As stated in the general setup of the EDOD experiment (link) the electrical and optical system shall trigger and capture the deployment of the drag sail. Furthermore a camera module for a cubesat satellite shall be developed and qualified during the REXUS mission.
To achieve the defined goals we need several subsystems as shown in the electrical block diagram below. A mission control module will act as head of the experiment and trigger the deployment of the sail while camera and lighting modules will capture the deployment of the sail. Furthermore a power supply unit will transform the 24 to 36V supplied by the REXUS Service Module to the necessary voltage levels.
Mission Control Module
The mission control module will be the master controlling all other modules of our experiment. It’s task is to interpret the information coming from the REXUS service module – via 2 data lines (SODS – start/stop of data storage and SOE – start/stop of experiment) for experiment control and a serial RS-422 telemetry interface to relay experiment status messages to the ground station.
Taking a high-speed video is not an easy task – especially in a difficult environment with extreme and extremely different lighting conditions, small available space, different temperatures and the imminent threat of a head-first impact in the Swedish tundra.
Our cameras need to capture only a 2 second long event – the deployment of the sail as detailed as possible – both in time and image resolution. As we only have very limited available space, making it impossible to capture the whole sail with only one camera we need multiple cameras while maintaining a low budget.
There are several possibilities for high-speed-cameras:
- professional solutions:
→ 150 to 2500fps at medium to high resolutions
→ quite to really expensive
→ no suitable structural shape
- internal development:
→ good integration possible as modules are build for this purpose
→ medium resolutions at 60 to 90 fps
→ cheap price-tag, enabling us to use several modules at the same time
To reduce risk at all sides we will combine a single professional camera and enhance the whole system with several internal developed cameras. Furthermore a cheap camera will be used if the live video-channel available from the REXUS service module is not required by the other experiments.
These modules will consist of an image sensor, a high-performance microcontroller/DSP with attached RAM and flash memory for data storage, as seen in the block diagram. To protect the captured data the image sensor will be physically separated from the data processing and storage, so that the only exposed component is the image sensor.
To illuminate the sail in the case of a night launch or when the sun is occluded by the sail we need a high performance lighting system.
The service module provides 2 lines with 28V, resilient to 3A peak and 1A mean to supply the experiments. As the lighting is (besides the trigger/ejection mechanism) EDOD’s only large consumer we can use quite a large number of high-performance LEDs to illuminate the sail as good as possible.
The captured data should be used as reference for simulation models for the further development of drag sails, so it is our goal to get as much information from the videos as possible. With a grid on booms and the sail we will be able to track each point in 3 dimensions. This method is called photogrammetry. In addition to the video we will add „normal“ sensors (for example a rotation speed sensor on the boom coil) as well.