Stoke Space is a well-funded startup space company from Kent, Washington working on the design of a fully reusable orbital rocket. Their proposed design is two stages to orbit with both stages fully reusable. More on that in a moment, but the purpose of this post is to link to their test flight yesterday, Sept. 14 on X. Just like when SpaceX launched Starhopper (video) - now more widely known as Hoppy - it was a test of several key concepts and a lot of design work.
Stoke Space announced they completed a short hop at their test facility in Moses Lake, Washington and said all goals were achieved. Like Starhopper was a concept test platform for Starship, the upper stage of the Starship/Super Heavy system, this test was the upper stage of their planned rocket.
During this test, known as Hopper2, we were able to successfully launch the Hopper test vehicle to an altitude of 30 feet and land at its planned landing zone following 15 seconds of flight. The test successfully demonstrated our novel hydrogen/oxygen engine, regeneratively cooled heat shield, and differential throttle thrust vector control system, as well as our avionics, software, and ground systems.
This test was the last test in our Hopper technology demonstration program. We successfully completed all of the planned objectives. We’ve also proven that our novel approach to robust and rapidly reusable space vehicles is technically sound, and we’ve obtained an incredible amount of data that will enable us to confidently evolve the vehicle design from a technology demonstrator to a reliable reusable space vehicle.
The first paragraph of that quote references the fundamental difference between their upper stage and everything else that's flying. This is a photo of the second stage from a different test, that you may have seen before.
The difference jumps out at you. Every other vehicle out there has
engines that are gimballed to steer the vehicle - thrust vector control is
achieved by changing the direction the engines are pointed. The engines are bigger and their large engine bells cover the entire area of the base, or close to it. Stoke, on
the other hand changes the thrust of the engines to change the direction of
the thrust vector. With the engines being farther from the center of the stage, the engines have more leverage and it makes room for their regeneratively cooled heat shield. The engines themselves are said to be conventional
liquid hydrogen and liquid oxygen engines with their nozzles implemented in that
one large circular structure. The control must be in feeding the fuel
and oxidizer to the engines
Andy Lapsa, chief executive of Stoke Space, said in an interview that the hop did allow for some additional testing, such as for position sensors. “It was the first opportunity to put every single component every single piece all together in the fully autonomous closed loop control system.” The flight was also a chance to look for “unknown unknowns,” or unforeseen issues that could be found only by flying the vehicle.
There were non-technical benefits to the hop as well, he added. “There is a very real emotional crescendo to a program like this to actually go and fly.”
Now that they feel the engineering choices made in the design of the second stage are correct and the second stage design work is complete, they've said it's time to move on to designing the first stage. The first stage will use methane/oxygen, like Starship, New Glenn and other newer vehicles. It will have seven engines. The whole rocket (which I can't find a name for) is relatively small lift vehicle; seven metric tons to low-Earth orbit.
Assuming SpaceX can get Starship operational, Stoke Space has an opportunity to become the second company to build a fully reusable rocket. No company has started with that singular goal for its first rocket.
Stoke Space's second stage, which they call Hopper, during Sunday's Hopper2 test. Photo credit: Stoke Space.