DEVELOPMENT AND IN-ORBIT VERIFICATION OF LARGE CFRP HELICAL HIGHGAIN ANTENNA ON THE AISAT MISSION

Kurzfassung

A deployment strategy for a 4 m long, ultra-light, high-gain, helical Antenna made from fiber-composite material will be presented. The antenna was designed to fly on the DLR NanoSatellite AISat for the receiving of signals from the Automatic Information System (AIS) for maritime applications. A description of the antenna deployment strategy including release mechanisms will be given. The proof of concept will be presented based on experimental results gained during the 15. DLR parabolic flight campaign (PFC) in March 2010. Aim of this campaign was to verify the antennas’ and the release mechanisms’ performance in weightlessness for the following space mission. Tests with gravity compensation devices in a laboratory are not well suited due to the very complex deployment behaviour like coupled dynamic longitudinal and torsion motions. Final, in-orbit demonstration was performed during the two years of operation after the successful launch of the DLR satellite AISat June 30, 2014 from Shriharikota (India). The AISat was developed at DLR Institute of Space Systems aiming at the worldwide receiving of AIS signals from ships. These signals can usually be received along coast lines or from ship to ship in eyeshot distance. They provide identity, position, velocity and heading of ships and are therefore used for ship tracking. A number of AI-satellites already exist but especially in areas with high ship fluctuation identification problems arose due to the high signal density. Therefore AISat has a distinctive ultra-light, high-gain, helical antenna which allows to focus on comparably small areas and thus enables a receiving of Class A and B and SART signals. The antenna is a 4 m long and 0.57 m in diameter deployable helix antenna made from fiber composite material, which can be stowed in a very flat volume with a height of 100 mm. The wire of the antenna is made from carbon fiber material with a diameter of 8 mm. It is covered with a copper cord for high electrical conductivity. Based on its design with 8 windings the total length of the wire itself is approx. 16 m. Through the dedicated usage of fiber composite materials this wire weighs less than 1 kg including the copper cord. In stowed configuration, held down by 3 release mechanisms, the antenna has stored elastic energy like in a spiral spring. After releasing the structure it deploys autonomously in orbit to a length of 4 m. When deployed, the antenna is still prestressed by means of control cords to increase its bending stiffness. During the 15. DLR PFC the deployment of the helix structure was verified. Four structures with different materials and different wire diameters for differing stiffness properties were tested. Additionally the prestressing of the most promising structure was altered. The deployment behaviour was video taped and reaction forces were recorded. This is a basis for further deployment predictions with changing designs and for reaction force predictions acting on the satellite for guidance and navigation control. The contribution will be concluded with a summary of the data received and lessons learned during the two years of operation of the AISat from 2014 to 2016.