JIUQUAN - Aerospace officials are confident of a successful space rendezvous and docking between orbiters, despite the inherent challenges and risks, a spokeswoman for China's manned space program said at a press conference Monday.

China plans to launch Shenzhou-8, an unmanned spacecraft, at 5:58 am Tuesday from the Jiuquan Satellite Launch Center in the northwestern Gobi desert, spokeswoman Wu Ping said.

The spacecraft will attempt to achieve China's first rendezvous and docking with Tiangong-1, an unmanned space lab module sent into space in late September.

"We have full confidence in the successful launch of Shenzhou-8, as well as the rendezvous and docking mission," Wu said.

But she added that it is difficult and risky to link up two vehicles traveling at high speeds in orbit, with a margin of error of no more than 20 cm.

There were collisions between space vehicles in past docking attempts, and recent docking missions involving the International Space Station did not always run smoothly, Wu said.

Nearly 100 contingency plans have been prepared to address problems that may occur during the mission, Wu said, adding that all people involved in the mission are confident about a successful docking.

The automated control system and docking system are crucial to the mission, and simulated tests have been done various times on the ground, she said.

In order for the Shenzhou-8 spacecraft to enter the orbital plane shared by Tiangong-1, the launch must be carefully timed to occur around the time that Tiangong-1's orbital plane intersects the launch site, Wu said, otherwise Shenzhou would have to use more propellant to adjust.

"We aim at launching Shenzhou-8 at the 'zero launch window,'" said Wu, referring to the precise prescribed launch time. "Such precision is achievable."

Technological modifications have been made to the carrier rocket to make it compatible with the mission. The rocket features a new control system and an improved thruster, according to Wu.

"Compared with Long March-2F rockets, the Long March-2FY8 has a greater payload, features higher orbital precision and is more reliable," Wu said.

The 58.3-meter-long Long March-2FY8 rocket has a total liftoff weight of 497 metric tons and a payload of 8,130 kg.