Chinese Long March 4B successfully Launches Yaogan 26 Satellite
China conducted a surprise launch on Saturday using the Long March 4B rocket to lift the Yaogan 26 satellite into orbit. Long March 4B blasted off from the Taiyuan Satellite Launch Center at 3:22 UTC and successfully delivered the clandestine Yaogan satellite to orbit, marking the seventh Yaogan launch of 2014.
The Yaogan satellite fleet was inaugurated in 2006 when its first satellite was launched by a Long March 4B. Officially, the satellites are used for scientific experiments, surveys of land resources and crop yield, and disaster monitoring. But the payloads they carry suggest that Yaogan is a military program used for reconnaissance purposes on a global scale. This is also supported by information released by Chinese sources and the structure of the satellite constellation as well as the pace at which it is expanded and replenished.
Previous Yaogan spacecraft carried electro-optical imaging instruments, Synthetic-Aperture Radar payloads or electronic intelligence systems. Satellites with optical payloads are built by the Shanghai Academy of Space Flight Technology while the SAR spacecraft were developed by the China Academy of Space Technology.
The first Yaogan satellite was launched back in April 2006 with details of its payload being kept under wraps by the Chinese until it later became known that the spacecraft carried a radar payload in its first generation. Three first generation Radar Satellites were launched between 2006 and 2010 (Yaogan 1, 3, 10) while the same period also saw the launch of four first-generation optical satellites (2, 4, 7, 11) followed by the launch of Yaogan 24 as a 1st generation optical satellite in 2014. These first generation satellites operated in sun synchronous orbits at an altitude over 630 Kilometers inclined 97.9 degrees.
Optical Yaogan Satellites
The second generation of Yaogan satellites was introduced in 2008 characterized by a lower operational orbit around 500 Kilometers in altitude. Three second generation optical satellites were launched (5, 12, 21). The second generation of SAR satellites followed in 2009 with the launch of Yaogan 6 continued by the Yaogan 13, 18 and 23 satellites.
Yaogan 8, launching in 2009, added another type of optical satellite to the constellation, operating in an orbit higher than all other Yaogan satellites reaching an altitude of 1,200 Kilometers at an inclination of 100.5 degrees. The satellite also carried an optical payload and was followed by Yaogan 15 and 19 that also entered this type of orbit.
Yaogan 9 offered a big surprise in 2010 when instead of a single spacecraft three satellites were launched at once, entering a triangular formation in an orbit of 1,080 by 1,100 Kilometers at an inclination of 63.4 degrees. This arrangement closely resembles the U.S. NOSS triplets that were used for electronic intelligence purposes until being replaced by duos of NOSS (Naval Ocean Surveillance System) starting to be launched in 2001. A total of five Yaogan triplet launches have taken place to date (9, 16, 17, 20, 25).
Launching in 2012, the Yaogan 14 satellite has entered a unique position in the constellation, reaching an initial working orbit below 475 Kilometers in altitude. The satellite, carrying an optical reconnaissance payload, currently operates from a lower orbit than any other Yaogan satellite.
The satellite that was launched on Saturday entered an orbit of 485 by 491 Kilometers at an inclination of 97.4° - suggesting a Yaogan-5 class payload, however, all of those satellites did not require the large 3.8-meter fairing which was used on Saturday and seen in photos of the launch. Furthermore, earlier comments made by Chinese officials indicated that Yaogan 21 was the last in the series of Yaogan 5 spacecraft. It is likely that Saturday's launch boosted a new type of Yaogan satellite into orbit, possibly the first in a new generation of optical satellites.
The CZ-4B launch vehicle is 45.8 meters in length and 3.35 meters in diameter. It has a launch mass of 249,200 Kilograms. The Long March 4B is based on the CZ-4 Family of launch vehicles and was developed by the Shanghai Academy of Space Flight Technology. Development of the Launcher began in 1989 and the CZ-4B completed its maiden flight on May 10, 1999 with the Fengyun 1C Weather Satellite.
The Long March 4B version was developed to accommodate larger satellites by outfitting the launcher with a bigger Payload Fairing and making design improvements. It features several modifications such as improved telemetry, tracking, control, and flight termination systems.
All three stages of the vehicle use Unsymmetrical Dimethylhydrazine and Nitrogen Tetroxide as propellants. The first stage uses a YF-21B engine which is a cluster of four YF-20B engines providing a total liftoff thrust of 2,971 Kilonewtons. The Engine Assembly has a weight of 2,850 Kilograms, is 3.3 meters in length and 3.5 meters in diameter. The engine nozzles are gimbaled for vehicle control. The first stage is 24.66 meters in length and holds 183,200 Kilograms of Propellants. Its empty mass is 9,990 Kilograms. First Stage burn time is 170 seconds.
The second stage is 10.41 meters long and has a fueled mass of 39,600 Kilograms. It is powered by a YF-24B main engine and a four-chamber YF-23F gimbaling vernier thruster for attitude control. The main engine delivers 742 Kilonewtons of vacuum thrust while the vernier engine provides 47.1 kN of thrust. The stage burns for 127 seconds before shutting down and separating from the third stage (vernier burn time is 137 seconds due to hot staging between the first two stages).
The upper stage of the Long March 4B launch vehicle is 4.92 meters long and has a reduced diameter of 2.9 meters. It has an empty mass of 1,700 Kilograms and holds 12,900 Kilograms of propellants. It is powered by a YF-40 Main Engine that provides 100.3 Kilonewtons of thrust. The third stage supports burns of up to 359 seconds to inject the payloads into their desired orbit. Long March 4B is topped by either a 3.35 or 3.8-meter payload fairing that is over 8.45 meters in length.