All Four Forces Act on an Airplane
When an airplane is flying straight and level at a constant speed, the lift it produces balances its weight, and the thrust it produces balances its drag. However, this balance of forces changes as the airplane rises and descends, as it speeds up and slows down, and as it turns.
Only Two Forces Affect a Spacecraft in Space
A spacecraft has weight, even in orbit, and uses thrust to reach space and to maneuver. But lift and drag—both created by movement through air—are absent in the near vacuum of space.