believed to have been 1–2 metre. The Zenit 4 had a mass of 6300 kg — around 1800 kg more than the Zenit 2. So, instead of the Vostok rocket, it was launched by the heavier Voskhod rocket. A total of 76 Zenit 4's were flown. First flight – Kosmos 22, 1963. Last flight – Kosmos 355, 1970. Zenit 4 M An improved version of the Zenit 4, the Zenit 4M carried a new camera, solar panels, and a restartable engine so the satellite's orbit could be altered during the course of its mission. The mission duration was 13 days. First flight – Kosmos 251, 1968. Last flight – Kosmos 667, 1974. Zenit 4 MK / Zenit 4 MKM These may have been versions of the Zenit 4 designed specifically to fly in lower orbits to improve image resolution. Some sources claim they were fitted with devices to compensate for aerodynamic drag and to withstand the effects of aerodynamic heating. First flight – Kosmos 371, 1970. Last flight – Kosmos 1214, 1980. Zenit 4 MT A special version of the Zenit 4M intended for topographical photography. It carried an SA-106 topographic camera, a laser altimeter and Doppler apparatus. First flight – Kosmos 470, 1971. Last flight – Kosmos 1398, 1982. Zenit 6U A "universal" version of the Zenit, intended for both low-altitude, high-resolution missions and higher-altitude, general observation missions. All flights used the Soyuz launch vehicle. There were 96 launches. First flight – Kosmos 867, 1976. Last flight – Kosmos 1685, 1985. Zenit 8 This was intended for military cartographic photography. It used a Soyuz launch vehicle and launches took place from both Baikonur and Plesetsk. It had a 15-day orbital life. Similar satellites were referred to using the "Resurs-DK No.1" designation. Kosmos 2281, was the last Zenit flight. First flight – Kosmos 1571, 1984. Last flight – Kosmos 2281, 1994. Following the end of the programme, one Zenit-8 satellite was launched on the maiden flight of the Soyuz-2 launch vehicle, as a DemoSat. The satellite was placed on a sub-orbital trajectory, and intentionally impacted the Pacific Ocean shortly after launch. References Reconnaissance satellites of the Soviet Union Reconnaissance satellites of Russia Satellites formerly orbiting Earth Satellite series Military equipment introduced in the 1960s