China launched a pair of satellites called Shiyan-12-01 and Shiyan-12-02 on board a Chang Zheng 7A rocket at 10:12 UTC. The pair of satellites launched to a geostationary transfer orbit (GTO) from the Wenchang Space Launch Center in China.
The purpose of the satellites is spatial environment detection and testing. Each of them has a weight of 3 tons. The development was executed by the China Association for Science and Technology (CAST), which has developed other payloads of this kind before, including the Shiyan-9 and Shiyan-11 payloads.
Shiyan satellites are technology pathfinders built by a variety of providers and institutes to research new kinds of satellite technologies for the Chinese Space Program. The first of these was launched in April 2004. Since then, more missions followed with a variety of experimental technologies. Most of the purposes and payload specifics are classified and not known to the public.
The last one that was launched was the Shiyan-11 technology satellite launched on a Kauizhou-1A rocket in November of 2021. It is suspected that the Shiyan-11 mission was used to demonstrate Earth imaging services. More details are not known at this point.
This is the third launch in three months for the Shiyan satellites. Shiyan-10 was launched in October 2021, and raised its orbit successfully after initial reports of a failure of launch appeared on social media, and the confirmation of a successful launch was delayed.
The initial development of the Chang Zheng 7 started in 2006. The goal was to increase payload capacity for the planned space station in Low Earth Orbit, because the current maximum of 8.1 tons by the Chang Zheng 2F was seen as not enough for the long term. Final permission to build the rocket was given in January of 2011, after initials plans to upgrade the Chang Zheng 2F were changed.
Ignition of the core stage and side boosters of the Chang Zheng 7A Thursday
An advantage of the initial CZ-7 was the smaller diameter, compared to the CZ-5. Because of this, a transport with the rail road is still possible and makes the operation and logistics of the rocket easier.
Over the long term, the CZ-7 is expected to replace the CZ-2F and launch crew to the space station, as well as a majority of Chinese flights. It was evolved into a CZ-7A variant in 2020, which features a hydrolox third stage to boost payload capacity’s and capabilities for deeper orbits.
The CZ-7A stands 60.13 meters tall with a diameter of 3.35 meters. It is a three stage launch vehicle with the option to add another Yuanzheng-1A fourth stage, similar to the Chang Zheng 3B. At liftoff, it has a mass of 573,000 kg.
After being fueled, the platforms around the rocket retracted hours before launch. About two hours before T-0, the rocket was fully cleared for flight and was standing by its own on the launch pad.
At liftoff, the K3 core module and the K2 boosters ignite. The K3 core module is powered by two YF-100 liquid engines that provide 2,400 kN of thrust together. They operate at a specific impulse of 300 seconds at sea level, and in contrast to previous vehicles of the Chang-Zheng family, do not use a hypergolic combination as a combustion source, but use Rocket Propellant-1 (RP-1) kerosene and liquid oxygen.
Chang Zheng 7A lifts off from Wenchang with Shiyan 12-01 and Shiyan 12-02
The YF-100 and the YF-115 are part of a new generation of rocket engines for Chinese launchers, with the goal to remove hypergolics from the launch infrastructure. The YF-100 is not only used on the CZ-7 and CZ-7A but also on the CZ-5 and CZ-6.
The four side boosters each use one of the YF-100 engines as well, providing an additional thrust of 4,800 kN and bringing the liftoff thrust of the Chang Zheng to 7,200 kN. The boosters stands 27 meters tall and 2.25 meters in diameter.
After the first stage burn is complete and the four side boosters are jettisoned, the second stage ignites. Using the same fuel mixture, it uses the smaller brother of the YF-100, the YF-115. Four of these are used on the second stage of the CZ-7A. They produce a thrust of 706 kN with 342 seconds of specific impulse. The second stage shares the same diameter as the first stage.
One of the big differences between CZ-7 and CZ-7A is the third stage that is only featured in the CZ-7A. It is fueled by liquid hydrogen and liquid oxygen and powered by two YF-75 engines, which are also used in the CZ-3. They produce 167 kN of thrust with a specific impulse of 438 seconds. Before ignition, it masses 21,000 kg.
The optional booster stage was never used so far on a CZ-7A, and only on one flight of the CZ-7. This flight features a new fairing which has a reduced diameter, but is longer compared to previously used CZ-7A fairings, in order to fit the two satellites.
The Wenchang Space Launch Site in Hainan, China was used for this launch. Previously used for suborbital test flights, it was converted into an orbital launch site and launches a variety of next generation vehicles of China, including the most powerful rocket of China, Chang Zheng 5. It was previously used to deliver payload to the China Space station using the CZ-7.
After delays, construction was started in 2007, and to make room for the new launch site, 6,000 people had to relocate in the process. Wenchang features three launch pads.