274
8 Propulsion Technology of Lunar Lander
distributed propellant tanks was usually applied for propulsion subsystems to lower
the center of gravity of the lunar lander.
For sphere and cylinder type tank, it was difficult to be mounted by flanges (large
flange size and heavy weight). Therefore it was usually to be mounted with the top
and bottom, while the axial load was endured by the bottom and the transverse load
was endured by the top (or the alternative option was the frames welded directly on
the tank shells to transfer force). Such design would lead to large concentrated load
in the tank bottom and instability of the shell. So the bearing capability of the tank
should be considered when it was designed.
For the main descent engine, the engine usually was installed in the center of
the lunar lander because of the landing safety. The thermal shield for the engine
should be configured to isolate effectively the instruments of the lunar lander from
high temperature thermal radiation of firing engine (the temperature of engine nozzle
might reach 1300~1400 °C). But it would influence the normal heat dissipation of
the engine and the operation reliability. So the temperature rising of the engine due
to the thermal shield should be considered to ensure the working temperature of the
engine within the safety margin when the engine was designed.
8.3.2 Functional Requirements
The lunar lander could be classified into non-recoverable and recoverable types.
For recoverable the lunar lander, the ascent propulsion subsystem was necessary to
implement ascending besides the descent propulsion subsystem for powered descent
and soft-landing.
There were following functional requirements for propulsion subsystem of
different robotic or manned the lunar landers.
(1) To provide force for orbit control such as LTO, LOI, circumlunar orbit, powered
descent, ascending and de-orbit.
(2) To provide force for attitude control such as LTO, circumlunar orbit, powered
descent, ascending and Earth Transfer Orbit.
(3) To provide force for translation, reaction control for near earth orbit, LTO,
rendezvous and docking on lunar orbit.
(4) To provide force for emergency return of manned the lunar lander.
According to the difference between lunar exploration missions and design of the
lunar landers, the configuration, demands and constraints of the propulsion subsystem
were different. For example, the functional requirements of propulsion subsystem
for non-recoverable the lunar lander were analyzed as follows.
(1) Usually the simple, reliable pressurized-feed orbit/attitude unified propulsion subsystem was used because of the lunar lander mass, mounting space,
propellant sharing, orbit control engine reigniting, reliability and etc.
8 Propulsion Technology of Lunar Lander
distributed propellant tanks was usually applied for propulsion subsystems to lower
the center of gravity of the lunar lander.
For sphere and cylinder type tank, it was difficult to be mounted by flanges (large
flange size and heavy weight). Therefore it was usually to be mounted with the top
and bottom, while the axial load was endured by the bottom and the transverse load
was endured by the top (or the alternative option was the frames welded directly on
the tank shells to transfer force). Such design would lead to large concentrated load
in the tank bottom and instability of the shell. So the bearing capability of the tank
should be considered when it was designed.
For the main descent engine, the engine usually was installed in the center of
the lunar lander because of the landing safety. The thermal shield for the engine
should be configured to isolate effectively the instruments of the lunar lander from
high temperature thermal radiation of firing engine (the temperature of engine nozzle
might reach 1300~1400 °C). But it would influence the normal heat dissipation of
the engine and the operation reliability. So the temperature rising of the engine due
to the thermal shield should be considered to ensure the working temperature of the
engine within the safety margin when the engine was designed.
8.3.2 Functional Requirements
The lunar lander could be classified into non-recoverable and recoverable types.
For recoverable the lunar lander, the ascent propulsion subsystem was necessary to
implement ascending besides the descent propulsion subsystem for powered descent
and soft-landing.
There were following functional requirements for propulsion subsystem of
different robotic or manned the lunar landers.
(1) To provide force for orbit control such as LTO, LOI, circumlunar orbit, powered
descent, ascending and de-orbit.
(2) To provide force for attitude control such as LTO, circumlunar orbit, powered
descent, ascending and Earth Transfer Orbit.
(3) To provide force for translation, reaction control for near earth orbit, LTO,
rendezvous and docking on lunar orbit.
(4) To provide force for emergency return of manned the lunar lander.
According to the difference between lunar exploration missions and design of the
lunar landers, the configuration, demands and constraints of the propulsion subsystem
were different. For example, the functional requirements of propulsion subsystem
for non-recoverable the lunar lander were analyzed as follows.
(1) Usually the simple, reliable pressurized-feed orbit/attitude unified propulsion subsystem was used because of the lunar lander mass, mounting space,
propellant sharing, orbit control engine reigniting, reliability and etc.