h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

In 1992 Space Shuttle Atlantis(STS-042) deployed a Tethered Satellite to study space plasma physics. They used a conductive tether. As the tether travelled through Earth's magnetic field it produced an electric charge (up to 60V during the experiment). While they were never able to fully extend the tether to it's 20km length, (they were only able to get it 267m out without tangling the tether) the experiment did yield some valuable data. An interesting thing about a conductive tether is that while it moves through the Earth's magnetic field it generates an electric charge at the cost of an EMF(electro motive force) opposite to the direction of the orbit. However, if a satellite with an onboard power source (such as solar panels) charges the tether it will act as an electric motor giving forward propulsion to the satellite and tether. Now, if a tethered satellite is attached to the Earth (like the space elevator or 'sky hook') could it be used for a power source? Well, if it's motion through the Earth's magnetic field is used to generate electricity it will slow the tether and satellite down destabilising it's orbit. If a solar array is used to generate electricity it will speed the satellite and tether, also destabilising it's orbit... Could the tether be charged just enough to counter it's EMF while still transmitting the solar array's electricity to Earth without decaying it's orbit?... Anyone?... Bueller?

Off the top of my head, I'd say that the space elevator is not moving with respect to the Earth's magnetic field, so it can't be used to generate electricity.

Hmmm... could be, could be....

But with a tethered satellite at Geosynchronous orbit at the hub, with a balancing tether extending even farther out, it will be well into the Van Allen radiation belts, so who knows what kind of charge it could pick up from all those particles screaming by. Either way, anyone trying to live at a geosynchronous orbit is going to have a heck of a time with life support and radiation shielding. And as Clarke pointed out, g*d have mercy on anyone below the tether should it fail.

(I still like the idea though.)


Count Zero

...a gloss on orbital bridge technology, having to do with the long transit times between the ground and outer space.

It doesn't necessarily have to be done all in one sitting, instead, one can have way stations along the course, allowing layovers for meals and rest and recreation, beginning, with the 'city above the clouds' in the low middle tropopause, with more waystations conveniently located at other altitudes...

A system like that can produce savings in parasitic weight being lofted to orbit.

...on the problem of tether power generation in a geostationary orbit, suppose the tether power generation platform is a centripetal artificial gravity system?

This might not be practical for the Earth, but would be, I think for the outer system giants.

Somebody pointed out to me recently that the whole tethered satellite generation system is a swizz. The tethered satellite will experience a force due to the magnetic field which will slow it down. The satellite will then have to be speeded up by firing chemical rockets. So all you have is a very expensive system for converting rocket fuel into electricity.

Yeah... that might have been me. It's been a major concern of mine for some time (see post 1 above). I've never heard anyone else mention it. I keep hoping one day I'll run into someone who actually knows about this stuff.


Recently a new thought occurs to me. The Shuttle Tethered Satellite tests did indeed create a large amount of electrical charge (and therefore an EMF retrograde to orbit). But this was at LEO. An actual anchored tethered satellite would be geosynchronous so the question then would be would it actually be traveling through the Earth's magnetic flux or just along with it. I'm sure there will still be some movement in the flux itself as evidenced by the movement of aurorae lines. But as opposed to a tether moving through the Earth's magnetic field it seems reasonable to presume that the magnetic field rotates along with the Earth itself. Or is the magnetic field moving relative to the Earth's surface? Is it generated by a flowing iron core moving at a different rate than the Earth rotates? I've read/heard that Mars lost its radiation belts when its core solidified and that one day the same will happen to the Earth.

It really does get complicated and confusing quickly.

Heh, and I go back and read your reply from 10 years ago and you'd already assumed that the tether would not be moving through the magnetic field.

Suppose your tether system originates on the moon, fabricated of Lunar materials, starting, perhaps in a very high elliptical orbit.

Stipulated it will gradually lose altitude due to conversion of some of its kinetic energy into electricity, but might still be a viable power generation system, at least temporarily.




Meanwhile, Have you seen anything on magnetron shielding for protection of space vehicles from charged solar wind particles adapted to driving the vehicle, on the principle that the distortion produced in the artificial magnetic field of the vehicle by solar wind pressure tends to drag the vehicle along with it?

I had to agree with Dr. Robert Forward's rave review of the concept, a case of a compact system with mechanics similar to a solar sail, based on an artificial magnetic field, trading power for speed which can potentially be combined with ionic propulsion, meanwhile helping to keep vehicles (and passengers safe from charged radiation.

Yet again, there are ramifications of magnetron shielding in close orbit about objects with strong magnetic fields that can be used to amplify gravity assist vectoring.

The tether system has been proposed for supplying braking energy for a kinetic instellar vessel approaching an alien star.

It hasn't been used yet matching orbits with one of the outer system giants.




This is a rather oddball suggestion in electrical propu!sion which may be on the level after all, though I still consider it doubtful.

http://www.digitaltrends.com/cool-tech/nasa-confirms-impossible-space-drive-actually-works-revolutionize-space-travel/?utm_source=o1&utm_medium=cpc&utm_campaign=o1




Puts in mind of some of Arthur C. Clarke's remarks on electrical space propulsion once upon a time to the effect that there were no electrical rockets yet.

The most successful to date is the ionic system being used by the Dawn Mission, now in transit between Vesta and Ceres.

In the science fiction of Larry Niven, which is set a few hundred years in the future, there are still some people who don't believe in reaction-less thrusters, even though they have been used for years.

NASA hasn't really confirmed that that thruster works. They basically just confirmed that they measured a small force but they do not know what may have produced the force. It wasn't even tested in a vacuum.

http://www.slate.com/blogs/bad_astronomy/2014/08/04/reactionless_motor_needs_more_evidence.html

This article has links to more detailed ones if desired.

Meanwhile, one of the other electromagnetic propulsion ideas mentioned is founded on active electromagnetic shielding against solar wind radiation.

The basis of it is discussed in this article.

http://www.islandone.org/Settlements/MagShield.html

The concept is first and foremost effective radiation shielding, the propulsive effect is a secondary side effect.

Myself, taking it from that standpoint, I'd go with a toroidal artificial gravity life support ring as the basic platform, with, rather than the central spindle of the classical illustrations of such structures, instead an open channel in the middle with a giant sized ring magnet generating the protective field with an axis coincident with the spin axis, operating in inner solar system conditions on a solar electric principle.

Though I don't think a platform like that can be stable enough in near Earth orbit in intetaction with the Terrestrial magnetic field, careful application of the propulsive effect out in L-5 can get a reduction in station keeping expenses.