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)