Relativity Drive.

[Bouncing Zabaglione Bros.]

A respected space engineer is developing a new method of propulsion. The story is on the New Scientist subscription site, but I do have a cut & paste of the whole story if a mod will let me know if it's okay to post the full thing here.

 

[Neeyik]

A synopsis of the article would be fine (or a clearly abridged version) but full c&ps are a no-no, I'm afraid.

 

[Bouncing Zabaglione Bros.]

A synopsis of the article would be fine (or a clearly abridged version) but full c&ps are a no-no, I'm afraid.

I'd love to be able to post an abridged version, but it really woudn't make much sense, and would just raise more questions here that are already answered in the article.

In fact, you can get more info by Googling "Shawyer emdrive" and "relativity drive". Apparently this has been around a little while, but Shawyer is entering third prototype stage and is being funded by the UK government, and courted by the Chinese government and US Air Force, hence the article in the current New Scientist.

 

[DudeMiester]

http://www.shelleys.demon.co.uk/fdec02em.htm

Not the same article, but the same topic. Quite an interesting thing he's got there. I have to wonder though, where does the energy go once it's put in? It must be creating some flow of energy in the opposite direction of it's force. For example, the thruster proposed here emits radio waves.

 

[London Geezer]

I was reading about this yesterday...

But in brief, (and u knew this was coming) how would it work...?

 

[_xxx_]

Perpetuum mobile AND even producing extra energy, now that's a perfect double!

// gone looking for old Star Trek episodes...

EDIT:

So it's a perpetual motion machine, which happens to be reactionless.
The best of both worlds

Check this: http://bbs.extropy.org/index.php?board=71;action=display;threadid=63139
And this: http://advancednano.blogspot.com/2006/09/propellant-free-microwave-space.html

 

[Bouncing Zabaglione Bros.]

Perpetuum mobile AND even producing extra energy, now that's a perfect double!

// gone looking for old Star Trek episodes...

Despite your ability to quote what other webmongs have posted in other forums and to post a silly picture, it's not exactly cut and dried:

Shawyer's calculations have not convinced everyone. Depending on who you talk to Shawyer is either a genius or a purveyor of snake oil. David Jefferies, a microwave engineer at the University of Surrey in the UK, is adamant that there is an error in Shawyer's thinking. "It's a load of bloody rubbish," he says. At the other end of the scale is Stepan Lucyszyn, a microwave engineer at Imperial College London. "I think it's outstanding science," he says. Marc Millis, the engineer behind NASA's programme to assess revolutionary propulsion technology accepts that the net forces inside the cavity will be unequal, but as for the thrust it generates, he wants to see the hard evidence before making a judgement.

Shawyer's electromagnetic drive - emdrive for short - consists in essence of a microwave generator attached to what looks like a large copper cake tin. It needs a power supply for the magnetron, but there are no moving parts and no fuel - just a cord to plug it into the mains. Various pipes add complexity, but they are just there to keep the chamber cool. And the device seems to work: by mounting it on a sensitive balance, he has shown that it generates about 16 millinewtons of thrust, using 1 kilowatt of electrical power. Shawyer calculated that his first prototype had a Q of 5900. With his second thruster, he managed to raise the Q to 50,000 allowing it to generate a force of about 300 millinewtons - 100 times what Cosmos 1 could achieve. It's not enough for Earth-based use, but it's revolutionary for spacecraft.

To review the project, the UK government hired John Spiller, an independent space engineer. He was impressed. He says the thruster's design is practical and could be adapted fairly easily to operate in space. He points out, though, that the drive needs to be developed further and tested by an independent group with its own equipment. "It certainly needs to be flown experimentally," he says.

Meanwhile Shawyer is looking ahead to the next stage of his project. He wants to make the thrusters so powerful that they could make combustion engines obsolete, and that means addressing the big problem with conventional microwave cavities - the amount of energy they leak. The biggest losses come from currents induced in the metal walls by the microwaves, which generate heat when they encounter electrical resistance. This uses up energy stored in the cavity, reduces the Q, and the thrust generated by the engine drops.

Fortunately particle accelerators use microwave cavities too, so physicists have done a lot of work on reducing Q losses inside them. The key, says Shawyer, is to make the cavity superconducting. Without electrical resistance, currents in the cavity walls will not generate heat. Engineers in Germany working on the next generation of particle accelerators have achieved a Q of several billion using superconducting cavities. If Shawyer can match that performance, he calculates that the thrust from a microwave engine could be as high as 30,000 newtons per kilowatt - enough to lift a large car.

This raises another question. Why haven't physicists stumbled across the effect before? They have, says Shawyer, and they design their cavities to counter it. The forces inside the latest accelerator cavities are so large that they stretch the chambers like plasticine. To counteract this, engineers use piezoelectric actuators to squeeze the cavities back into shape. "I doubt they've ever thought of turning the force to other uses," he says.

No doubt his superconducting cavities will be hard to build, and Shawyer is realistic about the problems he is likely to meet. Particle accelerators made out of niobium become superconducting at the temperature of liquid helium - only a few degrees above absolute zero. That would be impractical for a motor, Shawyer believes, so he wants to find a material that superconducts at a slightly higher temperature, and use liquid hydrogen, which boils at 20 kelvin, as the coolant. Hydrogen could also power a fuel cell or turbine to generate electricity for the emdrive.

In the meantime, he wants to test the device with liquid nitrogen, which is easier to handle. It boils at 77 kelvin, a temperature that will require the latest generation of high-temperature ceramic superconductors. Shawyer hasn't yet settled on the exact material, but he admits that any ceramic will be tricky to incorporate into the design because of its fragility. It will have to be reliably bonded to the inside of a cavity and mustn't crack or flake when cooled. There are other problems too. The inside of the cavity will still be heated by the microwaves, and this will possibly quench the superconducting effect. "Nobody has done this kind of work," Shawyer says. "I'm not expecting it to be easy."

 

[mcsven]

I'll need two of those if I'm going to get the sports almanac back from Biff and rescue the Doc.

In all seriousness, this looks very interesting. Thanks for the link.

 

[K.I.L.E.R]

Is this the new nuclear bomb?

 

[Frank]

Interesting! This actually seems like something that could very well work and give us a new paradigm for looking at applied forces!

I'm going to keep a close eye on it.

 

[MuFu]

Very interesting, especially given his stated desire to build a superconducting prototype within the next two years.

Relativistic thinking always does my head in. I am just about ok with the theoretical explanation for how the net force is generated, but here...

Then there is the issue of acceleration. Shawyer has calculated that as soon as the thruster starts to move, it will use up energy stored in the cavity, draining energy faster than it can be replaced. So while the thrust of a motionless emdrive is high, the faster the engine moves, the more the thrust falls. Shawyer now reckons the emdrive will be better suited to powering vehicles that hover rather than accelerate rapidly. A fan or turbine attached to the back of the vehicle could then be used to move it forward without friction. He hopes to demonstrate his first superconducting thruster within two years.

...blood started coming out of my ears. Why does the thrust drop off when the engine accelerates (edit - ignoring thermal losses for now)?

 

[_xxx_]

Hovering with a turbine behind, but how will he steer it? And save those pitiful pedestrians from being grilled? That will never get a nick from the officials.

 

[MuFu]

Hovering with a turbine behind, but how will he steer it? And save those pitiful pedestrians from being grilled? That will never get a nick from the officials.

Just thrust vector the turbine, use control thrusters and/or (aerodynamic) surfaces.

By the time this thing gets anywhere near efficient enough to keep a car aloft there shouldn't be any risk of grilling pedestrians. Still might not be a good idea to stand directly under one of the drives though, especially if it's tiny compared to the size of the car.