The toughest part of this project shows up right at the end of the burn: thermal stresses melted one side of the nozzle, and the run had to be aborted. What stands out is how the maker handled it. Delft Aerospace Rocket Engineering still pulled good data out of the firing, and the team is already refining the design that was on the stand. For a student group from Delft University of Technology working toward a launch next summer, that seems like a steady way to treat a setback.
The setup itself is worth admiring. The DHX-400 Nimbus hybrid engine was clamped horizontally to a steel stand inside a concrete bunker tunnel, with instrumentation wiring running along the mount and floor sensors, tripod gear and a control cabinet spread around the site. The propellant combination is a paraffin, sorbitol and aluminium powder grain fed by liquid nitrous oxide, all aimed at powering Stratos IV past the 100 km mark in summer 2020.
A few details caught my eye. A synthesized voice counted down from fourteen, and a tree stood near the nozzle as a playful way to show the scale of the thrust. When ignition came, the plume swept that tree straight down the tunnel, and sparks poured from the nozzle around 23 seconds in before the firing wound down into dark smoke and residual burning.
The open question for me is the nozzle. Melting on one side suggests the thermal loads are not evenly shared, and with a launch window that close, how quickly the redesign closes that gap may decide everything.
Project by Delft Aerospace Rocket Engineering. Watch it on their YouTube channel: