<Two bits worth

[Brian Mansur <bmansur@oc.edu>]

Brian here again with a very small amount of time to throw in a slight 
variant on the magsail idea.  I get the feeling that no one really thinks a 
magsail/ramscoop brake can be made to work.  But if it can, I suggest the 
following.

Looking back on LIT's (Seger's contribution I think) on Relativistic 
Particle Beam propulsion (RPBP), it is noted that a low .036 g acceleration 
was deemed possible by Zubrin for a magsail RPB driven starship weighing 
1000 tons at the cost of 11 GW/ton.

Now what I have noticed in our discussions is that the particle beam 
accelerators are a lot like stationary ion rockets that spew a particle 
stream that hits a magnetic sail/scoop on the starship tht either fuels the 
ship or imparts momentum with the particles' collection/collision or both.

Since we have always (I think) assumed that we could make an ion accelerator 
powerful enough to produce a 1g thrust, I wonder why we couldn't just rig 
one of these accelerator/ion rockets with a magsail, launch it ahead of the 
manned ship via RPB propulsion methods and use it as a kind of portable RBP 
source to stop the primary starship near Tau Ceti.

This would be analagous to stopping a ship by putting it in the exhaust of 
another rocket.  In this case, the exhaust is really a particle beam that 
can reach hundreds of AUs.

I make a couple of obvious assumuptions here (some I'm probably not seeing). 
 For one, I acknowledge that we will need many Terawatts to push this 
decelerator rocket and all of the fuel it will need to carry.  Since we are 
already assuming 1E18W for some other ideas, I assume it here.  I also 
assume that the decelerator is completely automated for at least some part 
of the duration of the starship deceleration phase.

By the way, the decelerator could be manned for the first part of its 
mission.  If we are willing to wait a while, we could launch it at a slower 
speed than the prime starship and it could begin pounding the faster moving 
Asimov with ions while still a ways off. The decelerator would speed up some 
while slowing the Asimov down and the two ships could be brought to equal 
speed near each other.   Note that the heavier we can make the decelerator, 
the better because the further the decelerator is from the Asimov, the 
harder it will be to hit it with a RPB.

Once the decelerator and Asimov are at equal speeds, they could dock and let 
the decelerator's crew transfer to the Asimov, leaving the decelerator on 
automatic.  The decelerator could then continue its job.

For getting back home, we could bring along another ion accerator like the 
one used to stop us.  It could be used as an ion rocket for in system 
shuttling (this is basically Kelly's Explorer design).  Again, the ion 
rockets we've discused so far sound powerful enough to mean that we need 
take only one.  Since we've kicked the idea of a launcher in Tau Ceti around 
a lot in previous discussions I'll stop here.

I'm not sure that my mail is getting through to everyone so I apologize.  If 
it is and this is old material to everyone, well, nuts.  I thought it was 
different enough to be worth posting.  I await comments.