China launches Compass duo via Long March 3B

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-3 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.

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.

Each of the four boosters has a 15.326 meter length with a 2.25 meter diameter, consuming 37,700 kg of N2O4 / UDMH. Equipped with a YF-25 engine capable of a ground thrust of 740.4 kN and a ground specific impulse of 2,556.2 Ns/kg.

The first stage has a 23.272 meter length with a 3.35 meter diameter, consuming 171,800 kg of N2O4 / UDMH. Equipped with a YF-21C engine capable of a ground thrust of 2,961.6 kN and a ground specific impulse of 2,556.5 Ns/kg.

The second stage has a 19.92 meter length with a 3.35 meter diameter, consuming 49,400 kg of N2O4 / UDMH. Equipped with a YF-24E cluster engine with a main engine capable of a vacuum thrust of 742 kN and a vernier engine with a vacuum thrust of 47.1 kN (specific impulses of 2,922.6 Ns/kg and 2,910.5 Ns/kg, respectively).

The third stage has a length of 12.375 meters with a 3.0 meter diameter, consuming 18,200 kg of LH2 / LOX. Equipped with a YF-75 engine capable of a vacuum thrust of 167.17 kN and a specific impulse in vacuum of 4,295 Ns/kg.

In recent years, the CZ-3B/E (Enhanced Version) launch vehicle was developed from the CZ-3B, increasing the GTO capacity up to 5,500kg. The CZ-3B/E has nearly the same configurations as the CZ-3B, except its enlarged core stage and boosters.

On May 14, 2007, the first flight of CZ-3B/E was performed successfully, accurately sending the NigcomSat-1 into pre-determined orbit. With the GTO launch capability of 5,500kg, CZ-3B/E is dedicated for launching heavy GEO communications satellite.

The CZ-3B and CZ-3B/E launch vehicles comprise of the vehicle structure, propulsion system, control system, measurement system (telemetry system and tracking & range safety system), propellant management and reaction control system, propellant utilization system, separation system and auxiliary system, etc.

The third stage includes the payload adapter, the vehicle equipment bay (VEB) and the cryogenic propellant tanks and engines. The payload adapter mates the satellite to CZ-3B and bears the mechanical loads. This cargo adapter also allows for use of one of the international standard interfaces designated as 937B, 1194 or 1194A. The payload fairings consist of the dome, bi-conic section, cylindrical section, and reverse cone section and separation mechanisms.

The Xichang Satellite Launch Centre is situated in the Sichuan Province, south-western China and is the country’s launch site for geosynchronous orbital launches.

Equipped with two launch pads (LC2 and LC3), the centre has a dedicated railway and highway lead directly to the launch site. The Command and Control Centre is located seven kilometers south-west of the launch pad, providing flight and safety control during launch rehearsal and launch. The CZ-3B launch pad is located at 28.25 deg. N – 102.02 deg. E and at an elevation of 1,825 meters.

Other facilities on the Xichang Satellite Launch Centre are the Launch Control Centre, propellant fuelling systems, communications systems for launch command, telephone and data communications for users, and support equipment for meteorological monitoring and forecasting.

The first launch from Xichang took place at 12:25UTC on January 29, 1984, when the CZ-3 Chang Zheng-3 (CZ3-1) launched the Shiyan Weixing (14670 1984-008A) communications satellite into orbit.

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