Why does a rocket curve?

A rocket bound for orbit does not need to go up so much as sideways. To stay in low Earth orbit a spacecraft must travel at about 7.8 km/s (roughly 28,000 km/h) parallel to the surface; altitude only has to be high enough, typically 200 km or more, to escape most of the atmosphere. A vehicle that climbed straight up would simply fall back once its engines stopped. So the flight profile starts vertical, to leave the dense lower atmosphere quickly, and then bends progressively toward the horizontal.

Shortly after lift-off, usually between 10 and 30 seconds into the flight, the guidance system commands a small pitch manoeuvre. From then on the rocket is allowed to follow a so-called gravity turn: because gravity pulls the velocity vector downward while thrust acts along the body axis, the trajectory curves naturally, and the vehicle keeps its nose aligned with the airflow. That alignment matters. In the first minutes, when aerodynamic pressure peaks (the point engineers call max Q), any large angle between the body and the airstream would generate side loads the structure is not designed to take.

Curving early also saves propellant, since every second spent fighting gravity vertically is a second of thrust that does not add orbital speed. The direction of the turn is chosen to match the target orbit and, wherever possible, to point downrange over ocean or unpopulated land, so that stages and any debris fall safely. The same arc is visible from the ground: the exhaust plume appears to lean over, and from a distance the rocket looks as if it were heading for the horizon, which, in the end, is exactly where it needs to go.