Gaofen-4, first Chinese Geostationary remote sensing satellite have been launched earlier than expected – on 28 December 2015.

It was loud afternoon in Xichang Satellite Launch Center. At 16:05 GMT, Long March 3B rocket with Gaofen-4 on atop starting to lift off. It is third Gaofen series satellite launched by CNSA, fifth of Gaofen constellation. After approximately of 25 minutes of flight rocket let satellite to reach appropriate orbit, according to USSTRATCOM, 205 km x 35807 km with inclination at 22.97°, where it will stay for eight years of operational life. It is basically imaging and remote sensing satellites for various purposes: disaster monitoring, precision agriculture, urban and road planning. It will utilize two imaging systems operating both in visible light and infrared; optical instruments are made by Beijing Institute of Space Machinery & Electronics. Some sources claim that with high resolution optical units are able to search war ships on east Pacific and Indian Ocean with high efficiency, but officially satellites are not operated or sponsored by PLA (Chinese army) like Yaogan series satellites. According some sources, Gaofen-4 was designed by Shanghai Academy of Spaceflight Technology (SAST) with utilization of SAST9000 bus, which is most up to date satellite bus designed by SAST. In spring 2015 bus was intensively tested – Gaofen-4 will be first time when it will be adopted and tested in GEO. Bus is officially mentioned as one of products by SAST but without any official specs. It is known, not officially, that SAST9000 was designed especially for GEO remote sensing and SAR satellites. SAST9000 is utilizing 3-axis stabilized attitude control and providing S band telemetry transmitting. It is possible that next Gaofen satellites will be launched in 2016: Gaofen-6, which is basically just like Gaofen-1 based on CAST2000 bus (about previous Gaofen satellites You can read in post below), Gaofen-3 basing on CS-L3000B designed as radar imaging satellite equipped with C band SAR radar and Gaofen-5 utilizing SAST5000B bus. Gaofen-5 will serve for various environment observations with onboard instruments like: hyper-spectral camera, spectral imager, greenhouse gas detector, high resolution atmospheric environment infrared detector, hyper-spectral camera. SAST5000B bus determines few details about Gaofen-5: it will weight around 5000 kg with propellant (MMH/MON-1), its operational life is at eight years (with optical payload). Voltage of bus is 42V, power provided by GaAs or Si solar arrays is up to 10000 W; onboard battery is Ni-H/Li-ion – depends on version. Telemetry is transmitted on S band.

CNSA utilized yesterday Long March 3B/E rocket heaviest in Long March 3 family and remaining operational since 2007.  It is fully liquid fueled roket with total height at  56.326 m, with diameter at 3.35 m. Mass of rocket is 458,970 kg, with payload capacity of 5500 kg. Each of four boosters is powered by one YF-25 engine each with thrust at 740.4 kN. First stage propulsion are four YF-21C with thrust at 2961.6 kN, second stage is powered by one central engine YF-24E with thrust at 742 kN and four vernier YF-23C engines with thrust at 47.1 kN. One YF-75 engine with thrust at 167.17 kN is propulsion of the third stage.