Space Tether to Send Satellites Soaring

[zavvy]

<b>Space Tether to Send Satellites Soaring</b><br /><br />LINK<br /><br />A 100-kilometre-long "fishing line" that spins freely in space may one day catch and fling satellites to higher orbits. The tether, set to begin a series of ground tests, could boost its targets' altitude using just solar power and the Earth's magnetic field.<br /><br />Traditional rockets use fuel to loft their payloads into the desired orbits. "The farther you want to go, the more fuel you need to put onboard," says Stephen Canfield, a mechanical engineer at Tennessee Technical University in Cookeville, US. <br /><br />But rockets could use less fuel if they instead launched satellites into low-Earth orbit before having the tether take over, boosting the satellites into higher, geosynchronous orbits - or even sending them on escape trajectories. The tether could also extend the life of existing satellites that begin to drop due to atmospheric drag. "This would reduce costs and be a reusable launch system in space," Canfield told New Scientist.<br /><br />Canfield is part of a team working on the tether, a NASA-funded project called the Momentum-Exchange Electrodynamic Reboost (MXER). The tether would be made of a material used in fishing lines and would have a mass at either end. It would be kept taut by spinning the masses - somewhat like a boomerang - in an elliptical orbit around Earth that dips down to low-Earth orbit (at an altitude of about 320 kilometres) before spinning out as far as 36,000 km.<br /><br />Brief fling<br />While in low-Earth orbit, "the payload and tether tip will come together at the same place at the same time and almost at the same velocity", says Canfield. The tether tip would attach and fling the satellite to a higher orbit - slowing the tether slightly as a result. Then, energy stored on solar panels would send electrical current down the tether and the travelling charge would interact with the Eart

 

[thalion]

Ever since I read an article in <i>Scientific American</i> about the possibilities of space tethers, I've been sold on the idea; I think it's great, even if for something simple like power generation. Think of the power a space tether might be able to produce in Jupiter's magnetic field, essentially for "free"...

 

[mrmorris]

<font color="yellow">" Think of the power a space tether might be able to produce in Jupiter's magnetic field, essentially for "free"... "</font><br /><br />1. You're mixing and matching tether concepts here.<br />2. Nothing comes for free.<br /><br />Tethers used for power generater are "Electrodynamic Tethers (EDTs)". Unlike the above -- they do not rotate (as such). Instead you have a kilometers-long cable in low-earth-orbit. Because the cable is cutting the magnetic lines of the Earth as it orbits -- there is a voltage difference at the two ends. A spacecraft can make use of that difference to power onboard systems.<br /><br />However -- if this is done -- the power used by the spacecraft is 'paid for' by robbing velocity from the cable/spacecraft system -- causing the orbit to decay. Ergo -- it's not 'free'. The spacecraft will be forced to expend propellant to maintain the orbit. <br /><br />In fact -- EDT's are actually being considered more commonly as a way to provide propellantless 'reboosts' to a satellite (or space station) by reversing the reaction. If power is pushed *into* the EDT, then the resulting reaction raises the orbit -- without requiring any propellant.

 

[tap_sa]

Obligatory tether link<br /><br />It does look like terminator tether for deorbiting is more production ready.

 

[mrmorris]

<font color="yellow">"..terminator tether for deorbiting ..."</font><br /><br />Yes -- I should have said 'changing' orbits rather than 'boosting' orbits. The point I was trying to make is that they're not really being looked at to produce electricity as such -- because gaining watts at the expense of propellant is not generally a good trade.

 

[thalion]

The velocity change could be a desired motion, saving propellant to move the spacecraft. It depends on what you want to do.

 

[mrmorris]

<font color="yellow">"The velocity change could be a desired motion..."</font><br /><br />Not really sure what you're getting at here. We're still talking about two types of tethers. The one that started the thread is a momentum-exchange tether. It has two weights separated by a tether several km long that is rotating about a common center. It's used to transfer energy from the angular momentum of the tether system to a satellite/spacecraft such that it can be accelerated rapidly from a LE orbit to a higher one (or the reverse, of course)<br /><br />The electrodynamic tether, by contrast, does not rotate, and does not transfer momentum. It works by interacting with the Earth's magnetic field as I indicated previously. <br /><br />The two tethers have nothing in common besides the fact that they both involve long strings in orbit.

 

[thalion]

I guess I was talking about the electrodynamic tether; I was unaware of the technical distinction.