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.

Nexø II Successfully Launches

The team at Copenhagen Suborbitals had a successful launch and recovery of their Nexø II this past weekend. Launching from the Baltic Sea on Saturday, August 4th, the 6.7m long, 0.3m diameter rocket ascended to an altitude of 6.5km (21,325ft), before coming down, first on a ballute and then its main chute. The liquid oxygen/ethanol fueled engine provided a nominal thrust of 5000N (1124N) and was intended to power the rocket to between 8-12km in altitude.

The flight was obviously a shortfall in the altitude expected but a success in every other way. It will be interesting to read the post-mortem as it becomes available.

In the meantime, check out the raw footage of the flight below.

Instagram Pic of the Week

Congrats to the team for a successful flight!

Nexø II Launch Postponed

Unfortunately, the delay is out of their hands, hopefully, the fires are under control soon.
The launch is now scheduled for this Saturday, August 4th with backup Sunday.

Nexø II at sea for it’s last major test before launch

The launch is currently scheduled for July 28th with a window of 8-11am UTC.

Video caption: Last week we performed the final test of Nexø II and all launch equipment at sea. This sea acceptance test (SAT) is the last step and a full launch rehearsal. All systems passed, so now Nexø II is ready for launch.

Please visit for more details.

If you like our project please go to: and sign up as a Copenhagen Suborbitals supporter.

It’s the support from people like you all over the world that makes this project possible!

CS: Final Harbour Acceptance Test

Video Caption: The lasts steps before launch of a rocket from sea is HAT (Harbour Acceptance Test) and SAT (Sea Acceptance Test).

This video shows the highlights from the recent HAT where Nexø II was mounted on the launch rail and all systems where checked as preparation to launch.

If you like our project please go to: and sign up as a Copenhagen Suborbitals supporter.

It’s the support from people like you all over the world that makes this project possible!

Nexø II Rocket Launch Windows Confirmed

Copenhagen Suborbitals Nexø II rocket is 6.7m in length and 0.3m in diameter. Powered by a 5000N thrust LOX/Ethanol liquid rocket engine and guided by jet vanes, the rocket is expected to reach an altitude of 12.6km (41,338.58ft).

You can read more about the Nexø II mission here.