Tryggvason served as a Payload Specialist on STS-85 (August 7–19, 1997), a 12-day mission to study changes in the Earth's atmosphere. During the flight, his primary role was testing MIM-2 and performing fluid dynamics experiments designed to examine sensitivity to spacecraft vibrations. This work was directed at developing better understanding of the need for systems such as the MIM on the International Space Station (ISS) and on the effect of vibrations on the many experiments to be performed on the ISS. The mission was accomplished in 189 Earth orbits, traveling 4.7 million miles in 284 hours and 28 minutes.