Lodestar is one of the experiments scheduled to fly on the BEXUS 27 high altitude balloon flight. The primary objective of the experiment is to investigate the effects of cosmic radiation on CIGS solar cells.

The REXUS/BEXUS programme is realised under a bilateral Agency Agreement between the German Aerospace Center (DLR) and the Swedish National Space Board (SNSB).

The Swedish share of the payload has been made available to students from other European countries through the collaboration with the European Space Agency (ESA).

Experts from DLR, SSC, ZARM and ESA provide technical support to the student teams throughout the project. EuroLaunch, the cooperation between the Esrange Space Center of SSC and the Mobile Rocket Base (MORABA) of DLR, is responsible for the campaign management and operations of the launch vehicles.

CIGS solar cells have great prospects as a thin-film photovoltaic technology due to its low mass, relatively high efficiency and low cost. A possible application of CIGS solar cells is in energy production in space, therefore it is relevant to study how CIGS solar cells degrade due to cosmic radiation influence. The primary objective of the experiment is to study the impact of cosmic radiation on CIGS solar cells. The primary objective for the flight is also the easiest objective to achieve, exposing the CIGS solar cells to cosmic radiation and collect the CIGS after flight. The secondary objectives revolve around collecting supporting data, but their success or failure will not make or break the experiment. In order to analyze radiation induced defects, the following observables will be studied before and after exposure of cosmic radiation at Uppsala University. Open circuit voltage (µV uncertainty), short circuit current (0.1fA uncertainty), capacitance, quantum efficiency (0.4 nm wavelength uncertainty), IVT and DLTS (Deep Level Transient Spectroscopy). We have performed a literature study and have not found any papers where IVT and DLTS measurement have been measured by other research groups on CIGS solar cells before and after exposure to cosmic radiation. This makes the experiment unique and of high interest to the CIGS group at Uppsala University. The measurements will be performed using high precision measuring devices from Uppsala University. In addition to this we will measure on-board temperature (2 degrees Celcius uncertainty), the total radiation counts (108 cpm/(μSv/h) uncertainty), Voc (1% uncertainty) and Isc (1% uncertainty) at regular intervals during the flight. We will also study the annealing process of the defects to determine the recovery rate. The solar cells in the experiment are placed on a horizontally facing plate to maximize the exposure. The in-flight measurements are done with arduinos which operate from a radiation shielded box. The box also contains reference solar cells protected from the radiation.

The LODESTAR experiment is supervised by Professor Jörgen Olsson, Department of Engineering Sciences, Solid State Electronics, Uppsala University.

Websites of our sponsors:

SNSB: http://www.snsb.se

DLR: http://www.dlr.de

ESA: http://www.esa.int

REXUS/BEXUS: http://rexusbexus.net/