 |
Science Fiction
Dictionary
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
|
 |
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
")
JWST Finds New World Of Turbulent Silicate Clouds
'THIS is Ceti Alpha V!' - Gene Roddenberry, 1982.
Spectroscopic Analysis Of DART Impact Debris Cloud (SF Prediction)
'... Wendis stared thoughtfully at the brilliant lines on the spectroscope screen.' - EC Tube, 1958.
M-Dwarf Stars May Not Have Habitable Planets
'Thus it came about that the search for a planetiferous sun near a white dwarf star was not unduly prolonged...' - EE 'Doc' Smith, 1934.
Too Soon To Doom Lunar Farside Observatories
'Earth never shone there, but life was good.' - Raymond Z. Gallun, 1954.
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.
|
 |
Science Fiction
Timeline
1600-1899
1900-1939
1940's 1950's
1960's 1970's
1980's 1990's
2000's 2010's
Current News
JWST Finds New World Of Turbulent Silicate Clouds
'THIS is Ceti Alpha V!'
3D Printed Cheesecake Not Quite Food Replicator Quality
With each successive print, our model needed to incorporate more structural ingredients to minimize print failures.
Spectroscopic Analysis Of DART Impact Debris Cloud (SF Prediction)
'... Wendis stared thoughtfully at the brilliant lines on the spectroscope screen.'
Modern App Provides Video Technology From Bradbury's 'Fahrenheit 451'
'A special spot-wavex scrambler also caused his televised image, in the area immediately about his lips, to mouth the vowels and consonants beautifully.'
Win $250K By Reading Ancient Scrolls Carbonized By Vesuvius
'... it was as if the upper part had been removed, like a cut deck of cards.'
Toy-Like Robot Well-Being Coaches Are The Best
Sumomo will get those office workers into good shape!
AI-Trained Snack App Avatar Goes On Dates For You
'... who let their handbag computers carry all the conversation.'
M-Dwarf Stars May Not Have Habitable Planets
'Thus it came about that the search for a planetiferous sun near a white dwarf star was not unduly prolonged...'
Too Soon To Doom Lunar Farside Observatories
'Earth never shone there, but life was good.'
Amitabh Bachchan Wins Personality Protection
'He led me down the Hall of Portraits to the ego-likeness of the Duke Leto Atreides.'
LIAM F1 UWT Clever Rooftop Windmill
'...a windmill on his roof...'
Scent-Identifying Robot Uses Machine Learning
'It's picking up diphenyl compounds and tetrahydrocarbons...'
Volvo's Autonomous Truck
'They were automatic trucks such as are used for making deliveries...'
Skiing On The Moon - Skiing on Asteroids?
'MacIntyre bent down without a word and picked up the wide skis necessary to negotiate the powdery ash.'
Liberty Lifter X-Plane From DARPA
'...the tremendous speed that the Jupiter was turning up under the thrust of her twenty-four screws whirling on the shafts of twelve powerful motors.'
Robot Performs 3D Bioprinting Inside The Body
'Probably Runciter's body contained a dozen artiforgs...'
More SF in the News Stories
More Beyond Technovelgy science news stories
|
 |