ON ORBIT DEPLOYMENT OF THE EU:CROPIS SOLAR PANEL BY GFRP TAPE SPRING HINGES

Abstract

Eu:CROPIS is a compact satellite featuring a biological payload. The Satellite was launched on December 3rd 2018. The cylindrical Satellite of 1m diameter has four deployable panels for power generation. Those panels are connected to the main structure by glass fibre reinforced polymer (GFRP) tape spring hinges. The hinges, comparable to curved metallic measuring tapes, have elastic energy stored when flattened and folded and thus deploy the panels by simply unfolding. When unfolded the hinges snap into their original shape and support the panels with considerable stiffness. No friction or mechanical locking is involved in the deploying process. The presented paper focuses on the practical handling of the hinges and the mechanisms during the final integration and the deployment process. The integration of the panels requires some special consideration. The hinges are not able to support the panels under gravity. The release mechanisms only work at a correct positioning of the panels. The measures taken to ensure the integrity and functionality of the hinges and mechanisms are described and examples are given for a correct and a false outcome. The separation is done by breaking a bolt with a heated bushing from shape memory alloy. Though reliable the separation cannot be timed down to the second and there is no direct feedback of the separation. To prevent an uneven opening of the panels several on orbit pre-tests are performed to ensure the functionality of the mechanisms for the actual deployment. At the actual separation the heating is monitored to ensure that all mechanisms are activated and the separation is working as proposed. Furthermore, a method was developed to detect the successful breaking of the bolts by use of the heating temperature data. The paper describes these checks and surveillance methods. As not all things go as planned some decisions were to be made before and at panel deployment. Also, the unfolding of the hinges was slower than during the on ground. Tests were made to simulate and understand the on-orbit behaviour. Lessons learned for further use of the mechanisms are presented.