of an orbital ring system, a rotating cable is placed in a low Earth orbit, rotating at slightly faster than orbital speed. Not in orbit, but riding on this ring, supported electromagnetically on superconducting magnets, are Ring Stations that stay in one place above some designated point on Earth. Hanging down from these Ring Stations are short space elevators made from cables with high tensile strength to mass ratio. Paul Birch found that since the Ring Station can be used to accelerate the orbital ring eastwards as well as hold the tether, it is possible to deliberately cause the orbital ring to precess around Earth instead of staying fixed in inertial space while the Earth rotates beneath it. By making the precession rate large enough, the Orbital Ring can be made to precess once per day at the rate of rotation of the Earth. The ring is now "geostationary" without having to be either at the normal geostationary altitude or even in the equatorial plane. This means that using the orbital ring concept, a Ring Station can be positioned above any point on Earth that is desired, and anywhere on the globe can be served by a space elevator instead of just the equator. A network of orbital ring systems crossing, for example, at the poles, could cover the whole planet with an array of elevators and geostationary ring stations.
[edit] Mass driver
A mass driver is basically a very long and mainly horizontally aligned launch track for spacelaunch, targeted upwards at the end.
It would use a linear motor to accelerate payloads up to high speeds. All existing and contemplated mass drivers use coils of wire energized by electricity to make electromagnets. Sequential firing of a row of electromagnets accelerates the payload along a path. After leaving the path, the payload continues to move due to inertia.
[edit] Launch loop
A launch loop or Lofstrom loop is a design for a belt based maglev orbital launch system that would be around 2000 km long and maintained at an altitude of up to 80 km (50 mi). Vehicles weighing 5 metric tons would be electromagnetically accelerated on top of the cable which forms an acceleration track, from which they would be projected into Earth orbit or even beyond.
The published cost estimates for a working launch loop are significantly lower than a space elevator, with a greater launch capacity, lower payload costs and similar or greater payload masses; and unlike the space elevator no new materials need to be developed.
However, it would constantly need around 200 MW of energy to keep it in place.
The system is designed to be suitable for launching humans for space tourism, space exploration and space colonization.
[edit] Space gun
A space gun is a method of launching an object into outer space using a large gun, or cannon.
However, even with a "gun barrel" through both the Earth's crust and troposphere, the g-forces required to generate escape velocity would still be more than what a human tolerates. Therefore, the space gun is restricted to freight and ruggedized satellites.
[edit] Spaceplanes
A spaceplane is a rocket plane designed to pass the edge of space. It combines some of the features of an aircraft and some of a spacecraft. Typically, it takes the form of a spacecraft equipped with wings.
However, they cannot yet reach further out in outer space without rockets, since all their other current propulsion mechanisms are dependent on the atmosphere. Therefore, so far, they have only been helpful with assisting proper rocket-driven vehicles through the first distance towards outer space, such as Scaled Composites White Knight.
However, some jet-engine based designs such as scramjets could potentially achieve orbit, and reusable designs like Skylon which uses precooled jet engines up to Mach 5.5 before employing rockets to enter orbit appears to have a mass budget that closes with a larger payload than pure rockets.
[edit] References
- ^ a b "Orbital Ring Systems and Jacob's Ladders - I-III" Note: in 1980s money
- ^ a b c d e f Launch Loop slides for the ISDC2002 conference
- ^ Hirschfeld, Bob (2002-01-31). Space Elevator Gets Lift. TechTV. G4 Media, Inc.. Archived from the original on 2005-06-08. Retrieved on 2007-09-13. “The concept was first described in 1895 by Russian author K.E. Tsiolkovsky in his "Speculations about Earth and Sky and on Vesta."”
- ^ In his book, "Structures or why things don't fall down" (pub Pelican 1978 - 1984), Professor J.E. Gordon considers the height of the Tower of Babel. He wrote, brick and stone weigh about 120 lb per cubic foot (2000 kg per cubic metre) and the crushing strength of these materials is generally rather better than 6000 lbf per square inch or 40 megapascals. Elementary arithmetic shows that a tower with parallel walls could have been built to a height of 7000 feet or 2 kilometres before the bricks at the bottom were crushed. However by making the walls taper towards the top they ... could well have been built to a height where the men of Shinnar would run short of oxygen and had difficulty in breathing before the brick walls crushed beneath their own dead weight."
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