[_fizz_buzz_]

1) you also need time decelerate

2) speed of light is a hard limit, you cannot keep accelerating and you need more energy the closer you get to that limit

[tokai]

> 1) you also need time decelerate

No that would be a waste of effort. A flyby mission definitely makes the most sense. The 3.5 years are with deceleration though.

[empiricus]

You mean flyby at almost the speed of light? For interstellar travel, I think usable flyby speed is almost the same as stop and look around speed.