Space startup Phase Four will be rolling out the next generation of its Maxwell radio-frequency plasma propulsion system next year, which the company says offers key performance improvements to allow spacecraft using it a wider range of maneuverability in orbit.

In general, when moving a satellite around in the vacuum of space, one cares about two key performance metrics: thrust and “specific impulse” (ISP), a measure of the system’s efficiency in how much thrust it provides per unit of propellant.

These trade-offs are especially salient for small spacecraft manufacturers. Systems with high thrust require carrying a lot of fuel – a costly choice for a satellite that could be the size of a mini-fridge. But propulsion tech that offers high ISP isn’t ideal either, especially if the satellite is heading to space in a rideshare mission and must reach its final orbit on its own. Often, traditional electric thrusters maximize specific impulse but at the expense of thrust – so while the thruster could be very efficient, maneuvers can take months.

Phase Four’s Maxwell thrusters have gotten rid of this trade-off, allowing customers to operate at a relatively high thrust mode or at a high ISP, explained CTO Umair Siddiqui. That means being able to perform both fast maneuvers when required or to enter a high ISP mode to save propellant.

The company introduced these innovations in its first product, the Maxwell Block 1 thruster. The new iteration of the Maxwell thruster, Maxwell Block 2, offers a performance improvement in these metrics of around 85%. “This is significant,” he said. “[An] 85% improvement in ISP or thrust means that much less propellant usage or that much less time you’re maneuvering in orbit.”

Phase Four’s Maxwell thrusters have a few other innovations as well. The traditional plasma thruster, called the Hall-effect thruster, generates thrust using cathode materials that are difficult to manufacture. The systems are also bulky, which isn’t ideal for many customers. To solve these problems, Phase Four’s thrusters use radio-frequency plasma sources, rather than a cathode and anode, to generate thrust. That means a smaller thruster that’s easier to manufacture and that can accept any gaseous propellant – not just expensive Hall-effect thruster propellants like xenon or krypton.

The aim is to maintain production runs of under four months for the Block 2, an approximate timeline that the company first hit with the Block 1 thruster. The ability to keep such a quick turnaround is due, in part, to the modular design of the products. The Maxwell engines use a “chassis” style that borrows, at least in philosophy, from the auto industry. “We can still use the same production line to fold in next generation developments, and that’s the requirement for the product,” Siddiqui said. “It’s a plasma thruster with manufacturability thought at the outset.”

The company, which was founded in 2015, has delivered ten Maxwell Block 1 systems to customers so far. This summer, Phase Four raised a $26 million Series B led by New Science Ventures LLC.

Originally published at

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