Chang Zheng 7 (Long March 7)

The CZ-7 (Chang Zheng-7, or Long March-7) is the medium-lift member of China’s next generation launch vehicles that have been developed based on several common rocket engines using environmentally friendly kerosene and cryogenic propellants. First flying in June 2016, the CZ-7 is expected to become China’s workhorse launcher, delivering spacecraft vehicles and satellites into Earth orbit.

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Background

The CZ-7 traces its origin to the CZ-2F/H concept first revealed in the mid-2000s. An upgraded variant of the CZ-2F launcher that had been used to send the Shenzhou spacecraft vehicle into orbit since 1999, the CZ-2F/H would retain the airframe of the CZ-2F but replace its hypergolic liquid engines with cleaner new-generation engines burning kerosene as fuel and liquid oxygen as oxidiser. The CZ-2F/H programme was later merged with the medium-lift member (3.35 m diameter) of the CZ-5 family to become a new design the CZ-7.

The CZ-7 programme was managed by the China Aerospace Science & Technology Corporation (CASC) consortium, with its subsidiaries responsible for the development of the various sub-systems. Beijing-based China Academy of Launch Vehicle Technology (CALT, or the 1st Academy) was in charge of the vehicle’s overall design, with its subsidiary Capital Aerospace Machinery Company (CAMC, or No. 211 Factory) responsible for the construction of the airframe. Xi’an-based Academy of Aerospace Propulsion Technology (AAPT, or the 6th Academy) was responsible for the development of the YF-100 and YF-115 rocket engines.

Development of the CZ-7 began in May 2010. The YF-100 engine first succeeded in ground testing in May 2012, followed by the first successful ground testing of the YF-115 engine in December 2012. The first ground test article began construction in September 2014 and the vehicle was delivered to the Wenchang Space Launch Centre for a one-month all-system launch campaign simulation in December of the same year. Assembly of the first flying vehicle CZ-7-Y1 began in early 2016, and the vehicle was successfully launched from Wenchang on 25 June 2016.

CASC predicted that 80% of China’s orbital launch missions over the next two decades would fall within the payload capacity range of medium-lift launch vehicles (MLV), i.e. payload mass between 2,000 to 20,000 kg. These include heavy geostationary telecommunications satellites, large Earth-observation satellites on Sun-Synchronous Orbit (SSO), as well as regular crewed and cargo resupply missions to the future Chinese Space Station on 400 km Low Earth Orbit (LEO). With a maximum payload capacity of 13,500 kg to 400 km LEO, the CZ-7 is well placed for these types of missions.

CASC revealed that the CZ-7 will be initially used to launch the Tianzhou automated cargo vehicle for resupply missions to the Tiangong 2 space laboratory and the future Chinese Space Station, but expected that the launcher will replace most member of the current CZ-2, 3 and 4 families of launch vehicles by 2021. Once the launch vehicle reaches certain degree of maturity in its design and technology, it will also be adopted for manned missions to launch China’s next generation multi-purpose crew vehicle.


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Design

Currently the CZ-7 can only be launched from the newly constructed Wenchang Space Launch Centre on Hainan island. However, the 3.35 m diameter of the vehicle (same of the existing CZ-2/3/4 families) means that the launch vehicle can be transported by railway to China’s three inland launch centres at Jiuquan, Xichang, and Taiyuan.

The basic variant CZ-7 is in a configuration of two-stage core vehicle with four strap-on liquid rocket boosters, all burning kerosene as fuel and liquid oxygen (LOX) as oxidiser. The entire launch vehicle stack is 53.1 m in length, with a total launch mass of 594 tonnes and a take-off thrust of 7,200 kN (734 tonnes). The launcher is capable of delivering 13,500 kg payload to a 200 x 400 km LEO (42° inclination), or 5,500 kg to a 700 km SSO. In addition, the launcher can be added with CLAT’s Yuan Zheng (YZ) family of upper stages for increased payload capacity and orbit insertion accuracy.

The core vehicle of the CZ-7 consists of two stages connected by an inter-stage structure, all 3.35 m in diameter. Each stage has two propellant tanks: an oxidiser tank at the front and a fuel tank at the rear, connected by an inter-tank ring section. Oxidiser is pumped to the engines via a pipe penetrating through the centre of the rear fuel tank. The two propellant tanks and the inter-tank ring section form part of the vehicle’s thrust and weight bearing load structure.


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CZ-7 Flight Sequence

T minus 7 secs:....Main engines and boosters ignition
T plus 0 sec:......Launch vehicle lift-off
T plus 167 secs:...Jettison of strap-on boosters
T plus 178 secs:...Main engine cut-off
T plus 182 secs:...First-stage separation and second-stage ignition
T plus 211 secs:...Payload fairing jettison
T plus 562 secs:...1st pair of second-stage engines cut-off
T plus 582 secs:...2nd pair of second-stage engines cut-off
T plus 603 secs:...Second-stage separation

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CZ-7 Mission History

Date           LV Serial   Centre        Payloads
-----------------------------------------------------------
2016-06-25     CZ-7 (Y1)   Wenchang      Sub-scale capsule
                                         Aolong 1 (ADRV)
                                         Tianyuan 1
                                         Tiange 1A/B
                                         Aoxiang Zhixing

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CZ-7 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 front end of the forward oxidiser tank is protected by a fibreglass heat insulation layer to prevent damage from the high pressure and hot stream of engine exhaust from the second-stage engine during stage separation.

The stage is powered by two single-chamber 1,200 kN-thrust YF-100 engines, each with a dual-way swinging nozzle to provide directional thrust and steering. The two main engines are 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 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-7 Strap-On Boosters

The first-stage of the core vehicle is assisted by four strap-on boosters at lift-off. The strap-on booster, which is 2.25 m in diameter, has a similar structure to the first-stage, consisting of oxidiser tank, inter-tank ring section, fuel tank, engine frame, and tail section. An aerodynamic nose is attached to the front end of the booster covering the upper bulkhead of the liquid oxygen tank.

Each strap-on booster is powered by a single 1,200 kN YF-100 engine with a swinging nozzle that can be pivoted at radial direction only. The strap-on booster is attached to the core vehicle at three hardpoints. Thrust from the booster is transferred to the core vehicle via the lower hardpoint that is mounted on the engine frame of the core vehicle’s first-stage.


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CZ-7 Second-Stage and YF-115 Engine

The second-stage maintains the overall diameter of the first-stage at 3.35 m and comprises (from front to rear): instrument compartment, oxidiser tank, inter-tank ring section, and fuel tank. The engines are directly mounted on the rear of the fuel tank. The instrument compartment at the front houses the flight control system, navigation platform, and gas canisters.

The stage is powered by four parallel single-chamber YF-115 engines, each producing 180 kN thrust. Two of the four engines are fitted with a fixed nozzle, while the other two are fitted with a dual-way swinging nozzle to provide directional thrust and steering. 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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YZ-1A Upper Stage

The Yuan Zheng-1A (YZ-1A, “Expedition 1A”) is a common upper stage that can be added atop of existing Chang Zheng launch vehicles. Developed by China Academy of Launch Vehicle Technology (CALT), the upper stage serves as a “space tug” to deliver spacecraft vehicles and satellites directly into their intended orbit without the need to use their own propulsion.

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. By employing a combined INS/GPS navigation package, the upper stage can achieve a much higher accuracy in orbit insertion compared with direct insertion by the launch vehicle.

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 can continuously operate for up to 48 hours, and can be restarted up to 20 times.


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CZ-7 Payload Fairing

The two-piece payload fairing of the CZ-7 is 4.2 m in diameter. It protects the onboard satellite or spacecraft against aerodynamic, thermal and acoustic environments that the launch vehicle endures during the ascent stage of the flight within the atmosphere. The payload fairing is connected together and secured to the second-stage of the launch vehicle by explosive bolts, which are detonated at around T plus 211 seconds to jettison the fairing.


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CZ-7 Specifications

General features
---------------------------------------------
Core stages.............2
Strap-on boosters.......4
Length..................53.075 m
Diameter................3.35 m
Mass, gross.............597 t
Mass, empty.............N/A
Lift-off thrust.........7,200 kN
Payload to 400 km LEO...13.5 t
Payload to 700 km SSO...5.5 t
First flight............2016-06-25
Launch centre...........Wenchang

First-stage
---------------------------------------------
Length..................25.083 m
Diameter................3.35 m
Mass, gross.............N/A
Mass, empty.............N/A
Mass, propellants.......N/A
Engine..................2 x YF-100
Thrust..................2,400 kN (sea-level)
Isp.....................N/A
Burn time...............N/A
Propellants.............LOX / Kerosene

Strap-on boosters
----------------------------------------------
Length..................29.903 m
Diameter................2.25 m
Mass, gross.............N/A
Mass, empty.............N/A
Mass, propellants.......N/A
Engine..................1 x YF-100
Thrust..................1,200 kN (sea-level)
Isp.....................N/A
Burn time...............N/A
Propellants.............Lox / Kerosene

Second-stage
----------------------------------------------
Length..................15.445 m
Diameter................3.35 m
Mass, gross.............N/A
Mass, empty.............N/A
Mass, propellants.......N/A
Engine..................4 x YF-115
Thrust..................720 kN (vacuum)
Isp.....................N/A
Burn time...............N/A
Propellants.............LOX / Kerosene

Payload fairing
----------------------------------------------
Length..................12.5 m
Diameter................4.2 m

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CZ-7_rollout_Wenchang_2016-06-22_6

CZ-7 rolls out to launch pad atop the Mobile Launcher Platform at the Wenchang Space Launch Centre (Credit: Xinhua News)


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CZ-7 rolls out to launch pad atop the Mobile Launcher Platform at the Wenchang Space Launch Centre (Credit: Xinhua News)


CZ-7 lift-off

CZ-7 (Y1) lifting off from Launch Complex 201 at the Wenchang Space Centre during its maiden flight on 25 June 2016 (Credit: Xinhua News)


CZ-7 lift-off

CZ-7 (Y1) lifting off from Launch Complex 201 at the Wenchang Space Centre during its maiden flight on 25 June 2016 (Credit: Xinhua News)


CZ-7 strap-on booster separation test

CZ-7 strap-on booster separation test (Credit: CASC)


YF-100

YF-100 liquid engine developed by Academy of Aerospace Propulsion Technology (AAPT) (Credit: CASC)


YF-115

YF-115 liquid engine developed by Academy of Aerospace propulsion Technology (AAPT)


Yuan Zheng 1A in YZ-7-Y1 mission

YZ-1A upper stage (Credit: CASC)


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