If you’ve never heard about Stoke Space before you shouldn’t be so surprised, however, we promise you that, by the end of this article, you’re gonna ask yourself why you didn’t hear about them before. Let’s jump right into it…
Right now, in 2023, we’re just entering a new era of space exploration that is focused primarily on reusability, not just about the rockets but every asset needed to make space exploration a more affordable and sustainable endeavor. As we are preparing to do so, we must look back to understand and know the history that allowed us to be here today in this right situation, and why.
While doing so, it’s obvious that you’re gonna stumble onto the beginning of space exploration and the majestic ’60s: years where everything was possible, let’s just dream and be sure that those dreams are gonna become reality.
That kind of mindset and wishful thinking was part of one of the most known engineers and rocket designers ever: we’re talking about Philip Bono. Just to understand the guy, by looking at his work, we can easily say that some of his ideas would be futurist nowadays: the most important aspect that drove his work was reusability.
As we’re gonna learn in a bit, the work of Stoke Space looks extremely familiar with some of Bono’s crazy ideas but that is not to undermine it or suggest it’s just a copycat, instead, it’s the total opposite. They’re dreaming big, extremely big, and they wanna make reusability finally a reality.
Until today, nobody has ever tried to achieve full reusability for real, if we count out SpaceX that is still trying to prove its concept through the Starship rocket.
The future is today
If we want to understand where this startup came from we must take a step back a few years and understand the background of a couple of key figures: Andy Lapsa and Tom Feldman, co-founders of Stoke Space. Both engineers grew up in the last decade working for some of the most important aerospace companies in the United States: Blue Origin and SpaceX.
As they made their way up into leading key positions in the propulsions teams of some of the most important development engine programs underway (BE-3 and BE-4 engines), they started thinking about how to accelerate their contribution to the development of a rapidly reusable rocket.
Even though they shared the same key vision as company founder, Jeff Bezos, they thought they could move faster, and in 2019 they started working toward this dream goal: “Stoke Space” was born.
“We’re on a mission: It starts with 100% reusable rockets.”
It sounds like it’d be a phrase that James T. Kirk would pronounce, and that’s just awesome.
Most of the first year was spent hiring brilliant minds and increasing the team to help them figure out the best and fastest path toward the company’s goal: understanding how to make a rapidly reusable rocket.
They quickly decided to skip a common step that most small aerospace startups did in the past, that is to create a small vector as a testbed to learn the basics of flying, and then increase the challenge by stepping onto something more difficult.
While Andy Lapsa took the “easy” task of finding new investors – a task that turned out to be as difficult, if not more, than designing the rocket itself – the team has started lying down some key features that their future rocket called “Nova” had to have:
- Fully and rapidly reusable;
- Cheap and easy to operate;
- Little to no inspections needed between flights;
- Robust enough to withstand some failures during launch.
Nobody knows what a reusable second stage looks like, yet
As 2020 was coming to an end, the first round of investments ended up, allowing Stoke Space to look more confident toward the future, and so the engineering team hit the pedal to the metal of development. They decided to start from the most difficult part of their rocket’s second stage: the engine.
Traditionally, a second stage does have one or more engines optimized for the vacuum of space, that’s because all of them until today have been expended and not recovered. Usually, all parts of a rocket are designed to be as light as possible to increase payload capacity, and a vacuum engine with an extended nozzle doesn’t have to deal with Earth’s atmosphere. The first thing to do if you want to recover the second stage is to protect in some way that engine, or engines.
One way to protect it could be to surround the expansion chamber with a heat shield (like the Space Shuttle did) or envelop it into the rocket itself (like the Starship is doing). Instead, Stoke Space went onto the opposite path.
They decided to have a single engine but split the exhaust into a ring of 30 smaller expansion chambers, similar to having 30 smaller thrusters. That has a few benefits: those smaller expansion chambers during ascent merge into one single plume acting as one single engine, plus, being smaller, they’re easier to protect during reentry.
Let’s learn from past mistakes
The second but not less important challenge is protecting the entire vehicle from the high temperatures that will envelop it during the reentry phase. In comparison, the Space Shuttle tried a rapid and reusable heat shield and failed miserably: let’s just think that after every flight NASA’s technician could spend up to 30,000 hours in maintenance of those tiles.
SpaceX, with its Starship rocket, is trying a different approach: let’s just wait and see if they will be able to tackle this problem. Lapsa’s expertise in rocket engine technologies came in handy and thought: “Why not try a regenerative cooling heat shield?”
The bottom part of Nova’s second stage, made out of stainless steel like the rest of the rocket, will be cooled down by the flow of the supercooled propellant (hydrogen in their case). Considering the engine will be an expander cycle, they want to use the hot plasma that will hit the surface as an advantage: the hot temperature will heat the propellant, on the other side of the surface, that’s gonna expand and turn up the turbine allowing other fluids to flow, and so on.
Moreover, considering that the bottom of the rocket is the heaviest part, because of the engine compartment, placing the heat shield will allow the rocket to re-enter exactly like a capsule.
Must learn to hop before trying to fly
Let’s not hide the fact that Stoke Space still has a lot of road ahead, but they’re surely not afraid to pursue it. Starting in 2021, they have begun testing their engine concept by putting it under numerous tests, allowing them to verify if the scheme was the right one.
As we’ve anticipated before, to increase the performance of the rocket, they decided to use hydrogen as the primary fuel. Without a doubt, the chemical fuel with the highest performance margin on the market, unfortunately, comes with some important drawbacks: dealing with a fluid that needs to be cooled down at ~20 kelvin (or −253°C), and that’s not a joke, but that challenge doesn’t seem to be scaring them at all.
As they moved along with engine tests, it was clear that speed and rapid iterative design were the mantra of the company. Just a year later, on September 17, 2023, they tried successfully to hop their second prototype. A lot of things had to go right for that test: ground infrastructure, vehicle systems, team procedures, ecc…
There’s nothing trivial about what’s coming
As far as we can tell, everything went extremely smoothly. This marks an important step to finalize the design of the second stage and move forward, to concentrate even more on the rest of the rocket.
In fact, during Tim Dodd‘s (aka Everyday Astronaut) last year visit to the company’s factory and test site, co-founder Andy Lapsa glimpse that they want to design a first stage with a full-flow staged combustion engine that will run on liquid methane and oxygen. We still lack details about this aspect of the rocket, but we can’t wait to know more about it.
Godspeed Stoke Space Team, you’re rocking! Let’s make us all dream big about the future of aerospace.
*Article Cover Image: Stoke Space