What do rocket launches and road trips have in common? For Hein Olthof and his co-founders at T-Minus Engineering, quite a lot. With a student-built rocket in the back, they drove 3,000 kilometers from Delft to Northern Sweden. What’s more, that rocket would go on to break the amateur altitude record. The road trip sparked a bigger question: could they turn their shared passion for rocket propulsion into something lasting?
Today, T-Minus Engineering is one of the few companies in Europe designing and launching rockets with solid-fuel propulsion systems. What began as a fun student project has evolved into a thriving aerospace business that supports clients across science, defense, and government sectors.
On a mars mission
Hein studied aerospace engineering at TU Delft, specializing in solid rocket propulsion. Together with Roel Eerkens, Mark Uitendaal, and Eric Smit, they founded T-Minus in 2011. Their goal was simple: keep building rockets and find a way to make them commercially viable.
Their early projects were modest, consisting of experimental launches, technical validation, and consultancy services. And over time, momentum grew, and the projects and customers continued to expand. For example, in one project, Hein and the team contributed significantly to the NASA InSight Mars mission, with the spacecraft still on Mars today.
These early assignments enabled the team to earn revenue. They allowed them to keep investing in their technology and company.
Building rockets to build a business
Another example is their DART product, a research rocket that reaches the edge of space and then returns to Earth. Its purpose is scientific. The rocket crosses the whole stretch of the atmosphere, up to 100 kilometers, collecting data on both ascent and descent. For context, most airplanes reach 10-12 kilometers. So, the DART goes ten times higher.
Meanwhile, T-Minus has launched missions all over the world. One of their rockets was launched in Australia during the COVID-19 pandemic. Despite a twelve-hour time zone difference, they relied on the internet to accompany the launch. The mission was a success. And, just a few months ago, they launched again in northern Sweden, under the lights of the north.
Those are the moments you remember. When air traffic over the Atlantic has to be rerouted because of your rocket, you know you’re doing something special.”
– Hein Olthof
YES!Delft and the early years
By the time T-Minus joined YES!Delft, they had already been in development for some years. What they needed was space — literally. They moved into a small office on the ground floor, just a few square meters. But what they gained was a place in a larger network of ambitious tech founders. YES!Delft gave them a platform to formalize their business plan and share their longer-term vision. They stayed in the building for nearly eight years before outgrowing it. Their current office is still nearby on Rotterdamseweg.
We weren’t the typical fast-scaling startup, but the YES!Delft team saw the value in what we were doing. Being part of the YES!Delft ecosystem enabled us to grow our network and our company.”
– Hein Olthof
What’s next
T-Minus continues to grow. Demand for their technology is increasing, and to meet this demand, the company is expanding its production capacity with a facility in Deventer, focusing on solid rocket propellants. It’s a complex and tightly regulated field, and T-Minus is one of the few companies in Europe operating at this level. At the same time, the team is developing new products for both space and defense. In Marknesse, they are looking for reinforcements. T-Minus is hiring engineers, technicians, and hands-on builders who want to help shape the next generation of propulsion systems. As Hein says in conclusion: “We’re a company that launches rockets. That comes with complexity but also with a kind of magic. And we’re just getting started.”
We’re a company that launches rockets. That comes with complexity but also with a kind of magic. And we’re just getting started.”–
Hein Olthof
