China: Shenzhou-8 set to land back on the earth

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China: Shenzhou-8 set to land back on the earth

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The re-entry capsule of China's unmanned spacecraft Shenzhou-8 is set to land back on Thursday.

17 November,2011 02:02 pm

Shenzhou-8 departed from the prototype space lab Tiangong-1 at 18:30 on Wednesday, to begin its preparation for the return trip to the earth.China had successfully completed its first two space docking tests that joined the Shenzhou-8 spacecraft, launched on Nov. 1, and the target orbiter Tiangong-1 on Nov. 3 and Nov. 14, respectively. Tiangong-1, a module of a planned space lab, has been in orbit since its launch on Sept. 29.After its departure with Tiangong-1, Shenzhou-8 resumes its operating mode and adjusts its trajectory, ready for its return around 19:00 (Beijing Time) on Thursday.After starting the return trip, Shenzhou-8 has been lowering its orbit altitude from the 350 km to 145 km. And then the propelling module separates with the re-entry capsule. The re-entry capsule adjusts its position with the larger end ahead, heading for the atmospheric layer - the re-entry phase.After penetrating the atmospheric layer, parachute-cabins hatch will be opened at the re-entry capsule is around 10 km above the surface, pulling out in a relay action the guide parachute, brake parachute, attached apex drogue and the main parachute.The main parachute with an area of 1, 200 square meters when fully unfolded, can reduce the descend speed to some seven meters per second. When the re-entry capsule is about one meter above the ground, the landing cushion engine will be turned on to ensure a soft-landing by the re-entry capsule at a speed of one to two meters per second.Despite various high technologies adopted, Shenzhou-8s return trip is still highly dangerous.Danger one: high temperature. When passing through the atmosphere, the friction between the re-entry capsule and the air will cause temperature rise to over 1,000 degrees Celsius, posing a great threat to the re-entry capsule. To cope with the issue, a special fire-proof structure is fixed outside the capsule.Danger two, communication black-out. Due to the severe friction at an extreme speed, a plasma zone will occur, causing the communication to be black-out. The re-entry capsule will lose touch with the earth, it will be a great challenge for the spacecraft during the period, which ends at a height of 40 km above the surface.Danger three: unsuccessful unfolding of the parachutes. The parachuting is closely linked to the safe landing of the re-entry capsule. The main parachute cant unfold directly, otherwise it will shattered by the airstream. The 1,200-square-meters main parachute also needs to be cut off the capsule at the moment of the landing, to avoid being pulled away by the main parachute fully loaded by strong wind.