A Starfleet transport class of the 23rd and 24th centuries, best known for the USS Jenolan, which crashed on a Dyson sphere.
The Sydney-class was a Starfleet transport design used from the late 23rd century into the 24th. Its boxy hull lacked a saucer section and was built for carrying passengers and cargo rather than combat or exploration.
In 2294 the Sydney-class USS Jenolan crashed on the surface of a Dyson sphere. Montgomery Scott survived by holding himself in the transporter buffer for 75 years until the Enterprise-D found the wreck in Relics. Scott and Geordi La Forge restored the Jenolan and wedged it in the sphere's entrance to hold it open for the Enterprise to escape.