The Chinese have launched a pair of navigation satellites, marking the first time a Long March 3B (Chang Zheng 3B) launch vehicle has been used for this kind of mission. The launch of the Compass-M3 and Compass-M4 satellites took place at 2050UTC on Sunday from the LC2 launch complex of the Xichang Satellite Launch Center.
Chinese Dual Passenger Launch:
Developed from the DFH-3B satellite platform, the Compass-M satellites are deployed in 21500~24100 km, 55 degree inclination intermediate circular orbits. The first Compass-M (31115 2007-011A) satellite was launched at 2011UTC on April 13th, 2007 by the CZ-3A Chang Zheng-3A (Y13) from the LC3 launch complex of the Xichang Satellite Launch Center.
China has developed two models for Compass-M satellites. The two satellites that were launched on Sunday, are based on the DFH-3B bus and are equipped with an apogee propulsion system for final orbit insertion. The second model is not equipped with an apogee propulsion system and is completely different from DFH-3 bus. Still under development, latter model will not fly until the second construction phase of the Compass constellation begins.
The Compass Navigation Satellite System (CNSS) is China’s second-generation satellite navigation system and was approved by the Chinese government in 2004. It is capable of providing continuous, real-time passive 3D geo-spatial positioning and speed measurement.
The system is initially used to provide high-accuracy positioning services for users in China and its neighboring regions, covering an area of about 120 degrees longitude in the Northern Hemisphere using five Compass-G, five Compass-IGSO and 4 Compass-M satellites.
The long-term goal is to develop a global navigation satellite network similar to the GPS and GLONASS by 2020, eventually consisting a constellation of 35 vehicles, including 27 MEO (21,500 km orbits) satellites, three IGSO satellites (inclined at 55 degrees) and five GSO satellites.
The system will have two kinds of services: a civilian service that will give an accuracy of 10 meters in the user position, 0.2 m/s on the user velocity and 10 nanoseconds in time accuracy; and the military and authorized user’s service, providing higher accuracies. The first phase of the project will provide coverage to the Chinese territory. However, the future the Compass constellation will cover the entire globe.
The satellites transmit signals on the: 1195.14-1219.14MHz, 1256.52-1280.52MHz, 1559.05-1563.15MHz and 1587.69-1591.79MHz, carrier frequencies.
The previous BeiDou-2 ‘Compass’ launch took place on February 24, 2011, when the CZ-3C Chang Zheng-3C (Y6) orbited the ‘Compass-G5′ (38091 2012-008A) satellite.
DFH-3B is an updated version of DFH-3 bus, a communications satellite bus whose capability is between high and medium ones. It is of a hexahedral structure, consisting of propulsion, service and communication modules, communication antennas and solar arrays and adopts 3-axis stabilized attitude control. Its dimensions are 2200mm × 2000mm × 3100mm, and its mass is 3,800 kg with a payload mass of 400 kg to 450 kg.
This satellite bus is applicable to communications and navigation satellites and deep space probes through adaptive modification.
China’s 5th launch in 2012 was also the 160th successful Chinese orbital launch, the 160th launch of a Chang Zheng launch vehicle, the 4th launch from Xichang in 2012 and the 72nd orbital launch from Xichang. This was the 5th space launch for China this year.
Launch vehicle:
This was the first double launch for the CZ-3B Chang Zheng-3B launch vehicle. For this double launch, CZ-3B was using the 3700Z fairing. This fairing has an external diameter of 3,700 mm, a total height of 10,796 mm.
The satellite was mated to the Payload Adapter (PLA) and encapsulated in the fairing. It was then shipped to the launch pad in the fairing and the complete assembly was mated to the launch vehicle. This fairing can be used with the 1194 and 1194A Payload Adapter interfaces.
For this fairing (like others used on the CZ-3B) the longitudinal release mechanism uses notched bolts, explosive cord, expanding hose, and two explosive bolts.
The Long March 3B (CZ-3B) is the most powerful launch vehicle in the Chinese space launch fleet.
The CZ-3B features enlarged launch propellant tanks, better computer systems, a larger 4.2 meter diameter payload fairing and the addition of four strap-on boosters in the core stage that give an additional help in the first phase of the launch.
The rocket is capable of launching a 11,200 kg satellite to Low Earth Orbit, or a 5,100 kg cargo to a Geosynchronous Transfer Orbit. The rocket has a total length of 54.84 meters and a core diameter of 3.35 meters....
