German startup Polaris Raumflugzeuge reported that its MIRA I demonstrator crashed with an innovative aerospace rocket engine. The demonstrator did not even have time to leave the runway and start the KVR engine, which veered sideways and, under the influence of a strong crosswind, overturned and burst into flames. The developer promised to make two and larger sizes instead of the destroyed copy and took the money for this from the budget.

About a year ago Polaris Raumflugzeuge was awarded a contract by the Bundeswehr Federal Office for Equipment, Information Technology and Technical Support (BAAINBw) to develop and build a full-scale prototype of the wedge air rocket engine. KVRD engines were developed in the 50s, and it was even planned to install them on the shuttles of the Space Shuttle program. However, the project never left the laboratories. It would be the first flight in history by a German demonstrator with four conventional turbojet engines and one experimental KVRD engine. But it hasn’t happened yet.

To replace the 4.25 m long MIRA I demonstrator destroyed in the accident, the company promises to build two MIRA II and MIRA III, each 5 meters long. The configuration of the engines and the profile of the airframe will remain the same: a wedge-shaped wing, four turbojet engines running on oxygen and kerosene and one KVRD on each.

Wedge air rocket engines are particularly interesting for spaceplanes where there is no room for both first and second stage engines at the same time. The rocket may have two stages or more when each of the bell-shaped nozzles is projected to its own height. If the nozzle is single, as in the space plane, it will be effective at only one altitude, causing a large waste of fuel at all other altitudes.

The nozzles of the KVRD engine are two, connected to one side of the bell half. The second missing side of the nozzle is created by the incoming air flow. Thus, it can be said that the nozzle profile changes automatically throughout the flight from sea level to vacuum, which generally ensures efficient operation at all altitudes. It is a pity that the Germans did not succeed this time; They didn’t even go so far as to launch KVRD into the air. It would be interesting to see this technology in action in real flight conditions.