Propellant supply plays a significant role in a satellite’s operational life. Optimizing satellite design for longevity is a critical step before any mission. A high-performing solenoid valve can help conserve charged pressure and extend the life of a satellite by creating an active barrier between the tank and the rest of the feed system.

Satellite systems require highpressure tanks to store propellant and use it as needed. For those using a gas, pressure in the tank decreases with each use. The tank must be reliably sealed throughout the pressure range when the propellant is not used. The amount of propellant in the tank represents the life of the satellite. If the tank leaks, the satellite will soon be dead in space. Whether propelled by chemical or electrical means, satellites must compensate for the expected fluid loss due to leakage by increasing the volume carried into orbit. Ordinarily, this would require larger or higher-pressure tanks.

Propulsion Systems Table
Propulsion Systems
Chemical Propulsion Systems Cold-Gas, Warm-Gas, Monopropellant, and Bipropellant Systems.
Electric and Ion-Propulsion Systems Hall Effect, Electrothermal, Grided Ion, RF, Electrospray, and FEEP.

As higher pressures require thicker walls, traditional solutions may add considerable weight to the system, thereby increasing launch costs overall. If launch costs are capped, the mission life must be de-rated to account for any leakage that may occur throughout the life of the satellite. A better solution is to use a small, reliable solenoid valve with minimal leakage to act as a barrier between the tank and the rest of the system until flow is desired.

THE CHALLENGE: RELIABLE, HIGH PERFORMANCE BARRIER SOLENOID VALVES

Solenoid Valves Used in Satellites Must Withstand the Rigors of Launch and Last Through the Mission

Whether intended to operate in low earth (LEO), middle earth (MEO), or global earth orbit (GEO), the most volatile moment in the life of a satellite occurs before it is even turned on. A satellite experiences very high gravitational forces due to vibration during launch. While all components of the satellite must be able to survive these extreme conditions in order to perform their intended functions, a barrier valve must overcome an additional hurdle: staying closed.

The barrier valve is a critical component within a satellite that is designed to remain closed even in the most severe environments. A common application for this type of valve is in the gas feed system for Hall-effect thrusters (HET), which utilize propellants such as xenon and krypton to guide the satellite to orbit. Once there, any failure by the propulsion system could disable the satellite or greatly reduce its mission. A reliable, lightweight, and reusable solenoid valve can be utilized as a barrier or isolation valve to mitigate such failures.

KEY CONSIDERATIONS FOR BARRIER SOLENOID VALVES USED ON SATELLITES

When selecting a solenoid valve, an engineer must consider typical specifications such as flow capacity, temperature, and whether redundant coils are needed for added reliability within their system. For barrier solenoid valves used within satellite applications, the following factors should also be examined to account for unique environmental challenges:

  • Leakage — As the main function of a barrier valve is to prevent the flow of fluid from the tank until expressly needed, the ability to avoid unwanted leakage is an imperative selection requirement. A pyrotechnic valve can technically be used as a single-use alternative option to the barrier solenoid valve. While this valve provides zero leakage, it is a single-use product that cannot be closed once utilized.

  • Operating Pressure Range — A satellite tank is initially charged to a very high pressure. As propellant is used throughout the life of the satellite, this pressure gradually decreases until it is no longer great enough for the feed system to work. A barrier solenoid valve needs to be able to open, close, and maintain leak-tight performance throughout this pressure spectrum.

  • Life Cycle —Life cycle requirements of satellite barrier valves ranges from hundreds to hundreds of thousands of cycles under varying pressure conditions. To provide exceptional leakage performance through these cycles, the materials of a barrier valve must be chosen carefully.

  • Envelope — As with any payload launched into space, reducing weight reduces launch costs. Also, barrier solenoid valves must be mounted on the satellite, where space is limited. Therefore, special awareness should be given to envelope size and weight specifications. Some solenoid valves have large coils that extend out from their housing, increasing the size and weight. Moving the center of mass away from the manifold can negatively impact the valve’s performance in vibration.
  • Vibration — While satellites do not experience vibrational loads in orbit they can be exceedingly high during launch. The barrier solenoid valve must be designed to remain closed under these extreme levels of vibration. If it cannot, the fuel tank could deplete before the satellite ever reaches space. Vibration is often specified with a root mean-square acceleration (grms) value. System design engineers should ensure the force-margin of the solenoid valve (or the forces holding the valve closed divided by the forces trying to open the valve) are high enough to handle peak vibration, not just the average.

  • Power Draw — While power is readily available in space, a means of cooling is not. A barrier solenoid valve opens frequently (and, in some cases, for long periods of time). Maximizing efficiency and limiting power draw from this valve helps to limit the need for active cooling. A latching barrier valve could also be considered.

  • Fluid Compatibility — Inert gases are used for many electric and ion-based propulsion systems; reactive fluids are often used in chemical propulsion systems. Whether using hydrogen, oxygen, or more reactive propellants, care should be taken to ensure that all materials are compatible and handled appropriately.

  • Response Time — As nothing can happen until the barrier valve is open, response time (the time it takes for the barrier valve to open or close once commanded) can be a significant consideration. Delays in closing may cause wasted flow.

THE SOLUTION: ZERO LEAK PNEUMATIC SOLENOID VALVES

The Lee Company’s Zero Leak Pneumatic Solenoid Valves feature a polyimide shaft tip to ensure a leak tight seal as tight as 1×10-6 standard cubic centimeters per second (sccs) on Helium. These pneumatic solenoid valves draw upon the design elements of The Lee Company’s field-tested line of piloting solenoid valves, historically recognized for their use within aircraft, weapon, launch vehicle, and satellite systems.

Lightweight and efficient, the smallest package weighs less than 0.14 lbs (2.24 oz). Utilizing a direct acting design that does not require pressure assistance to open, the valve flows up to 200 SLPM of air at 200 psi differential (3000 psia tank pressure). The 60-Ohm solenoid coil requires less than 4.2 watts to open the valve.

The Lee MultiSeal® radically simplifies port layout of these valves, providing reduced machining costs and superior reliability over traditional sealing methods. The space and weight savings directly translate to reduced fuel costs. Low power requirements, wide operating temperature and pressure ranges, and material compatibility have made this configuration the ideal solution for a wide range satellite systems.

Features readily available for your testing:

  • Latching: By incorporating permanent magnets into the coil design, a dramatic reduction in overall power consumption can be achieved particularly when operating with extended “ON” periods. Unlike traditional designs that require continuous voltage to energize the valve from its natural state, a latching solenoid requires only a momentary pulse of less than a joule to switch to and remain in state.

  • Pressure Range: This design can accommodate pressures up to 10,000psi, more than enough to seal the highest pressure tanks used in satellite systems.

  • Life: Variants with reduced seat stresses have been qualified for over one million cycles.
  • Materials: A wide range of materials are available to ensure optimal compatibility with fluids in use.

  • Dual Coil: A redundant coil can be added to maximize the reliability of the solenoid.