6.3 Mission Requirements and Characteristics
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6.3.2 Performance Requirements
In performance specifications of power system, the focuses were power output, main
bus voltage, solar array area, photoelectric conversion efficiency, capacity and life
of battery pack, and charging method.
1. Power Output
In all phases of the mission, the power output of power system of the lunar lander
should be higher than power requirement of the load and there should be certain
margin to deal with unexpected failures.
2. Main Bus Voltage
According to scale of spacecraft power, the main bus voltage could be divided into
three categories as 29 V, 42 and 100 V. Because the power scale of the lunar lander
was small, 29 V was suitable for main bus voltage.
3. Solar Array Area
The solar array area was closely related to configuration of the lunar lander. If solar
array area was too large, there would be waste in mass and cost. If the solar array was
too small, the power output of solar array would be insufficient, which might result
in catastrophic consequences. The power generation efficiency of solar cell should
also be considered when the solar array area was determined.
4. Photoelectric Conversion Efficiency
Photoelectric conversion efficiency was a key specification of solar cell, which
directly determined power output of solar arrays.
5. Battery Pack Capacity
The capacity of the battery pack determined the lunar lander’s ability to work in the
shadow period. In crucial phases such as launch, orbit change, eclipse in circumlunar
orbit and powered descent, the lunar lander was powered by the battery pack alone.
The capacity of the battery pack must meet the power requirement during crucial
phases and there should be certain margin to deal with accidents.
6. Battery Pack Life
The life of the battery pack was closely related to operation temperature, depth of
discharge, and discharge rate. According to mission profile of the lunar lander, when
the battery pack was operating at the maximum depth of discharge, the number of
cycles should be greater than the requirement to ensure the reliability of power supply
during nominal mission period.
7. Charging Method
The charging method should match the charging characteristics of the battery pack.
Usually the charging method of constant current-constant voltage was used for
lithium-ion battery packs, which could complete the battery charging in a short time
and ensure a high charging efficiency. The shift point of constant current to constant
voltage was very important.
203
6.3.2 Performance Requirements
In performance specifications of power system, the focuses were power output, main
bus voltage, solar array area, photoelectric conversion efficiency, capacity and life
of battery pack, and charging method.
1. Power Output
In all phases of the mission, the power output of power system of the lunar lander
should be higher than power requirement of the load and there should be certain
margin to deal with unexpected failures.
2. Main Bus Voltage
According to scale of spacecraft power, the main bus voltage could be divided into
three categories as 29 V, 42 and 100 V. Because the power scale of the lunar lander
was small, 29 V was suitable for main bus voltage.
3. Solar Array Area
The solar array area was closely related to configuration of the lunar lander. If solar
array area was too large, there would be waste in mass and cost. If the solar array was
too small, the power output of solar array would be insufficient, which might result
in catastrophic consequences. The power generation efficiency of solar cell should
also be considered when the solar array area was determined.
4. Photoelectric Conversion Efficiency
Photoelectric conversion efficiency was a key specification of solar cell, which
directly determined power output of solar arrays.
5. Battery Pack Capacity
The capacity of the battery pack determined the lunar lander’s ability to work in the
shadow period. In crucial phases such as launch, orbit change, eclipse in circumlunar
orbit and powered descent, the lunar lander was powered by the battery pack alone.
The capacity of the battery pack must meet the power requirement during crucial
phases and there should be certain margin to deal with accidents.
6. Battery Pack Life
The life of the battery pack was closely related to operation temperature, depth of
discharge, and discharge rate. According to mission profile of the lunar lander, when
the battery pack was operating at the maximum depth of discharge, the number of
cycles should be greater than the requirement to ensure the reliability of power supply
during nominal mission period.
7. Charging Method
The charging method should match the charging characteristics of the battery pack.
Usually the charging method of constant current-constant voltage was used for
lithium-ion battery packs, which could complete the battery charging in a short time
and ensure a high charging efficiency. The shift point of constant current to constant
voltage was very important.