[ExI] Physical limits of electromagnetic launchers

[Keith Henson]

On Sat, Jun 2, 2012 at 5:00 AM,  <extropy-chat-request at lists.extropy.org> wrote:
>
> 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.

I have seen arguments that more than a small fraction of c gets into
abrasion problems.  Out between galaxies this may be less of a problem

> 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 do want to consider power, then I need the mass of the probe
objects.  Small enough, bacteria size, electrostatic works better than
magnetic acceleration.

>> 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).

If I recall correctly, lasers are good out to a light year, and since
they can levitate objects on earth, they can accelerate at 1 g or
better.  I think that's 0.1 c.

The problem is slowing down at the target.  Of course there is
Drexler's method for that but it does take foresight.

A nice fresh G type star can make it from one galaxy to the next using
a hemisphere of light sails to convert the star into a fusion-photon
drive.  But you have to be really patient.

Keith