At some point between 2265 and 2270, the Mendel was dispatched by Starfleet to the unexplored Trexelian Expanse. The Mendel's captain send a distress call which was received by Starfleet. Admiral Sahkalin ordered the USS Trexelprise, which was also on a mission of exploration in the expanse, to investigate. The Trexelprise found the Mendel on the outer rim of the Koloran Nebula in Trexelian Sector 002. After several hailing attempts went unanswered, the Trexelprise's captain led a landing party to the Mendel. They found the Mendel's crew under alien influence or infected, which turned the crew aggressive. The infection began to spread to the Trexelprise before its chief medical officer and scientists were able to cure the affliction. The two Constitution-class ships subsequently joined for