Headscratchers / Star Trek S3 E7 "Day of the Dove"

• So beaming down from an orbiting starship to a planetary surface, where the relative velocity between the two points might be thousands of meters per second, is fine - but beaming to another part of the ship where the relative velocity is zero is difficult?
  • The most straightforward explanation is that the transporter has a minimum safe range, and that trying to focus the energies too closely is difficult (like trying to clearly see something very close to your eyes).
  • There's also more open space on a planet surface than in the corridors of an early, pre-refit Constitution Class starship, and the transporter, while in regular use, was still prone to errors and glitches. Heck, the advancements seen in Star Trek: The Next Generation are likely due to ironing out the bugs found during the original series. And even then, things like accidentally created doubles were possible.
  • Or because transporter emitters are directed outside the ship, in keeping with the purpose of beaming to a planet or another ship. Beaming within the ship means redirecting the emitters in a way they weren't designed for, hence the risk.