Electrodynamic Tethers: Clean Up Debris - Power or Boost Spacecraft

An electrodynamic tether (EDT) is a simple idea, but one with an amazing number of uses. An EDT system is made up of two masses in orbit connected by a long, flexible, electrically conductive cable; the tether is essentially a wire that moves through the magnetic field of the Earth (or another planet or large body). An EDT takes advantage of two basic principles of electromagnetism: current is produced when a conductive wire moves through a magnetic field, and the field exerts a force on the current. While it is not a colorful as the Rasta space tug from William Gibson's Neuromancer, it could provide a technology that takes low-flying satellites to a new level.


(From NASA Tethered Spacecraft)

An EDT can use these principles in two ways:

  • An EDT can generate electric current flow towards the planet; this can provide enough electricity to run experiments on board a satellite; this also causes the tether to experience a force from the planet's magnetic field that is opposite the tether's direction of motion. In other words, it slows the EDT system down (produces drag), lowering the EDT's orbit.
  • By adding a battery (or solar panel) to the EDT circuit, the induced current is overcome, reversing the current direction; the force experienced by the tether is now in the same direction as the EDT's motion. In other words, this produces thrust, raising its orbital attitude.
A tether moving from west to east through the Earth's northward-pointing magnetic field will experience a current flow down the tether. The anode end of the tether collects electrons from the ionosphere and ejects them from negatively charged cathode; the ionosphere is electrically conductive and completes the circuit. Steady current for onboard power results. A 20 kilometer tether in low earth orbit (LEO) could produce up to 40 kilowatts of power; this is enough to run manned research facilities.

As discussed, this method of creating electrical power has a serious side-effect, namely, that the spacecraft or satellite will experience drag. That is, it will slow down and seek a lower orbit, eventually crashing on the planet. However, there is a way to turn this "bug" into a feature. One problem that is getting worse around Earth is that of discarded "space junk" (see illustration below). This property of EDTs could be used to bring down this junk earlier and in a controlled fashion. At the end of a satellite's life (or a rocket stage, or anything else), it is given a signal to release a long wire antenna. A current will flow in the wire, and the satellite will begin to slow down, quickly heading for burn-up in the atmosphere.


(From Center for Orbital and Reentry Debris Study)

The second use of EDT is really amazing. The International Space Station will require over seventy tons of propellant over the next ten years to keep its orbit from decaying. All of this reaction mass must be hauled up the gravity well at a cost of $7,000 per pound (not $7, as previously stated)! A properly deployed EDT, combined with another power source, could actually push itself forward on the Earth's magnetic field, speeding the IST up without the use of any propellant.

This will have profound implications on missions to other planets, since satellite missions will no longer need to carry expendable propellant to continue their missions. An EDT can be used to alternately boost to a new location, and then reverse current and use the resulting drag force to decellerate and fine-tune its orbit. This greatly extends the useful life of these space probes.


(From NASA Tethered Spacecraft)

So why aren't EDTs in widespread use? The biggest problems are electromechanical; EDTs experience high voltages in space. Also, EDTs are prone to vibrations that produce significant mechanical forces. Also, development has been slow; a program planned for launch in 2004, ProSEDs, was repeatedly postponed and ultimately canceled.

Science fiction author David Brin has made a good story (from 1982) available; you might want to go read Tank Farm Dynamo. This story is a poignant tale of what might have been in the last century of American space travel. The story takes maybe fifteen minutes to read - it's well worth it! For another spacetug story, see ConeXpress OLEV - Will A Good Tug Save Hubble?.

A lot of the background information for this article was found in Electrodynamic Tethers in Space from the August issue of Scientific American; unfortunately, it's not free. Thanks to yet another alert reader for the scoop on this story.

Long space tethers don't need to be conductive to have unusual effects - take a look at Non-Conductive Tethers - Free Artificial Gravity In Orbit.

Scroll down for more stories in the same category. (Story submitted 11/5/2004)

Follow this kind of news @Technovelgy.

| Email | RSS | Blog It | Stumble | del.icio.us | Digg | Reddit |

Would you like to contribute a story tip? It's easy:
Get the URL of the story, and the related sf author, and add it here.

Comment/Join discussion ( 6 )

Related News Stories - (" Space Tech ")

NASA SEXTANT First With X-Ray Nav In Space
'You need at least four beacons for an accurate fix.' - Harry Harrison, 1956.

Subsurface Martian Ice Slabs Piece Of Cake For Miners
'One shy little fellow with bloodshot eyes of old-time drillman stood up. 'I'm an ice miner,' he said.' - Robert Heinlein, 1966.

I Want Massive Space Freighters!
Ah, the space freighters of old.

Our World Formed In A Bubble?
'The Worldcraft bubble glittered, catching the light...' - Philip K. Dick, 1953.

 

Google
  Web TechNovelgy.com   

Technovelgy (that's tech-novel-gee!) is devoted to the creative science inventions and ideas of sf authors. Look for the Invention Category that interests you, the Glossary, the Invention Timeline, or see what's New.

 

 

 

 

 

Current News

Fungi-Infused Concrete Repairs Itself
'I noticed that curious mottled knots were forming, indicating where the room had been strained and healed faultily.'

Shiftwear Display Shoes
'He unlaced her shoe and glanced at its readout.'

NASA SEXTANT First With X-Ray Nav In Space
'You need at least four beacons for an accurate fix.'

GM Introduces Cruise AV With No Steering Wheel
'How about the steering wheel?' ... 'I do not need one.'

Subsurface Martian Ice Slabs Piece Of Cake For Miners
'One shy little fellow with bloodshot eyes of old-time drillman stood up. 'I'm an ice miner,' he said.'

LG Rollable Version Of Niven's Poster TV
'A television that unrolled like a poster.'

Multi-Robot Farming On Highly Sloped Land
High Plains, indeed.

Aeolus Robot Brings Jetson's Rosie Closer
Domestic duties, robotically performed.

Sony's New, Cuter Aibo Robot Puppy
Engineered to be adorable.

Earth-1 Transformer Gundam Car
Is it a Gundam? Or maybe a Transformer.

Self-Driving Domino's Pizza Car
Yes, but can it negotiate entry at your Burbclave?

I Want Massive Space Freighters!
Ah, the space freighters of old.

When Will The Feds Ban Human Drivers?
'The first laws came out forcing the old machines off the highways...'

Our World Formed In A Bubble?
'The Worldcraft bubble glittered, catching the light...'

Will You Live To See EM Pulse Scattering By Ships Nearing Light Speed?
'...half a million kilometers away, the Stardrive went on.'

Jabil Integrated Textile Heart Monitoring
'Della's first present was an imipolex sweatshirt called a heartshirt…'

More SF in the News Stories

More Beyond Technovelgy science news stories

Home | Glossary | Invention Timeline | Category | New | Contact Us | FAQ | Advertise |
Technovelgy.com - where science meets fiction™

Copyright© Technovelgy LLC; all rights reserved.