This achievement requires that you reach a speed of 800 m/h. There is no way top tell how close you are really getting to this threshold. Some levels have objectives to reach certain speeds and they display a speedometer. However, once you reach the threshold (the largest is 650 m/h), the level will be complete. Normally there is no way to tell. After fully upgrading your jetpack and bat, this achievement should come without even trying, especially towards the end of the game when there are large planets with strong gravitational pull. Basically you just need to launch yourself past a huge planet until the gravity slows you to a stop, then you will quickly be accelerating back towards that planet. At this time use your jetpack full blast and narrowly dodge the planet on your return. This is somewhat like a slingshot and will really get you moving.