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Space tethers, a related technology, can provide some of the features of a space elevator without the surface structures of a space elevator.

Instead, payloads are transferred to the tether from suitable high flying aircraft (which may not exist yet).

Tethers can also be used for orbital transfers.

This is all in the white papers at Tethers Unlimited.

And everyone knows that tethers tug!

Read about tethers here.

You can always trust Rober Forward to come up with a good idea.

See his Terminator Tether page. It's a great way to bring down an orbiting mass without actually having to carry the mass of fuel that would be required for a deorbiting burn.

We actually have (at least) two usefull technologies for cleaning up space: tethers and wake shields. I don't know if the SVEC folks have considered building a wake shield specifically for NEO cleanup, though.

Make sure you equip your next satellite with a Termination Tether. It won't work in geosynchronous orbit, but you'll be moving your bird out of the slot with the last of its fuel anyway.

I have attended several panels by Dr. Robert L. Forward on the subject of space teathers and elevators using current materials. Interested parties should check out his company, Tethers unlimited Inc as well as his personal site. I don't know where he will next be lecturing, I last caught him at VikingCon 17 (Western Washington Universitie's SciFi convention).

Orbital momentum is worth about $1/(kgm/s).

This is because that's about how much it costs to generate that much orbital momentum -- which can be conserved.

Combined with a momentum conserving technology like momentum exchange tethers, this creates a very important potential market in orbital momentum.

The primary demand for this momentum would be transfer from low earth orbit to geosynchronous orbit and the primary supply for this momentum would be derelict low earth orbit satellites. A big issue here is who owns the momentum of derelict satellites? By the law of the sea, it should be those who can first demonstrate control the derelict satellite's momentum.

This market is particularly important.

• The bottleneck to technological civilization is commercially viable access to the unlimited environment of space.
• The bottleneck to space commerce is transport.
• The bottleneck to space transport is lofting propellant.
• The bottleneck to lofting propellant is reaction mass due to the fact that momentum is linear in velocity but energy is square in velocity. In other words every bit of reaction mass at orbital velocity buys you a lot of effective propellant and rocket at the ground.

Sounds like you need an unbreakable (or nearly so) tether. Dr Robert L. Forward has designed such a tether, and the uses discussed on the website include exactly this usage.

Tethers have long been a theoretical tool utilized in Science Fiction by authors like Larry Niven. They have recently been made real though by companies like Tethers Unlimited. Their site has a lot of information about how tethers work and what can be done with them.

AIAA-2000-3615 Design and Simulation of Tether Facilities for the HASTOL Architecture (Hoyt)

AIAA-2000-3866 Design and Sim of a Tether Boost Facility for GEO, Lunar, and Mars Transport (Hoyt, Grant, and Bangham)

AIAA-2000-3865 Computation of Current to a Moving Bare Tether, (Onishi & Martinez, MIT, and Cooke, AFRL)

AIAA-2000-3870 Future Application of Electrodynamic Space Tethers For Propulsion (Santangelo, Michigan Technic and Johnson, Nasa Marshall )

I apologize for not being able to link to the specific papers or give much additional information, since this panel ran at the same time as one I was more interested in and the papers are copyrighted by AIAA. The fact that technical publications are generally not available upon demand except in bulk or by federal express is increasingly irritating to me, since 1) they are available in .pdf format on CD-ROM at the conference anyway, and 2) many distribution systems exist which would allow the organizations to distribute them electronically and still get paid. Please complain (nicely) to Webmaster@aiaa.org about this, since my lonely voice is probably not loud enough to cause action.

Rev. Neh
propulsion geek

The plan is for every satellite to eventually have a tether. This is mainly to deorbit all inactive satellites, so they don't clutter space, but also as a means of movement. If you want to check out some good websites, go to Airseds (where I worked last summer). Or for the less intelligently inclined Tethers Unlimited.

• Scientific American: Space Tethers
• The Terminator Tether
• ProSEDS

The Iridium satellites are orbiting at 780km. This means they will stay up for thousands of years (at least) if they are not deorbited.

For an interesting discussion of the problem and a novel solution see the Terminator Tether.

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