Nexø II Post Flight Analysis

Thomas Pederson of Copenhagen Suborbitals offers an insight into why Nexø II did not reach its expected altitude of 12 km.

(Translated with google translate)

The first thing to hit is the low engine pressure. We start around 14 bar but reach T + 15 sec below 13 bar. Then it rises up to 14 bar again. The same type of course is seen on the pressure in the LOX tank and the pressure in the LOX side of the injector. It is therefore clear that the pressure in the engine has been too low due to the low pressure in the LOX tank.

(Referring to graphs in the original post,)

…Here we see both the pressure drops above the injector, but also the error between the injector pressure and the desired injector pressure. It can be seen that on the fuel side the error is below 1 bar throughout the trip, but on the LOX page the error is between 2 and 4 bar. It is quite violent. Thus, the LOX flow has been too low, which automatically produces a higher flow of fuel and thus low OF ratio. In addition, it means that fuel is consumed too quickly and we see that at T + 39.

The low pressure and thus the low thrust give rise to a lower acceleration than expected. The acceleration (vertical) is plotted at the bottom right along with the expected acceleration. It is seen that we lie a little all the way. Overall, it means a little lower acceleration and the premature MECO that we only reach approx. 6,500 meters over 12,000 meters.

It is therefore clear that around the T-18 something happens with the LOX tank pressure setting. Either we have a mistake on its pressure relief valve or we have a leak in the tank, so hell is coming in, but it is lost somewhere else. However, it seems strange with such a leak, we have had the system up at work pressure previously without problems. However, for the time being it is difficult to determine more precisely.

Great to see they have figured out why the rocket did not reach its mark and the possible cause of the problem. It was great to see the rocket fly after the delays of last year, looking forward to seeing what is next on their agenda.


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