[ExI] Physical limits of electromagnetic launchers

[Anders Sandberg]

OK, let's say I want to send off my payload using a circular launcher. 
Then it needs to hold against a centipetal force of mv^2/r (what is the 
relativistic version of this formula, BTW?)

For v on the order of 0.1c and m=0.03 kg, the force will be 2.7e13/r. So 
assuming materials can handle a few hundred gigapascals (what we get in 
diamond anvils) and that the payload is nice and flat with an area of 
0.01 m^2 (it is not actully pressed against the accelerator, but the EM 
fields will transfer the force) I get a max acceptable force of 10^9 N, 
which corresponds to r > 27 km. Thats actully not bad at all.

I suspect the real problem is coupling the accelerating fields with the 
payload without losing too much in Bremsstrahlung.  It scales with the 
square of the acceleration for both circular paths and linear ones, but 
in the linear case there is also a sixth power dependency on gamma, 
while the circular one is just to the fourht power.


[ OK, think I found a derivation of the relativistic formula:
http://www.physicsforums.com/showthread.php?t=187041

So the force would be mv^2/R(1-v^2/c^2) - for a 90% c payload the 
relativistic correction makes the force about 5 times larger, and in 
this case the radius need to be about 11,000 km. Still small. I think 
this approach has merit. ]

On 02/06/2012 23:36, Jeff Davis wrote:
> So could you try again, dispensing with the electric charge business
> and just going with maglev or something similar.

But maglev is electric charge, when you start looking at it 
relativistically! A pure magnetic field will look like it has electrical 
components when you move through it fast enough.


-- 
Anders Sandberg,
Future of Humanity Institute
Philosophy Faculty of Oxford University