CZ-7 payloads demonstrate cutting-edge technologies

Subscale re-entry capsule being recovered after landing in Inner Mongolia

On 25 June 2016, China’s new-generation medium-lift launch vehicle, the CZ-7 (Long March 7), made its inaugural launch successfully from the Wenchang Space Launch Centre on Hainan island.

According to its manufacturer, the CZ-7 will initially be used to launch the Tianzhou automated cargo spacecraft, which will resupply China’s space laboratory and future modular space station. However, the first Tianzhou vehicle won’t be launched until the CZ-7’s second flight, currently scheduled for April 2017.

Instead, the first CZ-7 rocket (vehicle serial: CZ-7-Y1) carried a fleet of seven payloads, including a new liquid-fuelled upper stage, a sub-scale prototype re-entry capsule, a robotic spacecraft designed to clear space debris, an in-orbit refuelling experiment, two data relay micro-satellites, and a 12U cubesat, with a total mass of 12 tonnes.

Yuan Zheng-1A upper stage

Atop the CZ-7-Y1 launch vehicle was a Yuan Zheng-1A (YZ-1A, “Expedition 1A”) upper stage, which acted as the third-stage of the launch vehicle to deliver the other six payloads into their intended orbits.

Similar to the Russian Fregat, the Yuan Zheng (YZ) series upper stages are designed to serve as a “space tug” to deliver its payload satellites and spacecraft directly into their intended orbit without the need to use their own propulsion. By employing a combined INS/GPS navigation package, the upper stage can achieve a much higher accuracy in orbit insertion than direct insertion by the launch vehicle. The basic variant YZ-1 was first flown in March 2015 as the fourth-stage of a CZ-3C, delivering a Beidou navigation satellite from the initial low ‘parking’ orbit into a high-altitude orbit.

Upper stage in Zhuhai Airshow 2012

Chinese indigenous upper stage

Yuan Zheng 1A in YZ-7-Y1 mission

YZ-1A

Compared with the YZ-1, the improved YZ-1A features a number of improvements in performance and capability. It can operate up to 48 hours, as opposed to 6.5 hours of the YZ-1. Instead of deploying payloads into a single orbit, the YZ-1A can deliver multiple payloads into different orbits. Finally, the YZ-1A can be restarted up to 20 times.

With its own propulsion, navigation and control systems, the YZ-1A upper stage is capable of flying a complex mission profile autonomously, performing a series of orbital manoeuvres to deploy its payloads at different altitudes and on different orbital planes.

The YZ-1A is powered by a 6.5 kN liquid engine that burns N2O4 as oxidiser and UDMH as fuel. The engine uses a turbo-pump and operates in a gas-generator cycle to allow multiple ignitions and precision control. The upper stage was developed by China Academy of Launch Vehicle Technology (CALT), which also designed and built the CZ-7 launch vehicle.

At T plus 603 seconds, the YZ-1A upper stage and payload stack was separated from the YZ-7’s second-stage and entered a 200 km by 400 km initial parking orbit. At T plus 38 minutes, the upper stage deployed the Aolong 1 robotic spacecraft. At T plus 102 minutes, the upper stage deployed a 12U cubesat named Aoxiang Zhixing. About 20 hours into the mission, the upper stage lowered to an altitude of 170 km to put the sub-scale capsule into its re-entry trajectory. The upper stage then lowered to an altitude of 130 km, before re-igniting its engine to resume to a higher orbit of 400 km. After orbiting the Earth for 29 times in about 40 hours, the upper stage made a controlled re-entry into the middle Pacific.

Sub-scale capsule

The largest payload of the CZ-7-Y1 mission was a sub-scale ballistic capsule, intended to demonstrate atmospheric re-entry for China’s next-generation multi-purpose crew vehicle. According to a research paper published in 2014, China is currently developing the concept of a multi-purpose crew vehicle that can bring Chinese astronauts to the Moon and beyond in the 2020s. The spacecraft vehicle will feature a single baseline crew capsule that can accommodate up to six astronauts. The capsule can then be attached to different service modules to fulfil different mission requirements, from lunar landing to a mission to to a Near Earth Asteroid or Mars.

Designed by China Academy of Space Technology (CAST), the sub-scale capsule is in a blunt cone shape similar to the NASA Orion spacecraft. The capsule is 2.3 m in length and 2.6 m in diameter, with a total mass of 2,600 to 2,800 kg. Onboard systems included batteries, propulsions, a guidance & navigation system, heat shield, parachutes, and a communications system capable of transmitting through the plasma occurring during the hypersonic atmospheric re-entry sequence.

The capsule was also fitted with sensors to collect aerodynamic and heating data during the atmospheric re-entry to validate the design of the future crew vehicle. The capsule also features a reusable airframe built from lightweight alloys, covered by expandable heat-resistant protective layers and shielding, indicating that partial reusability will be a key feature of the future crew vehicle.

The sub-scale capsule remained attached to the YZ-1A upper stage throughout its flight. After orbiting the Earth for 13 times in 19 hours, the upper stage performed its third orbital manoeuvre in the morning of 26 June to lower to an attitude of 170 km, where the re-entry capsule was separated and placed into its re-entry trajectory. The capsule then made an unpowered ballistic descent through the atmosphere. During the atmospheric re-entry, a supersonic stabilising chute was deployed to ensure the capsule’s blunt end remains pointing forwards.

After undergoing a radio communication blackout, the re-entry capsule deployed its main parachute to further slow down. At 15:41 CST (07:41 UTC), the capsule touched down at a landing site in the Badain Jaran Desert near the Jiuquan Satellite Launch Centre. Due to a lack of parachute cut-off mechanism, the capsule was dragged by strong winds after touchdown, leaving a nearly 1 km trail on the ground. The search crew eventually managed to recover the capsule, and the mission was declared to be a complete success.

ADRV / Aolong 1

Another unique payload lofted by the CZ-7/YZ-1A was the Active Debris Removal Vehicle (ADRV), or Aolong 1 (“Roaming Dragon 1”), also developed by CALT.

According to Chinese press reports, Aolong 1 was designed to actively capture and remove space debris objects using its onboard robotic arm. During the CZ-7-Y1 mission, Aolong 1 will demonstrate the removal of a simulated space debris object, capturing the object and then bring it to a re-entry trajectory to be burned up in the Earth atmosphere.

The technique demonstrated by Aolong 1 requires the spacecraft to have the capability to identify, rendezvous, and perform proximity operations with a non-cooperative target, either a retired satellite or a space debris object. However, the same technique could also be used against an operational satellite on orbit, raising concerns that China may be secretively testing a space-based anti-satellite (ASAT) system.

Tianyuan 1 in-orbit refuelling experiment

The YZ-1A upper stage also carried an in-orbit refuelling experiment package named Tianyuan 1, which remained attached with the upper stage throughout its mission. The experiment was designed to demonstrate the refuelling of an in-orbit spacecraft, including the management, transfer, and accurate measurement of liquid propellants under microgravity conditions. The Tianyuan 1 system was designed by the National University of Defence Technology (NUDT), an education and research institution of the Chinese People’s Liberation Army (PLA). Once operational, such a system can prolong the orbital lifespan of a satellite significantly.

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