Robert, Ryan, and Kirby Carlisle are three engineers who worked at SpaceX during the Falcon 9 era, seeing the revolution in the global launch industry from the inside.

The brothers launched rockets, refurbished rockets, and sold rockets. But when it came time for them to leave SpaceX and start their own space company—a lifetime dream for the Carlisle brothers—they chose not to build rockets. Rather, they focused on spacecraft.

In late 2022, the three Carlisles founded Argo Space to build infrastructure in space. Their vision was not just in-space transportation but also removing the need to use propellants from Earth to move around the heavens. They chose water, which is potentially harvestable on the Moon and found all over the Solar System, as a means of propulsion.

“We based the company on water,” Robert Carlisle said in an interview.

The availability of water is key to the company’s vision for building a transportation network between low-Earth orbit, geostationary orbit, and the Moon. This would open up a large number of affordable logistics options, such as satellite resupply, refueling, repair, redeployments, and more. And in the company’s vision, water is not just a propellant; it’s also a coolant and radiation shield. Much of the spacecraft, including its thrusters to the avionics, is cooled by water. This helps increase the propellant mass fraction of the spacecraft, meaning more mass is devoted to propellant, allowing the vehicle to go farther and do more things.

“In the long run, this water-based transportation will give us a commercial incentive, a profit motive to go harvest it from the Moon’s shallower gravity well,” Robert Carlisle said.

When even former SpaceXers can’t find a Falcon 9

Argo Space flew its first demonstration mission, dubbed Navigator, in July on a Falcon 9 rideshare. The company successfully made contact with the spacecraft, but one of its two rollout solar arrays failed to deploy. Controllers spent about half a day troubleshooting the issue and gathering data on the spacecraft’s health. Unfortunately, however, the spacecraft remained power-negative, draining its battery. There was not enough energy to test the propulsion system.

“We did get to validate the flight software, the ground software, the core avionics, the structures, and everything up to flight qualification, but no propulsion,” Robert Carlisle said. “So, you know, obviously that’s going to be a key goal on these next two missions.”

What are the next two missions? The company’s next-generation spacecraft, Chiron, is intended to pack high performance into a small, roughly 200-kg package.

The company plans two Chiron missions in 2027, both flying payloads for an undisclosed national security customer. The first mission is bound for low-Earth orbit, and the second to a geostationary transfer orbit. The goal across the two flights is to demonstrate Chiron’s propulsion system, including its ability to maneuver between different orbital environments.

It’s notable that the Carlisles spent much of their working lives at SpaceX to open up access to space with the Falcon 9 rocket, but neither of Argo’s next two missions will fly on a SpaceX vehicle. That’s because the company is pulling back on the commercial availability of the workhorse launch vehicle.

So Argo’s first Chiron mission is flying on an undisclosed new commercial rocket, definitely a calculated risk. And the second is going on an unspecified government-furnished launch vehicle. Argo Space probably would have preferred a rideshare on the Falcon 9 for its first Chiron mission, but one was not available within its schedule.

“We don’t want to be waiting around for another year and a half, two years plus to go get that ride,” Robert Carlisle said. “Right now you’ve got to get on a wait list, and it’s far out. There’s not launches available for sale.”

How does water actually work as a propellant?

Argo says it can achieve more than 2 km/s of delta-v in a roughly 200 kg spacecraft. That’s a lot of capability for a small vehicle, allowing it to do things like raise a circular orbit at about 400 km above the Earth’s surface to more than 5,000 km. It’s also equivalent to several decades of station-keeping in geostationary orbit.

The propulsion system is basically a small rocket that uses hydrogen and oxygen as propellants. However, instead of launching with separate tanks of liquid hydrogen and liquid oxygen, Chiron starts with liquid water. In space, the vehicle uses solar power to split water into hydrogen and oxygen gases and burns them to generate thrust.

Storing these propellants in their gaseous forms retains them in a less dense form but avoids the complexity of storage at cryogenic temperatures. However, the water itself can be stored as a relatively dense liquid at modest pressures until it is needed.

Electric-based propulsion is not new, of course. But Chiron takes a different approach, using electricity to split water and then a conventional rocket engine rather than ion thrusters. This provides more thrust than a conventional electric thruster with a similar amount of power.

Argonaut coming

This isn’t the first time water has been used as a propellant in space. In late 2017, two small satellites developed by NASA demonstrated a compact water-based propulsion system to maneuver in orbit. A commercial space company, Momentus, has used water propellant for in-space maneuvering as well.

But Argo is aiming to do this on a larger scale. After Chiron, the company is working on a vehicle called Argonaut, which has a maximum payload capacity of 1,400 kg and a maximum delta-v of 17 km/s per tank. This is a much more capable vehicle, and in September, Argo Space signed a deal with ispace to deliver ispace’s Lunar Connect communication relay satellite to lunar orbit later this decade. Argonaut could start to open up the lunar economy envisioned by Argo’s founders.

This is an awful lot for a company that has raised $20 million to date and has fewer than 30 people. But it helps that spacecraft are less capital-intensive to develop than rockets, said Kirby Carlisle, who, like a lot of SpaceX engineers, spent plenty of time in McGregor, Texas, working on rockets and engines. Argo can test most of its spacecraft systems in their facilities in El Segundo, California.

“I think something that people frequently kind of discount, or just forget about with rockets, is the enormous amount of ground infrastructure that you need,” Kirby Carlisle said. “We don’t need a McGregor, right?”