After entering its fifth day of flight in space, China's second manned spacecraft Shenzhou VI is prepared for a journey back home.
According to Sui Qisheng, commander-in-chief of the space program's landing system, said that in the return process the spaceship undergoes four stages of decelerating flight, free descending, aerosphere flight and landing.
With a return order from the ground control center, the spacecraft's position is adjusted and the re-entry capsule is separated from the orbital module. The orbiter remains running in orbit to carry out more experiments.
After the separation, the re-entry capsule's position is readjusted for a return trajectory. Retroengines are ignited to make the capsule deviate from its circular orbit and switch to the return trajectory.
Ignition timing must be extremely accurate, for one second means nine km of difference of the capsule's landing place.
Along the return trajectory, the spaceship maintains unpowered free descending. About 140 km above the Earth, the propulsion module is separated from the re-entry capsule, with the former to be burnt in the aerosphere.
The re-entry capsule keeps descending in the aerosphere. About 100 km above ground, strong friction between the capsule and aerosphere produces a large amount of heat on the surface of the capsule.
Accordingly, a high-temperature plasma gas layer over the capsule surface shields electromagnetic signals, making the capsule lose contact temporarily with the ground control center.
The blackout phenomenon disappears when the re-entry capsule drops to 40 km above the Earth, and its communication with the ground resumes.
When the capsule is only 10 km from the ground, the final landing phase is activated. The guiding parachute, deceleration parachute and main parachute are unfurled, and the capsule drops slowly.
When the capsule is one meter above the ground, four reverse-thrust rocket engines are ignited to achieve the capsule’s soft landing at a speed of one to two meters per second.
(Xinhua News Agency October 16, 2005)
