Chang Zheng 6 (Long March 6)

The CZ-6 (Chang Zheng-6, or Long March-6) is a liquid-fuelled, small-lift launch vehicle part of China’s next generation orbital launcher family, developed based on the same common rocket engines that use environmentally friendly kerosene and cryogenic propellants. The first all-new Chinese orbital launcher introduced in nearly two decades, the CZ-6 has been positioned as a small-load orbital launcher for small- and micro-satellites of under 1,000 kg mass, which puts the CZ-6 in the same class as the European Space Agency Vega and the Russian Angara-1.

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CZ-6 Development

China’s next generation expandable space launcher rocket family was first announced in February 2001, followed by more detailed descriptions during the Zhuhai Air Show in late 2002. The original concept was to assemble launchers of various capabilities from three baseline rocket modules of 2.25 m, 3.35 m and 5.00 m diameter, powered by either the 120 t-thrust YF-100 or the 50 t-thrust YF-77 liquid engines. The small-lift member of the family was to be based on the 2.25 m-diameter module powered by a single YF-100 engine, added with an upper stage powered by a YF-73 engine derived from the CZ-3’s third-stage.

However, the modular design concept was later abandoned in favour of a redesigned small-lift launcher, with a 3.35 m diameter first-stage powered by a single YF-100 engine, a 2.25 m diameter second-stage powered by a single YF-115 engine, and a 2.25 m diameter third-stage powered by an H2O2/Kerosene engine. The larger first-stage allowed the vehicle’s overall length to be significantly reduced, allowing a lower length/diameter ratio (LDR) which reduces the aerodynamic force on the rocket’s body structure and improves its stability during flight within the atmosphere.

The development of the small-lift launcher was originally headed by China Academy of Launch Vehicle Technology (CALT, or 1st Academy) of the China Aerospace Science & Technology Corporation (CASC) , but was later reassigned to Shanghai Academy of Spaceflight Technology (SASC, or 8th Academy) in July 2008. The Chinese government officially approved the CZ-6 development programme in 2009. SAST subsequently introduced further amendments to the rocket’s design, including introducing thrust vectoring control on the first-stage, self-pressurisation oxidiser tanks, a newly developed guidance, navigation and control (GNC) system, and the restartable third-stage.

Detailed design of the launcher was carried out by Shanghai Institute of Aerospace System Engineering (上海宇航系统工程研究所), or 805 Institute, a subsidiary of SAST. The rocket is fabricated at SAST’s subsidiary Shanghai General Factory of Aerospace Equipment Manufacturing (上海航天设备制造总厂), also known as No. 149 Factory. The YF-100 and YF-115 rocket engines were developed by Xi’an-based Academy of Aerospace Propulsion Technology (AAPT, or the 6th Academy).

The YF-100 rocket engine was certified in early 2012. The first ground testing of the CZ-6’s first-stage was conducted successfully on 27 November 2012, followed by a second successful testing on 3 April 2013. The CZ-6’s second-stage passed its ground testing in the first half of 2013, and the third-stage in July of the same year. The long-duration (500 seconds) ground testing of the YF-100 engine was conducted in August 2013.

At the same time, a new launch pad to support CZ-6 launch missions began construction at the Taiyuan Satellite Launch Centre (TSLC). Instead of an umbilical tower commonly seen in other Chinese launch complexes, the new launch pad featured only a simple umbilical structure providing gas, liquid and power supplies due to the rapid-launch capability of the CZ-6.

A non-flying example of the CZ-6 was delivered to the TSLC in late 2013 for an all-system launch campaign simulation. In December 2013 Chinese state-run media confirmed that the CZ-6 launch simulation had been completed, paving the way for the launcher’s maiden flight scheduled for 2014–15. However, it took another 20 months before the launcher made its maiden flight, mainly due to delay in the payloads rather than the launcher itself.

The first flying vehicle carrying the serial CZ-6-Y1 was delivered to the Taiyuan Satellite Launch Centre (TSLC) in August 2015. The launch was originally scheduled for 07:00 CST on 19 September (18 September, 23:00 UTC). However, the launch was aborted at T minus 10 minutes due to a technical issue. 24 hours later, at 07:01 CST on 20 September (19 September, 23:01 UTC), the rocket finally lifted off, lofting a multi-payload of 20 micro- and nano-satellites into orbit.


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CZ-6 Design

The whole launcher has a gross launch mass of 103,217 kg and a dry mass of 9,020 kg. The 1,340 kN thrust YF-100 engine gives the rocket a thrust-to-weight ratio of 1.2 at lift-off. The overall length of the launcher is 29.237 m. The launcher has a maximum payload capacity of 1,080 kg to a 700 km SSO, or 500 kg if only relying on Chinese domestic land-based tracking stations for telemetry and tracking.

The relatively small size and structural weight of the launcher made it possible for the vehicle to be assembled at its fabrication factory and then transported in one-piece on a wheeled transporter vehicle to the launch pad, where it is erected, checked, fuelled, and launched. The entire launch campaign takes only 7 days, in contrast to the 30—40 days launch campaign time required by conventional Chang Zheng launchers.


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CZ-6 Mission History

Date           LV Serial      Centre        Payloads
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2015-09-19     CZ-6 (Y1)      Taiyuan       20 nano-sats

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CZ-6 First-Stage & YF-100 Engine

The first-stage comprises (from front to rear): oxidiser tank, inter-tank ring section, fuel tank, engine frame, and tail section. The main engine is mounted on the engine frame secured to the rear of the fuel tank. The frame transfers the thrust of the engines to the vehicle’s thrust and weight bearing load structure.

The stage is powered by a single 1,200 kN-thrust YF-100 engine that burns kerosene as fuel and liquid oxygen (LOX) as oxidiser. Directional thrust and steering is provided by thrust vectoring control. The stage carries 76,000 kg of propellants and has a burn time of 155 seconds.

The YF-100 is a pump-fed staged combustion cycle liquid engine burning the LOX/kerosene bi-propellant, with adjustable thrust and variable mixture ratio. The engine’s pre-burner burns all the LOX mass flow with a low volume of kerosene to generate hot gas that powers the single turbine. The turbo-pump is a single-shaft design, with a single-stage oxygen pump and a dual-stage kerosene pump driven by the same turbine. It also has two low-pressure pumps that prevent cavitation. The engine has a heat exchanger to heat oxygen gas for LOX tank pressurisation, and also supplies high-pressure kerosene as hydraulic fluid for the thrust vector control actuators.


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CZ-6 Second-Stage and YF-115 Engine

The second-stage has a reduced diameter of 2.25 m and comprises (from front to rear): instrument compartment, oxidiser tank, inter-tank ring section, and fuel tank. The stage is powered by a single YF-115 engine producing 180 kN thrust. The stage carries 15,000 kg of propellants. The YF-115 is a small thrust version of the YF-100, also employing pump-fed staged combustion cycle and burning the the LOX/kerosene bi-propellant.


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CZ-6 Third-Stage

The third-stage, also 2.25 m in diameter, is powered by four parallel 1,000 N-thrust liquid engines burning hydrogen peroxide (H2O2)/Kerosene bi-propellant. With a dual-way swinging nozzle and restart capability, these engines would also serve as the rocket’s reaction control system (RCS) thrusters during the ascent flight, an arrangement intended to simplify the launcher’s control system and improve its reliability.


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CZ-6 Payload Fairing

The launcher could be fitted with two types of payload fairing, either 2.25 m or 2.60 m in diameter, in order to support different sizes of payload cargo.


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CZ-6 Specifications

General features
---------------------------------------------
Core stages.............3
Strap-on boosters.......0
Length..................29.237 m
Diameter................3.35 m
Mass, gross.............103.2 t
Mass, empty.............9.02 t
Lift-off thrust.........1,177 kN
Payload to 700 km SSO...1,080 kg

First-stage
---------------------------------------------
Length..................N/A
Diameter................N/A
Mass, gross.............N/A
Mass, empty.............N/A
Mass, propellants.......76 t
Engine..................1 x YF-100
Thrust..................1,340 kN (sea-level)
Isp.....................300 s (sea-level)
Burn time...............155 s
Propellants.............LOX / Kerosene

Second-stage
----------------------------------------------
Length..................N/A
Diameter................2.25 m
Mass, gross.............N/A
Mass, empty.............N/A
Mass, propellants.......15 t
Engine..................1 x YF-115
Thrust..................176.5 kN
Isp.....................N/A
Burn time...............N/A
Propellants.............Lox / Kerosene

Third-stage
----------------------------------------------
Length..................N/A
Diameter................2.25 m
Mass, gross.............N/A
Mass, empty.............N/A
Mass, propellants.......N/A
Engine..................4 x YF-85
Thrust..................4 kN (vacuum)
Isp.....................285 s
Propellants.............H2O2 / Kerosene

Payload Fairing
----------------------------------------------
Length..................N/A
Diameter................2.25 m or 2.60 m

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CZ-6A

Even before the CZ-6 made its maiden flight, SAST had already begun the conceptual design of a drastically modified version known as the CZ-6A. According to the PowerPoint presentation produced by SAST, the CZ-6A launcher would feature two 2.00 m diameter solid rocket strap-on boosters, a redesigned first-stage powered by two YF-100 engines, as well as a redesigned 3.35 m diameter second-stage.

The new launcher would be capable of delivering up to 4,000 kg payload to the SSO, making it on par with the CZ-7. Some sources also suggested that the CZ-6A could be fitted with SAST’s Tianyun-1 (TY-1) upper stage, which has multiple-payload, multiple restart, and long-duration flight capabilities. This will enable the CZ-6A to support the launch of geostationary satellites and deep space probes.


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CZ-6 in pre-launch preparation


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CZ-6 in pre-launch preparation


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CZ-6 being loaded onto the transporter vehicle in pre-launch preparation (Credit: SAST)


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CZ-6 roll-out to launch pad aboard the transporter vehicle


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CZ-6 rolled out to launch pad aboard the transporter vehicle


CZ-6 erection

CZ-6 being erected at launch pad


Taiyuan CZ-6

CZ-6 in launch position (Credit: SAST)


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CZ-6 in launch position


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CZ-6 launch


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CZ-6 in flight


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CZ-6 in flight


CZ-6 and 6A

Scaled models of the CZ-6 (right) and CZ-6A (left)


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