[ExI] Physical limits of electromagnetic launchers

[Anders Sandberg]

On 01/06/2012 15:49, Keith Henson wrote:
> v = at.  for v =1/10th c, 30,000,000m/s for a =~10g, 100 m/s^2, t
> =300,000 seconds or about 3.5 days of acceleration.

I think we can run the probes at much higher accelerations. If we go up 
to 1000g - definitely something solid state can handle - then we need 
just 3,000 seconds, or 45 million km. Still a long rifle, but not 
measured in astronomical units.

I suspect things get really tricky for ultrarelativistic launches. At 
this point the issue might be delivering the sizeable energy to the 
launcher (and handling dissipation losses): it is going to be a few 
times the mass-energy of the projectile.



> And you don't even want to think about the power this takes for
> constant acceleration near the end.

Yes, I do :-) Remember that I have a Dyson sphere to power the whole 
thing: the problem is not to have enough energy, but to avoid vaporising 
parts of the system by too high energy densities.


> If you need to get physical objects between stars, light sails and
> using the stars to power propulsion lasers seems to be a better idea.
> (Forward's idea.)

Yes, but in this case it is intergalactic colonisation. The lasers do 
not have enough range (both due to diffraction limits and the redshift).

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