I’m not sure many of you have heard about a recent technology called the Em-Drive, but it is the first “propellant-less” space/terrestrial drive developed. Thus far it has only been able to create around 2g of thrust, but the designer believes further iterations will be able to up that to tonnes of force via superconductors and niobium. It uses a magnetron connected to a specially shaped resonant cavity, the difference in wave velocity with it being higher on one side, creates measurable net force on its surroundings. The inventor believes that the technology will allow for both outer-space and earthbound vehicles to be developed.

http://news.uk.msn.com/Article.aspx?cp-documentid=877900
http://www.theengineer.co.uk/Articles/Article.aspx?liArticleID=295931
http://www.theengineer.co.uk/Articles/266633/Defying gravity.htm
http://www.emdrive.com/

My thought was that it would be a perfect fit with the Focus Fusion reactor(when it is developed of course), this would allow easy access to space and fast transit to neighboring planets, while only having to refuel occasionally.

I’d like to see what Eric Lerner has to say about this… it sounds really cool. Focus fusion is partially supported by JPL, and, before spending cuts, by NASA as a potential breakthrough spacecraft propulsion technology. There is an article somewhere on the site about it. It would be great if the emdrive could be coupled to a PFF reactor. I just wonder if the emdrive would be a better solution, given what the FF can do on its own.

The space industry is impressive for its engineering, maybe not so much for it’s science. For climate control we would need large solar sails to adjust the solar constant over the surface of the Earth.  Specific g performance may not be the parameter in demand rather total low payload and the thrust to pull the sails’ shadow into position over the poles fex

A copy of the EM Drive theory paper is now available to be downloaded in pdf format at the New Scientist website http://tinyurl.com/npxv8

Jolly Roger - 09 November 2006 10:42 PM

A copy of the EM Drive theory paper is now available to be downloaded in pdf format at the New Scientist website http://tinyurl.com/npxv8

The paper looks very flawed to me. The forces on the end-walls of the cavity seem to be correctly calculated (and, of course, there is a mismatch which provides the motive force this system is supposed to provide). However, the longitudinal component of the force on the cavity imparted by reflections from the tapered walls seems to be entirely omitted. I believe that these forces sum up to exactly cancel the mismatch calculated just from including the ends of the cavity. This is a similar mistake to assuming that if the cavity where filled with a perssurized gas, the gas would exert more force on the larger end than on the smaller end and so provide a resultant force on the cavity towards the larger end. This doesn’t happen because the pressure of the gas on the tapered wall exerts a resultant force towards the narrower end, exactly cancelling the effect.

I believe that the author also makes an error in calculating the limiting velocity. The problem is a relativistic one and therefore the solution has to be frame independent. This means that the limiting velocity has to be quoted relative to something, but the author only refers to a stationary system. In any system operating in free space with no external forces, any thrust has to be frame independent, which means that the only limiting speed (to an external observer) is the speed of light itself, although someone sitting inside the cavity would continue to feel exactly the same acceleration for however long energy continues to be put into the system.