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How Phase Four Is Simplifying Electric Propulsion To Propel The Space Economy

Umair Siddiqui
  • CTO
    Umair Siddiqui
  • Compact electric propulsion for space
  • Focus
  • 🌍
  • Employees
  • 11-50
  • Country
  • Founded
  • 2015

Tell us your background and about Phase Four

I’ve always been obsessed space. I credit my parents, who bought me a book on space when I was three, not knowing that years later, in high school, the New York Times would publish one of my opinion pieces on human space exploration. Human space exploration is “a large-scale research experiment, with results … more extraordinary than the modern mind can fathom,” I insisted, targeting peak Flesch-Kincaid score.

So in college, I tried to practice what I’d preached. I started working with Dartmouth professor Kristina Lynch on plasmas in near space. Lynch asked big questions like “how does plasma from the Sun impact space weather and the Earth?” Understandably, I’d like to think, I got really into plasma, and that led me to my PhD in plasma physics at the University of Wisconsin.

Human space exploration is a large-scale research experiment, with results … more extraordinary than the modern mind can fathom.

Phase Four is an in-space propulsion company. We develop small, simple plasma engines for spacecraft. This year, we’re delivering our first product, a turn-key electric propulsion system for small satellites, called Maxwell.

Maxwell: a plug-and-play system that includes thruster, power electronics, propellant, and propellant management.

We’ve received a DARPA grant and raised seed funding, which has gone into building a world-class team and a testing and design facility in El Segundo, California. We have a full machine shop and multiple vacuum chambers to enable rapid prototyping and testing. We’ve also signed several commercial contracts.

How did the idea for Phase Four come about and what was it like getting started?

In grad school, my research in plasma physics was funded by the Department of Energy’s fusion energy program, so I looked at one major issue confronting researchers and engineers in the field: hot plasma erodes the walls of fusion reactors and other plasma devices. I started by examining the interactions of plasmas with materials under a number of conditions.

Remember three year old Umair? My obsession with space and plasma meant I knew all about Hall thrusters and their various pain points. The Cold War-era Hall thruster, despite being fifty-year-old technology, is considered the gold standard in electric propulsion for satellites. They suffered from many of the same issues engineers were seeing in the walls of fusion reactors: they are eroded by high-energy ions--by the very plasma that Hall thrusters eject to generate thrust.

Could we build a simpler thruster?

Umair inspects a test setup in a large vacuum chamber
Those first few months were full of floor plans and measuring tape.

When we won our DARPA grant and secured seed funding, my top priority was building out our lab in El Segundo. Relying on outside testing facilities would mean a significant slowdown in our tech progress, and we needed to be able rapidly prototype and test in-house to meet the terms of our DARPA agreement.

Those first few months were full of floor plans and measuring tape. I was mapping out our power, water, and floor space needs for a machine shop, an electrical engineering workspace, and a vacuum facility.

How did you fund the company initially?

Phase Four was awarded $1 million DARPA seedling grant, which took us from the propulsion lab at Michigan to a fully flight-qualified thruster for cube-sats. That initial grant, plus seed funding we raised, took our RF thruster through thermal testing and vibe.

Why is the problem you are solving important and how does it help human space exploration?

You might be familiar with electric propulsion from Star Trek or other futuristic sci-fi shows, but the electric propulsion that many spacecraft today use—the Hall thruster—is technology from the 1950s. While Hall thrusters are great for the traditional space operations (i.e. launch one huge, expensive satellite), they’re ill-suited to large constellations and low cost propellants due to their complexity and their reliance on failure-prone components, like hollow cathodes and high voltage electronics.

Chris Cretel, a Phase Four propulsion engineer, runs a test firing in a large vacuum chamber

Our propulsion system is designed for the future of space: one moving toward mega-constellations and in-situ resource use. Phase Four’s RF thruster engineers the hollow cathode out of the equation entirely. It’s simple. Manufacturing is easily scaled up to mega-constellation demand. Without an easily manufactured engine, the next generation of internet mega-constellations will be massively delayed—and some will fail. The UN has declared internet access—access to information—to be a basic human right. We will be the engine of that solution.

Without an easily manufactured engine, the next generation of internet mega-constellations will be massively delayed—and some will fail.

Beyond that, I envision our propulsion technology unlocking missions around the Moon and Mars. Remember the DeLorean in Back to the Future? You could put whatever you wanted into the car to power it – it was fuel agnostic. Our RF thruster is the only plasma thruster that is truly propellant agnostic. It can use a number of more-plentiful resources, like methane and water, as propellant. This means that spacecraft orbiting the Moon and Mars could be refueled in space. It also means costs for mega-constellation fuels can be orders of magnitude lower.

What are some achievements you're proud of?

My proudest achievements are building Phase Four’s RF thruster, and working with our team to build a company. Last summer, we successfully operated a prototype thruster at 480 watts and measured the highest thrust efficiency ever measured(by 40x!) in an RF thruster on a thrust stand in its power class. That was the day I knew our technology had a real future. That was the day I knew “existing”thruster technologies were now “the past”. That was the day I knew Phase Four is going to be alright.

Laura Overly, Phase Four's director of supply chain

What have been some of your biggest challenges? How did you overcome them?

Hiring, fundraising, and hardware development. Hiring is surprisingly challenging. Skills don’t necessarily translate to fit, and the people you want are usually happily employed furthering other dreams. Fundraising for hardware development is a challenge–aerospace hardware has different timelines and needs than traditional venture-backed software companies. Like hiring, you need to find the right VC partners who understand aerospace hardware. Persistence, bordering on lunacy.

Austin Prater, a Phase Four aerospace engineer

One challenge Phase Four has had success overcoming is finding product-market fit, which I think is no small feat for any company. While we initially set out to simplify electric propulsion to enable cubesats, we've since spent a lot of time talking to prospective customers to understand where the market for electric propulsion is heading. Those conversations and constant feedback help us design a product that targets smallsats. We're going where the market is going, as opposed to where it's been.

When your team works together and trusts each other, you can achieve amazing things

What are exciting milestones coming up for Phase Four?

Delivering flight hardware to commercial customers, and demonstrating some game-changing applications of our tech. Stay tuned…

Longer term, we’re optimizing our engine from every angle. Our ultimate goal is to upend and replace legacy electric propulsion systems. There should be no reason to ever fly expensive, failure-prone technology for plasma propulsion.

What advice do you have for aspiring space entrepreneurs?

For me, the biggest lesson I’ve learned is to prioritize people. When your team works together and trusts each other, you can achieve amazing things. Do right by the team you build and the customers you work with.

Doing right by your team means a lot of listening. Listen to your customers, your investors, your mentors, your advocates. Get feedback as you're developing your product. Rapid tech development doesn't happen in a vacuum. Except when it does; see thruster testing in our large vacuum chamber:

How can the public support you with your mission?

We’re always hiring—check out our open positions at

Lastly, where can people find out more about Phase Four and follow along?

Keep up with us on Twitter at @phasefourplasma. Tune in to our science podcast, P4 What For?, on Spotify, Stitcher, Apple Podcasts, and Google Play.