At some point after launch, usually just before or after separation from the last booster stage, spacecraft are often made to "spin" (about the axis of their trajectory)? See e.g this You Tube video. What is the reason for this spin?
- Stabilization. Example: Pioneer
- Equalize heating (barbecue mode). Example: Apollo
- Deploy antennas & booms (via centripetal force). Example: IMAGE
- Maintain tension in a solar sail. Example: Cosmos 1
- Test general relativity. Example: LAGEOS
- Create artificial gravity. Example: Gemini
- Simplify or reduce weight of sensors (e.g. star trackers). Example: New Horizons
- Improve the accuracy of sensors. Example: Hipparcos
- Keep antennas/sensors pointing towards a central body. Example: GPS
Applying spin along an axis, usually the direction of travel, endows the craft with a degree of gyroscopic stability, enabling the craft to preserve consumables onboard as it makes navigation easier. SPin is also used in re-entry (like the beagle mars lander).
New Horizons, Pioneer 1 and 2, Voyager 1 and 2, as well as some sattellites all use a spin to gain gyroscopic stability.