Startup StokeSpace has successfully completed a 15-second vertical launch/vertical landing test of its Hopper VTVL reusable rocket, which is capable of reentering the atmosphere and landing after serving as the launch vehicle's second stage. Over the past few decades, orbital launch vehicles have undergone a number of redesigns. Where rockets used to be considered throwaway machines, today they are becoming more complex, reusable systems that both reduce costs and expand capabilities.
On September 17, 2023, Stoke Space conducted a Hopper 2 test at the Moses Lake base in Washington State. The Hopper prototype rocket was only 30 feet (9 meters) above the ground and the flight time was only 15 seconds. This may seem like a piece of cake, but its purpose is to demonstrate a range of advanced systems for future second-stage rockets.
One of the systems is a hydrogen/oxygen rocket engine. Judging from the published pictures, "Hopper" has a cone-shaped part at the bottom with a ring of thrusters around it. This seems to be a variant of "Aerospike". The curve of the tapered portion is like half the cross-section of a rocket bell, which contains the escaping gases. The air around the cone is like the other half. When the rocket rises, changes in ambient air pressure will cause the pneumatic thruster to automatically adjust the cross-section of the bell mouth to improve efficiency and
Another advantage of toroidal thrusters is that attitude control can be achieved by individually throttling the thrusters.
The flight also included the first test of a regenerative cooling heat shield, which will be needed if the rocket is to return to the atmosphere from orbit and then land, according to Stoke. Until now, heat shields have used either ceramic tiles or ablative phenol plastic covers. Ceramic tiles absorb heat but release it more slowly, while plastic covers remove heat as it burns. In regenerative cooling, rocket fuel circulates behind the shield, removing heat before the fuel enters the thruster.
Stork claims that when its rocket is put into service, it will be 100% reusable, with a 24-hour turnaround period.