8.4 Propulsion Subsystem Design [5–7]
293
chamber to minimize the propellant filling volume behind valve and ensure minimal
pulse impulse and rapid response. Redundant seat and seal structure were designed
to ensure reliable seal of valve.
5. Large Flux Latch Valve
Because of large thrust and flux of orbit control engine in the lunar lander propulsion
subsystem, large flux latch valve was generally used to control propellant feeding
for orbit control engine and avoid propellant loss in case of engine leak failure. The
large flux latch valve should be light weight, large flux, low flow resistance, reliable
seal, reliable action, long term compatibility with propellant and etc. Traditional
solenoid latch valve was not qualified for the task, so solenoid pneumatic latch valve
was applied more frequently. For example, the solenoid pneumatic latch valve was
used in propulsion subsystem of the Chang’E-3 lunar lander, which consisted of two
parts: pilot valve and master valve. Pilot valve was a kind of solenoid latch valve
to control gas driving master valve on/off switch. In order to ensure reliability of
dynamic seal in oxidizer, metal bellow instead of rubber seal was used as dynamic
seal. The swelling of rubber seal and compatibility with oxidizer were avoided.
6. Propulsion Control Unit
Propulsion control unit was a key node between GNC and OBDH subsystems, which
was also key driver of components in propulsion subsystem. Through timely and
accurate reception of control command from GNC and OBDH subsystem, it could
drive components of propulsion subsystem, and sends telemetry, status data back to
GNC and OBDH subsystem at the same time.
Based on reliability requirements, propulsion control unit was generally designed
according to dual or triple-redundancy principle. It consisted of DC/DC power, CPU,
flip latch, address decoder, PROM, RAM, I/O extension, RS422 or 1553B bus interface, power-driven circuit, watch-dog circuit and etc. For the two-phase stepping
motor for thrust throttling, chopping constant current control based on H-bridge
drive chip as the core was generally used to control stepping motor precisely, rapidly
and stably. For example, A/B dual redundancy with cold stand-by design was applied
in propulsion subsystem of the Chang’E-3 lunar lander. The LMD18200T based Hbridge drive chip as the core combined with 8-bit D/A converter AD558, LM139
comparator and time-based circuit LM555 were applied to establish closed-loop
control of two-phase stepping motor for 7500 N throttling engine. The power for
driving orbit/attitude control engine valve or solenoid valve could be designed in
series, parallel or series-parallel combination to ensure reliable on/off switch.
8.4.7 Ground Test and Propellant Filling of Propulsion
Subsystem
1. Ground Test of Propulsion Subsystem
293
chamber to minimize the propellant filling volume behind valve and ensure minimal
pulse impulse and rapid response. Redundant seat and seal structure were designed
to ensure reliable seal of valve.
5. Large Flux Latch Valve
Because of large thrust and flux of orbit control engine in the lunar lander propulsion
subsystem, large flux latch valve was generally used to control propellant feeding
for orbit control engine and avoid propellant loss in case of engine leak failure. The
large flux latch valve should be light weight, large flux, low flow resistance, reliable
seal, reliable action, long term compatibility with propellant and etc. Traditional
solenoid latch valve was not qualified for the task, so solenoid pneumatic latch valve
was applied more frequently. For example, the solenoid pneumatic latch valve was
used in propulsion subsystem of the Chang’E-3 lunar lander, which consisted of two
parts: pilot valve and master valve. Pilot valve was a kind of solenoid latch valve
to control gas driving master valve on/off switch. In order to ensure reliability of
dynamic seal in oxidizer, metal bellow instead of rubber seal was used as dynamic
seal. The swelling of rubber seal and compatibility with oxidizer were avoided.
6. Propulsion Control Unit
Propulsion control unit was a key node between GNC and OBDH subsystems, which
was also key driver of components in propulsion subsystem. Through timely and
accurate reception of control command from GNC and OBDH subsystem, it could
drive components of propulsion subsystem, and sends telemetry, status data back to
GNC and OBDH subsystem at the same time.
Based on reliability requirements, propulsion control unit was generally designed
according to dual or triple-redundancy principle. It consisted of DC/DC power, CPU,
flip latch, address decoder, PROM, RAM, I/O extension, RS422 or 1553B bus interface, power-driven circuit, watch-dog circuit and etc. For the two-phase stepping
motor for thrust throttling, chopping constant current control based on H-bridge
drive chip as the core was generally used to control stepping motor precisely, rapidly
and stably. For example, A/B dual redundancy with cold stand-by design was applied
in propulsion subsystem of the Chang’E-3 lunar lander. The LMD18200T based Hbridge drive chip as the core combined with 8-bit D/A converter AD558, LM139
comparator and time-based circuit LM555 were applied to establish closed-loop
control of two-phase stepping motor for 7500 N throttling engine. The power for
driving orbit/attitude control engine valve or solenoid valve could be designed in
series, parallel or series-parallel combination to ensure reliable on/off switch.
8.4.7 Ground Test and Propellant Filling of Propulsion
Subsystem
1. Ground Test of Propulsion Subsystem