A Launch Loop is a metal loop in an evacuated tube that spins at high speed on magnetic bearings. As it speeds up one side of the loop is projected up to a high altitude. Vehicles are electromagnetically accelerated on top of the tube up to orbital speeds and can be launched into low earth orbit or beyond.
For safety and astrodynamic reasons, launch loops would be located in the ocean near the equator, well away from habitation.
The launch loop is due to Keith Lofstrom. It is essentially a hybrid of the orbital ring concept and the space fountain. It is an oval ring around 2000 km long, on one side of the ring it has two base stations about 2000km apart on Earth which can launch and catch the moving loop to and from high altitude. Although the loop is very long, the loop and sheath is very thin, only around 5 cm diameter, and is cable-like.
The loop starts off at ground level, and is contained in an evacuated tube. The loop is spun up on magnetic bearings to 14 km/s. As the speed increases one half of the loop is arranged to push upwards into an approximate arch shape, until it reaches its operating altitude of around 60-80 kilometers where the loop is restrained and shaped by tensile cables.
To launch, vehicles are electromagnetically accelerated up the arch at around 3g acceleration, until they are above the atmosphere and at orbital velocity, and are then released, and a rocket engine is then employed to circularise the trajectory to an Earth orbit.PDF version of Lofstrom's 1985 launch loop publication (AIAA 1985)
Lofstrom estimates that initial loop could cut the costs to access space to $300/kg, or with a larger loop and 5 year payback and full usage that cost for accessing space with a launch loop could be as low as $3/kg. the ISDC2002 slide show
Uses for launch loops
* launching humans
* launching propellant
* launching upper stages
* launching building materials
* launching tools, machinery
* launching lifesupport (food, air, water)
* launching radiation shielding
* antipodal or long distance suborbital travel
* launching Server Sky
* lunar launch loops
Uses for smaller-scale launch loops
* Power storage
* Telecommunications platforms
* Surveillance platforms
Groups benefiting from building launch loops
* NASA would find it easier to fund missions further afield than at present
* Space tourists
* America's military (since it would enable SPS, and reduce dependence on oil imports)
* American tax payers since it would reduce military costs, and hence taxes
* Colonists for the Moon, Mars and elsewhere