Translated from a blog in danish, written by Jesper Rosendal.


A couple of weeks ago we held a debriefing event in our workshop. We went through a detailed analysis of the launch of Nexø I, and we told about what went well, what went wrong, what we learned and what we need to improve and do better. Around 50 guests visited at Refshale island that Sunday. Thank you very much for attending. It’s always nice to meet and talk to our Copenhagen Suborbital supporters.

Debriefing with Flemming Nyboe. Photo: Carsten Olsen.

Debriefing with Flemming Nyboe. Photo: Carsten Olsen.

Those who were not able to attend shouldn’t feel left out, as we filmed all sessions, and will publish the video at a later time. Carsten, who is editing the video material, just started on a new job. This limits the spare time he has available to edit the footage, prolonging the process somewhat. We hope you will show patience while waiting for the finished video.

Nexø II

The next rocket to be launched above the Baltic Sea will be Nexø II. We are already into the build process, and anticipate to have completed the rocket in time for a May campaign, just as the weather conditions becomes acceptable for launch.
When we had parts fabricated for Nexø I, we ordered two complete sets. This means that major parts of Nexø II are already preassembled. There are however still some parts that needs to be fabricated during fall.
The main difference from Nexø I to Nexø II will be the DPR module (Dynamic Pressure Regulation). We are presently procuring a suitable high pressure tank for the DPR module, and several bids are being investigated. Once the right tank has been obtained, the module’s design will be completed around it.

Blog author Jesper Rosendal working on Nexø II. Photo: Carsten Olsen.

Blog author Jesper Rosendal working on Nexø II. Photo: Carsten Olsen.

One of the major issues of the Nexø I launch was the fact that the LOX was much warmer than it should be. This was partly due to the cooling effect of degassing being inhibited by the impaired performance of the vent valve, and also due to the very nice sunny weather, heating the LOX tank from the outside.
We did manufacture an insulating mantle of polystyrene foam, but during cold flow test it was found that the mantle was stuck on the tank because af ice forming between tank and mantle. We didn’t dare risk this happening at launch, so we decided to omit the mantle.
The launch showed us that LOX tank insulation is needed for Nexø II. Which is why we are presently working on a solution that will provide efficient insulation without getting stuck on the tank’s outer wall.
Nexø I was a rather heavy rocket compared to its size and engine thrust. Even if it wasn’t a problem for Nexø I to lift off the ramp, we would like to try changing the weight to thrust ratio and trim Nexø II a bit.
To lighten Nexø II (apart from the additional DPR module), we are considering exchanging some of the aluminium parts with carbon fibre parts, namely outer shell panels and fins. We are communicating with a company specialising in building carbon fibre parts who has shown an interest in helping us.
Our calculations show that we can expect to raise apogee by 140 meter for each kilogram of reduced weight. Maybe not much compared to the 15 km goal, but every meter count.

The fleet

We have left our fleet of ships in Nexø harbour. But we have not abandoned them. One of our local members is keeping a watchful eye on them.
The reason for keeping the ships in Nexø instead of returning them to Copenhagen is a wish and a need for having them lifted onto the slipway for maintenance and painting. Nexø harbour is well equipped in this regard, because of it being home to a large fishing fleet in the 1980’es. The harbour also has a shipyard, and friendly and helpful craftsmen.

Vostok can be lifted onto the slipway by the harbours ship elevator. Sputnik is another matter, as her 12 by 14 meter size prohibits using the ship elevator. She will have to be lifted by crane. But no mobile crane on Bornholm have the required lifting capacity, the main reason for Sputnik not visiting the slipway last winter. We are thus forced to determine if and when a visiting crane has time – and capacity – to lift Sputnik out of the water in the near future.
No matter what, a delegation of CS members will arrange weekend trips to Nexø in the forthcoming months, to do much needed ship maintenance.


Our dutch intern, Jop Nijenhuis, has developed a gimbal system, based on the BPM-5 engine and the Nexø support structure, during his time with CS. The system is hydraulic powered by parts designed by Jop in cooperation with the Bosch Rexroth company. The system looks very promising, and will be put through its paces in our test stand this fall. Whether we will fly a Nexø III rocket with a gimbal system remains to be decided upon.

The almost finished gimbal system by Jop. Photo: Carsten olsen.

The almost finished gimbal system by Jop. Photo: Carsten olsen.

Jop has produced a small animation of the gimbal system:


The BPM-5 engine and the Nexø rocket both have a size suitable for testing different elements of a rocket launch. But as you know, our ultimate goal is to launch a human into space, and that isn’t doable with a nexø-sized rocket. Thus we need to scale up to a larger engine and larger rockets. Our engine group is busy doing calculations for a BPM-100 engine. Our goal is to have it ready for test next summer. This will require – apart from building the engine – that we find a suitable test site for a 100 kN rocket engine.

Blog author Jesper Rosendal working on the avionics section. Photo: Carsten Olsen.

Blog author Jesper Rosendal working on the avionic section. Photo: Carsten Olsen.

All this to tell you a bit about what is happening in the rocket shop right now. All of the above, and more, will be described in more detail on this blog in the forthcoming months.

The last thing to get a mention in this blog is a feature about Copenhagen Suborbitals, produced by german TV channel Pro7 for their science program, Galileo:

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