Even spacecraft that are designed and optimized for a single mission need to be carefully balanced experimentally, and have ballast added before flight.
- Why did New Horizons have to be spin-balanced to grams-level precision? (With quarters!)
- Balancing Perseverance Mars Rover; couldn't they just "move stuff around a little" rather than add 6+ kg of dead weight?
- How to find the moment of inertia of the Viking capsule?
The Space Shuttle was reusable and had a comparatively short turn-around time, each time with a different payload.
Was the shuttle's mass distribution or at least its moments of inertia measured pre-flight? If so was ballast ever added then to balance it?