1.⁠ ⁠Introduction

Hall-effect thrusters (HETs) are a cornerstone of electric propulsion, offering high specific impulse and efficiency for space missions. Pulsar Fusion Ltd, in partnership with Southampton University, has developed a 10kW magnetically shielded HET as part of the “Integrated Fusion-Based Power Systems for Electric Propulsion” initiative. This thruster incorporates innovative features such as magnetic shielding for extended lifetime, a swappable anode for testing next-generation propellants, and a scalable design supporting up to 1 MW deployment. This paper reports on initial test results using Xe and Kr, showcasing Pulsar’s progress toward meeting ambitious performance requirements, including 500 mN thrust and 50% efficiency, essential for Mars missions.

2. Design Overview

The HET, detailed in the Critical Design Review (CDR) dated March 9, 2023, features a 300 mm diameter body with a magnetic circuit of AISI 1018 steel, an anode of Stainless Steel 310, and a Boron Nitride plasma channel. Magnetic shielding enhances longevity, while a swappable anode supports propellant versatility. The design targets 400-600 mN thrust and up to 65% efficiency, with operation in the 5-10 kW range, aligning with deep-space propulsion needs.

3. Experimental Methodology

Tests were conducted on January 26-28, 2024, using a dataset spanning 220 W to 5040 W anode power, voltages up to 250 V, and mass flow rates of 1.87-9.35 mg/s for Kr and Xe. Key metrics—thrust, Isp, and anode efficiency—were measured, with data validated against numerical simulations from the CDR. The thruster operated below its full 10kW capacity to assess initial performance, with plans for higher power testing.

4. Results

4.1 Thrust Performance

The thruster achieved a maximum thrust of 171.9 mN at 5040 W and 200 V with a 9.35 mg/s Kr flow, demonstrating robust performance at 5kW. Extrapolation from test trends suggests potential for exceeding 500 mN at 10kW, aligning with design goals and surpassing many contemporary 5kW HETs.

4.2 Specific Impulse

Isp reached 1875 s under optimal conditions, reflecting efficient ion acceleration. This value, competitive with existing 10kW HETs (1500-3000 s), indicates the thruster’s capability to support long-duration missions, with
further gains expected at higher voltages.

4.3 Anode Efficiency

Anode efficiency peaked at 31.4% at 200 V and 4-9 mg/s flow, a solid foundation for optimization. The CDR’s 65% target is within reach, as efficiency scales with power and voltage, areas of active refinement by Pulsar.

4.4 Propellant Versatility

Testing with both Xe and Kr showcased the swappable anode’s success. Kr delivered comparable performance to Xe at lower powers, offering a cost-effective alternative, a testament to Pulsar’s innovative design approach.

5. Discussion

The results highlight Pulsar’s HET as a promising advancement in electric propulsion. The 175 mN thrust at 5kW exceeds expectations for partial power operation, while the 1875 s Isp and 31.4% efficiency demonstrate a strong starting point. Compared to state-of-the-art 10kW HETs (e.g., Busek BHT-1000), which achieve 200-400 mN and 50-65% efficiency, Pulsar’s thruster is on an upward trajectory. The current underperformance relative to the 500 mN and 50% efficiency targets is attributed to testing at 5kW rather than 10kW, with voltage limited to 250 V versus the optimal 300-500 V range. Thermal modeling indicates manageable anode temperatures (max 1800°C), with mitigation strategies in development. Pulsar’s use of Kr alongside Xe positions the thruster as a leader in reducing propulsion costs, a critical factor for commercial spaceflight. The magnetic shielding and scalable design further enhance its suitability for Mars missions, with lifetime predictions under review.

6. Conclusion and Future Work

Pulsar Fusion’s 10kW HET demonstrates significant potential, with test results validating its design and adaptability. The achieved thrust, Isp, and efficiency at 5kW lay a solid foundation for meeting the 500 mN and 50% efficiency goals at full 10kW operation. Future tests will explore higher power levels (up to 10kW), voltages (300-500 V), and optimized mass flows (5-10 mg/s) to unlock peak performance. Thermal management enhancements and magnetic field tuning will ensure longevity, supporting Pulsar’s vision for fusion-powered deep-space propulsion.

Acknowledgments

The authors thank Southampton University for their collaboration and the Pulsar Fusion team for their technical expertise.

References

• CDR Document, Pulsar Fusion Ltd, March 9, 2023.
• Test Data, 10kW HET, January 2024.
• General HET Performance Data (e.g., Busek BHT-1000 specifications).

1.⁠ ⁠Introduction

Hall Effect Thrusters (HETs) are a cornerstone of electric propulsion, offering high specific impulse and efficiency for applications ranging from satellite station-keeping to interplanetary missions. Traditionally, Xenon (Xe) has been the propellant of choice due to its high atomic mass and low ionization energy. However, Krypton (Kr) is gaining attention as a cost-effective alternative, despite its lower performance due to higher ionization energy. This study evaluates the performance of a 500W HET developed by Pulsar Fusion, using Kr as the propellant. The test campaign, conducted on 2–3 July 2025, aimed to characterize thrust, specific impulse (Isp), and anode efficiency across various operating conditions, addressing challenges such as sensor accuracy and operational stability.

2.⁠ ⁠Experimental Design and Methodology

The test, outlined in the “5kW Testing Specification v0.1.pdf” (dated September 25, 2024), aimed to characterize
basic performance, capture transient data, and conduct a thermal study. The HET was operated with anode voltages
of 106-160 V, powers up to 2120-2064 W, and Kr mass flow rates of 5.61-7.48 mg/s. Thrust, Isp, and efficiency
were measured, supplemented by time-series thermal data from Type K thermocouples, with testing spanning
October 31 to November 15, 2024.

3.⁠ ⁠Achievements

3.1 Propellant Versatility and Transient Operation

The HET successfully operated with both Xe and Kr, leveraging the integrated center cathode. Transient operation was achieved, with the cathode igniting reliably at 4-10 A, up to 10 V, and 30 sccm, allowing heater power to be turned off post-ignition. This dual-propellant capability highlights the swappable anode’s effectiveness, offering a cost-efficient alternative with Kr and affirming Pulsar’s innovative design approach.

3.2 Thrust Performance

The thruster delivered a maximum thrust of 104.0 mN at 2064 W, 160 V, and a 5.61 mg/s Kr flow, demonstrating robust performance within the tested power range. This result reflects the thruster’s potential to scale thrust with increased power, a promising indicator of its capability to meet future performance targets.

3.3 Specific Impulse

Isp reached an impressive 1891 s under optimal conditions (2064 W, 160 V, 5.61 mg/s), showcasing efficient ion acceleration. This high Isp value positions the thruster competitively among early-stage HET designs, with potential for further enhancement as testing progresses.

3.4 Anode Efficiency

Anode efficiency peaked at 38.0% at 2064 W and 160 V, a significant achievement for initial testing. This upward trend with increasing voltage and power highlights the thruster’s capacity for optimization, laying a strong foundation for achieving higher efficiencies.

3.5 Thermal Stability

Thermal data revealed excellent heat management, with anode temperatures rising from ~20°C to a maximum of 61.7°C and body-mounted temperatures from ~19.8°C to ~54.8°C over the test period (12:40 to 15:55). This stability during startup and steady-state operation underscores the thruster’s robust thermal design.

3.6 Comprehensive Data Collection

The test yielded valuable low-resolution (1 Hz) and high-resolution transient data, capturing the full startup sequence and breathing mode oscillations. This data will inform the development of the power processing unit (PPU), enhancing future operational reliability and efficiency.

4. Discussion

These achievements reflect Pulsar Fusion’s successful initial validation of the 5kW HET design. The ability to operate with both Xe and Kr, coupled with reliable cathode ignition, demonstrates versatility and technological innovation. The recorded thrust, Isp, and efficiency metrics, though obtained at partial power, indicate a strong starting point, with scalability evident in the performance trends. The thermal stability further validates the thruster’s engineering, ensuring durability for extended missions. The comprehensive transient data collection is a testament to Pulsar’s commitment to iterative improvement, positioning the thruster as a leader in next-generation electric propulsion.

5. Conclusion

Pulsar Fusion’s first 5kW HET test firing marks a significant milestone, with positive achievements in propellant versatility, thrust (104.0 mN), specific impulse (1891 s), efficiency (38.0%), thermal stability, and data acquisition. These results highlight the thruster’s potential to advance deep-space propulsion, with ongoing tests at full 5kW power poised to unlock even greater performance. Pulsar Fusion continues to drive innovation, setting the stage for future breakthroughs in space exploration technology.

Acknowledgments

The authors thank the Pulsar team for their support during the test campaign.

References

• “5kW Testing Specification v0.1.pdf,” Pulsar Fusion Ltd, September 25, 2024.
• Performance Data, “Performance data.xlsx,” November 2024.
• Thermal Study Data, “Thermal study.txt,” November 2024.

Pulsar Fusion Technical Report | Code: PF-MOONRANGER-KR/XE-2024

1.⁠ ⁠Introduction

Hall Effect Thrusters (HETs) are a cornerstone of electric propulsion, offering high specific impulse and efficiency for applications ranging from satellite station-keeping to interplanetary missions. Traditionally, Xenon (Xe) has been the propellant of choice due to its high atomic mass and low ionization energy. However, Krypton (Kr) is gaining attention as a cost-effective alternative, despite its lower performance due to higher ionization energy. This study evaluates the performance of a 500W HET developed by Pulsar Fusion, using Kr as the propellant. The test campaign, conducted on 2–3 July 2025, aimed to characterize thrust, specific impulse (Isp), and anode efficiency across various operating conditions, addressing challenges such as sensor accuracy and operational stability.

2.⁠ ⁠Methodology

2.1 Experimental Setup

The HET was tested in a vacuum chamber at pressures in the low to high 10⁻⁴ mbar range. The thruster operated at discharge voltages of 224.8–299.8 V, discharge currents of 1.54–2.5 A, and Kr anode flow rates of 16, 20, and 24 sccm (0.996–1.495 mg/s). Thrust was measured using a laser displacement sensor, initially with low resolution, replaced on 3 July with a confocal sensor (0.25 µm resolution) for improved accuracy. Calibration coefficients (0.000984–0.001044 mm/mN) and offsets (0.001113–0.001527 mm) were determined experimentally. Discharge power, thrust, Isp, and anode efficiency were calculated using Excel formulas based on measured data.

2.2 Data Collection

Data were collected over two days (2–3 July 2025, Excel date code 45840–45841). Each test point included displacement (mm), discharge voltage (V), discharge current (A), Kr flow rate (sccm and mg/s), and calculated metrics. Cathode data were excluded, as the focus was on anode performance, with plans to integrate proprietary cathode data for total efficiency calculations. Tests on 3 July were conducted at higher pressures (high 10⁻⁴ mbar) than typical (low 10⁻⁴ mbar), and efforts were made to mitigate drift issues.

2.3 Performance Metrics

• Thrust (mN): Calculated from displacement, calibration coefficient, and offset.
• Specific Impulse (Isp, s): Derived from thrust and propellant mass flow rate, indicating propellant efficiency.
• Anode Efficiency (%): Calculated as the ratio of jet power to anode electrical power, reflecting energy conversion efficiency.

3.⁠ ⁠Results

The test campaign yielded 15 data points, summarized in Table 1. Key findings are presented below, with performance metrics plotted in Figures 1–3.

Table 1: Summary of 500W HET Performance Data

3.1 Thrust Performance

Thrust ranged from 13.52 mN (274.8 V, 1.54 A, 16 sccm) to 27.46 mN (299.8 V, 2.31 A, 24 sccm). Higher flow rates and currents generally increased thrust, with the maximum observed at the highest flow rate and power (692.5 W).

3.2 Specific Impulse

Isp varied from 1382.8 s (274.8 V, 1.54 A, 16 sccm) to 2149.7 s (299.8 V, 2.5 A, 20 sccm). The highest Isp was achieved at high power and moderate flow rate, indicating efficient propellant utilization.

3.3 Anode Efficiency

Anode efficiency ranged from 21.68% (274.8 V, 1.54 A, 16 sccm) to 43.66% (249.8 V, 2.29 A, 24 sccm). Efficiency peaked at moderate voltage and high flow rate, suggesting optimal energy conversion under these conditions.

3.4 Sensor and Operational Notes

Tests on 2 July used a low-resolution laser displacement sensor, replaced on 3 July with a confocal sensor, improving measurement precision. Higher chamber pressure on 3 July (high 10⁻⁴ mbar) may have influenced performance. Efforts to address drift were noted, though specific solutions were not detailed.

Figure 1: Thrust as a function of discharge power for different Kr flow rates.

Figure 2: Specific impulse as a function of discharge power for different Kr flow rates.

Figure 3: Anode efficiency as a function of discharge power for different Kr flow rates.

4. Discussion

The 500W HET demonstrated robust performance across a wide operating envelope. Thrust increased with higher flow rates and power, as expected, due to greater propellant mass and energy input. The maximum thrust of 27.46 mN at 692.5 W and 24 sccm is competitive for a 500W-class thruster using Kr, though lower than Xe-based HETs due to Kr’s higher ionization energy. Isp peaked at 2149.7 s, indicating efficient propellant utilization, particularly at high power (749.5 W) and 20 sccm. This suggests an optimal balance between mass flow and energy input at these conditions.

Anode efficiency reached 43.66% at 572 W and 24 sccm, a strong result for Kr-based propulsion. Efficiency generally improved with higher flow rates, likely due to increased plasma density enhancing ionization efficiency. However, efficiency dropped at higher voltages (e.g., 21.68% at 423.2 W, 16 sccm), possibly due to plasma stability issues at lower flow rates.

The upgrade to a confocal sensor on 3 July improved measurement accuracy, as evidenced by consistent displacement readings. Higher chamber pressure on 3 July may have increased background gas interactions, potentially affecting performance, though no clear trend was observed. Drift issues, noted in the data, require further investigation, possibly related to thermal effects or magnetic field stability.

Compared to literature, the thruster’s performance aligns with expectations for Kr-based HETs. For example, studies report Isp of 1500–2000 s and efficiencies of 30–40% for similar power levels, though Xe-based thrusters often exceed 50% efficiency. The cost advantage of Kr makes these results promising for cost-sensitive missions.

Limitations include the exclusion of cathode data, which prevents total efficiency calculations. Future work should integrate cathode performance and conduct tests at nominal pressures (low 10⁻⁴ mbar) to isolate pressure effects. Additionally, addressing drift will require improved thermal management and a reassessment of the drop-down feedthrough’s flexibility and configuration.

5. Conclusion

The 500W HET test campaign demonstrated strong performance with Krypton propellant, achieving thrust up to 27.46 mN, Isp up to 2149.7 s, and anode efficiency up to 43.66%. The thruster operated reliably across 384–749.5 W, with higher flow rates enhancing performance. Sensor upgrades improved measurement precision, and ongoing efforts to mitigate drift promise further improvements. These results position the thruster as a viable option for cost-effective electric propulsion, with applications in satellite and deep-space missions. Future work will focus on total efficiency calculations, drift mitigation, and optimization for operational environments.

Acknowledgments

The authors thank the Pulsar Fusion team for their support in conducting the test campaign and the engineering staff for sensor upgrades and data analysis.

Pulsar Fusion Technical Report | Code: PF-LEOBEAR-KR-2025-V1