Nearing the completion of the global coverage of its navigation satellite system, China launched a new pair of navigation satellites on Saturday from the Xichang Satellite Launch Center, Sichuan province. The launch of Beidou-3M21 (Beidou-50) and Beidou-3M22 (Beidou-51) took place from the LC3 Launch Complex using a Long March-3BGZ/YZ-1 – Chang Zheng-3BGZ/YZ-1 – launch vehicle. Launch time was 00:55 UTC and it took four hours to complete the mission.
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 into 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.
The satellites are equipped with lightweight hydrogen maser clocks, which will serve as a more stable precision frequency reference to make the satellite navigation system work more accurately.
This was the sixth launch dedicated to the replenishment of the Beidou Navigation Satellite System in 2019. Launch activities started on April 20th with the launch of Beidou-3IGSO-1 (Beidou-44) satellite from the LC3 Launch Complex of the Xichang Satellite Launch Center using the Long March-3B/G2 (Y59).
The second launch took place on May with the Long March-3C/G2 (Y16) orbiting the Beidou-2GEO8 (Beidou-45) satellite also from the LC2 Launch Complex from Xichang. Beidou-3 IGSO-2 (Beidou-46) was launched on June 24 using the Long March-3B/G2 (Y60) from the LC3 Launch Complex.
This was followed by the launch of Beidou-3M23 (Beidou-47) and Beidou-3M24 (Beidou-48) on September 22, using the Long March-3B/YZ-1 (Y65/Y13) from the LC2 Launch Complex, and by the launch of Beidou-3 IGSO-3 (Beidou-49) on November 4, using the Long March-3B/G2 (Y61) from the LC2 Launch Complex.
Launch activity for the Beidou Navigation Satellite System will continue until years end with China orbiting two navigation satellites schedule for launch in December using a Long March-3BGZ/YZ-1 to launch the Beidou-3M21 (Beidou-52) and Beidou-3M22 (Beidou-53) satellites.
The Beidou Navigation Satellite System (BDS) has been independently constructed, developed and operated by China taking into account the needs of the country’s national security, economic and social development.
As a space infrastructure of national significance, BDS provides all-time, all-weather and high-accuracy positioning, navigation and timing services to global users.
Along with the development of the BDS service capability, related products have been widely applied in communication, marine fishery, hydrological monitoring, weather forecasting, surveying, mapping and geographic information, forest fire-prevention, time synchronization for communication systems, power dispatching, disaster mitigation and relief, emergency search and rescue, and other fields.
Navigation satellite systems are public resources shared by the whole globe, and multi-system compatibility and interoperability have become a trend. China applies the principle that “BDS is developed by China, and dedicated to the world”, serving the development of the Silk Road Economic Belt, and actively pushing forward international cooperation related to BDS. As BDS joins hands with other navigation satellite systems, China will work with all other countries, regions and international organizations to promote global satellite navigation development and make BDS further serve the world and benefit mankind.
China started to explore a path to develop a navigation satellite system suitable for its national conditions, and gradually formulated a three-step development strategy: completing the construction of BDS-1 and provide services to the whole country by the end of 2000; completing the construction of BDS-2 and provide services to the Asia-Pacific region by the end of 2012; and to complete the construction of BDS-3 and provide services worldwide around 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.
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).
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 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 Long March-3B/YZ-1 (Chang Zheng-3B/YZ-1) version of the Long March-3B 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.
The rocket structure also combines all sub-systems 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 general mission launch sequence for the CZ-3B/G2 missions is similar to the one used for the YZ-1 missions.
The fuelling of the third stage with LOX and LH2 starts at L-7h. The first and second stages, as well as the four strap-on boosters, use hypergolic propellant fuelled earlier. At L-1h 20m is the launch vehicle control system power on and function checkout followed by the telemetry system power on and function checkout.
At L-40m the fairing air-conditioning is turned off and the air-conditioning pipe is dropped-off. Technicians also proceed with the flight program loading and check-up. The gas pipes for the first stage second and are dropped-off. The pre-cooling of the third stage engines takes place at L-20m and at L-13m takes place the third stage propellants topping.
Between L-15m and L-10m, the spacecraft umbilical disconnection takes place and at L-3m the telemetry and tracking systems power is switch-over and the third stage propellant fueling pipe is disconnected.
The disconnection of the gas pipe for the third stage is disconnected at L-2m followed by the control system power switch-over at L-1m 30s. Control system, telemetry system and tracking system umbilical disconnection takes place at L-1m as well as the swinging-off of the rods. The TT&C systems start at L-30s and ignition comes at L-0s.
Eleven seconds after lift-off takes place the pitch-over maneuver. Boosters separation occurs at T+2m 21s followed at T+2m 39s by the separation between the first and second stages. Fairing jettison comes at T+3m 55s.
The separation between the second and third stage takes place at T+5m 44s, with the third stage igniting for the first time. This burn ends at T+10m 12s. The vehicle is now on a preliminary orbit until T+20m 56s when the third stage starts its second burn.
This burn will last for 3 minutes and 6 seconds, ending at T+24m 2s. After the third stage shutdown takes place at T+24m 22s an attitude adjustment before Yuanzheng-1 separation with the two satellites at T+25m 42s.
The upper stage will then execute a series of maneuvers to deliver the satellites to its orbits.
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 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.