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Unmanned space vehicles | Insight modelling and wire deployment investigations prove promising after the current two-year investigation, the earliest use of the technology would be for the 2025-30 timeframe. However, without traditional jet propulsion, a key problem is how to manoeuvre an autonomous craft around in space. Researchers from ETH Zurich and ETH spin-off company Celeroton have therefore developed an ultra-fast magnetically levitated electric motor for reaction wheels to do this job. Electrically driven reaction wheels of this kind are used in satellites to change their attitude. The reaction wheel is connected to an electric motor via a shaft, and as soon as the flywheel driven by this motor rotates in one direction about its own axis, a torque is transmitted to the satellite, which then rotates in the opposite direction. This rotation can be controlled exactly via the motor. In existing systems, the rotors and reaction wheels are typically mounted on ball bearings that wear down relatively quickly and so operate at less than 6000 rpm. They also have to be stored in a hermetically sealed housing with a low-pressure nitrogen atmosphere to avoid oxidisation of the materials and evaporation of the lubricant. In addition, as the ball bearings are not exactly identical, the difference in size can create micro-vibrations in the satellite, reducing the positioning accuracy. However, the ETH prototype can be operated at up to 150,000 rpm, as the rotor floats in a magnetic field and does not require bearings or lubricant. “Magnetic support also allows us to avoid the vibrations,” says Arda Tüysüz, a researcher at ETH Zurich’s Power Electronic Systems Laboratory. The new system is complex though, so sophisticated power electronics are needed to steer and control it, but Tüysüz says this ties in perfectly with the laboratory’s expertise. Transport Autonomous operation is also a key technology for transportation in space, from equipment supplies to the International Space Station to space tourism. Two companies are using autonomous boosters that return to Earth. Space-X has been returning its Falcon landers to autonomous barges in the Atlantic and Pacific oceans so that the landers can be re-used, while Blue Origin has been returning its sub-orbital New Shephard lander to New Mexico, controlling its aerofoils automatically to keep the lander upright for landing. The success of New Shephard has led to the company announcing its next- generation system, New Glenn. This will use a new engine, the BE-4, developed by Blue Origin and providing 550,000 lb of thrust – more than four times the take- off power of the current BE-3 engine. Seven BE-4 engines in a 7 diameter booster will send up to six people into space without a pilot. The design work for New Glenn started in 2012, but the first launch is not scheduled until 2020, although the BE- 4s will be used on other, non-returnable launch craft in 2017. Work is also starting on the generation of booster to follow this one, New Armstrong, says the company which was set up by the founder of Amazon, Jeff Bezos. Conclusion There are several types of autonomous operation in space systems. Delivering a booster stage safely back to Earth, either on the ground or the ocean, requires a complex control system linked to the aerofoils and rocket motors. Up in space, an autonomous inertial navigation system is being developed to guide a craft to its destination. When it arrives, there will be a wide range of autonomous functions required, from mining samples and minerals to return to Earth to exploring through liquid environments. New propulsion systems also play their part in new craft designs. The different missions will have a range of varying design criteria, but almost all will have a large element of autonomy. As rovers and excavators head to the Moon, and other projects look further out into the Solar System, the opportunities of autonomous system design will help unlock the mysteries of space. 65 Unmanned Systems Technology | October/November 2016 The New Shephard booster from Blue Origin lands autonomously (Courtesy of Blue Origin)