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Tanks for Electric Propulsion Systems

Writer's picture: Dr. C. V. S. KiranDr. C. V. S. Kiran

Tanks are indispensable for modern spacecraft equipped with electric propulsion systems for storing Propellants. They not only enhance mission efficiency and longevity but also enable ambitious exploration goals such as interplanetary missions and space sustainability initiatives. Their continued development is vital to the future of space exploration and satellite technology.

Xenon tanks are critical for modern spacecraft, particularly those using electric propulsion systems like ion and Hall-effect thrusters, enabling high-efficiency, long-duration missions. They store xenon at high pressures, providing a steady, regulated supply for precise maneuvers such as station-keeping, orbital transfers, and interplanetary travel. Compact and robust, these tanks play a vital role in reducing fuel consumption, extending mission lifespans, and supporting space sustainability efforts like collision avoidance and deorbiting. As key components in geostationary satellites, space tugs, and satellite constellations, xenon tanks are indispensable for advancing space exploration and commercial satellite operations.

Key Applications of Xenon Tanks in Space

  1. Station-Keeping in Geostationary Satellites

    • Maintaining precise orbital positions for communication satellites.

    • Extending operational lifespans through efficient use of xenon propellant.

  2. Interplanetary Missions

    • Missions like NASA’s Dawn spacecraft (Ceres and Vesta exploration), BepiColombo (ESA-JAXA), Starlink Satellites (SpaceX) rely on xenon tanks for electric propulsion systems that operate over several years.

  3. Satellite Constellations

    • Xenon tanks are critical for collision avoidance and orbit adjustments in low-Earth orbit constellations like Starlink and OneWeb.

  4. Space Tug Missions

    • Orbital transfer vehicles (OTVs) use xenon-based propulsion systems for satellite repositioning, repair and deorbiting.

  5. Deorbiting End-of-Life Satellites

    • Xenon tanks support deorbiting thrusters to ensure space debris mitigation and compliance with space sustainability guidelines.

Key Parameters for sizing of tanks

  • Mission Type

    • Interplanetary missions require larger tanks to support high Δv\Delta vΔv.

    • LEO and MEO missions often use smaller tanks due to lower Δv\Delta vΔv requirements.

  • Storage Pressure:

    • Higher pressures (e.g., 15 MPa) reduce tank volume but increase structural requirements.

  • Thruster Efficiency:

    • Higher Isp (e.g., Hall-effect thrusters vs. ion thrusters) reduces xenon mass requirements, allowing smaller tanks.

  • Xenon Mass Requirement

  • Xenon Density

    • Xenon has a high density at storage pressures:

      • At 10 MPa (100 bar): ~730 kg/m3

      • At 15 MPa (150 bar): ~1100 kg/m3

  • Tank Volume

Challenges in Xenon Tank Design

  • Pressure Management: Storing xenon at high pressures (~100–200 bar) requires robust and lightweight tank materials like Ti-6Al-4V or composite overwrapped pressure vessels (COPVs).

  • Thermal Cycling: Tanks must withstand extreme temperature fluctuations in space (-150°C to +150°C).

  • Leak Prevention: Ensuring gas-tight seals and minimizing permeability are critical for long-term missions.

Artistic View of COPV Xenon Tanks

Composite Overwrapped Pressure Vessels (COPVs) are the next generation of lightweight, high-performance storage tanks designed for demanding space applications. By combining a metallic or polymeric liner for impermeability with a high-strength composite overwrap, such as carbon fiber-reinforced polymers, COPVs achieve exceptional strength-to-weight ratios. These tanks can withstand high pressures while significantly reducing mass compared to traditional all-metal designs, making them ideal for propellant storage, such as xenon for electric propulsion. Their lightweight nature enables enhanced payload capacities, extended mission durations and improved efficiency in satellite and spacecraft operations, marking a revolutionary advancement in propulsion and fuel storage technology.

For composite overwrapped pressure vessels (COPVs) storing xenon, the choice of liner material is critical to ensure impermeability, compatibility with xenon, and resistance to high-pressure conditions. Metallic liners are the preferred choice, with titanium alloy Ti-6Al-4V (Grade 5) being the most widely used due to its excellent strength-to-weight ratio, corrosion resistance, fatigue resistance and thermal stability. This titanium alloy is ideal for space applications, where extreme conditions like thermal cycling and radiation are common. For cost-sensitive or lower-pressure applications, aluminum liners offer a viable alternative. In certain cases, advanced options like metal-polymer hybrid liners or surface treatments can combine the benefits of metals and polymers. Titanium alloy liners remain the gold standard for their lightweight properties and proven performance in aerospace environments.

Future Trends in Xenon Tanks

  • Reusable Systems: Development of reusable spacecraft and orbital transfer vehicles increases the demand for reliable xenon storage systems.

  • Alternative Propellants: Research is ongoing into alternative noble gases (e.g., krypton) for cost reduction, but xenon remains the primary choice for high-performance missions.

  • Additive Manufacturing: Innovations like 3D-printed titanium tanks could reduce costs and lead times.

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