10-20-2007 11:20

1. Orbit design and flight sequence control

Under the condition of three-body movement of the earth, the moon and its satellite, the orbit design of lunar exploration satellite is more complicated than that of the previous earth satellite. The lunar satellite will be sent into the highly elliptical earth orbit atop a launch vehicle first. After separating from the launch vehicle it will enter into the earth-moon transfer orbit through three accelerations in the phase-modulated orbit (16h, 24h, 48h) by its own propulsion system, during which it needs to carry out several orbit adjustments and attitude maneuvers so as to ensure to be captured by lunar gravity. After operating in the earth-moon orbit for 4-5 days, it will enter into the lunar acquisition orbit. Then, it will enter into the target lunar orbit and carry out pre-designed missions after three brakings and experiencing three different orbit phases.

2. The three-vector control problem of the lunar satellite's attitude control

During the flight orbiting the moon the satellite should be always oriented to the earth, the moon and the sun: all the onboard detectors should be kept facing the lunar surface to complete the scientific exploration missions; the transmitting/receiving antennas should be maintained facing the earth to receive the commands from the earth and transfer scientific data to the earth for the ground application research; the solar panels should be oriented to the sun to acquire the power for normal operation. During the flight orbiting the moon, the three bodies of the earth, the moon and the sun rotate relatively, so the attitude control is a three-vector control process. We need to make more new theoretic research in such respects as the satellite overall structure, quality distribution and multi-axial control and tracking etc., which also bring up many challenges in the project implementation.

3. The satellite environment adaptability design

The complexity of the space environment during the satellite operation has higher requirements of the environment adaptability and reliability for the satellite and its instruments. For instance, the strong radiation environment in the earth-moon space will exert great effect on the electronics; the temperature change ranges greatly from 130℃ of the side facing the sun to -170℃ of the side back to the sun, so it has stricter requirements of temperature control for the detectors.

4. Long-range TT&C and communication

The biggest challenge in the Phase I of the Lunar Exploration Program is TT&C system, because its transmission capability should reach the long distance enough. China's previous satellites can reach the distance as far as 80,000 km, but the distance between the moon and the earth is about 400,000km, which brings up new challenge to the TT&C system. In addition, the lunar satellite must carry out many attitude maneuvers during its flight to the moon and operation orbiting the moon. The distance from east to west in China is only 5,000km, which is also a challenge to TT&C continuity. China hasn't set up a deep space TT&C network. At present, the combination of space TT&C network and astronomical observation network can meet the basic needs of TT&C, but with a small margin. This is a difficult problem urgent to be solved now.


Editor:Liu Fang