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Re: My Two Bits Ain't Worth 1E-15 (Take 2)

On Wed, 28 Feb 1996, Brian Mansur wrote:
> Jumping to a tangent, I wonder if this idea could help solve some problems 
> of decelerating Kevin's MARS.  I noticed that his design is launched by 
> using a beam that hits a sail.  The trouble seemed to be how to reverse the 
> beam's direction to in order slow the ship.

The simplest way to do it would be a mirror, but then the mirror speeds 
up way too fast, and the reflected maser light doppler shifts into the 
Extremely Low Frequency (ELF) region.

> The solution we've dissused to date is to harnessing that previously 
> reflected power to run an ion accelerator that speeds its RM up to such a 
> high velocity that very little RM is needed to stop the ship (compared to 
> fusion powered ion rocket that can only carry so much power in fusion fuel). 

The problem is that the masers give a push toward TC, so the engine must 
push back even harder.  Unfortunately, there is not enough power in the 
maser beam to use the minimum amount of mass in the exhaust stream.  The 
only solution I can think of is to turn up the amount of mass in the 
exhaust stream.  My original MARS design called for using the lineac for 
both accelleration and deaccelleration phases.  If instead, we use maser 
sailing for the acceleration portion, and keep all the RM for the decell 
phase (using a lower Exhaust Velocity) Then I think we can slow down.

> One last tangent.  Some concerns I've had with Kevin's design is how to rig 
> a stable sail while keeping the Asimov hab and drive modules from being 
> fried.
> The best idea I can come up with is to rig the sail like an umbrella.  While 
> reflecting the maser beams, it pulls the Asimov hab module along like an 
> open umbrella pulls a man on a windy day.  I seem to recall that Kevin 
> adressed the shielding of the hab section by putting it front of the sail. 
>  From an engineering standpoint (like I know anything about egineering), 
> this seems more difficult than tying cable from the rim of the sail to the 
> hab section and just letting the sail tow it along.  Do you know what the 
> group decided on this topic?  Couldn't we just put more shielding on the 
> side of the hab section facing Sol?

Two points.
1) The design I am envisioning now is like you just described.  The Sail 
tows the "Asimov", and the photon pressure keeps the sail open.

2) shielding should be pretty easy, just about any metal should reflect 
the maser beam.  while in a Microwave oven this causes sparks, I'm sure 
that this is because of feedback between the microwave tube and the 
reflecting surface.  since we will be a long way from the generator, I 
think we won't have to worry about that