Technical design

The main priciple behind the technical design of the experiment.

Experiment description

The experiment is to take pictures in the IR spectrum of astronomical targets outside the solar system for scientific analysis. The IR camera will be stabilized by a gimbal.

The experiment set-up consists of the following main parts:

  • NIR camera (red): This will provide the data on the astronomical targets we want to observe. This camera will be stabilized in order to achieve the best quality of images possible.
  • Telescope (yellow): The telescope which will be used to obtain high quality images of astronomical targets.
  • Guiding telescope and camera (green): This will provide images in the visible spectrum with a larger field of view compared to the main telescope in order to find our targets.
  • Stabilization system (purple): The stabilization system is a gimbal where the telescope will be mounted on. Its purpose is to point and keep the camera steady while making the intended images.
  • Control system (blue): The control system regulates the gimbal and logs the data from the IR camera together with the data from the other sensors. There will be multiple astronomical targets which the system can choose to image, to always have a target of interest in view. The log will be send over the E-link telemetry system during the flight.

There are distortions in the surface and lower atmosphere like IR-reflection and scattering of light. Also in the vicinity of the surface there is a significant amount of light pollution. Therefore a more satisfactory signal to noise ratio can be achieved at higher altitudes due to the relative lack of IR interference. The BEXUS balloon will reach an interesting height where the only light pollution is the solar irradiance and this can be blocked with an additional heat shield/ baffle. Additionally at this altitude, the above mentioned atmospheric effects can largely be avoided.

The telescope will be mounted on the side of the gondola,slightly outside of it. Due to the limited field of view of the system, the selected target will change multiple times during the flight. As the gondola rotates, this motion will be compensated while making the images. If the target gets out of the field of view due to this motion, the target is changed.

Timeline and process flow

Before flight:

Before the flight necessary calibration will be undertaken and the system will go into sleep mode to save power. The system will stay in this mode until at least a height of 20 km is reached.

End of ascent phase & start floating phase:

  • Cooling of the camera will start.
  • The sensors will determine the position and spatial orientation of the gondola.
  • The telescope will be orientated towards the astronomical targets that will be studied.

During floating phase:

The telescope will be pointing steadily into the direction of the astronomical target that is being studied. The images will be made by using different integration times. The data is logged on the system and sent to the ground station through the BEXUS E-link.

Because of the rotation of the gondola, the telescope might sometimes lose line of sight of the most recently studied astronomical target. In this case other astronomical targets within the new field of view of the camera will be photographed.

Descent phase & landing:

The gimbal will be positioned to have the highest probability to keep the telescope and camera intact on impact with the ground. Then the entire system will be shutdown.

After landing:

  • The batteries of the system can be removed.
  • The data stored onboard will be removed and stored safely.
  • The raw data from the log and received by the ground station will be analysed and refined.

Data obtained

  • Images in the near IR spectrum.
  • Orientation of the IR camera relative to the gondola. This is measured by a gyroscope.
  • Position of the gondola in WGS; orientation of the gondola in degrees relative to magnetic north. This is measured by a gyroscope, accelerometer, GPS and compass/ magnetometer.
  • Guiding scope images.