WASHINGTON – Stoke Space has tested a highly efficient engine it is developing for the first stage of its fully reusable launch vehicle.
The company, based in Kent, Washington, announced on June 11 that it had fired the engine briefly on June 5 at a test site in Moses Lake, Washington. The engine, designed to produce a maximum thrust of 100,000 pounds, increased to 50% of its rated thrust in the two-second test.
The purpose of the test was to see how the engine started and stopped, Stoke CEO Andy Lapsa said in an interview. “All the complexity and a lot of the risk is in the temporary startup and the temporary shutdown,” he said. “The duration of the test was short because the goal was to demonstrate the transient and then go back.”
The engine uses a design called full-flow staged combustion, in which both the engine’s fuel and oxidizer — liquefied natural gas and liquid oxygen, respectively — pass through separate preburners before entering the main combustion chamber. This approach offers greater efficiency and a longer engine life, but is more complex to develop. It is currently only used on SpaceX’s Raptor engines that power the Starship vehicle.
Lapsa said Stoke chose this approach because it was needed for rapidly reusable launch vehicles. “In a world of rapid reuse, you need high performance,” he said. “Full combustion gives you the highest possible performance under the least stressful conditions.”
Engine testing is currently focused on transient conditions during start-up and shutdown. The company is building a larger test facility that will be completed later this summer and will allow for longer duration testing, including a full qualification test campaign.
Stoke plans to use seven of the engines in the first phase of Nova, the fully reusable medium-lift launch vehicle it is developing. The upper stage uses a very different engine technology, with liquid oxygen and liquid hydrogen fueling an engine integrated into an actively cooled heat shield, allowing the upper stage to return for a powered landing. The company tested that system last September with a flight of a prototype “hopper”.
Lapsa said there is some similarity between the booster and higher stage engines in areas such as technology used in the engines’ turbomachinery, as well as analysis tools. “Furthermore, it is a completely new and different system.”
Stoke is making progress on other aspects of the vehicle. The engine tests used flight electronics and software, he said, and the company is conducting a “design iteration” on the upper stage. That work is being funded by a $100 million Series B round the company raised last October.
“In many ways all systems are in order and the last big question mark I felt on my shoulders was the first stage engine, and in particular getting the engine successfully through the transients and back,” he said.
Lapsa said after the hopper test last September that the company had an internal goal to begin orbital flight testing in 2025, with a desire to accelerate that schedule where possible. He declined to provide an updated schedule after this engine test, saying it depends on when the company can begin work at the vehicle launch site at Cape Canaveral’s Launch Complex 14, which the Space Force assigned to Stoke last year.
He noted that the test took place just 18 months after the company began designing the engine. “I think you’ll find over time that just as fully fast reusable rockets will make all others obsolete, I think over time these high-performing engines that make this mission possible will also make the lower-performing variants will make it redundant,” he said. . “I think it’s an essential technology mountain to climb, and I’m very excited to be on that mountain.”