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Here is a table of some maser sail numbers.

I think that 50 g/m^2 is kind of heavy, but as Tim said, this is going to 
be subject to some severe torture.  Perhaps the RR will sweep away the 
ICM particles, but I don't know.  No matter what the final density is, 
i think these numbers will behave the same way, (ie limiting values on 
heat load and stress)

Ship's  Sail  Sail   Sail    Total   Accel   Maser   Refl  Excess  Stress
Mass   Radius Dens   Mass    Mass            Energy  Eff.  Energy
Kg       Km   g/m^2   Kg      Kg     M/s^2   Watts    %    KW/m^s  Pascals
5E5      10    50   1.57E+07  1.6E+07  10  2.43E+16  0.99  773.8  0.515915
5E5     100    50   1.57E+09  1.6E+09  10  2.36E+18  0.99  750.2  0.500159
5E5     500    50   3.93E+10  3.9E+10  10  5.89E+19  0.99  750.0  0.500006
5E5    1000    50   1.57E+11  1.57E+11 10  2.36E+20  0.99  750.0  0.500002
5E5    5000    50   3.93E+12  3.93E+12 10  5.89E+21  0.99  750.0  0.5
5E5   10000    50   1.57E+13  1.57E+13 10  2.36E+22  0.99  750.0  0.5
5E5  100000    50   1.57E+15  1.57E+15 10  2.36E+24  0.99  750.0  0.5	

Ship's mass is just the hab section  (no core, no RM tanks)
sail density does not include guy wires to the ship.
Excess energy is the part of the maser beam that does not reflect

Several things have become clear to me since I ran these numbers (in Excell)
and I should think they will become clear to you as well.

1) the sail is the heaviest part of the ship.  Even at 50 g/m^2, and 100 
Km in radius, the sail alone approaches my original MARS design (now a 
smoking ruin ;( )

2) both thermal energy and sail stress approach some limiting value as 
the sail expands, so endlessly expanding the sail (even if we could do 
it) would not solve any of the major problems (heat load and stress)

3) Stress is miniscule  I don't where you guys have been getitng your 
stress numbers, but they are out of whack.

for figure checking, reading line 3 with a sail of 100Km radius, and a 
total mass of 1.57E9 Kg we find that the force of acceleration is 
1.57 E10 newtons, and the total area is 3.14 E10 meters which of course 
is .5 pascals (even a wet nose tissue could stand up to that)

4) smaller sails may be better.  Why in the world you would need a sail 
the size of Luna, much less Jupiter, is beyond me.

5) Thermal load is a big problem.  750 KW on .05 Kg is a big worry.
I have not calculated the limiting temperature yet, but I am hopeful that 
titanium alloy will stand up to the load.  To do this model, I will use 
heat capacity and blackbody radiation equation.  I do not have time right 
now, but expect it soon.