Meteor-3-5, launched in 1991, is in a slightly higher orbit than Meteor-2-21, and operated until 1994. It transmitted on 137.300 MHz. Mechanically, it is similar to Meteor-2-21. Which satellite was in operation depended on the sun angles and consequently the seasons. Meteor-3-5 was usually the (Northern Hemisphere) "summer" satellite while 2-21 was in operation for approximately the half-year centered on winter. The satellite carried the second Total Ozone Mapping Spectrometer (TOMS) aloft as the first and the last American-built instrument to fly on a Soviet spacecraft. Launched from the Plesetsk, Russia, facility near the White Sea, on 15 August 1991, Meteor-3 TOMS had a unique orbit that presents special problems for processing data. Meteor-3 TOMS began returning data in August 1991 and stopped in December 1994.