Keith Loftstrom's visionary concept of his Launch Loop might well
deserve a re-visit, even though it's capability would only
electrically lift a rocket propelled launch vehicle up to just above
the atmosphere, riding on a circulating belt bridging two places on
the ground. From just above the atmosphere, it still takes most of
the lift energy to boost to GEO to be added by a reaction engine
propelled launch vehicle involving the heavy fuel and associated
heavy reaction engine launch vehicle. Using a Lofstrom Launch Loop to
get a head start above the atmosphere would enable engines designed
to work efficiently in a vacuum instead of compromising with ones
working in dense air. The big advantage with Lofstrom's Launch Loop
is that it's kinetically supported lifting structure would not
continue on up to be occupying the equatorial plane all the way up to
GEO, physically conflicting sooner or later with satellites and the
ISS orbiting below GEO, which includes a lot of corporate and
international vested interests which would need to be bought out and
promised better capabilities as installed in GEO before they would
release their claim to their part of space in LEO. And it's possible
the new materials based on carbon nanotube composites would now have
the tensile strength needed by the Launch Loop belt and its high
altitude bend-point tethers.

To have the potential of the 3$/kg to GEO, for building SPS there,
the lifting structure needs to go all the way up to GEO, such as by a
vertical space elevator or by an eccentric earth-encircling hoop
"space escalator" structure that occupies an orbital transfer
trajectory from the earth's surface up to GEO, where it would
directly place payload without need of rocket boost to stay in GEO.
Thus the need to deal with the conflicts of interest within the
equatorial plane through LEO and up to GEO.

Loftstrom's brilliant 1982 "Launch Loop" introduced the concept of a
belt using its outward centrifugal force where it is bent, to
kinetically support the structure up high, but would only go up to
the fringes of the atmosphere from where a rocket with its heavy fuel
would still need to do the remainder of the work to get into GEO; Rod
Hyde's "Starbridge" would have gone straight up by using
electrodynamic drag against upward-moving free-falling mass from
accelerators in the ground, but also would only go up little beyond
the atmosphere, requiring rocket propulsion from there to get into
GEO if that is where one wants to go to put the SPS; Earle Smith's
1985 elliptical band "Texas and Universe Railroad" concept from
ground to GEO was another step, except the orbital mechanics from
Texas was a major problem. To get to the really low energy costs from
ground to GEO, either a vertical space elevator using a tether
material capable of supporting its own weight without using a tapered
cross-section (such as a carbon-nanotube-based 1300 kg/m3 material of
above 80 GPa strength), using it's double-band pulley's at the ground
and out near the counterweight beyond GEO; or else to use the hoop
around the planet type structure, which uses high velocity
circulating mass inside itself to provide the outward centrifugal
force to support the weight of the track structure and to deliver the
lift energy along itself to move payload up and down between ground
and GEO; essentially a huge perimeter high velocity synchronous motor
with multiple armatures. This concept used the outward centrifugal
structure part of Lofstrom's "Launch Loop"; the upward lift by
electrodynamic braking of Hyde's "Starbridge"; Earle Smith's
elliptical planet-encircling part of his "Texas and Universe
Railroad" concept, as parts of its concept; for example see Cline,
James E. D. “Kinetically Supported Bridge Vehicle Lift To GEO.” Space
2002 Robotics 2002 Conference Proceedings, ASCE, 2002, 8-21. Online
see http://www.escalatorhi.com and http://www.kestsgeo.com for some
info re these concepts in html. For either of these techniques to be
useful for long term use up to GEO, there are the big conflicts with
existing satellites in LEO that would have to be resolved; so a near-
term compromise approach to get started might be to seriously explore
Lofstrom's Launch Loop concept to provide electrically powered lift
to least get above the atmosphere, while not conflicting with other
users of LEO at this time. However, the need to retain the vision of
an entirely electrically powered delivery from ground up to GEO needs
to be maintained for truly economical and environmentally friendly
large scale placement of construction materials into GEO; so, what
about an electromagnetic mass launcher supported just above the
atmosphere atop a Loftstrom Launch Loop?

Jim Cline