In April, 2163, the Pioneer returned to Earth to take aboard a team of engineers led by Doctor Tobin Dax. Sheehan worked closely with Dax, to solve engineering problems caused by the mixture of different Federation member races' technologies. During a trial run, the deflector shields interfered with the ship's warp field, creating an unstable wormhole. During the accident Sheehan suffered severe injuries and was in coma for several days.
Once Pioneer escaped the disaster, he was taken to a medical facility. Chief medical officer Doctor Therese Liao believed Sheehan needed months to recover, "and there's no telling when or if he'd be fit for duty again". He was temporarily replaced by Tobin Dax. (ENT - Rise of the Federation novel: A Choice of Futures)
|Federation Starfleet||Y. Achrati • Bergmann • Chen • P. Collier • T. Dax • C. Detzel • B. Grev • J. Guzman • Kano • Karthikeyan • E. Kemal • S. A. Kirk • Konicek • T. Liao • T. Mayweather • K. Mishima • P. Morrow • K. Ndiaye • A. Osunwoke • H. Polanski • M. Reed • R. Sangupta • A. Sheehan • R. Tallarico • A. Tatopolous • C. Tucker • V. Williams • S. Yuan|