China's first lunar probe, Chang'e-1, on Monday successfully entered the moon's orbit in a key step of its long journey in lunar exploration.
Following commands, Chang'e-1 started braking at a position 300 km away from the moon and entered its orbit Monday morning, making it China's first circumlunar satellite, the Beijing Aerospace Control Centre said.
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, Wang Yejun, BACC chief engineer said.
The speed of Chang'e-1 reached about 2.3 km per second when it started braking. A too early braking was likely to have caused the spacecraft to fly away from the moon and braking it too late would have led it to crash into the moon, scientists said, explaining the critical nature of the step.
After the braking, the probe's speed was slowed down to 1.948 km per second and it is now travelling along a 12-hour elliptical moon orbit, the scientists said, according to Xinhua news agency.
"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 programme.
The probe is expected to brake twice more in the following two days to further slow it down to enter a round orbit, where it is 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.
Space scientists had carried out one orbital correction to ensure that the satellite travelled on its preset orbit.