China has successfully launched the second Chang Zheng 7A (CZ-7A) rocket from the Wenchang Spacecraft Launch Site on Hainan Island, thus recovering from the first failed launch that took place almost one year ago. Carrying the mysterious Shiyan 9/Xinjishu Yanzheng-6-02 satellite, liftoff took place at 17:51 UTC on 11 March from the LC-201 launch complex.
The Chang Zheng 7A represents a new step in replacing the older families of hypergolic fuelled launchers that have been the workhorse of the Chinese space program since its inception in the 1960s.
Xinjishu Yanzheng-6-02/Shiyan 9 satellite
Onboard the Chang Zheng 7A (Y2) rocket was the secretive Xinjishu Yanzheng-6-02 satellite (XJY-2-02), or New Technology Validation-6-02.
The true nature of this satellite is not known; however, Chinese space forums point to the satellite being a prototype of a high-resolution and high orbit optical remote sensing or military applications satellite equipped with an optical membrane lens using diffractive optics.
The new satellite was possibly developed by the China Academy of Space Technology.
After launch, the satellite’s name was revealed as Shiyan 9.
Chang Zheng 7A
Chinese officials have not provided a reason for the failed launch of the first CZ-7A on 16 March 2020, but indications point to the second stage losing pressurization a few seconds after separating from the first stage.
Development of the Chang Zheng 7 launch vehicle (or Long March 7 as it is sometimes referred to outside of China) began in May 2010. It was originally designated Chang Zheng 2F/H.
The Chang Zheng 7A liftoff. (Credit: Wu Tong Xiaoyu)
The rocket is China’s new-generation, medium-lift orbital launch vehicle developed by the China Academy of Launch Vehicle Technology and created as a way to modernize the CZ-2F to be used on uncrewed and crewed missions in China’s human space program.
While the CZ-7 will mainly be used for orbiting the new Tianzhou logistics cargo vehicle for the modular Tiangong space station, the CZ-7A variant will be used for orbiting satellites in high energy orbits.
To this end, CZ-7A is a three-stage launch vehicle standing 60.1 meters tall and 3.35 meters in diameter with a gross liftoff mass of approximately 573,000 kg. The rocket’s propellant tanks dispense with the highly-toxic hypergolic fuel of the CZ-2, CZ-3 and CZ-4 rocket families.
Rocket components are transported to the launch site from the industrial city of Tianjin using two dedicated cargo ships, the Yuanwang-21 and the Yuanwang-22. The components are then offloaded at the Qinglan seaport serving the Wenchang Spacecraft Launch Site.
The rocket is powered by the YF-100 engine on the boosters as well as the first and second stages. The YF-100 uses kerosene as fuel and liquid oxygen as oxidizer. The first stage uses two engines while the side-mounted boosters each use a single engine.
The second stage uses four YF-115 engines that also run on kerosene and liquid oxygen.
Development of the YF-100 began in 2000 at the Academy of Aerospace Liquid Propulsion Technology. The engine was certified by the State Administration of Science, Technology and Industry for National Defence in May 2012.
The YF-100 is a staged combustion cycle engine producing 1,199.19 kN of thrust at sea-level with an isp (specific impulse) between 300 seconds and 335 seconds from sea-level to vacuum, respectively. The YF-100 will also be used on the CZ-5 and CZ-6 launch vehicles.
Launch success confirmed by CASC: https://t.co/cJdTIKF2LH pic.twitter.com/ELFb93aI89
— Andrew Jones (@AJ_FI) March 11, 2021
The YF-115 is also a staged combustion cycle engine that produces 176.5 kN thrust in a vacuum with a specific impulse of 345 seconds.
The CZ-7A also employs a hydrogen-oxygen burning third stage derived from the Chang Zheng 3B/G3 – which is what delineates the CZ-7A from the CZ-7. The third stage is equipped with two YF-75 engines, each producing 167.17 kN thrust with a specific impulse of 438 seconds.
A typical flight sequence for the CZ-7A sees the launcher begin its pitch program 15 seconds after liftoff. Booster shutdown follows 2 minutes 53 seconds after launch, with separation from the first stage one second later.
First stage shutdown takes place 2 minutes 57.5 seconds into flight followed by stage two ignition and then fairing separation at T+4 minutes 40.7 seconds and second stage shutdown at 7 minutes 42 seconds.
The third stage then ignites for 3 minutes 35 seconds. After the end of this first burn, a coast phase follows until approximately T+24 minutes and 42 seconds into flight when the third stage re-ignites for its second burn.
This lasts 3 minutes 36 seconds. Spacecraft separation usually takes place just over 30 minutes after launch.
Wenchang Spacecraft Launch Site
Wenchang is located on Hainan Island off the southern coast of China and is equipped with two launch complexes. LC-101 is used for the Chang Zheng 5 launch vehicle family while LC-201 is used for the Chang Zheng 7.
The launch pads are served by two vehicle assembly and integration buildings. LC-101 is served by Building 501 while LC-201 is served by Building 502. Each building is 99.4 meters tall, permitting the assembly and testing of the launch vehicle in a full, vertical and stacked position.
Some photos of the LM-7A taking flight at around 17:51 UTC, from people watching there: pic.twitter.com/m3v1gAnz4G
— Cosmic Penguin (@Cosmic_Penguin) March 11, 2021
This is a different approach to launch vehicle preparation than is used at other Chinese launch centers where rockets are stacked and tested for flight on the launch pads.
After being stacked at the vehicle assembly and integration building on top of a mobile launch platform, the rocket is rolled 2.8 kilometers to the launch pad.
There, a mobile structure is placed above the flame trench and the necessary umbilical connections between the fixed structures and the mobile platform are established ahead of the flow to launch.
Wenchang is the newest of China’s spaceports and provides additional versatility that isn’t available at the other three launch sites. Wenchang also allows for an increased performance for launch vehicles gained from Earth’s rotation because of its proximity to the equator.
Wenchang also crucially allows China to launch in a southeasterly direction over the south Pacific, avoiding the possibility of rocket debris falling onto populated areas – which has occurred during numerous Chinese launches.
(Lead image credit: Wu Tong Xiaoyu)