While many parents are understandably quick to criticise computer games as mindless time wasters with a narcotic grip on their offspring, engineers at Surrey Satellite Technology Ltd (SSTL) see in the latest addition to Microsoft's Xbox system a shortcut to resolving several conundrums of spacecraft design.
Xbox's Kinect add-on is a chocolate box-sized three-camera system that detects and analyses gamers' movements and translates them into control instructions. Inspired by Massachusetts Institute of Technology researchers who used Kinect to help a model helicopter achieve autonomous flight, SSTL's Shaun Kenyon wondered if this off-the-shelf capability could be used in space.
Specifically, Kenyon and University of Surrey lecturer Chris Bridges, who are working together on a project to build a shoebox-sized "cubesat" around the electronics in a standard Google Android smartphone, wondered if they could harness Kinect's situational awareness capability to allow two cubesats to autonomously dock and undock in orbit.
This smartphone-based spacecraft - a 10x10x30cm box with four 10x30cm solar panels called STRaND-1 (Surrey Training, Research and Nanosatellite Demonstrator) - is designed to show that low-cost, high-performance results can be attained from a very small satellite built quickly from commercial off-the-shelf components. Taking SSTL's founding concept, that advanced electronics can be the basis of small, relatively inexpensive satellites that provide much of the performance of traditional large, high-cost spacecraft, STRaND-1 will attempt to take pictures of Earth, communicate with the ground and maintain its orientation using the smartphone as a camera, radio and motion detector. Its touchscreen will also, hopefully, be able to detect cosmic radiation. A launch could come later this year, if a piggyback ride with a larger payload can be arranged.
But for STRaND-2, the team will literally be stripping the guts out of Kinect boxes and building them into two standard 30cm cubesat boxes. After launch, these twins will be separated. Once the Kinect systems have scanned the local area, the satellites will be instructed to carry out an autonomous docking manoeuvre, with the help of this onboard spatial awareness system.
Docking systems are, of course, used frequently on large spacecraft, and the European Space Agency's Automated Transfer Vehicle robotic supply ships have, as their name implies, autonomously docked with the International Space Station.
But while docking is unmapped territory for small, low-cost missions, achieving such a capability has potentially huge benefits. As Bridges notes: "It may seem far-fetched, but our low-cost nanosatellites could dock to build large and sophisticated modular structures such as space telescopes.
"Unlike today's big space missions, these could be reconfigured as mission objectives change, and upgraded in-orbit with the latest available technologies."
Other potential applications include spacecraft maintenance missions, with a low-cost "snap-on" nanosatellite providing an existing spacecraft with backup power, propulsion or additional computing power. Without actually docking, Kinect-enabled spacecraft could even engage in formation flying - another approach to reconfigurability.
Formation flying would also provide some protection against the destruction of a mission by orbiting space debris. An array of small satellites that lost, for example, one unit to a debris strike may be able to continue its mission, whereas a single spacecraft is much more vulnerable to complete loss in a strike.
Kenyon and Bridges add that another potential application for a small satellite with spatial awareness is to launch relatively low-cost missions to remove specific pieces of orbiting debris. By locating and attaching to a piece of debris, a small satellite could, conceivably, slow it down enough that Earth's gravity would pull it in.
When it comes to debris, SSTL knows of what it speaks. Until 2009, when an Iridium communications satellite was destroyed by a defunct Russian military satellite uncontrollably falling out of orbit (see box), SSTL had the dubious distinction of having been the only operator to have had a spacecraft actually hit by debris.
That strike truncated a balancing arm that helped the satellite maintain its orientation. In that case the mission was saved by ground controllers, but the event deftly illustrates that, in space, keeping track of what is in the local area is no game.
Source: Flight International
