Rubicon Space Systems employees, from left to right, Daniel Cavender, propulsion director, Allison Lentz, propulsion engineer, Nathan Daniel, electrical systems engineer, and Mackenzie Kilcoin, propulsion systems engineer. Credit: Rubicon Space Systems

SAN FRANCISCO – Daniel Cavender has worked extensively with ASCENT, the non-toxic propellant developed by the Air Force Research Laboratory.

When ASCENT, short for Advanced Spacecraft Energetic Non-Toxic, was first flown on NASA’s Green Propellant Infusion Mission, Cavender was the assistant chief engineer for the NASA Technology Demonstration Missions program office overseeing the program. Cavender was also the project manager for the ASCENT-fueled propulsion system on NASA’s Lunar Flashlight, a cubesat designed to observe water ice deposits on the moon that failed to reach lunar orbit.

After leaving NASA last year, Cavender moved to the private sector to encourage the adoption of ASCENT.  Cavender is the director of Rubicon Space Systems, a division of Plasma Processes LLC, a Huntsville, Alabama, company that specializes in high-temperature materials. 

Lunar Flashlight experienced problems with its propulsion system. Do you know what happened?

I don’t want to get out in front of my NASA colleagues on this, but we are confident that the problem did not originate with the thrusters. We and NASA have reason to believe this was a Foreign Object Debris [FOD] issue, unfortunately. A cubesat sized chemical propulsion system has all the challenges that a large one does. And because it is so small, it is more sensitive to FOD. Because of the size constraints, we could not put filters everywhere. So, we relied heavily on precision cleaning, inspections and contamination controls. But there was a process slip at some point. We’ve seen examples in thruster testing of what FOD does to the valves or to a thruster. The data and behavior of Lunar Flashlight was right in line with what we’d seen from ground testing.

Aside from the problem, what can you say about the Lunar Flashlight propulsion system?

We developed that entire propulsion system from paper to product in 20 months during the COVID-19 pandemic. The whole team at the Marshall Space Flight Center, Jet Propulsion Laboratory and Georgia Tech gave so much of themselves to make it happen. Everyone involved was rightfully proud of the accomplishment. While Lunar Flashlight fell short of the moon, it still did a lot of ASCENT propulsion technology validation.

For Rubicon’s part, we were extremely proud of the thruster. It was originally qualified for .5 kilograms of throughput. We ended up doing a delta qualification to get it up to three kilograms. That is more than 17 hours of firing time. One pulse was 101 minutes long. Even though some of the Lunar Flashlight thrusters were not working well, they all worked well initially. One of the thrusters achieved over 10 hours of firing time, until it too was starved for fuel. To us, that was significant validation in space.

What brought you to Rubicon Space Systems?

Plasma Processes built the thrusters for Lunar Flashlight and did some other NASA and Air Force-related ASCENT thruster work. When they were bought by a private equity group, the board of directors asked me over to talk about the technology. I gave them the rundown because I was the NASA Green Propulsion Working Group chair. I laid out a strategy for how the company could build both ASCENT thrusters and propulsion systems.

They liked the vision and asked if I wanted to come over and make it happen. I thought, “I’ve spent five or six years trying to develop the technology, maybe I’ve got a chance here to go and actually try to infuse it too.” So, I left NASA, and we started Rubicon Space Systems, a division of Plasma Processes. We felt the name was necessary to distinguish it as a unique business unit from the rest of the company.

Even though we only have a handful of people that work in the propulsion division, we have reach back to a company with nearly 60 people. We build all the critical parts in house: the catalysts, the chambers, the injectors. We are not just focused on the thrusters, but also on the cubesat and small satellite propulsion systems that would use those thrusters.

Will ASCENT ever replace hydrazine?

No, I don’t believe it will. It is an alternative. We encourage everyone to look at their mission trades and do what is important for them. We know payload safety review panels look more favorably on lower hazard technologies. For some people ASCENT may be the difference between being able to get a ride-share opportunity. For others it may be about heritage or known high reliability. Good engineering must come first. I see cubesats and small satellites as being the way to continue to build ASCENT heritage over time because of the usually higher risk tolerance posture. Then, after we’ve got a good foothold in the market hopefully others will begin to take notice.

Is Rubicon selling ASCENT-fueled thrusters and propulsion systems?

Our team has achieved flight heritage on our 0.1N thruster, and we’re close to completing the first low-rate production run. We have orders for one-newton and five-newton thrusters with government customers for deliveries beginning in the first quarter of 2024. We just sold our first propulsion system as well, which is exciting. We are developing larger propulsion systems, and a new 110-newton thruster. There definitely is an appetite in the market for ASCENT propulsion.

Debra Werner is a correspondent for SpaceNews based in San Francisco. Debra earned a bachelor’s degree in communications from the University of California, Berkeley, and a master’s degree in Journalism from Northwestern University. She...