High Performance with Low Average Power

Phase Four’s Maxwell engines deliver high end plasma performance with novel high duty cycle operations

At the core of our Maxwell engine is the Radio-Frequency Thruster (RFT).? Phase Four has brought the RFT from lab concept to commercial on-orbit propulsion system in less than five years.? Five years may seem like a long time but when compared to other space propulsion technologies, many of which were developed during the Cold War, the RFT is still early in its evolution.? Phase Four’s engineering team is still exploring unique aspects of the RFT and how it’s starting to change how electric propulsion can be utilized on orbit by small satellite operators

We are currently carrying out a ‘stress test’ campaign with a Maxwell Block 1 engine in one of our facility’s vacuum chambers? This includes running at the highest power set point over a full propellant fill.? As part of this test campaign we are also operating the system at various duty cycles to demonstrate how robust the RFT is for ignition.? So far over 52 hours the system has undergone 5,000 ignition (on/off) cycles.? Maxwell is still running strong and showing no signs of being adversely affected by the stress test.? We are already sharing with customers how they can use their Maxwell engines on orbit in innovative ways in order to make their spacecraft more agile.?

Because we have developed a rapid and robust ignition mechanism for Maxwell, the system can be turned on and start to generate thrust in about 1 second.? It can also be shut off abruptly and turned on again when desired without any concern for over-stressing a particular element in the engine.? In real world terms this means a much lower power draw on a satellite bus over every orbit with the advantage of performance normally reserved for higher power plasma propulsion systems.? For example, a satellite operator could run a 400 W Maxwell Block 1 engine with a 42% duty cycle to achieve a 16 N-s total impulse maneuver over 100 minutes.? While the Maxwell engine delivers 6.6 mN thrust in this particular scenario, it only draws an average of 185 W. And unlike other plasma thrusters there is no in-rush current above steady state power draw levels.? Lower powered propulsion systems with steady state power draws of 120-140 W deliver much lower thrust and require significantly more time to complete a similar propulsive maneuver (over 200 minutes in some cases).

The take home for Maxwell engine operators is:

• The system is simple to ignite and can operate in a duty-cycled fashion (on/off cycles) without stress to the engine
• Duty-cycled operations require decreased average power during thruster firing
• The increased performance for small satellites means more rapid on orbit maneuvers such as orbit raising, station-keeping, phasing or formation flying
• And again, because Maxwell offers rapid, safe ignition, the thruster is always ready to be used for collision avoidance or other short lead time maneuvers?

As our Block 2 Maxwell enters production early next year, our customers will have access to an even higher performance engine with the unique advantages that the Radio-Frequency Thruster offers.? Also, watch this space as our Block 2 performance specifications are expected to be available soon (and we’re already seeing increased performance over initial estimates)!

About Phase Four

Phase Four is a disruptive provider of next generation electric propulsion (EP) solutions for small satellites. The company was founded in 2015 to address the demands of the rapid proliferation of satellite constellations and to accelerate the advancement of its radio-frequency thruster (RFT). The Phase Four RFT represents a revolutionary new architecture that realizes lower cost, mass-manufacturability, miniaturized power electronics, and propellant agnosticism over incumbent technologies, without compromising performance. In 2021 Phase Four’s Maxwell turn-key propulsion system achieved flight heritage and is now being regularly utilized by small satellite operators. Learn more at www.phasefour.io

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