Unmanned Systems Technology 028 | ecoSUB Robotics AUVs I ECUs focus I Space vehicles insight I AMZ Driverless gotthard I InterDrone 2019 report I ATI WAM 167-BB I Video systems focus I Aerdron HL4 Herculift

48 Insight | Unmanned space vehicles LightSail 2, the first project aimed at demonstrating controlled solar sail-based propulsion in low-Earth orbit. Although a LightSail 1 had been launched in 2015, with identical physical dimensions (10 x 10 x 30 cm when stowed; 32 m 2 with sails deployed) it was only intended to test and demonstrate the sail deployment mechanism. The LightSail 2 was launched from Prox-1, a small carrier spacecraft, and a few days later the sails were unfurled. Once deployed, the sails are kept at 165 º relative to the LightSail 2’s central hub for the rest of the year-long mission, to present a hemispherical view to the sun sensors and allow enough solar power to be generated to maintain attitude. The system’s solar sails are made from an aluminised BoPET (biaxially- oriented polyethylene terephthalate) known as Mylar that is manufactured in four triangular sections 4.6 microns thick. Their deployment is powered by an electric motor that drives a spindle, which in turn actuates an extending boom made from an alloy known as Elgiloy. As it moves away from the Sun, the LightSail 2 autonomously points its sail normal vector directly away from it, to maximise the solar radiation pressure on the sail, ensuring that the projection of the thrust onto the orbital velocity increases the orbital energy. When moving towards the Sun, the craft autonomously switches to a ‘feathered’ configuration to prevent the solar radiation pushing into the open sails. The onboard electronics use a 5.6 Ah battery pack which, combined with the typical 8.5 W produced by the solar cells (up to a maximum of 24 W; 6 W per sail at maximum solar exposure), enables power to be accumulated. Also launched in the AFRL mission was the unmanned Green Propellant Infusion Mission spacecraft, which is trialling the first ever in-orbit use of hydroxylammonium nitrate (HAN) as a key propellant component. HAN is intended to provide a non-toxic and higher specific impulse fuel than the more common hydrazine-based propellants. Specific impulse is the total impulse – or change in momentum – delivered per unit of propellant burned, and data thus far suggests that HAN’s specific impulse is nearly 50% higher for a given tank volume than typical hydrazine monopropellants. Its propellant, nozzles and valves were developed by the AFRL, Aerojet Rocketdyne and the Glenn Research Center, with Aerojet being responsible for the propulsion demonstrator payload. The propulsion system incorporates four 1 N thrusters for attitude control, and a single 22 N primary divert thruster. The propellant feed configuration is largely typical of hydrazine-based systems, though with a few redesigns to make it compatible with the dynamics of the new fuel, such as its higher viscosity. Meanwhile, the Indian Space Research Organisation continues to develop its Gaganyaan orbital spacecraft, with the design of the crew module having been completed earlier this year. The project is projected to undertake its first launch by December next year, for which it will be uncrewed and fully autonomous. The Gaganyaan is a 3.7 t capsule-type craft which, on its first manned mission in December 2021, will carry a crew of three into orbit before returning to Earth after up to seven days. The crew module is attached to a ‘service module’ that incorporates two liquid-propellant engines, the two modules being collectively referred to as the ‘orbital module’. The service module is expected to weigh about 3 t. October/November 2019 | Unmanned Systems Technology The LightSail 2 has been designed and built to demonstrate the capabilities of solar sail technology. It uses aluminised Mylar sails that are about 5.6 m in length and wide when fully extended (Courtesy of Josh Spradling/The Planetary Society) HAN is intended to provide a non- toxic and higher specific impulse fuel than the more common hydrazine-based propellants