In Star Trek: The Original Series, a subspace viewer projects a three-dimensional image for long-distance communication.
The subspace viewer is a communication display used aboard starships and at major facilities. It allows a person to see a remote participant as a projected image while communicating across interstellar distances. The device reflects the series’ vision of advanced communications beyond ordinary radio or television.
Subspace communication is a recurring Star Trek concept: it allows messages to cross vast distances far more quickly than conventional signals. A subspace viewer is the display technology associated with the visual presentation of such a communication, rather than the entire faster-than-light communications network.
It is easy to confuse the viewer with the portable communicator carried by landing parties. The communicator sends and receives signals, while the subspace viewer presents a larger, three-dimensional visual image. Later Star Trek productions portray similar functions using more advanced displays and holographic systems.