Is there a mouse+WASD option enabled for Tachyon?
If not, how do you map it?
Those keys are used, but keyboard keys are used for strafing, rolling, "sliding", ect. You steer your ship with the mouse, and forward or backwards movement is controlled by keyboard (Thrust). Somewhat similar to Freelancer a bit, but a little more involved. I believe you can change keyboard commands to suit your tastes, but the WASD is not used to move forward or backwards, or right and left. Here's a pic of the controls, in the event you or someone else hasn't picked up the game yet, and want to know how it all works....
edit: Just fyi, you can remap buttons under options-->input remap * Also, in the event you have a joystick, it also has joystick support, although I haven't used it