Fun little game, quite addictive really. Took me 10+ tries to complete it, my only issue was when you reach the area with many asteroids you can avoid most of them by sitting at the right/left of the screen, your not completly safe there however it made that section of the level very easy.
Also I'd also consider reducing the amount you slow down by. I completed the level almost entirly without having the need to slow down. So maybe it dosen't need to reduce it that much? Or possibly add a bar that recharges, so you can only use 5 second bursts of the reduced speed or something.
Just thought I'd give you my feedback, great game though. It was a challenge.