China launches Tianhe module, start of ambitious two-year station construction effort

China launched a Chang Zheng 5B rocket with the Tianhe station core module to low Earth orbit, marking the start of an ambitious two year construction effort of the nation’s new multi-module space station.

Liftoff of the historic mission occurred at 23:23 EDT on Wednesday, 28 April — which was 03:23 UTC on Thursday, 29 April — from the Wenchang Spacecraft Launch Site on Hainan Province island, People’s Republic of China.

Tianhe seeks “harmony of the heavens”

Launch of the Tianhe module marks a transition from China’s original human spaceflight goals to the start of a permanent presence in space. China is effectively banned from participation in the International Space Station program due to geopolitical strife with the United States.

Tracing its roots to 1992 as part of the initial plans for China’s human spaceflight program, the Tianhe module will take the next step from the initial Tiangong program — which saw the gradual evolution of single-module Chinese space labs in a “space laboratory” learning phase.

Tianhe, “harmony of the heavens”, will be the bedrock of the Chinese Space Station (CSS), like Zarya was for the International Space Station in 1998.  However, Tianhe is based heavily on the Functional Cargo Block (FGB) elements of the Russian space program — which formed the core of Mir and which serves as the grounding design of the Zvezda service module of the International Space Station.

The Tianhe module in preparation for launch. (Credit: CMS)

The docking hub on the forward part of Tianhe is configured to allow the addition of two science modules on the two radial ports, while also providing docking access for the Tianzhou and Shenzhou cargo and crew spacecraft, respectively, on the forward and nadir docking ports.

Like Mir, unsurprising given Chinese-Russian technological cooperation on this program and the docking system’s compatibility with Russian spacecraft, the Chinese Space Station’s new modules will be delivered robotically and will have to autonomously dock themselves to Tianhe.

But only the forward and nadir docking ports are outfitted with rendezvous equipment.  This means the two future science modules, Wentian (“Quest for the heavens”) and Mengtian (“Dreaming of the heavens”), cannot dock directly to their planned radial port locations.  Instead, they will have to first dock themselves to the forward port on Tianhe.

To account for this, each module will carry a Russian Lyappa robotic arm — like the ones used on Mir for the same purpose — to move the module from the forward port to its respective permanent location on a radial port of Tianhe’s docking hub.

In addition to the docking relocation Lyappa arm, Tianhe and Wentian will both launch with an additional Canadian-style robotic arm for exterior station operations.

This dual-arm redundancy on the CSS is also seen with Tianhe in a different way.  During the China International Aviation & Aerospace Exhibition in 2018, Chinese officials revealed that two Tiahne modules had been built, with the second to serve as a backup, or insurance, in case of a launch failure.

If unneeded as a backup, it is possible Chinese space officials could opt to launch the second control module to join the station as part of an in-planning future expansion of the outpost beyond its initial three module baseline.

As with Mir and the ISS, the CSS will receive regular cargo resupply deliveries from the Tianzhou cargo crafts.  In addition to delivering crew supplies, experiments, station equipment, and EVA/spacewalk items, the crafts will — like the Russian Progress vehicles — be able to transfer fuel, oxygen, and water to the station.

The Tianzhou crafts will launch on Chang Zheng 7A rockets from a neighboring pad at the Wenchang Spacecraft Launch Center from the pad Tianhe will depart from.  The first Tianzhou mission, Tianzhou 2, is scheduled for May.

Crewed flights to the outpost will begin shortly thereafter, with the planned Shenzhou 12 mission currently scheduled to launch in early June from the Jiuquan Satellite Launch Center in Inner Mongolia, China.

The first crewed flight will carry three taikonauts, Nie Haisheng, Deng Qingming, and Ye Guangfu, to Tianhe for initial activation, functionality checkouts, and preparations for future crews.

Nie will become the first Chinese person to visit two different space stations, having previously commanded the Shenzhou 10 mission to Tiangong 1, China’s first space station.  Both Deng and Ye will make their first space flights on Shenzhou 12.

Following Shenzhou 12, a second Tianzhou cargo run, Tianzhou 3, is planned for September, with the Shenzhou 13 crewed mission launching afterward in October.

The Wentian and Mengtian modules — with additional solar panels attached — are scheduled to launch in the first half and second half of 2022, respectively.

Rendering of a completed Chinese Space Station. (Credit: UNOOSA/CNSA)

In all, at least four crewed missions are planned to complete construction of the Chinese Space Station, which will serve as a laboratory for biomedical, astrophysical, mechanical, and potentially in-space servicing for an upcoming, co-orbital, Hubble-like space telescope.

Currently, in development, the 2 meter diameter primary mirror telescope would be able to dock itself to the Chinese Space Station for servicing.

Chang Zheng 5B

At 16.6 meters long and 4.2 meters wide, the 22 metric ton Tianhe module will be taken to orbit by the Chang Zheng 5B (CZ-5B) – which is also known as Long March 5B in the west.  This variant of the rocket has a single core stage with four large side-mounted boosters and is designed to carry large payloads into low Earth orbit.

First flown in 2016, the Chang Zheng 5 and 5B are the heavy-lifting members in a series of new rockets China has developed to replace its ageing fleet.  With the launch of Dong Fang Hong 1 in April 1970, China became the fifth country to place a satellite into orbit with a rocket of its own development.  

The Chang Zheng 1 used for the launch was derived from the Dong Feng 4 missile, but this design quickly gave way to a series of larger rockets derived from the more powerful Dong Feng 5.  These vehicles – the Chang Zheng 2, 3 and 4 series – remain in service and until the last few years accounted for almost all of China’s orbital launches.

These older rockets came with many of the drawbacks associated with offshoots of liquid-fueled ballistic missile programs, including a reliance on toxic and inefficient hypergolic propellants.  With China looking to cement its position as a major space power, the replacement of its launch systems with more powerful, capable, and modern purpose-built designs became a priority.

The Tianhe mission patch. (Credit: CNSA)

The result is four interconnected families of rockets – the Chang Zheng 5, 6, 7 and 8.  Of these, CZ-6 is the smallest, with a capacity of about 1,500 kilograms to low Earth orbit.  The largest – Chang Zheng 5B, the same type that will be used for Tianhe’s launch – can launch about 25,000 kilograms to a similar orbit.  

The CZ-5 was the first of the new rockets to proceed into development, with authorization for the project granted in 2004.

The Chang Zheng 5 family consists of two rockets – CZ-5 and CZ-5B.  The CZ-5 has an upper stage to enable payload delivery to higher orbits, with the option of fitting a further stage – YZ2 – on top of this when missions require. This positions CZ-5 to deliver payload to geostationary orbit or beyond, including the Tianwen-1 Mars mission and the Chang’e-5 moon mission.

The CZ-5B is conversely optimized for taking heavier payloads into lower orbits and only uses the four boosters and core stage.

Chang Zheng 5B’s core stage is 5 meters in diameter and contains cryogenic propellants – liquid hydrogen and liquid oxygen – consumed by its twin YF-77 engines.  The four boosters clustered around the core are each 3.35 meters in diameter with each carrying a pair of YF-100 engines burning rocket-grade kerosene and liquid oxygen.

The boosters for Chang Zheng 5B form the basis of the rest of China’s new fleet of rockets, with a single booster serving as the first stage of both the Chang Zheng 7 and Chang Zheng 8 vehicles and a shorter modification with a single engine used on the Chang Zheng 6.

The Tianhe-1 launch marks the seventh flight for the Chang Zheng 5 family.  The first flight occurred in November 2016 with the Shijian 17 spacecraft, an experimental communications payload which was successfully inserted directly into geostationary orbit with the aid of a YZ2 upper stage. 

A second launch, in July 2017, targeted geostationary transfer orbit with the heavier Shijian 18 satellite – intended to demonstrate the new DFH-5 satellite bus on orbit.  This failed to reach orbit after the rocket underperformed during first stage flight.  An investigation determined that “complex thermal conditions” caused one of the turbopumps feeding the first stage YF-77 engines to fail 5 minutes and 46 seconds into the flight.

With changes to the engines made, Chang Zheng 5 returned to flight at the end of 2019 with the successful launch of Shijian 20, a replacement for the lost Shijian 18.  This success paved the way for a trio of high-profile missions in 2020: a prototype for China’s next-generation crewed spacecraft, the Tianwen-1 probe bound for Mars, and the Chang’e-5 mission to the Moon – the first lunar sample-return mission since the 1970s.

Chang Zheng 5 rockets launch from the Wenchang Satellite Launch Centre, located on Hainan island off China’s southern coast.  Wenchang is China’s newest major launch site with facilities for the Chang Zheng 5, 7 and 8 rockets.  The Chang Zheng 5 launch pad is Pad 101.  Pad 201 – located 650 meters northeast of Pad 101 – is used by the CZ-7 and 8 rockets.

A Chang Zheng 5 rocket launches the Tianwen-1 mission to Mars on 23 July 2020.

The CZ-5B was integrated vertically, using an assembly building 2.8 kilometers to the north of the pad.  Following its arrival at Wenchang on 21 February and stacking in this assembly building, Chang Zheng 5B rolled to the launch pad atop its mobile launch platform on 23 April.

With Tianhe’s launch, Chang Zheng 5B will join an elite group of rockets that have launched space stations.  Only Russia’s Proton-K rocket has previously launched the core blocks of modular space stations – Mir and the International Space Station – as well as deploying the monolithic Salyut stations. 

The United States used a modified two-stage version of a Saturn V Moon rocket to launch Skylab – also a monolithic station – in 1973.  Aside from Proton launching the Zarya and Zvezda modules, the Space Shuttles Endeavour, Discovery, and Atlantis delivered the vast majority of the components of the International Space Station and also a small docking module to Mir, while Soyuz and Falcon 9 rockets have also launched small modules to the ISS.

(Lead image credit: Xinhua News Agency)

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