Space Forum / Space Flight / October 2003

It's based on work by Dr. Brad Edwards, now of ISR (Institute for
Scientific Research, Inc., a West Virginia think tank) that was funded
by NIAC (NASA Institute for Advanced Concepts).  The intent was to
develop a space elevator design that could be built in the near term
(nominally 15 years) and be at least competitive with existing launchers
for current markets (i.e., not require huge increases in space activity
to be practical).  

The basic design is a 100,000 km by 1-meter by 1-micron-thick ribbon of
carbon-nanotube composite fibers, mass around 80 tons, with a 20 ton
load capacity.  The "climbers" use simple friction drive (treads clamped
around the ribbon) to go up the ribbon at 200 km/hr, taking about a week
to reach GEO.  Climbers are powered by laser power beaming from the
ground, and are 7 tons empty (13 ton payload).  The ribbon is
"bootstrapped" -- an initial few-cm ribbon is deployed down from GEO,
and small (initially 1-ton) climbers carrying ribbon spools widen the
initial ribbon until it reaches full width.  The ribbon is anchored on a
floating platform in the Pacific, which among other things allows the
bottom of the ribbon to be moved to dodge LEO satellites as needed.

It's a very interesting concept, but has (not surprisingly) lots of
practical problems.  Some are addressed in Edwards' NIAC reports (see
www.niac.usra.edu) and a book he put out (search Bradley C. Edwards on
Amazon) but work on the concept is still at a very early stage.  The
most fundamental issue is whether carbon nanotube (CNT) composites will
actually achieve the required tensile strength -- individual nanotubes
are strong enough (upwards of 150 GPa tensile strength) but it's not
clear if it will be possible to make long cables with a large fraction
of the raw-nanotube strength to weight; the baseline cable design
assumes ~60 GPa cable strength.  

If the CNT materials work(and they probably will get close enough to
make an elevator possible, though perhaps not with the performance
Edwards assumed) then there are a bunch of other things to worry about
-- collisions with LEO satellites and meteoroids, dynamic stability,
ribbon wear, etc., etc. Many fun Ph.D. theses to be had....

There was just a workshop on the subject (which is what prompted the
flurry of press articles); you can see the presentations at
<http://www.isr.us/spaceelevatorconference/presentations.html>

(There's even one by me; I didn't plan to talk at the conference, but I
objected to some of the economic estimates in another talk and got
challenged to do better, so I literally put a talk together overnight.)

Jordin