Chang’e-4 lunar probe satellite enters Halo orbit
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The relay satellite for the Chang’e-4 lunar probe, which is expected to land on the far side of the Moon at the end of the year, has entered the planned orbit, the China National Space Administration said yesterday.
The satellite, named Queqiao (Magpie Bridge) and launched on May 21, entered the Halo orbit around the second Lagrangian (L2) point of the Earth-Moon system, about 65,000 kilometers from the Moon, at 11:06am yesterday after a journey of more than 20 days.
“The satellite is the world’s first communication satellite operating in that orbit, and will lay the foundation for the Chang’e-4, which is expected to become the world’s first soft-landing, roving probe on the far side of the Moon,” said Zhang Hongtai, president of the China Academy of Space Technology.
While in orbit, the relay satellite can see both the Earth and the far side of the Moon. The satellite can stay in the Halo orbit for a long time due to its relatively low use of fuel, since the Earth’s and Moon’s gravity balances the orbital motion of the satellite.
“From Earth, the orbit looks like a halo of the Moon, which is where it got its name,” said Zhang Lihua, project manager of the relay satellite.
He said the Halo orbit was a three-dimensional irregular curve. It is extremely difficult and complex to maintain the satellite in orbit.
“If there is a tiny disturbance, such as gravitational disturbance from other planets or the Sun, the satellite will leave the orbit. The orbit period is about 14 days. According to our current plan, we will conduct orbit maintenance every seven days.” Zhang Lihua added.
In order to set up a communication link between Earth and the planned Chang’e-4 lunar probe, space engineers must keep the satellite stable and control its altitude, angle and speed with high precision.
Next, the team will test the communication function of the relay satellite.
Weighing about 400 kilograms and with a designed life of three years, the satellite carries several antennas. One, shaped like an umbrella with a diameter of 4.2 meters, is the largest communication antenna ever used in deep space exploration, according to Chen Lan, deputy chief engineer of the Xi’an branch of CAST.
Tidal locking
Tidal forces of the Earth have slowed the Moon’s rotation to the point where the same side always faces the Earth, a phenomenon called tidal locking. The other face, most of which is never visible from Earth, is the far side or dark side of the Moon, not because it’s dark, but because most of it remains unknown.
With its special environment and complex geological history, the far side is a hot spot for scientific and space exploration.
The Aitken Basin of the lunar south pole region on the far side has been chosen as the landing site for Chang’e-4. The region is believed to have great research potential. However, landing and roving require a relay satellite to transmit signals. Establishing a communication link is essential for the success of the Chang’e-4 mission.
A lunar optical imaging detector developed by Saudi Arabia is installed on a micro satellite launched together with Queqiao.
The camera, which began to work on May 28, has conducted observations of the Moon and acquired a series of clear lunar images and data. Three of the images was unveiled yesterday.
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