Now, with the lessons learned from the Stratos II launch campaign the team decided to get back to the drawing board. Here they put the obtained experience to use. Over the course of the one year, the team addressed bottle necks, redesigned critical components, and performed more and new tests of the different subsystems. Due to the amount of changes and improvements in the design, we felt the new rocket deserved a new designation, so it was rechristened as Stratos II+.
Like the Stratos II, the Stratos II+ was designed to fly up to break the European altitude record carrying a scientific payload and to be recovered after the launch. Because hardly any of the required systems can be bought of-the-shelf every single subsystem was designed and developed in-house. This made the Stratos II+ project one of the most technically advanced student projects at the TU Delft. It combines high power experimental propulsion, sub- and supersonic aerodynamics, advanced safety systems, telecommunication, supersonic re-entry, recovery systems and international coordination with a foreign launch site.
In total, the Stratos II+ had a length of 6.9 metres, with most of this length taken up by its single stage hybrid rocket engine. This engine, the DARE developed DHX-200 Aurora, runs on nitrous oxide as oxidiser and a mixture of sorbitol (coffee sweetener), paraffin (candle wax) and aluminium powder as fuel. It has a total impulse of 180 kNs and a total burn time of around 23 seconds.
A dual parachute system was housed in capsule section of the rocket. The first of the two parachutes was was a small drogue parachute, which released just after apogee (the highest point of the trajectory) to stabilise the rocket during the supersonic descent. The second parachute was the main parachute, which took care of most of the deceleration to ensure a soft touchdown in the Atlantic Ocean.
In the upper section of the nose cone the flight computer, power- and data management systems, down-links and commercial payloads were situated. The flight computer and telemetry were in-house developed and measure various system parameters such as tank and combustion chamber pressure, accelerations, atmospheric pressure, the orientation of the Earth’s magnetic field, and the power being consumed by the different subsystems.
All of the important subsystems were subjected to ground testing during various test campaigns. Most notable here are the test campaigns during which the hybrid rocket engine was static (ground) tested. In total we performed fourteen test fires at the facilities of TNO Rijswijk in the Netherlands and DLR Trauen in Germany.