Long March 3A lofts Beidou-22 satellite

by Rui C. Barbosa

China conducted its third successful orbital launch of the year on Tuesday, orbiting another navigation satellite. The Beidou-22 (or Beidou-2 I6) satellite was launched by a Long March-3A rocket from the Xichang Satellite Launch Center. Liftoff was confirmed – several hours after the event – as occurring at 20:11 UTC.

Chinese Launch:

Tuesday’s launch was the second of a series of Beidou launches schedule for 2016, making another step in the strengthening and completion of the Beidou program in 2020.

The new satellite, the sixth Beidou-2IGSO, is based on the DFH-3 Bus and features a phased array antenna for navigation signals and a laser retroreflector.

The spacecraft dimensions are 2.25 by 1.0 by 2.2 meters. Usually the satellites are on a 21,500 – 21,400 km nominal orbit at 55.5°. The new satellite will be used to replenish the current operating regional system.

2015-07-25-130556The Phase II B1 open service signal uses QPSK modulation with 4.092 megahertz bandwidth centered at 1561.098 MHz.

The Beidou Phase III system includes the migration of its civil Beidou 1 or B1 signal from 1561.098 MHz to a frequency centered at 1575.42 MHz – the same as the GPS L1 and Galileo E1 civil signals – and its transformation from a quadrature phase shift keying (QPSK) modulation to a multiplexed binary offset carrier (MBOC) modulation similar to the future GPS L1C and Galileo’s E1.

The current Beidou constellation of geostationary (GEO) and four middle Earth orbiting (MEO) spacecraft are transmitting open and authorized signals at B2 (1207.14 MHz) and an authorized service at B3 (1268.52 MHz).

Real-time, stand-alone Beidou horizontal positioning accuracy was classed as better than 6 meters (95 percent) and with a vertical accuracy better than 10 meters (95 percent).

The Compass Navigation Satellite System (CNSS) is China’s satellite navigation system, approved by the Chinese government in 2004, capable of providing continuous, real-time passive 3D geo-spatial positioning and speed measurement.

The Chinese navigation system is being developed and deployed in three phases: Phase 1 (starting in 2003), consisted of an experimental regional navigation system, BeiDou-1, which provided active navigation service; Phase 2 (started in 2012), consisted of a reduced satellite constellation and provides open service over China.

This phase aimed at deploying a system with passive positioning and timing capability over a regional area; Phase 3 (starting in 2020), by 2020, the system would reach full operational capability with a constellation of 27 MEOs plus 5 GEOs and the existing 3 IGSOs satellites of the regional system. CNSS would provide global navigation services, similarly to the GPS, GLONASS or Galileo systems.

CNSS is expected to support two different kind of general services: RDSS and RNSS. In the Radio Determination Satellite Service (RDSS), the user position is computed by a ground station using the round trip time of signals exchanged via GEO satellite. The RDSS Long term feature further includes: short message communication (guaranteeing backward compatibility with Beidou-1), large volume message communication, information connection, and extended coverage.

The Radio Navigation Satellite Service (RNSS) is very similar to that provided by GPS and Galileo and is designed to achieve similar performances.

2015-09-30-002738The 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 be dual use, based on a civilian service that will provide an accuracy of 10 meters in the user position, 0.2 m/s on the user velocity and 50 nanoseconds in time accuracy; and the military and authorized user’s service, providing higher accuracies. The first phase of the project will involve coverage of the Chinese territory. However, the future Compass constellation will cover the entire globe.

Launch vehicle:

The Long March 3A is a three-stage liquid launch vehicle, which has inherited the mature technology of the Chang Zheng-3. An upgraded liquid hydrogen and liquid oxygen cryogenic third stage has been developed to enable CZ-3A performing greater geostationary transfer orbit (GTO) capability.

The rocket is equipped with a more flexible and sophisticated control system which supports substantial attitude adjustments to orient the payloads before spacecraft separation and provides adjustable satellite spin-up rotation rate. It has paved the way for the development of Chang Zheng-3B and Chang Zheng-3C, and become the basic type of GTO launch vehicles.

The Long March 3A is mainly used for GTO missions; it also can be used for LEO, SSO and polar orbit missions, as well as dual-launch and multiple-launch missions.

The launch capability to GTO is 2,650 kg, while the lift-off mass is 241,000 kg.

The first stage and second stage of the rocket employ storable propellants, i.e. unsymmetrical dimethyl hydrazine (UDMH) and nitrogen tetroxide (N2O4), and the third stage uses cryogenic propellants, i.e. liquid hydrogen (LH2) and liquid oxygen (LOX).

On the first stage the Long March 3A uses a DaFY6-2 engine with 2961.6 kN of thrust, while the second stage is equipped with a DaFY20-1 main engine (742 kN) and four DaFY21-1 vernier engines (11.8 kN each). The third stage is equipped with two YF-75 engines (78.5 kN each).

The fairing diameter of the Long March 3A is 3.35 meters and has a length of 8.89 meters.

The launch success rate of the Long March 3A is 100 percent since its maiden flight on February 8, 1994 when it successfully launched two experimental satellites (the Shijian-4 and the Kuafu-1, a DFH-3 model). It was awarded the “Gold Launch Vehicle” title by China Aerospace Science and Technology Corporation in June 2007.

Launch Site:

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 kilometres south-west of the launch pad, providing flight and safety control during launch rehearsal and launch.

Down range Tracking and Control stations of the launch center are located in Xichang City and Yibin City of Sichuan Province, and Guiyang City of Guizhou Province. Each of them houses tracking and measurement equipment for the powered phase of a launch vehicle flight.

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.

During 1993-1994 Xichang underwent extensive modernization and expansion, in part due to the requirements of the CZ-3 launcher family and in part to meet commercial customer needs. More recent modernization adapted both launch pads for all launchers of the CZ-3 launcher family.

The first launch from Xichang took place at 12:25UTC on January 29, 1984, when the Long March (Y1) was launched the Shiyan Weixing (14670 1984-008A) communications satellite into orbit.

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