Sunday, May 29, 2011

(in work) High Stage One

Source Document:  ISEC's 2015 EarthPort Final Report.
Space elevator combines with LLL
High Stage One of the space elevator supports a platform at 40 km altitude where payloads are
transferred from a funicular railcar to a tether climber for onward travel up the tether towards the
GEO node (see Figure ). It deals with the sometimes large forces generated by winds and ice,
transferring these forces to the Earth’s surface. This relieves the tether of the fluctuating tensions
caused by Earth’s turbulent atmosphere. Otherwise, these forces would at times more than triple
the load on the tether, if the tether reaches down to the surface.
High Stage One is an adaptation of the Launch Loop originally proposed by Keith Lofstrom as a
direct-to-orbit launch mechanism. High Stage One is roughly 1/12 the size of the Launch Loop
but uses the same concept of holding up the structure by changing the direction of the
momentum vectors of rotors traveling inside evacuated tubes using magnetic levitation to
minimize friction.
Figure D-1 High Stage One
Another benefit of High Stage One is that it is easy to move the tether to avoid space debris,
because the base of the tether is in very thin air. It is possible to swing a 5-ton weight from the
platform, causing a lateral wave to be propagated up the tether in the required direction. By
contrast, moving it at the surface involves getting a ship underway, and that would sometimes
have to be against opposing storms.
Each of the two surface stations has to sustain a load of 27,000 metric tons to support everything
above it. This is not particularly large for ocean-going vessels, but it is a different requirement
from the Marine Node where the tether reaches to the surface. Position-keeping is still required
so as to maintain the overall stability. Depending on the depth and the state of the ocean bottom,
the surface station may use anchors, active position-keeping, or a combination of the two.
Figure shows more detail of a surface station. Most of the weight is experienced at the ramp,
which will either be suspended from the ship or will have its own flotation supports. There is
also a large horizontal force tending to pull the ambit away from the rest of the surface station.
This could be sustained by anchors or by long underwater cables joining the two surface stations,
which are 112 km apart.
One of the surface stations will house the Floating Operations Platform (FOP). High Stage One
requires the FOP to manage the following two additional tasks beyond those needed for the Earth
Port with the tether reaching the surface.
1. The transfer of payloads to tether climbers on the platform: the funicular can raise
payloads at any time, but the tether climbers can only commence climbing at dawn, due
to their need for solar power, or at the time dictated by the disposition of other tether
climbers, so as to manage the overall load on the tether. Climbers will be loaded and
prepared on the platform ready for departure. The platform at 40 km altitude is
effectively a spacesuit environment. Most operations will be handled remotely from the
FOP. Service personnel will be able to make visits for maintenance purposes.
2. Maintenance and health checks on High Stage One: Every component of the rotors
traveling at high speed inside the evacuated tubes will be checked automatically, with the
results being monitored at the FOP. The structure consists of five pairs of tubes. Routine
maintenance will involve bringing down one pair of tubes for servicing while the
remaining four pairs continue to operate and support the platform and funicular.
Figure D-2 Detail of surface station


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