China's first lunar probe, Chang'e-1, completed its second braking on Tuesday's morning, which further decelerated the satellite to get it closer to its final orbit.
Chang'e-1, following the instructions of the Beijing Aerospace Control Center (BACC), started the second braking at 11:21 a.m. and entered a 3.5-hour orbit with a perilune of 213 km and an apolune of 1,700 km at around 11:35 AM after completing the braking.
"The second braking was done just as accurately as the first one and the satellite has entered the orbit just as designed," said Zhu Mincai, head of the Beijing Aerospace Control Center (BACC).
"The second braking has laid a good foundation for the probe's entry into its final working orbit tomorrow," Zhu said, adding that scientists and engineers will continue their calculation and measurement in the afternoon to ensure a success maneuver on Wednesday.
"So far, orbital transfers of the probe have all been done accurately," said Bian Bingxiu, a researcher with the China Aerospace Science and Technology Corporation.
"The precise ground maneuvers and orbital transfers have saved a lot of fuel, which may prolong the probe's working time on its final orbit by around one year," Bian said.
Zhu Mincai said that the probe will brake for the third time at around 8:09 AM on Wednesday to enter its final orbit, marking success of the probe's whole flying journey to the moon.
The third braking will slow down the probe's speed to 1.59 km per second to put it on a 127-minute round polar circular orbit, where it was originally planned to stay a year for scientific explorations.
"In the prolonged period, the probe can carry out some other scientific tests, which may help acquire experience for China's second- and third-stage moon missions," Bian said.
The launch of Chang'e-1 kicks off the first step of China's three-stage moon mission, which will lead to a moon landing and launch of a moon rover at around 2012. In the third phase, another rover will land on the moon and return to earth with lunar soil and stone samples for scientific research at around 2017.
The BACC cancelled two pre-set orbital corrections while the probe traveled along the earth-moon transfer orbit from Oct. 31 to Nov. 5, calling them "unnecessary" as Chang'e-1 had been running accurately on the expected trajectory.
So far, the satellite has experienced four orbital transfers, one orbital correction and two brakings. All these maneuvers usually consumed a great deal of fuel, scientists explained.
Because of the planned maneuvers, the fuel that the 2,300-kg Chang'e-1 carries accounts for nearly half of the satellite's total weight.
Before the second braking, Chang'e-1 was traveling along a 12-hour elliptical moon orbit, with a perilune of about 210 km and an apolune of about 8,600 km.
Chang'e-1 successfully completed its first braking and entered the moon's orbit at around 11:37 AM on Monday, which made it become a "real" circumlunar satellite.
The probe, named after a legendary Chinese goddess who flew to the moon, blasted off on a Long March 3A carrier rocket on Oct. 24 from the Xichang Satellite Launch Center in southwestern Sichuan Province.
The probe is expected to fulfil four scientific objectives, including a three-dimensional survey of the Moon's surface, analysis of the abundance and distribution of elements on lunar surface, an investigation of the characteristics of lunar regolith and the powdery soil layer on the surface, and an exploration of the circumstance between the earth and the moon.
(Xinhua News Agency November 6, 2007)
