At this moment it is not yet certain what motor will propel the Stratos II rocket. DARE is developing both a solid propellant motor and a hybrid propellant engine in parallel. In this post an introduction and update about the hybrid engine.
Dawn is a DARE project that aims to develop a hybrid rocket engine for use within DARE and specifically for use in the Stratos II project. The team is designing and building an engine with liquid oxidizer and solid fuel to compete with the solid rocket motor team. Both teams are working on their own rocket engine but only one of them will be used for Stratos II.

The Dawn project was started up just before the summer holiday 2010 by Arjan Fraters. He composed a team of eight DARE members including himself to realize this project. These are: Arjan Fraters, Michael Eiche, Stefan Powell, Ragiel Wildvank, Tobias Knop, Ingo Gerth, Ralph Huijsman and Rob Hermsen
Most of the systems engineering was done before and during the holidays. Then during the first period of the new academic year the first designs for all the different parts of the subsystems where made. The second period of this year was used for the production of different parts of the engine and for the construction of a test bench to do concept tests on, for example for the injector and for propellant tests.

Subsystems

At the beginning of the project the engine was divided into several subsystems. These subsystems are displayed in figure 1. The different subsystems were divided over the team members who have been working on designing the parts and have now started on the production of these parts.

Figure 1: A simple schematic of the hybrid rocket engine. The numbers denote the positions of the different subsystems.

1. Nozzle 2. Combustion chamber 3. Igniter 4. Injector 5. Feed system 6. Oxidizer tank; (Electronics not shown)

Tests

The Dawn team is going to conduct many tests to prove the concepts of the different feed systems. The first test has already been done. This was a test done before the Christmas holidays with a small test combustion chamber in which the ignitor was tested.
The igniter consists of a standard propellant grain which is commonly used in DARE and an electrical ignitor with black powder. If a current is applied to the electrical igniter it lights the little charge of black powder, which in turn ignites the propellant grain. The propellant grain burns up in a few seconds, during which it heats the combustion chamber and the fuel grain. The idea is that when the oxidizer flow starts, the fuel grain will be hot enough to start burning with the oxidizer.
The purpose of the first test was to see to see if the propellant grain would ignite and what effect the heat of the igniter grain would have on the fuel grains. Also a one-way-valve, which is part of the feed system, was attached to the other end of the combustion chamber to see if the valve could hold the heat and the pressure.
We learned from the test that with this way of ignition the hybrid engine has a good chance of success because the surface of the fuel grains that were in the casing was melted by the heat from the ignition grain. Furthermore the grain burned for a few seconds so that we now know that the timing for starting the oxidizer flow after ignition is not that critical. Also the one-way-valve worked fine.
More tests from the hybrid propulsion group will certainly follow after this first successful test.

Figure 2: The test setup of the igniter test. The wires for the electrical ignition can be seen right. The one-way-valve can be seen on the far left.

Figure 3: The combustion chamber at ignition. The black powder charge in the combustion chamber has just been lit and the gasses escape through the exit hole.

Figure 4: The black powder has burned up and now only the igniter grain is burning. The grain burned for about 4 seconds. The one-way-valve performed correctly and did not let anything through.