By Carlos Fernandes
Ships automatically broadcast their identification, position, speed, and course using the AIS - Automatic Identification System. It is a VHF radio-based service that enables ship-to-ship, ship- to-coast, and ship-to-satellite communications for safe navigation.
However, the AIS system is becoming saturated, with channels becoming congested when multiple vessels operate near each other, for instance, near busy ports. Furthermore, data can be easily manipulated.
The VDES - VHF Data Exchange System is a recent generation that will operate in parallel with AIS, featuring wider bandwidth and a broader range of services, offering bidirectional communication with advanced security features. Like AIS, the system includes a satellite layer to ensure global coverage.
The Portuguese LUSIADA constellation, comprising twelve polar orbit satellites, is scheduled to support the World’s first commercial VDES service. The satellites were built within the NEWSPACE Portugal project, with PRR funding, and will be operated by the LusoSpace company.
One of IT’s roles in the project was to design a deployable antenna for the constellation of 8U CubeSats, operating in the AIS/VDES 156 MHz to 162 MHz band (about 1.9 m wavelength) with 6 dBi gain and opposite-sense circular polarization for the dual AIS and VDES radio front-end. The challenge was to meet these requirements while simultaneously fitting the antenna into a 200×100×30 mm3 pre-launch volume (equivalent to less than 0.5U), behind the propulsion module, and deploying it in space to a very compact length, less than a quarter wavelength. A non-conventional antenna configuration was proposed to circumvent severe platform constraints that would otherwise allow only for a minimalist, very low-gain antenna.
The concept development, electromagnetic design, fabrication, and test of the engineering model was carried out at the Instituto de Telecomunicações/IST Nanosat Lab by a team led by Carlos Fernandes from IST/IT, with João Felício from IST/IT, Sérgio Matos and Jorge Costa from ISCTE-IUL/IT, Tiago Carneiro, an Aerospace Engineer at IT, and laboratory technicians. Experimental tests of the engineering model conducted at IT spanned electromagnetic, temperature, and vibration characterization. The team has also fabricated in-house some of the main components of eleven antenna flight units and assembled all in the clean room installed at the IST Nanosat Lab.
The antenna development involved other project partners, namely for the design of the antenna deployment mechanism and fabrication of the antenna frame, with coordination from LusoSpace. Final electromagnetic tests were performed at ANACOM.
The antennas were delivered to LusoSpace for final integration into the 8U CubeSats. The satellite launch is scheduled for 2026 by SpaceX.
The team is already working on the next satellite projects in full cooperation with the emerging national NewSpace industry.