An ascent thruster was an integral part of the propulsion system of the mag-lev carriages used on a Nezu colony planet. When it seemed possible that Tuvok might be the only passenger left conscious in the oxygen-deprived Alixia, Neelix hastily tried to instruct the Vulcan in thruster operation. Neelix began his tutelage by insisting there was a minimum safe temperature for ascent thrusters, but was cut off before he could give any specifics. (VOY: "Rise")
It was also briefly mentioned by 7 of 9 that a child aboard Voyager was a contributing engineer involved in the development of ascent thrusters. The aft ascent thruster of the U.S.S. Voyager was dedicated to the memory of Naomi Wildman.