Samstag, 25. August 2018 - 21:30

Raumfahrt - Long March 3B launches latest Chinese GPS satellites

25.08.2018

2018-08-25-075446-1170x717

A new pair of navigation satellites were launched on Friday by China, marking its 23rd orbital launch this year. The launch of Beidou-3M11 and Beidou-3M12 took place from the LC3 Launch Complex of the Xichang Satellite Launch Center, Sichuan province, using a Long March-3B/Y1 (Chang Zheng-3B/Y1) launch vehicle. Launch time was 23:52 UTC and took around four hours to complete the mission.

Also designated Beidou-35 and Beidou-36, the MEO satellites are the Medium Earth Orbit component of the third phase of the Chinese Beidou (Compass) satellite navigation system. The satellites are part of a fleet that will expand the system to a global navigation coverage.

The satellites are using a bus that features a phased array antenna for navigation signals and a laser retroreflector, with a launch mass 1,014 kg. Spacecraft dimensions are noted to be 2.25 by 1.0 by 1.22 meters. Usually, the satellites reside in a 21,500 – 21,400 km nominal orbit at 55.5 degrees.

Three new pairs of Beidou-3M satellites are schedule to launch before years end. Beidou-3M13 and Beidou-3M14 will be launched in September, followed by Beidou-3M15 and M16 in October. Beidou-3M17 and Beidou-3M18 will be launched in November.

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 Phase II B1 open service signal uses QPSK modulation with 4.092 megahertz bandwidth centered at 1561.098 MHz.

The current Beidou constellation 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.

Render of a BeiDou-3 satellite by J. Huart.

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 aims for full operational capability by 2020 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 supports two different kinds 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.

The Chinese Navigation Constellation – via beidou.gov.cn

The long-term goal is to develop a global navigation satellite network similar to the GPS and GLONASS by 2020 eventually consisting of 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.

This mission is also the seventh flight of the Long March-3B/YZ-1 (Chang Zheng-3B/YZ-1) version of the Long March-3B.

The launcher was developed from the Chang Zheng-3A. The CZ-3B features enlarged launch propellant tanks, improved computer systems, a larger 4.2 meter diameter payload fairing and the addition of four strap-on boosters on the core stage that provide additional help during the first phase of the launch.

Long March 3B – via Xinhua.

The rocket is capable of launching an 11,200 kg satellite to a low Earth orbit or a 5,100 kg cargo to a geosynchronous transfer orbit.

The CZ-3B/G2 (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 with CZ-3B bar its enlarged core stage and boosters.

On May 14, 2007, the first flight of CZ-3B/G2 was performed successfully, accurately sending the NigcomSat-1 into pre-determined orbit. With the GTO launch capability of 5,500kg, CZ-3B/G2 is dedicated for launching heavy GEO communications satellite.

The rocket structure also combines all sub-systems together and is composed of four strap-on boosters, a first stage, a second stage, a third stage and payload fairing.

The first two stages, as well as the four strap-on boosters, use hypergolic (N2O4/UDMH) propellant while the third stage uses cryogenic (LOX/LH2) propellant. The total length of the CZ-3B is 54.838 meters, with a diameter of 3.35 meters on the core stage and 3.00 meters on the third stage.

On the first stage, the CZ-3B uses a YF-21C engine with a 2,961.6 kN thrust and a specific impulse of 2,556.5 Ns/kg. The first stage diameter is 3.35 m and the stage length is 23.272 m.

Each strap-on booster is equipped with a YF-25 engine with a 740.4 kN thrust and a specific impulse of 2,556.2 Ns/kg. The strap-on booster diameter is 2.25 m and the strap-on booster length is 15.326 m.

The second stage is equipped with a YF-24E (main engine – 742 kN / 2,922.57 Ns/kg; four vernier engines – 47.1 kN / 2,910.5 Ns/kg each). The second stage diameter is 3.35 m and the stage length is 12.920 m.

The third stage is equipped with a YF-75 engine developing 167.17 kN and with a specific impulse of 4,295 Ns/kg. The fairing diameter of the CZ-3B is 4.00 meters and has a length of 9.56 meters.

The Yuanzheng-1 (“Expedition-1″) uses a small thrust 6.5 kN engine burning UDMH/N2O4 with a specific impulse at 3,092 m/s. The upper stage should be able to conduct two burns, having a 6.5 hour lifetime and is capable of achieving a variety of orbits.

It will be adapted for use on the CZ-3A/B/C series mainly for direct MEO/GEO insertion missions (mostly for the navigation satellites of the Beidou GNSS).

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.

The Launch Site – Google Earth

Equipped with two launch pads (LC2 and LC3), the center 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.

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 Chang Zheng-3 (CZ3-1) was launched the Shiyan Weixing (14670 1984-008A) communications satellite into orbit.

Quelle: NS

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China launches new twin BeiDou navigation satellites

China sends twin BeiDou navigation satellites into space via a single carrier rocket from Xichang Satellite Launch Center in Xichang, southwest China's Sichuan Province, Aug. 25, 2018. (Xinhua/Liang Keyan)

XICHANG, Aug. 25 (Xinhua) -- China on Saturday successfully sent twin BeiDou navigation satellites into space on a single carrier rocket.

The Long March-3B carrier rocket lifted off from Xichang Satellite Launch Center in southwest China's Sichuan Province at 7:52 a.m.. It was the 283rd mission of the Long March rocket series, said a source of the launch center.

The twin satellites entered orbit more than three hours after the launch. After a series of tests, they will work together with 10 other BeiDou-3 satellites already in orbit.

The twin satellites were developed by the Innovation Academy for Microsatellites of the Chinese Academy of Sciences.

Named after the Chinese term for the Big Dipper, the BeiDou system started serving China in 2000 and the Asia-Pacific region in 2012.

Quelle: Xinhua

Raumfahrt - Long March 3B launches latest Chinese GPS satellites

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