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62 This gives a longer cycle life, higher torque transfers and the ability to operate more effectively in what is an abrasive, dusty environment. The increasing need for autonomous operation demonstrated by Osiris-Rex and the Lunar-X teams has led to a project called Raven, which is starting at the International Space Station in 2016, to develop an autonomous navigation system based around the STIM300 and STIM210 IMUs from Sensonor to help future robotic spacecraft automatically rendezvous with other objects in motion, such as a satellite in need of fuel or an asteroid such as Bennu. The key to Raven is to use a single suite of sensors, avionics and algorithms to navigate a spacecraft to cooperative objects, legacy satellites that were not designed to be serviced, or natural planetary bodies. It contains three separate sensors that span multiple wavelengths, coupled with high- performance, reprogrammable avionics that process imagery. The vision processing and navigation algorithms convert the imagery collected by the sensors into an accurate relative navigation solution between Raven and the vehicle. Raven also uses a two-axis gimbal to point its sensors at the vehicle to increase the time it has to follow the vehicle into docking or berthing. The STIM gyroscopes are standard sensors used in combination with a star tracker and Kalman filter to orient and stabilise a vehicle, as well as provide feedback on the motion induced by its reaction wheels. Using a commercial-off- the-shelf product rather than a specific space part cuts costs, but Sensonor has also started developing a ‘space optimised’ version of its STIM300 unit. Hans-Richard Petersen, Sensonor’s vice-president of sales and marketing, says, “By serving the space market on equal terms with our other customers, we can help reduce the cost of manufacturing and launching space payloads. Our STIM products have five to ten times less weight than the next-best alternative with similar performance.” Bringing together all the data from the sensors is a key requirement, and silicon chip designer Microsemi is addressing that with a new generation of high-speed signal processing radiation-tolerant FPGAs, the RTG4s. Their reprogrammable logic, based on flash memory look-up tables, is said to offer complete immunity from radiation- induced configuration upsets, which is a big problem in autonomous space systems. The current RTG4s support space applications requiring up to 150,000 logic elements and clock speeds of up to 300 MHz. Marco Caceres, senior analyst and director of space studies for Virginia- based consultancy Teal Group, says, “We expect that the next ten years will see an increase of about 25% in the number of new spacecraft of 50 kg mass or larger. These new craft will have more sophisticated payload electronics October/November 2016 | Unmanned Systems Technology Insight | Unmanned space vehicles NASA is planning to develop an autonomous submarine to explore the liquid ‘oceans’ of Titan (Courtesy of NASA) The Osiris-Rex space vehicle, seen here being assembled, is travelling to the asteroid Bennu to mine its surface (Courtesy of NASA)