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Tiangong space station

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This article is about the upcoming installment of a Chinese modular space station. For an overview of the Chinese space station programme as a whole, see Tiangong program.
Scale rendering of the space station

The Chinese large modular space station is a planned space station to be placed in Low Earth orbit between 340 and 450 km above the surface. The planned Chinese Space Station will be roughly one-fifth the mass of the International Space Station and about the size of the decommissioned Russian Mir space station. The Chinese station is expected to have a mass between 80 and 100 tonnes (180,000 and 220,000 lb). Operations will be controlled from the Beijing Aerospace Command and Control Center in China. The planned launch date of the core module, the Tianhe (“Joining of the Heavens”), is 2021.[1] In 2017, the Chinese launched the Tianzhou-1 ("Heavenly Vessel") cargo spaceship, which is based on the Tiangong 1 and 2 space laboratories.[2]

Overview

The construction of the station will manifest the third phase of the Tiangong program. It builds on the experience gained from its precursors, Tiangong-1 and Tiangong-2.[3][4][5] Chinese leaders hope that research conducted on the station will improve researchers' ability to conduct science experiments in space, beyond the duration offered by China's existing space laboratories.[2]

Origin of name

Deng Xiaoping decided[citation needed] that the names used in the space program, previously all chosen from the revolutionary history of the PRC, would be replaced with mystical-religious ones. Thus, the new Long March carrier rockets were renamed Divine arrow (神箭),[6][7] space capsule Divine vessel (神舟),[8] space shuttle Divine dragon (神龙),[9] land-based high-power laser Divine light (神光)[10] and supercomputer Divine might (神威).[11]

These poetic[12] names continue as the first, second, third, fourth and fifth Chinese Lunar probes are called Chang'e after the Moon goddess. The name "Tiangong" means "heavenly palace". Across the PRC the launch of Tiangong 1 inspired a variety of feelings, including love poetry. Within the PRC, the rendezvous of space vehicles is compared to the reunion of the cowherd and the weavergirl.

Wang Wenbao, director of the CMSE, told a news conference in 2011 "Considering past achievements and the bright future, we feel the manned space programme should have a more vivid symbol, and that the future space station should carry a resounding and encouraging name. We now feel that the public should be involved in the names and symbols, as this major project will enhance national prestige and strengthen the national sense of cohesion and pride."[12][13][14] Imagery of the Chinese space program has been used by the Party (government) to strengthen its position and promote patriotism since the late 1950s and early 1960s.[15]

On October 31, 2013, China Manned Space Engineering announced the new names for the whole program:[4]

Structure

The CSS will be a third generation, modular space station. First generation space stations, such as early Salyut, Almaz, and Skylab, were single piece stations and not designed for resupply. Second generation Salyut 6 and 7, and Tiangong 1 and 2 stations, are designed for mid-mission resupply. Third generation stations such as Mir, the International Space Station, and the CSS are modular space stations, assembled on-orbit from pieces launched separately. Modularised design methods can greatly improve reliability, reduce costs, shorten development cycle, and meet diversified task requirements.

Solar arraySolar array
Solar arraySolar arrayDocking portSolar arraySolar array
Wentian
laboratory		Tianhe
service module		Mengtian
laboratory
Solar arrayEVA hatchDocking portDocking portSolar array

[3]

Technology exchanges

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.[17] 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.[18]

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.[19] Deputy Chief Designer, Huang Weifen, stated that near the end of 2009, the Chinese agency began to train astronauts on how to dock spacecraft.[20]

Modules

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.

Construction timeframes

In 2011, the space station was planned to be assembled during 2020 to 2022.[21] 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.[22] By 2018 this had slipped to 2020-2023.[23][24] A total of 12 launches are planned for the whole construction phase, now beginning in 2021.[25][26]

Systems

Electrical

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 spacecraft will replenish fuel for the station's propulsion engines for station keeping, to counter the effects of atmospheric drag.

Docking

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.[27][28][29] There have been contradictory claims on the compatibility of the Chinese system with both current and future docking mechanisms on the ISS.[29][30][31]

Experiments

The programmed experiment equipment for the three modules as of June 2016 are:[5]

  • 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)

Resupply

The station will be resupplied by crewed and robotic spacecraft.

Crewed mission

Main article: Next-generation crewed spacecraft

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.[32]

The new crewed spacecraft has cargo section that allows astronauts bringing cargo back to Earth, whereas Tianzhou cargo resupply spacecraft is not designed to bring any cargo back to Earth.[32]

Cargo resupply

Main article: Tianzhou (spacecraft)

Tianzhou (Heavenly Vessel), a modified derivative of the Tiangong-1 spacecraft, will be used as robotic cargo spacecraft to resupply this station.[33] The launch mass of Tianzhou is expected to be around 13,000 kg with a payload of around 6,000 kg.[34] 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.[35]

Scheduled missions

  • All dates are UTC. Dates are the earliest possible dates and may change.
  • Forward ports are at the front of the station according to its normal direction of travel and orientation (attitude). Aft is at the rear of the station, used by spacecraft boosting the station's orbit. Nadir is closest the Earth, Zenith is on top.
Key
  Uncrewed cargo spacecraft are in light blue colour
  Crewed spacecraft are in light green colour
  Modules are in beige colour
Launch date (NET) Spacecraft Launch vehicle Launch site Launch provider Docking/berthing port
29 April 2021[36] Tianhe Long March 5B China Wenchang LC-1 China CASC None
12 May[37] Tianzhou 2 Long March 7 China Wenchang LC-2 China CASC Tianhe aft
12 June Shenzhou 12 Long March 2F China Jiuquan SLS-1 China CASC Tianhe forward

Safety

Orbital debris

Main article: Space debris
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[38] small needles from the American military Project West Ford.[39] These objects, in addition to natural micrometeoroids,[40] 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.[41]

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.

Radiation

Main articles: Coronal mass ejection and Aurora (astronomy)

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.[42][43] But without the limited protection of the Earth's magnetosphere, China's planned crewed mission to Mars is especially at risk.

Video of the Aurora Australis taken by the crew of the ISS on an ascending pass from south of Madagascar to just north of Australia over the Indian Ocean

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.[44]

International co-operation

See also: Chinese exclusion policy of NASA

Cooperation in the field of crewed space flight between the CMSEO and the Italian Space Agency was examined in 2011, participation in the development of China crewed space stations and cooperation with China in the fields such as astronauts flight, and scientific research was discussed.[45] Potential areas and ways for future cooperation in the fields of development of crewed space station, space medicine and space science have also been discussed during the meeting.

On 22 February 2017, the China Manned Space Agency (CMSA) and Italian Space Agency (ASI) signed an agreement to cooperate on long-term human spaceflight activities.[46] The consequences of this agreement could be important, considering, on the one hand, the leading position Italy has achieved in the field of human spaceflight with regard to the creation and exploitation of the International Space Station (Node 2, Node 3, Columbus, Cupola, Leonardo, Raffaello, Donatello, PMM etc.) and, on the other hand, the important human spaceflight programme that China is developing, especially with the creation of the Tiangong-3 Space Station.[47]

End of orbit

The Chinese large modular space station is designed to be used for 10 years and will accommodate three astronauts.[48] Chinese crewed spacecraft use deorbital burns to slow their velocity, resulting in their re-entry to the Earth's atmosphere. Vehicles carrying a crew have a heat shield which prevents the vehicle's destruction caused by aerodynamic heating upon contact with the Earth's atmosphere. The CSS has no heat-shield; however, small parts of space stations can reach the surface of the Earth, so uninhabited areas will be targeted for de-orbit manoeuvres.[22]

See also

References

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