The USS Orpheus was a Federation research vessel in service to Starfleet in the mid-23rd century.

Prior to his posting aboard the USS Enterprise in the early 2250s, Spock served aboard the Orpheus under the command of Admiral Pranang. During his service aboard the Orpheus, Spock grew distasteful at Pranang's cavalier attitude, when long-term research missions were abandoned in favor of investigating instrumental anomalies, which often amounted to nothing. (TOS novel: The Children of Kings)

The information regarding Spock's assignment to the Orpheus is partly conjectural. In one passage, Spock refers to serving aboard the research vessel and his distaste at his commanding officer's attitude to the mission. In a later passage, the Orpheus and Admiral Pranang is referred to, again by Spock, when he remembered that when he made a brief report to Pranang, it would amount to a hundred words. Considering the evidence that Spock served under Pranang at some point, it has been linked to the passage regarding the research vessel.
Community content is available under CC-BY-SA unless otherwise noted.