Non-rocket spacelaunch
Non-rocket spacelaunch refers to theoretical concepts for launch into space where much of the speed and altitude needed to achieve orbit is provided by a propulsion technique that is not subject to the limits of the rocket equation. Although all space launches to date have been rockets, a number of alternatives to rockets have been proposed. In some systems, such as a combination launch system, skyhook, rocket sled launch, rockoon, or air launch, a portion of the total delta-v may be provided, either directly or indirectly, by using rocket propulsion.
Present-day launch costs are very high – $2,500 to $25,000 per kilogram from Earth to low Earth orbit. As a result, launch costs are a large percentage of the cost of all space endeavors. If launch can be made cheaper, the total cost of space missions will be reduced. Due to the exponential nature of the rocket equation, providing even a small amount of the velocity to LEO by other means has the potential of greatly reducing the cost of getting to orbit.
Launch costs in the hundreds of dollars per kilogram would make possible many proposed large-scale space projects such as space colonization, space-based solar power and terraforming Mars.
Comparison of space launch methods
Static structures
In this usage, the term "static" is intended to convey the understanding that the structural portion of the system has no internal moving parts.Space tower
A space tower is a tower that would reach outer space. To avoid an immediate need for a vehicle launched at orbital velocity to raise its perigee, a tower would have to extend above the edge of space, but a far lower tower height could reduce atmospheric drag losses during ascent. If the tower went all the way to geosynchronous orbit at approximately, objects released at such height could then drift away with minimal power and would be in a circular orbit. The concept of a structure reaching to geosynchronous orbit was first conceived by Konstantin Tsiolkovsky.The original concept envisioned by Tsiolkovsky was a compression structure.
Building a compression structure from the ground up proved an unrealistic task as there was no material in existence with enough compressive strength to support its own weight under such conditions.
Other ideas use very tall compressive towers to reduce the demands on launch vehicles. The vehicle is "elevated" up the tower, which may extend above the atmosphere and is launched from the top. Such a tall tower to access near-space altitudes of has been proposed by various researchers.
Tensile structures
Tensile structures for non-rocket spacelaunch are proposals to use long, very strong cables to lift a payload into space. Tethers can also be used for changing orbit once in space.Orbital tethers can be tidally locked or rotating. They can be designed to pick up the payload when the payload is stationary or when the payload is hypersonic.
Endo-atmospheric tethers can be used to transfer kinetics between large conventional aircraft or other motive force and smaller aerodynamic vehicles, propelling them to hypersonic velocities without exotic propulsion systems.
Skyhook
A skyhook is a theoretical class of orbiting tether propulsion intended to lift payloads to high altitudes and speeds. Proposals for skyhooks include designs that employ tethers spinning at hypersonic speed for catching high speed payloads or high altitude aircraft and placing them in orbit.Space elevator
A space elevator is a proposed type of space transportation system. Its main component is a ribbon-like cable anchored to the surface and extending into space above the level of geosynchronous orbit. As the planet rotates, the centrifugal force at the upper end of the tether counteracts gravity, and keeps the cable taut. Vehicles can then climb the tether and reach orbit without the use of rocket propulsion.Such a cable could be made out of any material able to support itself under tension by tapering the cable's diameter sufficiently quickly as it approached the Earth's surface. On Earth, with its relatively strong gravity, current materials are not sufficiently strong and light. With conventional materials, the taper ratio would need to be very large, increasing the total launch mass to a fiscally infeasible degree. However, carbon nanotube- or boron nitride nanotube-based materials have been proposed as the tensile element in the tether design. Their measured strengths are high compared to their linear densities. They hold promise as materials to make an Earth-based space elevator possible.
Landis and Cafarelli suggested that a tension structure extending downward from geosynchronous orbit could be combined with the compression structure extending upward from the surface, forming the combined structure reaching geosynchronous orbit from the surface, and having structural advantages over either one individually.
The space elevator concept is also applicable to other planets and celestial bodies. For locations in the Solar System with weaker gravity than Earth's, the strength-to-density requirements aren't as great for tether materials. Currently available materials could serve as the tether material for elevators there.
Endo-atmospheric tethers
An endo-atmospheric tether uses the long cable within the atmosphere to provide some or all of the velocity needed to reach orbit. The tether is used to transfer kinetics from a massive, slow end to a hypersonic end through aerodynamics or centripetal action. The Kinetics Interchange TEther Launcher is one proposed endo-atmospheric tether.Dynamic structures
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 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.Orbital ring
An orbital ring is a concept for a giant artificially constructed ring hanging at low Earth orbit that would rotate at slightly above orbital speed that would have fixed tethers hanging down to the ground.In a series of 1982 articles published in the Journal of the British Interplanetary Society, Paul Birch presented the concept of orbital ring systems. He proposed a rotating cable 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. Birch claimed that the ring stations, in addition to holding the tether, could accelerate the orbital ring eastwards, causing it to precess around Earth.
In 1982 the Belarusian inventor Anatoly Yunitskiy also proposed an electromagnetic track encircling the Earth, which he called the "String Transportation System." When the velocity of the string exceeds 10 km/sec, centrifugal forces would detach the string from the Earth's surface and lift the ring into space.
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. 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 structure would constantly need around 200 MW of power to keep it in place.The system is designed to be suitable for launching humans for space tourism, space exploration and space colonization with a maximum of 3 g acceleration.
Pneumatic freestanding tower
One proposed design is a freestanding tower composed of high strength material tubular columns inflated with a low density gas mix, and with dynamic stabilization systems including gyroscopes and "pressure balancing". Suggested benefits in contrast to other space elevator designs include avoiding working with the great lengths of structure involved in some other designs, construction from the ground instead of orbit, and functional access to the entire range of altitudes within the design's practical reach. The design presented is "at 5 km altitude and extending to 20 km above sea level", and the authors suggest that "the approach may be further scaled to provide direct access to altitudes above 200 km".A major difficulty of such a tower is buckling since it is a long slender construction.
Projectile launchers
With any of these projectile launchers, the launcher gives a high velocity at, or near, ground level. In order to achieve orbit, the projectile must be given enough extra velocity to punch through the atmosphere, unless it includes an additional propulsion system. Also, the projectile needs either an internal or external means to perform orbital insertion. The designs below fall into three categories, electrically driven, chemically driven, and mechanically driven.Electromagnetic acceleration
Electrical launch systems include mass drivers, railguns, and coilguns. All of these systems use the concept of a stationary launch track which uses some form of linear electrical motor to accelerate a projectile.Mass driver
In essence, a mass driver is a very long and mainly horizontally aligned launch track or tunnel for accelerating payloads to orbital or suborbital velocities. The concept was proposed by Arthur C. Clarke in 1950, and was developed in more detail by Gerard K. O'Neill, working with the Space Studies Institute, focusing on the use of a mass driver for launching material from the Moon.A mass driver uses some sort of repulsion to keep a payload separated from the track or walls. Then it uses a linear motor to accelerate the payload to high speeds. After leaving the launch track, the payload would be at its launch velocity.