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8 Propulsion Technology of Lunar Lander
8.4.2 Determination of Major Specifications of Propulsion
Subsystem
1. Propellant Option
The option of propellant was a comprehensive issue and generally determined when
the concept design of the lunar lander was proposed. It should be considered including
physical properties of propellant, mix ratio, vacuum specific impulse, density, cooling
performance, vacuum ignition performance, storability, toxicity, safety, technical
readiness, and etc.
1) Specific impulse of engine
The choice of propellant with high specific impulse and high density was an important factor to reduce propellant load, tank volume and subsystem structural mass.
For the lunar lander propulsion subsystem, large total impulse and light structure
weight were generally required. Usually bi-propellant based on N 2 O 4 (MON-1 or
MON-3 as an alternative)/MMH hypergolic propellant instead of mono-propellant
would be more suitable with specific impulse performance between N 2 O 4 /N 2 H 4 and
N 2 O 4 /UDMH. Recently, along with increasing demand for high specific impulse
and environmentally friendly propellant, propellant like LO x /LH 2 , LO X /HC (LCH 4 ,
LC 3 H 8 , RP-1) was developed very fast. The special advantage of such propellant
with possibility of in situ production on Moon or Mars made it possible to support
long term lunar base or Mars base and space transfer platform.
2) Long term storability in space
The long term storability of propellant was also an important factor for spacecraft. Due to restriction of the lunar lander mass, power consumption, lifetime,
thermal control, engine and etc., there was still certain gap for application of
liquid hydrogen/liquid oxygen, liquid oxygen/nontoxic hydrocarbon-based fuel, high
specific impulse cryogenic propellant. After it was synthetically analyzed including
physical properties such as frozen point, boiling point, density, saturated vapor pressure and technical readiness of engines, the conventional long term storable propellant
was selected to simplify thermal control, reduce structural mass and development
difficulties.
3) Re-ignition and pulse performance of engine
For attitude and orbit control of spacecraft propulsion subsystem, it was required to
be capable of re-ignition in vacuum for orbit control engine and firing in pulse mode
from tens of thousands to hundreds of thousands pulses for attitude control thrusters.
For different propellant, the vacuum start-up performance, especially short pulse
repeatable performance of engine might be different to some extent. Past research
showed that hypergolic bipropellant based on N 2 O 4 (MON-1)/MMH had excellent
vacuum ignition performance.
4) Engine cooling performance
8 Propulsion Technology of Lunar Lander
8.4.2 Determination of Major Specifications of Propulsion
Subsystem
1. Propellant Option
The option of propellant was a comprehensive issue and generally determined when
the concept design of the lunar lander was proposed. It should be considered including
physical properties of propellant, mix ratio, vacuum specific impulse, density, cooling
performance, vacuum ignition performance, storability, toxicity, safety, technical
readiness, and etc.
1) Specific impulse of engine
The choice of propellant with high specific impulse and high density was an important factor to reduce propellant load, tank volume and subsystem structural mass.
For the lunar lander propulsion subsystem, large total impulse and light structure
weight were generally required. Usually bi-propellant based on N 2 O 4 (MON-1 or
MON-3 as an alternative)/MMH hypergolic propellant instead of mono-propellant
would be more suitable with specific impulse performance between N 2 O 4 /N 2 H 4 and
N 2 O 4 /UDMH. Recently, along with increasing demand for high specific impulse
and environmentally friendly propellant, propellant like LO x /LH 2 , LO X /HC (LCH 4 ,
LC 3 H 8 , RP-1) was developed very fast. The special advantage of such propellant
with possibility of in situ production on Moon or Mars made it possible to support
long term lunar base or Mars base and space transfer platform.
2) Long term storability in space
The long term storability of propellant was also an important factor for spacecraft. Due to restriction of the lunar lander mass, power consumption, lifetime,
thermal control, engine and etc., there was still certain gap for application of
liquid hydrogen/liquid oxygen, liquid oxygen/nontoxic hydrocarbon-based fuel, high
specific impulse cryogenic propellant. After it was synthetically analyzed including
physical properties such as frozen point, boiling point, density, saturated vapor pressure and technical readiness of engines, the conventional long term storable propellant
was selected to simplify thermal control, reduce structural mass and development
difficulties.
3) Re-ignition and pulse performance of engine
For attitude and orbit control of spacecraft propulsion subsystem, it was required to
be capable of re-ignition in vacuum for orbit control engine and firing in pulse mode
from tens of thousands to hundreds of thousands pulses for attitude control thrusters.
For different propellant, the vacuum start-up performance, especially short pulse
repeatable performance of engine might be different to some extent. Past research
showed that hypergolic bipropellant based on N 2 O 4 (MON-1)/MMH had excellent
vacuum ignition performance.
4) Engine cooling performance