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German grant will give a lift

May 13, 2023


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An award from the German government's Bundesamt für Ausrüstung, Informationstechnik und Nutzung der Bundeswehr (BAAINBw) or Federal Office of Bundeswehr Equipment, Information Technology, and In-Service Support could see a Linear AeroSpike (LAS) rocket engine make its first flight test.

Rocket science has been regarded as something tough to understand. However, the going gets easy for those who have managed to crack it. In its initial years, Elon Musk's SpaceX recorded scores of failures, but once it got its bearings right, it managed to launch and even relaunch its rockets with a rapid turnaround.

This has been made possible as not much has changed in rocket design and execution over the years. The rocket nozzle design, for instance, has not changed in over 100 years. But Bremen-based Polaris wants to change the status quo and make the first flight of a LAS rocket engine.

A standard feature of all rockets is the bell-shaped nozzle that allows the gases from the combustion chamber to escape at an accelerated pace and generate thrust. The design of the nozzle has remained a constant feature of rockets for decades, limiting what rockets can do.

The issue is that the design works well at one ambient pressure, but as the rocket ascends, it becomes less efficient. To overcome this, scientists use multi-stage rockets so that different nozzles can be deployed to maximize efficiency.

One way to overcome the hassle of multi-stage rockets is using a Linear AeroSpike (LAS) engine. The concept has been around since the 1950s and has also been experimented with by NASA for its Space Shuttle successor, X-33/VentureStar and the SR-71 Blackbird.


At first glance, the LAS might look like a radically different design. However, a deeper look and one finds that it too follows the cross-section of the bell-shaped nozzle but has one side which is open. The combustion chambers are arranged in series on top.

When the hot gases leave the chambers, the spike of the design contains one side, while the air pressure takes the place of the missing cross-section of the bell-shaped nozzle. When the rocket ascends and air pressure drops, the virtual bell is designed to expand and maintain the efficiency of the engine.

Since a single-stage rocket can work efficiently, scientists can use this design to make smaller, lighter rockets that carry heavier payloads. In other applications, this could translate to higher ranges or speeds that exceed a few Machs.

The natural question that follows is that if scientists have known this for more than 50 years, why hasn't a LAS engine been tested in flight so far? The reason is due to the tremendous amount of heat generated in the design and the lack of materials that can handle them.

With the advances made in 3D printing, it has now become easier to not only use newer materials but also design better cooling systems to get these systems into action.

Polaris has already built three such demonstrators, and the German government grant plans to make the scaled spaceplane demonstrator bigger than its predecessors.