3D - printed valve mount for the DHX-200 with valve and servo.

The decision has been made; Stratos II will fly on a hybrid rocket engine. A full scale one-stage hybrid engine using nitrous oxide as oxidizer and as a fuel sorbitol with a number of additives will be used to carry the payloads on board of the rocket to the 50km mark.

The decision was made by the team before the Christmas break. A large number of criteria were taken into consideration to make sure the best choice for either a solid rocket or a hybrid was made. After a long and elaborate trade-off it was concluded that both systems, given their current state of development and the possibilities they offer for the Stratos II mission, would both be viable alternatives. From the trade-off, neither of both systems was came out as the absolute better system. The decision was eventually made by the leaders of all the sub-teams of Stratos II to continue the development of Stratos II based on the hybrid engine system.

It should be said that this does not mean the end of the solid motor research. For the solid rocket team it means that they will be moved back under the direct cover of the DARE umbrella, instead of under the Stratos II project. The research based on the ALAN-7 propellant will continue and can result in high performance solid motors that can be used in projects in the future.

3D - printed valve mount for the DHX-200 with valve and servo.

The hybrid rocket engine Aurora

Since the decision the team has made significant process towards the final testing and development of the full scale engine. Most parts have been ordered and the first parts have already arrived. Some of these parts can be seen in the accompanying figures. These show an assembly of the main valve from the N₂O feed system and the actuation servo for this valve. These are both fixed in the white servo mount. This is a part that is 3D printed. It was fully designed in the computer in such a way that both valve and servo fit in it with very small tolerances, required for the valve actuation. Printing this part instead of manufacturing it in metal allows complex shapes to be made for a relatively low price and work load, but still with high material strength and production precision.

In the 3D-printed part the name of the engine can be seen, the DHX-200 Aurora. This stands for: Delft Hybrid eXperimental – 200 kNs. This last number is the approximate amount of total impulse that the engine is expected to deliver, but you could also read it as the engine main diameter: 200mm. “Aurora” is the informal name for the engine, and next to reverencing to the northern lights phenomena, it also means “Dawn” in Latin.

The hybrid engine team is working full speed now towards a full scale test of the motor they hope to conduct at TNO at the end of March.