(translation, Automatic translation przy użyciu AWB (0))
A '''launch loop''' or '''Lofstrom loop''' is a published design for an [[active structure]] [[Maglev (transport)|maglev]] [[cable transport]] system intended for [[orbital launch]] that would be around 2,000 km (1,240 mi) long and maintained at an altitude of up to 80 km (50 mi). A launch loop would be held up at this altitude by momentum of the belt as it circulates around the structure. 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 [[
The system is designed to be suitable for launching humans for [[
[[Image:LaunchLoopRotor.svg|thumb|right|Launch loop accelerator section (return cable not shown)]]
A launch loop is proposed to be a structure around 2,000 km long and 80 km high. The loop runs along at 80 km above the earth for 2000 km then descends to earth before looping back on itself rising back to 80 km above the earth to follow the reverse path then looping back to the starting point. The loop would be in the form of a tube, known as the ''sheath''. Floating within the sheath is another continuous tube, known as the ''rotor'' which is a sort of belt or chain. The rotor is an [[
Although the overall loop is very long, at around 4,000 km circumference, the rotor itself would be thin, around 5 cm diameter and the sheath is not much bigger.
===Ability to stay aloft===
When at rest, the loop is at ground level. The rotor is then accelerated up to speed. As the rotor speed increases, it curves to form an arc. The sheath forces it to follow a curve steeper than the rotor's natural ballistic curve, which, in turn, exerts a [[
Once raised, the structure requires continuous power to overcome the energy dissipated. Additional energy would be needed to power any vehicles that are launched.<ref name=launch1985/>
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. The payload applies a magnetic field which generates [[
If a stable or circular orbit is needed, once the payload reaches the highest part of its trajectory then an on-board [[
The eddy current technique is compact, lightweight and powerful, but inefficient. With each launch the rotor temperature increases by 80 [[
===Capacity and capabilities===
Closed orbits with a perigee of 80 km quite quickly decay and re-enter, but in addition to such orbits, a launch loop by itself would also be capable of directly injecting payloads into [[
To access circular orbits using a launch loop a relatively small 'kick motor' would need to be launched with the payload which would fire at [[apogee]] and would circularise the orbit. For [[
Launch loops in Lofstrom's design are placed close to the equator<ref name=launch1985/> and can only directly access equatorial orbits. However other orbital planes might be reached via high altitude plane changes, lunar perturbations or aerodynamic techniques.
Launch loops would be quiet in operation, and would not cause any sound pollution, unlike rockets.
Finally, their low payload costs are compatible with large-scale commercial [[
===Difficulties of launch loops===
A running loop would have an extremely large amount of energy in the form of linear momentum. While the magnetic suspension system would be highly redundant, with failures of small sections having essentially no effect at all, if a major failure did occur the energy in the loop (1.5×10<sup>15</sup> [[
While this is a large amount of energy, it is unlikely that this would destroy very much of the structure due to its very large size, and because most of the energy would be deliberately dumped at preselected places when the failure is detected. Steps might need to be taken to lower the cable down from 80 km altitude with minimal damage, such as parachutes.
The turnaround sections are potentially unstable, since movement of the rotor away from the magnets gives reduced magnetic attraction, whereas movements closer gives increased attraction. In either case, instability occurs.<ref name=launch1985/> This problem is routinely solved with existing servo control systems that vary the strength of the magnets. Although servo reliability is a potential issue, at the high speed of the rotor, very many consecutive sections would need to fail for the rotor containment to be lost.<ref name=launch1985/>
The cable sections also share this potential issue, although the forces are much lower.<ref name=launch1985/> However, an additional instability is present in that the cable/sheath/rotor may undergo [[
===Competing and similar designs===
* [[Non-rocket spacelaunch]]
* [[Orbital ring]]
* [[Roller coaster]]/[[Mass driver]]
* [[Space elevator]]
* [[Space gun]]
* [[Space fountain]]
* [[Space tourism]]
* [[Belt (mechanical)]]
* [[Reactive centrifugal force]] - the force that would hold up the loop against gravity
* [[Cable transport]]
* [[Tether propulsion]]