Fuel-Flexible Spacecraft Electric Propulsion System | STTR

OUSD (R&E) critical technology area(s): Space Technology

Objective: Develop a fuel-flexible spacecraft electric propulsion system capable of operating efficiently on air, water, or mixtures of water/carbon dioxide or nitrogen/hydrogen at >30% electrical efficiency.

ITAR: The technology within this topic may be restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 3.5 of the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

Description: Spacecraft electric propulsion (EP) systems typically rely on noble gas fuels (xenon, krypton, argon) stored in high pressure tanks. These fuels are unattractive for sustained ambient-air operation in very Low Earth Orbit (vLEO), or for liquid refueling operations in higher orbits using water or chemical rocket fuels as output propellants. Furthermore, thruster development to date has been highly specific to individual fuels, requiring costly development of entirely new systems for new propellants—for example, optimizing for air in a vLEO environment versus water in a possible future higher orbit refueling architecture. These dependencies limit total propulsive capability and overall mission flexibility and responsiveness.

This topic seeks a system able to operate on air (20-50% O2, balance N2), water (H2O), mixtures of water and carbon dioxide (CO2) derived from combusted hydrocarbons, or nitrogen-hydrogen mixtures derived from decomposed NH3 (ammonia) or N2H4 (hydrazine), using as much shared componentry as possible. Developing a flexible fuel EP system capable of accepting a variety of molecular propellants offers a unique capability for a single product line to serve a significantly larger mission space and total addressable market. This STTR topic seeks to develop a complete, integrated fuel-flexible propulsion system that bridges the gap between laboratory demonstration and fieldable spacecraft technology capable of utilizing in-situ resources.

Phase I

This topic is soliciting Direct to Phase II (DP2) proposals only. To qualify for this DP2 topic, applicants must provide concrete evidence of prior Phase I-equivalent capability. Specifically, the applicant must have demonstrated:

• Performance: >30% anode thruster efficiency on air or water.
• Durability: >100 hours of cumulative operation on a single test article on air or water demonstrated at the performance level above.
• Evidence Required: Vacuum thrust stand test data validating thrust, mass flow, power, efficiency and duration claims. Testing must have been conducted in a facility operating at a background pressure of < 3x10-5 Torr during full-power operation, using thrust stands calibrated in-situ.

Phase II

The Phase II effort will focus on developing a complete, integrated fuel-flexible propulsion system capable of operating across air, water, and nitrogen/hydrogen species. The product will undergo envelope qualification for vibration, shock, and thermal cycling.

The system components will include a fully integrated system including the thruster, power processing unit (PPU), flow control system, and a standardized bus control interface and protocol (e.g., RS485-based or similar) allowing demonstrated operation via the bus control.

The STTR research institution will lead the gas species-specific fundamental research to improve and extend efficient operation across all critical gas species. The STTR small business will focus on productization, system integration, and robustness.

Year 1/Base: System Design, Interface Definition, and Prototyping

• Month 1: Kickoff meeting presenting program schedule plans for Year 1
• Month 3:
  • Finalize system requirements
  • Review university-led research on performance using air, water, and chemical exhaust mixtures
  • Identify standard physical and fluidic interfaces to connect to external hydrocarbon and hydrazine chemical systems
• Month 6:
  • Review design for the integrated thruster system
  • University-led laboratory demonstration and technical report validating efficient performance transfer mechanisms across gas species (air, water, CO2, N2+H2)
  • Present conceptual design for gas generation/conversion mechanism(s) that will accept and regulate the hydrocarbon combustion and hydrazine decomposition feeds
• Month 9:
  • Engineering model prototype design complete for thruster and supporting systems
  • Presentation of final test plans
• Month 12:
  • Delivery of technical report on integrated engineering model prototype system design
  • o Delivery of technical report on vacuum test results for prototype hardware across all gas species, including functional demonstration of gas feed system(s)

Year 2/Option: Qualification, Life Testing, and Design Iteration

• Month 1: Kickoff meeting presenting program schedule plans for Year 1
• Month 3: Updated system design based on Year 1 test results, initial environmental testing (vibration, shock, thermal-vacuum), and other lessons learned
• Month 6: Written report on updated performance testing across all gas species
• Month 9:
  • Complete 200-hr short duration wear tests on all gas species, or minimal time to evaluate wear rate following thruster burn-in
  • Identify preferred gas species for 1000-hr wear test based on initial results and business case
• Final deliverables:
  • TRL 6 hardware including thruster head, flow systems and power processing unit
  • Final test report on system design, performance results including thrust, Isp and overall thruster efficiency, and summarizing completed 1,000-hour and 200-hour wear tests
  • Technology Transition & Spaceflight Integration Plan

Phase III dual use applications

Phase III efforts will focus on flight qualification, scaling, and transition to acquisition for operational spacecraft. The transition target is versatile use across:

1. vLEO satellites for air-breathing propulsion
2. Rideshare-compatible inert water-fueled satellites with no pressurant tanks required
3. Multimode propulsion systems capable of high specific impulse electric propulsion using:
   • a. combustion exhaust (H2O+CO2) from hydrocarbon-based chemical rocket fuels
   • b. decomposition exhaust (N2+H2) from hydrazine (N2H4) based chemical rocket fuels

Target military transition includes Space Development Agency (SDA) or DARPA vLEO constellations. Target commercial transition includes imagery, communication and satellite servicing vehicles, or deep-space In-Situ Resource Utilization (ISRU) architectures.

References

[1] J. L. Rovey, C. T. Lyne, A. J. Mundahl, N. Rasmont, M. S. Glascock, M. J. Wainwright, and S. P. Berg, "Review of chemical-electric multimode space propulsion," Progress in Aerospace Sciences, vol. 118, Art. no. 100627, 2020.

[2] R. Bendimerad, D. Savransky, and E. M. Petro, "Optimization of refueling strategies for electric propulsion space missions," Journal of Spacecraft and Rockets, 2024, doi: 10.2514/1.A36441.

[3] T. Andreussi et al., "A review of air-breathing electric propulsion: from mission studies to technology verification," Journal of Electric Propulsion, vol. 1, Art. no. 31, 2022.

Keywords

Spacecraft Propulsion, Hall Thruster, Fuel-Flexible, Air-Breathing, VLEO, In-Situ Resource Utilization, ISRU, Oxygenic Propellants, Multimode Propulsion

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