Replying to posts: Re: Lofstrom launch loop for SPS
Posted by: "Ian Woollard" ian.woollard@... wolfekeeper
Tue Dec 4, 2007 8:03 pm (PST) "The Lofstrom loop concept is capable
of injecting payloads directly into GT(geosynchronous transfer
orbit), and a relatively small kick motor can circularise the orbit
in GEO (delta-v ~1.6km/s). The presence of the kickmotor reduces the
payload by 40% or equivalently increases launch costs by about 70%
from those from the loop to LEO; but the launch costs are low to
start with."

And to Post: "Re: Lofstrom launch loop for SPS
Posted by: "Ian Woollard" ian.woollard@... wolfekeeper
Tue Dec 4, 2007 8:03 pm (PST) "As I understand it, the current idea
behind the Lofstrom loop is that it accelerates the payload by it
being magnetically dragged by the loop which is moving at 14 km/s, so
no separate electromagnetic mass launcher is needed per se."


Reply by James E. D. Cline <jedcline1@...> :

There appears to be some cross-pollination of ideas going on between
the Lofstrom Launch Loop and the KESTS type structure concepts.
Certainly Lofstrom's Launch Loop was a strong inspiration to me in
the late 1980's when I was conceiving the KESTS structure concepts.
The two kinds of kinetic structures have their own mix of strengths
and weaknesses; and now there is a real need to get adequate SPS
built in GEO ASAP and that needs to be the goal. And after reading
your post I recalled being stopped after giving a conference
presentation about KESTS to GEO, by someone who clearly had the
Lofstrom Launch Loop mixed up with KESTS, despite my presentation's
graphics showing the radical difference between the two kinds of
kinetic structures.
Originally in 1985 I had testified before the National Commission on
Space, urging the serious examination of Lofstrom's Launch Loop
concept, among a few others. See http://www.kestsgeo.com/pages/
geniefiles/g475.html Yet my suggestions were ignored in the resulting
NCS report; mulling over the why of it for a couple years resulted in
the KESTS concept. So it is worthwhile re-evaluating it all in light
of more recent materials advances since the mid-1980's.
The Loftstrom Launch Loop basic configuration, of a truncated
vertical triangular shape, consists of a continuous belt in
continuous circulation between four relatively sharp bend points. Two
bend point pulleys are on the ground, widely spaced, the other two
bend point pulleys are up near the launch altitude, sufficiently
above the atmosphere. The two pulleys at high altitude are anchored
by tethers reaching to the ground at angles appropriate to the belt's
bending angles up to there. In operation, the high velocity
continuous belt loop is deflected by a ground pulley upward until
reaching the nearest tethered pulley at launch altitude, where the
high velocity belt then takes on the chosen vehicular launch slope,
along a length sufficient to impart some kinetic energy to the
rocket boosted spacecraft occurring before the belt reaches the
second tethered pulley, where that pulley deflects the belt downward
towards the second of the two pulleys on the ground. The remainder of
the belt's loop path either is routed relatively low to the earth
surface, or else returns via another upward sling to travel at a
lower bend point pair of the two altitude bend pulley sites, then
down to the first ground pulley, completing the launch loop.

The strength of materials and magnetic fields needed to do the
bending of the Launch Loop belt, was, and continues to be, a major
concern to me. Given that modern belt and tether materials, based on
carbon nanotube matrix materials, enable tethers operating through,
say, 150 km altitude change from ground level, and also the high
velocity belt loop's stretch; but the perimeter if the 14 km/s belt
needs to be matched by that of perimeter of the pulleys doing the
deflection; their rotational velocity would be enormous and thus
strength of materials similarly. Using magnetic fields to do the belt
bending would require huge fields across a long radius, given the
relatively small magnetic component of the high velocity belt's
materials.

To overcome the need for such extreme bending forces and the
electromechanical mechanisms required to bend the belt through say a
270 degree angle at each of the two ground bend points, is why the
KESTS to GEO (is acronym for Kinetic Energy Supported Transportation
Structure to Geostationary Earth Orbit) used the Earth's
gravitational field to provide the bend of a loop around the planet,
thus no significant mechanical localized bend points involved in such
a structure, and thus minimum material stresses. Such a structure
could also reach a peak altitude far lower than GEO, of course, such
as only up to LEO. The ability to go directly to GEO has the benefit
of needing no added kick for payload to be in GEO. But, there is that
aforementioned problem of the prior occupiers passing through the
equatorial plane, disastrous conflict of spatial presences
eventually. If a KESTS were to provide a similar lift function as a
Lofstrom Launch loop, lifting up only to the fringes of the
atmosphere, it would be operating within the atmosphere's denser
areas most of the way around the planet, thus requiring much
interaction with wind and drag. It also needs to operate in the
equatorial plane, in its basic forms.

Thus we return to examine the Lofstrom Launch Loop concept, as it
could operate from higher latitudes and need not be oriented exactly
parallel to the equatorial plane. It could have a baseline between
the two pulleys on the ground of only several hundred kilometers if
need be; surely available in the American western desert areas. Then
the problem of the structural requirements of the pulleys and/or
magnetic field belt benders: to get their stresses down to values
possibly reachable with modern materials, the belt needs to go quite
a bit slower than the 15 km/s area needed to supply most of the
kinetic energy of launched vehicles needed to reach GEO. The much
lower belt speed translates to much less speed to give to the
vehicles it launches. Those spacecraft thus need to have the fuel,
large tanks and engines to provide the remainder of the delta vee to
get up into GEO from that launch altitude of say 150 km, with an
initial push from the Launch Loop of a couple km/s.

That is why I suggested that maybe a vehicular mass accelerator could
be "permanently" supported up above the fringes of the atmosphere by
such a Lofstrom Launch Loop, shoving against the Launch Loop's
momentum up there, to provide the added delta vee for the payload
vehicles to get in range of GEO, where it would still need a bit of
onboard reaction force to place it into GEO.

Jim Cline <jedcline1@...>





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