Case Studies

A launch vehicle uses a turbopump that is driven by a hot gas turbine. Due to high levels of horsepower, RPM, flow rates and pressures in this system, specific design features, materials, and fabrication methods must be used to ensure high performance as well as space flight levels of reliability. For static sealing applications in this area, metal seals are used to prevent leakage of a fluid through a joint that has no relative motion of the mating surfaces.

There are a variety of satellites, each with a specific function and supporting a specific aspect of our daily life. It can be used to enhance navigation, GPS or internet communication; to monitor tides; or  to forecast weather. In order to link with each function, a satellite carries instrumentation that needs to operate for many years since maintenance is not possible on a satellite. Instrumentation also needs to be protected from the outside atmosphere, all of which are possibly detrimental, as well as internal corrosive fluids and substances that are carried by the satellite for its other functions (such as hypergolic fuels that power its thrusters).

What provides energy to satellites? A common answer is the sun! Most satellites are equipped with solar panels that convert solar energy into electricity to power the intricate systems onboard. These panels can achieve about 34% efficiency vs. the 15 to 20% from most commercial solar panels. When a satellite is launched on a rocket, the solar panel arrays are folded to stay within the space constraints of the payload section. When the satellite reaches its targeted position, the solar panels and antennas are deployed, producing a wingspan of 40 meters! Truly a feat of engineering design since the solar panels need to be compact for launching, expanding and optimum operation.

Launch vehicles are most often propelled using fluids with liquid oxygen being the most common oxidizer and fuel being liquid hydrogen or kerosene and most recently liquid methane. All these fluids (except kerosene) are commonly stored at cryogenic temperatures.

Sealing is critical when liquid oxygen or hydrogen are involved since they are easily ignitable. Any small amount of leakage can create a hazardous situation, which can lead to a potential explosion of the whole launch system. Leakage requirements are therefore quite stringent.

A critical part of a satellite is its structural subsystem, which is designed to survive launch loads and protect the operation of other subsystems. Structures are often classified into primary and secondary components, the latter includes struts and brackets that are used in different configurations as needed. Several satellite elements in static or relative movement are linked together by structural bracket connectors that are fixed securely to the satellite body. Similar to many “flying vehicles,” satellites are designed with materials as light and compact as possible, especially in small and nanosatellites.

In order to handle all the fluids used on a launch vehicle such as in the propulsion system, many different type of valves are installed that also require radial and dynamic seals. Some are poppet valves, which are unique due to the reciprocating movement of the shaft leaving the seal unsupported.  

As a flow control device, the valve allows the flow of pressurized fluid (liquid or gas) in one direction only. In normal operations, they are in shut-off position where sealing is secured by static seals that are designed to withstand any blowout.