Water turns into plasma then propels spacecraft sounds like science fiction — until you talk to Rob Schwarz, CTO of Momentus. We sit down with Rob to unpack how a microwave electrothermal thruster heats steam, creates a plasma, and pushes it through a nozzle for efficient in-space propulsion, all while avoiding the electrode erosion that limits many electric thrusters.

It's also our chance to ask questions about space dynamics, which Rob patiently answers.

We zoom out to the business and mission reality of modern spaceflight: small satellites keep getting cheaper, but big rockets and rideshare launches still dominate the cost curve. That’s where an orbital transfer vehicle, the classic space tug idea, promises a “stage four” that can distribute payloads to their operational orbits without forcing every satellite to haul lifetime fuel. Rob explains the staging logic, the refueling problem, and why transfer demand has grown slower than many expected.

We talk about Momentus’ modular Vigoride spacecraft, thermal control challenges, and why in-space manufacturing experiments like advanced semiconductor crystal growth may benefit from microgravity’s reduced buoyancy-driven separation. We also tackle the big question people always ask about electric propulsion: why not nuclear, and what the radiator and engineering trade-offs look like in practice.