[ExI] Physical limits of electromagnetic launchers

[Anders Sandberg]

On 02/06/2012 15:39, Keith Henson wrote:
> 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 

Would love to get some proper numbers on this. I have heard the 
arguments, but not seen any proper calculations.

I suspect a series of Whipple-shields in front of the vehicle can fix a 
lot of the abrasion problem.


> 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.

In our case the standard probe payload mass is about 30 grams, if I 
remember right. We also have an extreme case of 500 tons, but that is 
not something we take very seriously.

> 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.

Yes, a lot of laser propulsion systems could be done in this scenario. A 
Dyson shell is  pretty good phased array.


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

Which one was that? Eric suggested a moving railgun that fired the 
payload backwards, possibly even repeating in order to seed along its 
line of travel. In our model we assume the payload to be a small rocket 
(fission, fusion or preferably antimatter), although for intergalactic 
colonisation over long distances the expansion of the universe can be 
used to shed velocity!


> 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.

It is nice when you have plenty of luggage.

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