Copenhagen Suborbitals Nexø I rocket launches with mixed results

Yesterday Copenhagen Suborbitals launched their rocket Nexø I, their most advanced vehicle yet, from a floating platform in the Baltic Sea. (See earlier posting). The good news is that the rocket lifted off successfully with its liquid-fueled engine (Ethanol and Liquid Oxygen) and active guidance system and was successfully recovered. The bad news is that it failed to reach its planned altitude and the parachute system failed to open: The Nexø I rocket launched – Copenhagen Suborbitals –

It was a beautiful launch with a not so great landing. The rocket flew to about 1514 meters before a catastrophic failure occurred.

Even though it didn’t go completely as planed we still see it as a partially success. A lot of sub systems actually work as they should.

Nexø-1 Rocket liftoff

We managed to recover the rocket. We will therefore have a good chance of finding the root cause of the failure.

We will post more about the launch and crash after we have had a closer look at the rocket and telemetry data.


Here is a video of the webcast. The countdown to liftoff starts at the 3 hr 20 min 8 sec mark:

Today there is some preliminary analysis: Preliminary impressions from Nexø I flight event. – Copenhagen Suborbitals

We have not yet had opportunity to examine data, parts or footage.

A tentative speculation on root cause would be simple LOX [Liquid Oxygen] overload. In other words a problem with measuring the correct amount of LOX in the tank, which we have encountered previously, and worked on solving via several methods. We will look into this.

Too much LOX will result in a too small gas pocket in the tank – which equals too little gas propellant energy and a premature loss of tank pressure in the LOX tank, again resulting in an increasing O/F-ratio mismatch. The engine subsequently extinguished.

The GNC didn’t detect acceleration below minimum, as this detection was removed from the algorithm prior to the mission, based on the fact that the acceleration, through the use of pressure blow-down at relatively low altitude, would be very low before the occurrence of MECO.

The GNC instead used the chamber pressure. This was low at an unusually early time. The GNC treated this as a sensor failure, and instead an estimated pressure, based on a table generated from earlier tests, was used.

Thus the GNC didn’t signal the deployment of the parachute, as it was under the (false) impression that the engine was still operating as expected.