The pilot of the Ares IV command module, lost in 2032 when a graviton ellipse swallowed his ship during Earth's first crewed mission to Mars.
John Kelly was a human astronaut on Earth's Mars mission of 2032. While his two crewmates were on the surface, his Ares IV command module was consumed by a graviton ellipse, a phenomenon that leaves subspace for short periods, stranding them for weeks. His disappearance nearly ended human spaceflight.
In One Small Step, Voyager encounters the same ellipse, and Chakotay, Tom Paris and Seven of Nine retrieve the module. Seven reads Kelly's logs of his last days, in which he went on recording data about the phenomenon until his death, and the crew holds a funeral in his honour.