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8 Propulsion Technology of Lunar Lander
Inner diaphragm separated gas cavity from liquid cavity to prevent propellant from
gas. When the propellant tank worked, propellant was expulsed along with deformation of metal diaphragm. During flight, propellant sink operation was not necessary
and there was no propellant slosh. In addition, there should be pressure differential
to deform metal diaphragm, so it could endure acceleration along various directions.
3. Gas Tank
Gas tank was used to store pressurized gas with high pressure and good seal performance. The major types of high pressure gas tank in spacecraft propulsion subsystem
were titanium gas tank and metal liner with composite wrapping. Under the same
pressure and volume, the mass of composite wrapped gas tank was lighter. The main
failure mode was leaking mode prior to burst, so it was safer than metal gas tank.
Along with the development of carbon fiber materials, wrapping technology and
non-destructive examination method, composite wrapped gas tank was developed
rapidly. The lightweight, large volume of high pressure gas tank was widely used in
propulsion subsystem. According to different structures of inside liner, composite
wrapped gas tank was classified into welded titanium alloy inside liner and seamless
aluminum alloy inside liner. The former one was easy to be welded with titanium
pipelines and has good sealing in connection. Due to weld seam and heat affected
zone vulnerable to failure in titanium inside liner, it was necessary to match the
deformation between inside liner and wrapped layer and specify high requirements
of welding process. The latter one was easy to be formed, manufactured with equal
strength design (especially for hemisphere-cylinder structure) with excellent fatigue
resistance. The disadvantage was that it cannot be welded with titanium pipelines,
so double-sealing screw thread connection was generally applied. For example, a
35 MPa and 100 L composite wrapped gas tank with seamless aluminum inside liner
for sealing pressurized gas and wrapped layer for bearing load of gas pressure was
used in propulsion subsystem of the Chang’E-3 lunar lander.
4. Attitude Control Thruster
Attitude control thruster was used for attitude control, stabilization, adjustment, orbit
correction, hover and translation during LTO, circumlunar and powered decent,
which was also used to deplete remnant propellant after landing. Generally the
specific impulse of attitude control thruster should be high and the thruster should
be stable in continuous firing for thousands of seconds or more, hundreds of thousands of pulse firing, and especially small pulse of 10~20 ms minimal duration. In
order to satisfy requirements of attitude control thruster, not only efficient internal
combustion and boundary film cooling was necessary for long term reliable work,
but also reducing filling volume of injector head and enhancing fast response of
valve was necessary to conduct short pulse. At the same time, because the number
of pulse was large, anti-jamming, anti-leak and anti-clogging should be emphasized
in thruster design. For example, for the 150 N thruster in propulsion subsystem of
the Chang’E-3 lunar lander, film and radiation cooling was applied. High temperature resistant niobium alloy sprayed with anti-oxidization coating is used for thruster
chamber cylinder part. Oxidizer and fuel valves were installed on the head of thrust
8 Propulsion Technology of Lunar Lander
Inner diaphragm separated gas cavity from liquid cavity to prevent propellant from
gas. When the propellant tank worked, propellant was expulsed along with deformation of metal diaphragm. During flight, propellant sink operation was not necessary
and there was no propellant slosh. In addition, there should be pressure differential
to deform metal diaphragm, so it could endure acceleration along various directions.
3. Gas Tank
Gas tank was used to store pressurized gas with high pressure and good seal performance. The major types of high pressure gas tank in spacecraft propulsion subsystem
were titanium gas tank and metal liner with composite wrapping. Under the same
pressure and volume, the mass of composite wrapped gas tank was lighter. The main
failure mode was leaking mode prior to burst, so it was safer than metal gas tank.
Along with the development of carbon fiber materials, wrapping technology and
non-destructive examination method, composite wrapped gas tank was developed
rapidly. The lightweight, large volume of high pressure gas tank was widely used in
propulsion subsystem. According to different structures of inside liner, composite
wrapped gas tank was classified into welded titanium alloy inside liner and seamless
aluminum alloy inside liner. The former one was easy to be welded with titanium
pipelines and has good sealing in connection. Due to weld seam and heat affected
zone vulnerable to failure in titanium inside liner, it was necessary to match the
deformation between inside liner and wrapped layer and specify high requirements
of welding process. The latter one was easy to be formed, manufactured with equal
strength design (especially for hemisphere-cylinder structure) with excellent fatigue
resistance. The disadvantage was that it cannot be welded with titanium pipelines,
so double-sealing screw thread connection was generally applied. For example, a
35 MPa and 100 L composite wrapped gas tank with seamless aluminum inside liner
for sealing pressurized gas and wrapped layer for bearing load of gas pressure was
used in propulsion subsystem of the Chang’E-3 lunar lander.
4. Attitude Control Thruster
Attitude control thruster was used for attitude control, stabilization, adjustment, orbit
correction, hover and translation during LTO, circumlunar and powered decent,
which was also used to deplete remnant propellant after landing. Generally the
specific impulse of attitude control thruster should be high and the thruster should
be stable in continuous firing for thousands of seconds or more, hundreds of thousands of pulse firing, and especially small pulse of 10~20 ms minimal duration. In
order to satisfy requirements of attitude control thruster, not only efficient internal
combustion and boundary film cooling was necessary for long term reliable work,
but also reducing filling volume of injector head and enhancing fast response of
valve was necessary to conduct short pulse. At the same time, because the number
of pulse was large, anti-jamming, anti-leak and anti-clogging should be emphasized
in thruster design. For example, for the 150 N thruster in propulsion subsystem of
the Chang’E-3 lunar lander, film and radiation cooling was applied. High temperature resistant niobium alloy sprayed with anti-oxidization coating is used for thruster
chamber cylinder part. Oxidizer and fuel valves were installed on the head of thrust