Aviation company Polaris Raumflugzeuge receives a contract from the German government Bundesamt für Ausrüstung, Informationstechnik und Nutzung der Bundeswehr (BAAINBw) (Federal Office of Equipment, Information Technology and Operational Support) to develop and fly the revolutionary Linear AeroSpike (LAS). ) engine that replaces the traditional rocket nozzle with a plug in the form of a curved wall.

Conventional rockets are easily recognized by their bell-shaped nozzles, which accelerate the ejection of hot gases from the combustion chamber. This is a highly successful design that has changed little over a century, but still leaves much to be desired, especially since chemical rockets are already operating close to their theoretical limits.

Alternatively, engineers have been considering LAS since the 1950s. Developed from older plug-in injector engines, the idea behind the aerospike engine is that it takes a regular rocket bell nozzle and cuts off one side.

The rocket bell nozzle works by accelerating the flow of gases, controlling their expansion. This is done using a bell geometry designed for a given ambient air pressure. This creates a problem because air pressure changes with altitude, meaning a rocket designed for sea level loses effectiveness as it climbs.

This is one of the reasons for multistage rockets. At high altitudes the auxiliary engine needs another rocket engine. Even if it is the same motor used for starting, the top stepper motor needs a different bell configuration to handle the pressure difference.

The Aerospike overcomes this problem by having one side of the pointed tip the same cross section as the bell nozzle and the other being open and having a series of combustion chambers at the top. As the hot gases leave the chambers, the pointed end contains one side, while the air pressure from the other side replaces the missing section of the bell.

If set correctly, the spike will be optimally adjusted to operate at sea level. As it goes up and air pressure drops, the virtual bell expands, maintaining engine efficiency. This gives engineers the opportunity to create an engine that is as efficient as a conventional engine to run from ground to space, but also simpler, smaller and lighter. This means more space and weight are freed up for more fuel and the ability to lift larger loads. It also means ships with higher altitude, range and Mach plus speed.

The problem is, it’s one thing to tinker with an aircraft engine in theory, it’s another thing to create it in practice. The biggest hurdle is that they generate huge amounts of heat, which requires new materials and cooling systems to work with, as well as 3D printing technology to make them.

However, that didn’t stop NASA from developing a successor version of the space shuttle X-33/VentureStar and testing a cold flow demonstrator behind the SR-71 Blackbird.

Under the new contract, Polaris is tasked with developing and launching the LAS engine that can be integrated into a scalable space demonstration aircraft that is larger and heavier than the company’s previous three vehicles. If successful, this will be the first time an aero thruster is operated in flight.