Unmanned Systems Technology 001 | UAV Factory Penguin C | Real-time operating systems | Hirth S1218 two-stroke twin | Base stations | ASV C-Enduro | Composites | Datacomms

Earth for a connection, they can instead connect to the orbiter. In the 16 minutes it takes Odyssey to go from horizon to horizon, it and the rovers can establish a link for about 10 minutes to transfer data over UHF at rates of up to 128 kbit/s, transferring 60 Mbits in the process. This in turn will take between 90 minutes and 5 hours to be transmitted back to Earth via the Deep Space Network (DSN) on the ground, which has three highly sensitive antennae to receive data from all the craft in space. Odyssey has two antennae for communicating with Earth. The low-gain antenna is omnidirectional, and was only used when the spacecraft was near Earth. Because it radiated signals in all directions, the low-gain antenna did not need to be pointed at Earth to enable a comms link. Now, the medium-gain directional antenna points to Earth for the link. The rovers communicate directly with Earth via low-gain and high-gain antennae. The low-gain antenna is omnidirectional and transmits radio waves at a low rate to the DSN antennae on Earth. The high-gain antenna is steerable and so can direct a beam towards Earth for higher data rates. The data transmission rate from the rovers direct to Earth varies from about 12 kbit/s to 3.5 kbit/s, and they can only transmit directly for at most three hours a day owing to power and thermal limitations, even though Earth may be in view for a much longer period. The latest craft to reach Mars, the Maven orbiter, will also act as a relay for data from the rovers back to Earth. This uses Electra radio technology, which is already in use on the Mars Reconnaissance Orbiter and the Curiosity rover. The Electra radios are software-defined, enabling the data transmission rate to be adjusted autonomously to suit variations in signal strength due to the changing transmission angle and distance as the orbiter crosses the sky over a rover. Conclusion Communications play a vital role in the control of and feedback from autonomous systems. For road vehicles, the progression from the current V2V and V2I systems to fully autonomous driving is a key step, as the ability to take information from a wider range reduces the real-time processing requirements and so leaves more processing cycles available for other activities such as local hazard detection. Silicon chipsets that are flexible enough to handle the different frequency bands and protocols through a software-defined radio architecture have not only been shown to work in field trials but have now moved into production to reduce the overall cost of the equipment that is ready to roll out in vehicles in 2016 and 2017. Despite years of coordinating efforts, however, incompatible automotive implementations are still being planned, a situation that becomes only more complex when the roadside infrastructure is taken into account. Military autonomous systems have been addressing these issues for many years, and architectures such as Publish Subscribe can provide a framework that is independent of the hardware and software protocols used in a UAV or military vehicle and in the infrastructure, and still delver real-time performance. This is already being demonstrated in several projects, including consumer vehicles, and there are currently ten commercial suppliers of DDS to give developers confidence that the technology will continue to be supported. Developers now have agreed frequency bands and standardised radio and software frameworks that can provide a unified network under which autonomous vehicles are a viable proposition. 73 Datacomms | Insight When the Mars rovers cannot ‘see’ the Earth for a connection, they can instead connect to the orbiter The UHF transceiver in the Maven satellite is also used in the Mars Reconnaissance Orbiter as well, to communicate with the rovers on the surface of Mars via UHF (Courtesy of NASA) Unmanned Systems Technology | November 2014