QUOTE
Bussard-Ram wouldn't work in reverse (to decelerate).
That depends on how the ram works in the first place. Also, on how the propulsion system can be aimed. If you have the ability to flip the
propulsive component of your ram-and-laser setup around, then the ram still faces forward. Heck, at that point, the act of scooping up more interstellar gas, would itself help decelerate you (since that effect on your own inertia would no longer be working
against your efforts, but instead, be owrking
with it).
Let's say the laser puts out ... oh, a more sane number: 0.00000125G of "push", and the rams produce 0.00000025G of "push". While accelerating, your net thrust is 0.0001G: subtract the Ram force from the Laser force. But your
deceleration instead
adds the two, for 0.0000015G of force. You accelerate for 2/3 of the trip, then decelerate for 1/3 of it.
I'm not up to doing the math myself (honestly, it makes my head swim just to try and figure those equations out - it's been a quarter century since I was in highschool, even!!), to know how long it would take to travel, say, 20, 40, 100, or 200 lightyears, with those numbers: 2/3 time-to-target at 0.0000010 gravities acceleration, then 1/3 time-to-target at -0.0000015 gravities deceleration.
But ... 0.000001 gravities is 0.0000098m/sec. Close enough to call it 0.00001m/sec ... so slow, you could out-WALK the thing for months, if not years, of it being in operation. Nonetheless, one year is ... well, 365.25x24x60x60 = 31,557,600 seconds, so, our velocity should be ... 3,155.76 meters per second, about 0.015c; even allowing for dilation effects, you should be able to hit 0.05c within ten or twenty years.
Now, sure, sure. At that speed, even instantly accelerating from a dead stop (HA!), it would take 300 years of ship-time to go ~15 light years to reach that mesoplanet. But, you know? That's still a damned sight better than two to three
thousand years.