Development, Testing and In-Orbit Verification of a Large CFRP Helical Antenna on the AISat Mission

Abstract

A design for a 4 m long, ultra-light, high-gain, helical Antenna made from fiber-composite material will be presented. The antenna was designed for the DLR NanoSatellite Mission AISat to receive signals from the Automatic Identification System (AIS) of 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 and several development tests. Finally, in-orbit demonstration was performed during the two years of operation of the AISat after the successful launch on June 30, 2014 from Sriharikota (India). The AISat satellite was developed at the DLR Institute of Space Systems aiming at the worldwide receiving of AIS signals. These signals can usually be received along coast lines or from ship to ship in range of sight. They provide identity, position, velocity and heading and are therefore used for ship tracking. A number of AIS satellites already exist but especially in areas with high ship traffic density 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 on the Earth surface. IT thus shall enable the receiving of Class A and B and SART signals especially in high traffic density zones. 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 of merely 100 mm height. 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, in which it is held down by 3 release mechanisms, the antenna has stored elastic energy like in a spiral spring. After release the structure deploys autonomously in orbit to a length of 4 m. When deployed, the antenna is still pre-stressed using control cords in order to increase its bending stiffness.