China will postpone the launch of its next mission to the Tiangong space station until later this month.
Two sources familiar with China's manned space programme said the launch date of Shenzhou 13 spacecraft, initially scheduled for Sunday, had now been pushed back to a "later date in October".
One of the sources, based at the Jiuquan satellite launch centre, said the delay would allow the ground crew and astronauts to make better preparations for the mission and was based on feedback from the Shenzhou 12 crew, who spent 90 days on board the space station.
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"The change of launch time is not related to any technical issues. A bit more time will allow us to make things better for the crew's six-month stay," the source said. "There is no rush as this is the last launch this year. We want to perfect it."
Another Beijing-based source said mid-October was the most likely launch time.
The latest mission - which unlike Shenzhou 12's all-male team, will include at least one woman - will spend six months in orbit and will continue the work of building the space station.
The Jiuquan source said advanced preparations were being made to ensure that the crew can live on board for such a long time and the Tianzhou 3 cargo ship had recently carried six tonnes of supplies, ranging from fuel and food and even skin care products, to the station.
"We have prepared enough things for them to celebrate the Lunar New Years in orbit too," the source said. "It will be the first time we have Chinese astronauts celebrating Lunar New Year 400 kilometres above the ground."
Fang Fang, assistant chief engineer of the Tianzhou 3 cargo spacecraft, told the state broadcaster CCTV that the mission has supplied the crew with food, water and other daily necessities that they will need during their stay on board.
Fang said the space station has an in-orbit logistics management system, which tracks all the items currently available in the space station and marks them with ribbons for easy identification, green for food and dark blue for space station equipment.
Shenzhou 12's crew returned to earth last month carrying several items that went on display at a ceremony in Beijing this week.
China's space project officials, including Hao Chun, director of the China Manned Space Agency, and China's first astronaut Yang Liwei, handed over the items taken from the capsule, including Chinese, Pakistani and Namibian flags to give to diplomats from those countries.
They also passed seeds that had been stored on the station to officials from Yunnan and Ningxia to plant on their soil.
Richard de Grijs, a professor of astrophysics at Macquarie University in Australia, said the Shenzhou 13 mission represents the "carefully planned" next step in China's learning curve.
"China is the junior member of an elite group. Whereas its counterparts in the West and in Russia have gained a lot of experience in long-duration space missions, China is just setting off," he said.
He said the early long-duration missions "will undoubtedly be challenging, if only from a psychological perspective" for the astronauts.
"Consider the living arrangements of the three (astronauts). Although they will have their individual, private areas, the entire space station is currently just 16.6m (54.5ft) long, with a maximum diameter of 4.2m. The crew will live in very close proximity to each other for a long time."
He said the first space stations, the Soviet Salyut vessels were a similar size - 15m in length and with a maximum diameter of 4.15m. But the first few missions were composed of two crew members each, except for the first - Salyut 1 - where three cosmonauts spent 23 days in space in June 1971, and died during Soyuz 11's re-entry when the capsule depressurised.
Meanwhile, the US Skylab was significantly larger, at 25.1m long and 6.61m in diameter, so its crew had access to quite a bit more personal space.
De Grijs said while he had no doubt that the Chinese crew were highly disciplined and psychologically stable, the tight living arrangements will "likely challenge the crew quite significantly".
He said the Shenzhou 13 mission is predominantly aimed at gaining experience at long-duration human survival in space, although the crew will carry out experiments as well.
De Grijs also said Tianzhou-3's cargo included replacement parts for the urine treatment system, which the crew will install when they move into the station's core module Tianhe.
During the Shenzhou 12 mission, the system converted some 600 litres of urine into more than 500 litres of water, which was used to generate oxygen and for cleaning, he added.
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