Quick question about a STL trip

Assume our starship masses a cool one million tons. The trip is 100
light years. The ship's top acceleration is 20 cm/s^2, or 2% of a
gravity; its top speed is 0.25c. (These numbers chosen for story
purposes, obviously.)

So it accelerates for about 12.5 years, coasts for nearly a century,
then decelerates the same.

Questions:

1) Assume a straight fusion drive. What's the mass ratio?

2) Okay, what about an antimatter drive? How much better?

3) Is there any way to decelerate at least a little without carrying
reaction mass to do it? Assume there's no braking laser or such at
the target star, but can we use magnetic fields or a modified ramscoop
or something? (I have the impression that ramscoops are better at
slowing you down than at speeding you up...) I ask because even a
modest reduction in the reaction mass needed to decelerate helps a lot
with the mass ratio.

4) I was going to ask what's the power output, but I have just enough
math to do that myself. Let's just say you won't want to park this in
low Earth orbit... at a couple of hundred km up, the power output
would be enough that you'd feel the warmth on naked skin.

Thanks much in advance,


Doug M.

.

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