3.2 Principles of System Design
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(7) Assuring reliability and safety. The reliability was one of the most important
key performance indicators of lunar lander as well as safety in system design.
The development and launch of lunar lander was a high investment and high risk
engineering project. In space history, the failure probability of lunar lander as
well as other deep space probes was higher than Earth satellites because of the
specific environment, uniqueness and irreversibility of critical control point.
So it should be paid more attention to design of reliability and safety.
To achieve the system optimization, the fundamental principles for conventional
spacecraft should be followed and specific requirements of lunar lander should be
carefully considered as well.
3.3 Mission Analysis
Mission analysis was the primary task of the system design of spacecraft. The input
of the mission analysis was mission goals and user’s requirements. The output of
the mission analysis was a series of specifications of function and performance in
qualitative or quantitative form.
3.3.1 Analysis of Mission Characteristics
There are several differences from lunar soft landing to conventional Earth satellites
as followings [2, 7]:
(1) Powered descent and deceleration. There is barely no atmosphere near lunar
surface, i.e. the pressure is 10
−14 atm (1 atm = 1.013 × 10
5 Pa). So the lunar
lander could not be decelerated by airbraking. The velocity of lunar lander
relative to the Moon should be decelerated to several meters per second, which
meant that near 1.7 km/s Delta V be provided by propulsion system of lunar
lander. At the same time, the attitude of lunar lander should be controlled
precisely during powered descent to make sure that the vertical and horizontal
velocity of lunar lander relative to the Moon meet the requirements of soft
landing, and lunar lander was landed safely at the predefined location. The
thrust of the engine should be throttlable as well. Those factors should be
considered when the propulsion system was designed.
(2) Autonomous navigation and control during powered descent and landing.
Because the time was short and the Delta V was big, guidance, navigation
and control could not be realized by ground control for the powered descent
and landing. The sensors such as speedometer, ranging and terrain identification of the guidance, navigation and control subsystem could help to realize
autonomous navigation and control for powered descent and landing of lunar
lander. The capability of the guidance, navigation and control subsystem to
53
(7) Assuring reliability and safety. The reliability was one of the most important
key performance indicators of lunar lander as well as safety in system design.
The development and launch of lunar lander was a high investment and high risk
engineering project. In space history, the failure probability of lunar lander as
well as other deep space probes was higher than Earth satellites because of the
specific environment, uniqueness and irreversibility of critical control point.
So it should be paid more attention to design of reliability and safety.
To achieve the system optimization, the fundamental principles for conventional
spacecraft should be followed and specific requirements of lunar lander should be
carefully considered as well.
3.3 Mission Analysis
Mission analysis was the primary task of the system design of spacecraft. The input
of the mission analysis was mission goals and user’s requirements. The output of
the mission analysis was a series of specifications of function and performance in
qualitative or quantitative form.
3.3.1 Analysis of Mission Characteristics
There are several differences from lunar soft landing to conventional Earth satellites
as followings [2, 7]:
(1) Powered descent and deceleration. There is barely no atmosphere near lunar
surface, i.e. the pressure is 10
−14 atm (1 atm = 1.013 × 10
5 Pa). So the lunar
lander could not be decelerated by airbraking. The velocity of lunar lander
relative to the Moon should be decelerated to several meters per second, which
meant that near 1.7 km/s Delta V be provided by propulsion system of lunar
lander. At the same time, the attitude of lunar lander should be controlled
precisely during powered descent to make sure that the vertical and horizontal
velocity of lunar lander relative to the Moon meet the requirements of soft
landing, and lunar lander was landed safely at the predefined location. The
thrust of the engine should be throttlable as well. Those factors should be
considered when the propulsion system was designed.
(2) Autonomous navigation and control during powered descent and landing.
Because the time was short and the Delta V was big, guidance, navigation
and control could not be realized by ground control for the powered descent
and landing. The sensors such as speedometer, ranging and terrain identification of the guidance, navigation and control subsystem could help to realize
autonomous navigation and control for powered descent and landing of lunar
lander. The capability of the guidance, navigation and control subsystem to