We observe a peculiar behaviour on the LOX side not experienced before during static test. The stable pressure at around 13 bar from T + 10 to T + 40 seconds more or less reveals what has gone awry. The stable pressure can have one of two causes, either the main valve is closed, or the pressure is maintained by rapid evaporation of LOX forming GOX (Gaseous OXygen). The former can be excluded as the position of the main valves is logged by the ECU (Engine Control Unit), and these data show both valves open until splashdown. The other cause is better known as VaPak or autogenous pressurisation.
Having pressurisation through VaPak from T + 10 seconds is an obvious indication that the LOX has been warm, is has only been held at sub-critical state by a high pressure. In this state the slightest fall in pressure will result in the LOX shifting to super critical state where it evaporates at a rate high enough to maintain a stable pressure. This may sound like a fantastic feature, but for Nexø I it proved fatal. In its present design, the BPM-5 engine injector isn’t capable of working correctly with super critical LOX, the injector is designed to inject fluid, LOX, and not GOX or some obscure combination of LOX and GOX for that matter. Had we just had a thermal sensor in the LOX dome, we would now know the exact conditions …
Based on the pressure charts we can conclude that the LOX has been close to going critical from the very start. From this we can assume that we have had GOX flow through the injector from the very start, resulting in a lowered mass flow. This has again resulted in lowered chamber pressure and thus a higher than expected fuel flow. This explains both the low engine thrust and the relatively fast depletion of the fuel tank, resulting in the tank being depleted at T + 24.4 seconds.
Video Cation: Animation of the July 23rd 2016 flight of Nexø I.
A brief teaser video of the launch before a full-length version sometime soon!
Copenhagen Suborbitals are busy gearing up to fly their Nexo I & II rocket missions this summer, a recent successful cold flow test puts the team another step forward in achieving flight.
Copenhagen Suborbitals have unfortunately delayed the flight of Nexo I to 2016.
The team had been working hard to meet the launch window of 26-27th September, but due to problems arising in testing, that included several faulty valves, without working the team to breaking point, the window could not be met.
Never the less leading up to the 2016 flight of Nexo I the team will continue to build Nexo II, (similar to Nexo I but with an onboard tank pressurization system), carry out more BPM-5 rocket engine tests and start the design work on the BPM-100 rocket engine that will power the Spica rocket and eventually propel a man to space.
You can read the full update and press release here about the delay.