China's first lunar probe, Chang'e-1, successfully completed its first braking at perilune and entered the moon's orbit Monday morning, becoming China's first circumlunar satellite.
Chang'e-1, following the instructions of the Beijing Aerospace Control Center (BACC), started braking at 11:15 AM at a position around 300 km away from the moon and entered the moon's orbit at around 11:37 AM after completing the braking, according to the BACC.
The braking was performed just in time to decelerate the probe, enabling it to be captured by the lunar gravity and become a "real" circumlunar satellite, said Wang Yejun, chief engineer of BACC.
"The first braking at perilune is a key moment in the long journey of Chang'e-1," Wang said.
The speed of Chang'e-1 reached about 2.3 km per second when it started braking. It would likely fly away from the moon if the braking was too early, or it would crash into the moon if the braking was too late, scientists said.
After the braking, the probe's speed was slowed down to 1.948 km per second and is now traveling along a 12-hour elliptical moon orbit, with a perilune of about 200 km and an apolune of about 8,600 km.
"The orbit that Chang'e-1 is now moving on fully tallies with the one we have designed and the speed is within a normal range," said Ji Gang, an engineer of monitoring and controlling branch of the moon probe program.
The probe is expected to brake for another two times in the following two days to further slow down to enter a round orbit, where it is supposed to start "working" formally.
Chang'e-1 will then stay a year in the 127-minute round orbit, which is 200 km from the moon's surface, for scientific explorations.
China's first lunar probe, Chang'e-1, 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 completed its fourth orbital transfer on Oct. 31, which shifted it to the earth-moon transfer orbit and pushed it to fly to the moon "in a real sense".
It was previously moving around the earth and experienced three orbital transfers, which lifted it up first to a 16-hour orbit with an apogee of 50,000 km, then to a 24-hour orbit with an apogee of 70,000 km and next to a 48-hour orbit with an apogee of more than 120,000 km.
On Nov. 2, BACC successfully carried out an orbital correction for Chang'e-1 to ensure that it traveled on the pre-set orbit.
A second orbital correction scheduled for Nov. 3 was called off because it was "unnecessary" -- Chang'e-1 had been running accurately on the expected trajectory, a BACC scientist said.
(Xinhua News Agency November 5, 2007)
