Using Sling Shot Power to Hurl Into Orbit

the_2nd_coming writes "space.com has an article about a new application of a very old technology. NASA is putting money into Momentum-eXchange/Electrodynamic Reboost tether technology -- MXER for short -- an innovative concept that if implemented would station miles and miles of cart-wheeling cable in orbit around the Earth. Then, rotating like a giant sling, the cable would swoop down and pick up spacecraft in low orbits, then hurl them to higher orbits or even lob them onward to other planets."

Comments

Been there, done that

[NetDanzr]

From the top of my head, I can remember two identical proposals in sci-fi works:

• The Fountains of Paradise by Atrhur C. Clarke
• Mars Trilogy by Kim Stanley Robinson

I'm sure there are more.

Re:Been there, done that

[podperson]

Those both were space elevators -- a different technology NASA is also exploring.

Re:Been there, done that

[crmartin]

And, in fact, Tethers Unlimited, the company proposing this beast, was founded by scientist, engineer and science fiction writer Dr Robert L Forward. Sadly, Dr Forward died last September.

not a sling shot

[proj_2501]

A sling shot is not the same as a sling.

A sling shot uses a rubber band to propel its payload.

A sling uses the sudden stop of centripedal force.

Sling shot = Dennis the Menace.
Sling = David killing Goliath

Slings are good for hunting small animals, apparently.

Borrowed from good sci-fi...

[praedor]

By Gregory Benford. In either "Great Sky River" or "Tides of Light" Benford (physicist and astronomer at UC, Irvine), can't recall which, there is an organism that does this...only its ends actually come much farther down into the atmosphere than NASA's proposal. This organism was even used by the main character in the story to hitch a ride into space.

Re:Cable Strength

[foolish]

The people making the tethers, TUI (www.tethers.com) are making it out of Spectra fibres. You can check out their website for the full gist, but they have fabrication down pat.

So, yes, this is the real deal, not something 'down the road 5 years'.

--foolish

Important differences

[f97tosc]

In the works you site they build an elevator all the way from surface to space; in other words it is extremely long.

In this case, the craft is much shorter and already in space. Rather than lifting something all the way along a cable, you accelerate it by swinging a shorter cable and throw it off.

From an energy perspective, you exchange rockets working inefficiently for a short time for solar-powered engines working efficiently but slowly for a long time. In the space elevators you mention, you rather use more conventional engines like in an electric train.

Tor

Re:A waste of time?

[Tmack]

Maybe this stuff will be strong enough to overcome the limit. Its definately a step in the right direction. Im too lazy to run through the material engineering aspects of it all right now and actually figure the needed strength/weight ratio needed. Im sure its something insanely strong.

Tm

Re:SciFi does it again

[foolish]

Robert Forward was one of the principals at TUI [www.tethers.com] and was a contemporary of RAH, Clarke and Sheffield.

So he actually figured out how to make the damn things work, and spent about a decade trying to pitch it to NASA... but the failure of a single stranded Tether experiment made them really 'gun shy' of the technology, even though the Hoyt/Forward tether is multi-stranded.

Re:What I don't get...

[Richard_J_N]

That's the electrodynamic bit. The conducting tether cuts magnetic field lines. This induces a voltage and causes a current to flow along it. (You emit ions at both ends to complete the circuit). Normally, that causes electromagnetic damping (like a dynamo). But, if you use solar cells to drive the current the opposite way, you can get a propulsion force... See here for more.

Re:Degrading Orbit

[Fjord]

This thing is definitely cool. The other posters were right in pointing out that it regains the energy via converting solar energy into momentum by applying a current to the Earth's Magnetic field. I just wanted to point out the purpose of the devices name:

Momentum-eXchange: this refers to how the tether adds momentum to the spacecraft

Electrodynamic Reboost: this refers to the mechanism that recharges the orbit

The one poster is right about the momentum-exchange working both ways in that spacecraft coming back could tether down and reboost the device. However, in most cases the craft will be leaving a payload up there (such as a satillite, or even just burned fuel/oxygen) so it would never regain as much momentum as it lost. The electrodynamic reboost ensure it keeps flying.

Re:Are they serious?

[barakn]

At least part of the cable has to be conductive. That's the Electrodynamic Reboost mentioned in insufficient detail in the article. They run a current through the cable, and the Earth's magnetic field then exerts a force on the cable that pushes it up into a higher orbit. Each cable will have multiple layers.