Orbit insertion
Orbit insertion is the task for entering a desired stable orbit after launch or arrival in the sphere of influence of another celestial body.
Orbit insertion after launch
After launch, the important task is to avoid all obstacles on the way to the desired orbit:
- Atmosphere
- Terrain
Direct ascent
The simplest way to to fly at a point on the new orbit and accelerate to the orbit velocity at this point in one powered phase. This is a preferred strategy for rocket stages with engines, which can't be restarted, but causes very high gravity losses.
Two-Burn strategy
For reducing gravity losses, one way is to aim for inserting into a nearly stable orbit just above the obstacles (for example 130 km for earth or 15 km on the moon), which has its apogee at a point of the target orbit. A second burn matches the velocity vector to the orbit velocity of the target orbit.