Space Navigation (1) – 1967 NASA
Part 1 of an old NASA film on space navigation. Spacecraft navigation comprises two aspects: (1) knowledge and prediction of spacecraft position and velocity, which is orbit determination, and (2) firing the rocket motor to alter the spacecraft’s velocity, which is flight path control.A spacecraft on its way to a distant planet is actually in orbit about the sun, and the portion of its solar orbit between launch and destination is called the spacecraft’s trajectory. Orbit determination involves finding the spacecraft’s orbital elements and accounting for perturbations to its natural orbit. Flight path control involves commanding the spacecraft’s propulsion system to alter the vehicle’s velocity. Comparing the accurately determined spacecraft’s trajectory with knowledge of the destination object’s orbit is the basis for determining what velocity changes are needed.