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.
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 ")
SpaceX Wants A Moonbase Alpha
'And he had been sent with troops, supplies and bombs to command Russia's most trusted post, the Moonbase.' - L. Ron Hubbard, 1948.
NASA Wants Self-Driving Or Remote-Controlled Vehicles For Lunar Astronauts
'THE autobus turned silently down the wide street of Hydropole. Robot-guided, insulated from noise and cold...'
Orbital Mechanics, The Liftoff, The Turnover, The Retrograde Burn
'...the huge vessel had spun, with a sickening lurch, through a complete half-circle, the instant the power was reversed.' - EE 'Doc' Smith, 1928.
Can A Human Land A SpaceX Rocket On Its Tail?
'If she starts to roll sideways — blooey! The underjets only hold you up when they’re pointing down, you know.' - Stanley G. Weinbaum, 1936.
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
SpaceX Wants A Moonbase Alpha
'And he had been sent with troops, supplies and bombs to command Russia's most trusted post, the Moonbase.'
Vast Apartment Living Will Get Even More Vast
'What is your population', I asked. 'About eighty millions.'
NASA Wants Self-Driving Or Remote-Controlled Vehicles For Lunar Astronauts
'THE autobus turned silently down the wide street of Hydropole. Robot-guided, insulated from noise and cold...'
Elon Musk Says Robotaxis Will Be Ready This August, 2024
'The car had no steering wheel, and no one drove!'
Moonwalkers AI-Controlled Electric Shoes
Now that's power walking that Hugo Gernsback would have approved.
Steve Jobs: 'Capture The Next Aristotle - With AI'
'It was disturbing to think of the Flatline as a construct...'
No Tips! Robotic Food Delivery In Phoenix
'...he rewired the delivery robot so that it would serve him midnight snacks.'
Electric Catamaran 'Explorer Eco 40m' Has 'Solar Skin'
'On went the electric-yacht faster and still faster.'
Orbital Mechanics, The Liftoff, The Turnover, The Retrograde Burn
'...the huge vessel had spun, with a sickening lurch, through a complete half-circle, the instant the power was reversed.'
Harvest Power From Tears And Blinking With Smart Contact Lens
'...he realized that it was not quite a clear lens. Speckles of colored brightness swirled and gathered in it.'
Europa Clipper Plate Carries A Special Message
'...a universal cryptogram — yet it is one which can be interpreted by any intelligent creature on any planet in the Solar System!'
Micro-Robots Are Smallest, Fully Functional
'With a whir, the Scarab shot from the concealing shadows of the corner where it had hidden itself.'
AI Enhances Images Your Brain Sees
'I could have sworn the psychomat showed pictures almost as sharp and detailed as reality itself'
Illustrating Classic Heinlein With AI
'Stasis, cold sleep, hibernation, hypothermia, reduced metabolism, call it what you will - the logistics-medicine research teams had found a way to stack people like cordwood and use them when needed.'
Deflector Plasma Screen For Drones ala Star Wars
'If the enemy persists in attacking or even intensifies their power, the density of the plasma in space will suddenly increase, causing it to reflect most of the incoming energy like a mirror.'
DIY Robotic Hand Made After Loss Of Fingers
'I made them... with the fine work of the watchmaker...'
