Double rockets are similar to normal rockets, but shoot back and front. Even though they shoot both ways, the damage is not different from normal rocket, making double rockets a better choice. The ultimate version of double rocket is the double freeze rocket, but this is much weaker than cutter rocket, unlike the comparison between double rocket and rocket.
To obtain double rockets, you'll need to get to stage 20 prestige 0.
If you flip over, double rockets can fire at the enemy. If you somehow get behind the opponent, if the enemy doesn't have have double rocket or blade (and upright) you can easily destroy the opponent. You can try and get your machine behind the enemy using boosters and backpedals, and use double rocket.