Launch loop
This circulation, in effect, transfers the weight of the structure onto a pair of magnetic bearings, one at each end, which support it.
Launch loops are intended to achieve non-rocket spacelaunch of vehicles weighing 5 metric tons by electromagnetically accelerating them so that they are projected into Earth orbit or even beyond.
[2][4] It is a fleshed-out version of PORS specifically arranged to form a mag-lev acceleration track suitable for launching humans into space, but whereas the orbital ring used superconducting magnetic levitation, launch loops use electromagnetic suspension (EMS).
The rotor is an iron tube approximately 5 cm (2 inches) in diameter, moving around the loop at 14 km/s (31,000 miles per hour).
[2] Due to the possibility of the loop failing and falling to Earth, it is normally considered as running between two islands outside of heavy shipping routes.
[2] To launch, vehicles are raised up on an 'elevator' cable that hangs down from the West station loading dock at 80 km, and placed on the track.
[2] Launch loops in Lofstrom's design are placed close to the equator[2] and can only directly access equatorial orbits.
This would be a similar situation to that faced by the Apollo astronauts, who had radiation doses about 0.5% of what the space elevator would give.
While the magnetic suspension system would be highly redundant, with failures of small sections having essentially no effect, if a major failure did occur the energy in the loop (1.5×1015 joules or 1.5 petajoules) would approach the same total energy release as a nuclear bomb explosion (350 kilotons of TNT equivalent), although not emitting nuclear radiation.
Therefore, for safety and astrodynamic reasons, launch loops are intended to be installed over an ocean near the equator, well away from habitation.
The published design of a launch loop requires electronic control of the magnetic levitation to minimize power dissipation and to stabilize the otherwise under-damped cable.
[2] This problem is routinely solved with existing servo control systems that vary the strength of the magnets.
[2] However, an additional instability is present in that the cable/sheath/rotor may undergo meandering modes (similar to a Lariat chain) that grow in amplitude without limit.
Lofstrom believes that this instability also can be controlled in real time by servo mechanisms, although this has never been attempted.
In works by Alexander Bolonkin it is suggested that Lofstrom's project has many unsolved problems and that it is very far from a current technology.
In 2008,[10] Bolonkin proposed a simple rotated close-loop cable to launch the space apparatus in a way suitable for current technology.
Another project, the space cable, is a smaller design by John Knapman that is intended for launch assist for conventional rockets and suborbital tourism.
The space cable design uses discrete bolts rather than a continuous rotor, as with the launch loop architecture.
The two disadvantages of this are: the greatly reduced time available for the arriving launch vehicle to hook up at the lower end of the rotating skyhook (approximately 3 to 5 seconds), and the lack of choice regarding the destination orbit.
