Chinese large modular space station

A model of the launcher for modules, the Long March 5

The assembly method of the station can be compared with the Soviet-Russian Mir space station and the Russian orbital segment of the International Space Station. If the station is constructed, China will be the second nation to develop and use automatic rendezvous and docking for modular space station construction. Shenzhou spacecraft and space stations use a domestically made docking mechanism similar to, or compatible with, the Russian designed APAS docking adapter.

During the cordial Sino-Soviet relations of the 1950s, the USSR engaged in a cooperative technology transfer program with the PRC under which they taught Chinese students and provided the fledgling program with a sample R-2 rocket.

The first Chinese missile was built in 1958 reverse-engineered from the Soviet R-2, itself an upgraded version of the German V-2 rocket.[16] But when Soviet premier Nikita Khrushchev was denounced as revisionist by Mao, the friendly relationship between the two countries turned to confrontation. As a consequence, all Soviet technological assistance was abruptly withdrawn after the 1960 Sino-Soviet split.

Development of the Long March rocket series allowed the PRC to initiate a commercial launch program in 1985, which has since launched over 30 foreign satellites, primarily for European and Asian interests.

In 1994, Russia sold some of its advanced aviation and space technology to the Chinese. In 1995 a deal was signed between the two countries for the transfer of Russian Soyuz spacecraft technology to China. Included in the agreement was training, provision of Soyuz capsules, life support systems, docking systems, and space suits. In 1996 two Chinese astronauts, Wu Jie and Li Qinglong, began training at the Yuri Gagarin Cosmonaut Training Centre in Russia. After training, these men returned to China and proceeded to train other Chinese astronauts at sites near Beijing and Jiuquan. The hardware and information sold by the Russians led to modifications of the original Phase One spacecraft, eventually called Shenzhou, which loosely translated means "divine vessel." New launch facilities were built at the Jiuquan launch site in Inner Mongolia, and in the spring of 1998 a mock-up of the Long March 2F launch vehicle with Shenzhou spacecraft was rolled out for integration and facility tests.[17]

A representative of the Chinese crewed space program stated that around 2000, China and Russia were engaged in technological exchanges regarding the development of a docking mechanism.[18] Deputy Chief Designer, Huang Weifen, stated that near the end of 2009, the Chinese agency began to train astronauts on how to dock spacecraft.[19]

Panel views of the Chinese Tianhe Space Station core module

The 'Tianhe' Core Cabin Module provides life support and living quarters for three crew members, and provides guidance, navigation, and orientation control for the station. The module also provides the station's power, propulsion, and life support systems. The module consists of three sections, living quarters, service section and a docking hub. The living quarters will contain a kitchen and toilet, fire control equipment, atmospheric processing and control equipment, computers, scientific apparatus, communications equipment to send and receive communications via ground control in Beijing, and other equipment. A Canadian-style SSRMS robotic arm will be transported into space folded under the Tisane service section. Additionally, the Wentian experiment (described below) will also carry a duplicate stowed second SSRMS robotic arm. In 2018 fullscale mockup of CCM was publicly presented at China International Aviation & Aerospace Exhibition in Zhuhai. The video from CNSA revealed that the Chinese have built two of these core modules. Artist impressions have also depicted the two core modules docked together to enlarge the overall station.

Wentian supplemental experiment module

Mengtian supplemental experiment module

The first of two Laboratory Cabin Modules 'Wentian' & 'Mengtian' respectively, will provide additional navigation avionics, propulsion and orientation control as backup functions for the CCM. Both LCMs will provide a pressurised environment for researchers to conduct science experiments in freefall or microgravity which could not be conducted on Earth for more than a few minutes. Experiments can also be placed on the outside of the modules for exposure to the space environment, cosmic rays, vacuum, and solar winds.

Like Mir and the Russian orbital segment of the ISS, the CSS modules will be carried fully assembled into orbit, in contrast to the US Orbital Segment of the ISS, which required spacewalking to interconnect cables, piping, and structural elements manually. The axial port of the LCMs will be fitted with rendezvous equipment and will first dock to the axial port of the CCM. A mechanical arm similar to the Russian Lyappa arm used on the Mir space station will then move the module to a radial port of the CCM.

In 2011, the space station was planned to be assembled during 2020 to 2022.[20] By 2013, the space station's core module was planned to be launched earlier, in 2018, followed by the first laboratory module in 2020, and a second in 2022.[21] By 2018 this had slipped to 2020-2023.[22] Total of 12 launches are planned for the whole construction phase.[23]

Electrical power is provided by two steerable solar power arrays on each module, which use photovoltaic cells to convert sunlight into electricity. Energy is stored to power the station when it passes into the Earth's shadow. Resupply ships will replenish fuel for the station's propulsion engines for station keeping, to counter the effects of atmospheric drag.

Foreign sources have stated that the docking mechanism strongly resembles APAS-89/APAS-95, with one American source going as far as to call it a clone.[24][25][26] There have been contradictory claims on the compatibility of the Chinese system with both current and future docking mechanisms on the ISS.[26][27][28]

The programmed experiment equipment for the three modules as of June 2016 are:[4]

• Space life sciences and biotechnology
  • Ecology Science Experiment Rack (ESER)
  • Biotechnology Experiment Rack (BER)
  • Science Glove-box and Refrigerator Rack (SGRR)
• Microgravity fluid physics & combustion
  • Fluids Physics Experiment Rack (FPER)
  • Two-phase System Experiment Rack (TSER)
  • Combustion Experiment Rack (CER)
• Material science in space
  • Material Furnace Experiment Rack (MFER)
  • Container-less Material Experiment Rack (CMER)
• Fundamental Physics in Microgravity
  • Cold Atom Experiment Rack (CAER)
  • High-precision Time-Frequency Rack (HTFR)
• Multipurpose Facilities
  • High Micro-gravity Level Rack (HMGR)
  • Varying-Gravity Experiment Rack (VGER)
  • Modularized Experiment Rack (RACK)

The Next-generation crewed spacecraft is designed to carry to the Chinese space station with the capability for the moon exploration, replacing previous generation of Shenzhou spacecraft.

China’s next-generation crew carrier is reusable with a detachable heat shield built to handle higher-temperature returns through Earth’s atmosphere. The new capsule design is larger than the Shenzhou, according to Chinese officials. The spacecraft is capable of carrying astronauts to the moon, and can accommodate up to six to seven crew members at a time, three more astronauts than that of Shenzhou.[29]

The new crewed spacecraft has cargo section that allows astronauts bringing cargo back to Earth, whereas Tianzhou cargo resupply ship is not designed to bring any cargo back to Earth.[29]

Tianzhou (Heavenly Vessel), a modified derivative of the Tiangong-1 spacecraft, will be used as robotic cargo spacecraft to resupply this station.[30] The launch mass of Tianzhou is expected to be around 13,000 kg with a payload of around 6,000 kg.[31] Launch, rendezvous and docking shall be fully autonomous, with mission control and crew used in override or monitoring roles. This system becomes very reliable with standardizations that provide significant cost benefits in repetitive routine operations. An automated approach could allow assembly of modules orbiting other worlds prior to crewed missions.[32]

A 7-gram object (shown in centre) shot at 7 km/s (the orbital velocity of the station) made this 15 cm crater in a solid block of aluminium.

Radar-trackable objects including debris, with distinct ring of GEO satellites

The CSS will be operated in Low Earth Orbit, 340 to 450 kilometers above the Earth at an orbital inclination of 42 to 43 degrees, in the centre of the Earth's thermosphere. At this altitude there is a variety of space debris, consisting of many different objects including entire spent rocket stages, dead satellites, explosion fragments—including materials from anti-satellite weapon tests (such as the 2007 Chinese anti-satellite missile test, the 2019 Indian anti-satellite test and the 1985 U.S. ASM-135 ASAT anti-satellite test), paint flakes, slag from solid rocket motors, coolant released by RORSAT nuclear powered satellites and some clumps remaining from the 750,000,000[33] small needles from the American military Project West Ford.[34] These objects, in addition to natural micrometeoroids,[35] are a significant threat. Large objects could destroy the station, but are less of a threat as their orbits can be predicted. Objects too small to be detected by optical and radar instruments, from approximately 1 cm down to microscopic size, number in the trillions. Despite their small size, some of these objects are still a threat because of their kinetic energy and direction in relation to the station. Spacesuits of spacewalking crew could puncture, causing exposure to vacuum.[36]

Space debris objects are tracked remotely from the ground, and the station crew can be notified. This allows for a Debris Avoidance Manoeuvre (DAM) to be conducted, which uses thrusters on station to change orbital velocity and altitude, avoiding the debris. DAMs will take place if computational models show the debris will approach within a certain threat distance. Usually the orbit will be raised saving fuel, as the station's orbit must be boosted periodically to counter the effects of atmospheric drag. If a threat from orbital debris is identified too late for a DAM to be safely conducted, the station crew close all the hatches aboard the station and retreat into their Shenzhou spacecraft, so that they would be able to evacuate in the event it was damaged by the debris. Micrometeorite shielding is incorporated into the station to protect pressurised sections and critical systems. The type and thickness of these panels varies depending upon their predicted exposure to damage.

Stations in low earth orbit are partially protected from the space environment by the Earth's magnetic field. From an average distance of about 70,000 km, depending on Solar activity, the magnetosphere begins to deflect solar wind around the Earth and space stations in orbit. However, solar flares are still a hazard to the crew, who may receive only a few minutes warning. The crew of the ISS took shelter as a precaution in 2005 in a more heavily shielded part of that station designed for this purpose during the initial 'proton storm' of an X-3 class solar flare.[37][38] But without the limited protection of the Earth's magnetosphere, China's planned crewed mission to Mars is especially at risk.

Subatomic charged particles, primarily protons from cosmic rays and solar wind, are normally absorbed by the Earth's atmosphere, when they interact in sufficient quantity their effect becomes visible to the naked eye in a phenomenon called an aurora. Without the protection of the Earth's atmosphere, which absorbs this radiation, station crews are exposed to about 1 millisievert each day, which is about the same as someone would get in a year on Earth, from natural sources. This results in a higher risk of crew members developing cancer. Radiation can penetrate living tissue and damage DNA, cause damage to the chromosomes of lymphocytes. These cells are central to the immune system and so any damage to them could contribute to the lowered immunity experienced by crew. Radiation has also been linked to a higher incidence of cataracts in astronauts. Protective shielding and protective drugs may lower the risks to an acceptable level.

The radiation levels experienced on ISS are about 5 times greater than those experienced by airline passengers and crew. The Earth's electromagnetic field provides almost the same level of protection against solar and other radiation in low Earth orbit as in the stratosphere. Airline passengers, however, experience this level of radiation for no more than 15 hours for the longest intercontinental flights. For example, on a 12-hour flight an airline passenger would experience 0.1 millisievert of radiation, or a rate of 0.2 millisieverts per day; only 1/5 the rate experienced by an astronaut in LEO.[39]