The three Chinese astronauts aboard the Shenzhou VII spacecraft were in fine health on Friday, ready for the extra-vehicular activities (EVA) scheduled for Saturday, a spokesman for the space mission said.
Zhai Zhigang and Liu Boming started assembling the 120-kg EVA spacesuits since 10:20 am, Wang Zhaoyao, a spokesman for China's manned space program, told a press conference in Beijing on Friday. Xinhua reported that they finished the work in about 12 hours.
The two space suits were fixed to the module wall in parts when the spaceship was launched, to be assembled by the astronauts later.
Unpacking the suits comprises 21 steps and each step is divided into sub-steps and detailed moves.
Once the suits are assembled, the astronauts started testing and wearing them, in addition to a 100-minute rehearsal in the orbital module before the spacewalk.
"A job that people can finish in one hour on Earth usually needs two to three hours in space," Li Xiqiang, a researcher for the Shenzhou VII mission, said at a separate press briefing. But he promised the astronauts would not feel exhausted. "There's enough time for them to take a rest."It was the first time for the two to assemble the suits in zero-gravity as it is impossible to create a real zero-gravity condition on Earth.
One of the astronauts will walk out of the orbital module at 4:30 pm on Saturday, Wang said. "Since it is the first spacewalk for China ... there are many uncertainties. We will very likely adjust the time for EVA according to the astronauts' conditions," he said.
The astronauts will make a series of difficult moves in space, Wu Bin, the expert in charge of astronaut training with the China Astronaut Research and Training Center, told Xinhua.
Zhai, the No 1 astronaut, is most likely to walk into space. Assisted by Li, who will stay on in the orbital module during the process, Zhai will take a test sample of solid lubricant from the surface of the spacecraft, which was placed there before the launch.
The astronaut, tied to the spaceship with two safety wires, is scheduled to walk along the orbital module exterior.
"Actually, it is not like walking, but floating," Wu said.
A set of handrails on the spaceship surface will help the astronaut move, he said. He must make sure that both wires are tied to the handrails before taking any step forward.
During the mission, the astronauts will depressurize and re-pressurize the cabin, as well as exit and re-enter the orbital module.
To ensure the safety of the astronaut who will do the spacewalk, the space suit is equipped with three oxygen tanks. An 8-m-long electricity wire, linking the astronaut with the spaceship, will send his physiologic data back and act as a spare safety wire.
"The EVA is expected to last 20 minutes. If the time for opening and closing the module door is factored in, it will be 30 to 40 minutes," Wang said.
The historic moment will be broadcast live.
The spaceship will aslo release a 40-kg satellite which will circle the orbiter and send back images to mission command.
Earlier on Friday, Shenzhou VII shifted from an oval orbit to a more stable circular orbit 343 km above Earth.
The spaceship atop a Long March II-F rocket lifted off at 9:10 pm on Thursday from Jiuquan Satellite Launch Center in Gansu province, in China's third manned space mission.
新华网北京9月26日电（记者李志晖 李惠子）中国载人航天工程新闻发言人王兆耀26日说，根据飞行计划安排，航天员将于27日16时30分前后执行出舱活动任务。目前，舱外航天服组装与测试进展顺利。
根据飞行程序安排，轨道舱门从打开至关闭，整个过程约有半个小时到40分钟左右，其中航天员舱外活动约20分钟。届时，出舱活动将向中国和世界媒体公开透明地播出。
王兆耀同时指出，出舱活动对中国来说是首次进行，在技术上受多方面因素影响，具体出舱时间需要根据舱外航天服和航天员的状态确定。
他说，北京时间26日10时20分，从飞船运行第9圈起，航天员翟志刚、刘伯明开始进行轨道舱状态检查和舱外航天服的组装与测试等工作。之后，将穿着舱外航天服在轨道舱进行约100分钟的在轨训练，为执行出舱活动作准备。航天员景海鹏在返回舱值守，并随时监控飞船运行工况。
据介绍，神舟七号飞船发射升空时，舱外航天服及部分组件处于分解打包状态，航天员需对舱外航天服舱载对接系统和舱外航天服进行启封，安装测试空气净化器、氧瓶、电池组、无线遥测装置等可更换部组件，检查与调整服装尺寸，还将对各种接口及服装内环境温度、氧气供给、通信连接等进行调整测试与系统检查。根据地面模拟结果，整个过程约需12小时。
王兆耀说，由于出舱活动的真空和失重环境难以在地面进行完全真实的模拟演练，舱外航天服、气闸舱等新研制产品和新技术采用是首次进行飞行验证。另外，航天员要完成对舱外航天服的在轨组装、测试、穿脱，出舱，取回科学实验装置，返回轨道舱、气闸舱泄复压等操作，时间长，难度大，因此，这次出舱活动任务具有高风险。
“要顺利完成这次出舱活动，必须保证产品质量可靠、航天员训练有素、组织指挥精确、测控通信连续稳定。”他说。