At least three sub-classes of this design were in service during the 2120s:
- The DY-500 subclass: The SS Mariposa was of this sub-class
- The DY-500-B subclass: The HMS Lord Nelson was of this sub-class
- The DY-500-C subclass: The SS Hokule'a was of this sub-class
|DY-100 class: SS Botany Bay|
|DY-245: SS Hatteras • DY-430: SS Urusei Yatsura|
|DY-500: SS Mariposa • HMS Lord Nelson (DY-500-B) • SS Hokule'a (DY-500-C)|
|DY-732: VK Yuri Gagarin • HMS New Zealand (DY-732 [N])|
|DY-950: DEV Eagle Valley • DY-1200: VK Velikan|
The 1979 reference book Star Trek Spaceflight Chronology depicts two 21st century spaceship versions of the DY-500 class ships, both of them designed by Rick Sternbach. There, they were also called the Wheeler class, and were described as an extensive upgrade to the DY-100 series. They were both similar to the canon 22nd century version, the so called "uprated" one the most. In the book, these older sublight explorer ships were in use from 2019 to 2055, and powered by advanced fission. Notwithstanding referenced to in Star Trek: The Next Generation - The Continuing Mission, page 85, as being a homage to the DY-100-class of the original series, the DY-500 designation had already been used in The Spaceflight Chronology, and Okuda's interpretation of ten years later, was such a very close approximation of the (uprated) one depicted in that book (page 35), that a homage to that work can be considered a more than likely explanation.
The novel Prime Directive states that the main hulls of DY-500s were surplus submarine shells reconfigured to transport cryogenic cargo in space.