get into space with current technology

--- In ssi_list@... "timothy gibbs"
> tango man mentions tethers, are these made of the same materials
that panamabob seems to think are unrealistic?

Within the tether family of technology there are a number of
different concepts. The most well known is the orbital elevator that
starts on the ground and using unobtanium material, is built past
GSO. Coming down on the scale of wonder technology is a skyhook,
which is like an orbital elevator, or tower, but doesn't come down
to the ground. Rather, it is a few hundred miles long and orbits in
LEO. Because it is so long the top and the bottom occupy two
different orbits, thus they should have different orbital speeds.
The actual orbital speed of this skyhook is determined by its center
of mass, thus the bottom is moving slower than it should in its
orbit and the top faster. This means that you can dock at a slower
speed, climb the tower, release your payload and get a velocity
boost.

What I am advocating is even further down the technology scale and
it is a rotating tether that works on the principle of momentum
exchange. Have you ever gone ice skating, formed a human chain with
your friends, come to the corner of the rink and been whipped
around, and are now going faster than you could have if you
propelled yourself. The mass of the chain of people transferred some
of its momentum to you and because you were less massive you got a
big boost in your velocity.

An orbital tether would consist of a central mass and a series of
cables with a grapple/docking clasp at the end. This series of
cables would rotate about its center. A suborbital shuttle would
intersect the grapple as it rotated through the "bottom" its 50-100
mile arc, the grapple would pick up the payload, and as it rotated
from a low orbit to a high orbit, it would release the payload. Now
the more massive we make the orbital tether, or rotovator, the more
effectively it can exchange momentum. You may now be thinking that
there ain't no such thing as a free lunch (tanstaafl) and the
rotavator has now lost energy and lowered its orbit and will need
energy to reboost. This is where electrodynamic reboosting comes
into play. A conductive cable is lowered into the Earth's atmosphere
and from the solar array on the rotovator, electrical current is run
through the cable. This creates an interaction with Earth's magnetic
field and the rotovator is reboosted, over time, into a higher
orbit. This is another form of momentum exchange and the Earth is
transferring its momentum to the rotovator, thus the Earth loses
energy in its orbit, but the loss is miniscule in terms of scale.

So with a rotovator, the more mass we add to it over time, the more
momentum it can transfer and we don't need no "high falutin" types
of new material. Kevlar will do just fine, but a more radiation
resistant material like Spectra 2000 will be even better.

Thus a system consisting of two lower tech components - a suborbital
shuttle which is easier and cheaper to build and operate goes up to
intersect the grapple of a big, dumb mass which transfers its
momentum to the payload.

TangoMan