A spacecraft has to point somewhere. Solar panels need the Sun. Antennas need Earth. Cameras need the target. Attitude control keeps the vehicle oriented correctly, and it operates in an environment with no air and no friction to damp unwanted motion.

Three main methods handle the job. Reaction wheels spin internal masses to rotate the spacecraft. Thrusters fire small bursts of propellant. Magnetic torquers push against Earth's magnetic field, useful in low orbits.

Typical attitude modes

• Nadir pointing, facing Earth
• Sun-safe mode, panels toward the Sun
• Inertial hold, fixed relative to the stars
• Slew manoeuvres between targets

Reaction wheels wear out and saturate. When they do, thrusters or magnets must desaturate them, spending precious fuel. Engineers build in redundancy because a stuck spacecraft cannot be reached for repair.