was doing useful work when it lost its ability to point steadily in a desired direction. The problem is that sunlight pushes the craft around just enough so it loses track of its target, and with two of its four stabilising wheels offline it can't get images of a high enough quality. Now engineers have worked out that if they keep the craft in a careful orbit where the sun shines with equal pressure on the whole of one side they can get away with only two stabilisers. Testing's underway, ready for a mission review. Presumably that could then lead to heating and cooling problems.

AN IDEA WITH WHEELS: Aircraft need massive engines to fly through the air, but make a lot of noise and waste a lot of fuel using them to taxi on the ground. That's where the WheelTug comes in. It's a system of small electric motors powerful enough to move a huge aircraft around on the tarmac, using only the plane's auxiliary power unit. The system could save each plane around $700 per flight. The WheelTug also means pilots don't have to wait for the plane to be pushed back from the gate. Very efficient.

BUY A LITTLE LIGHT: Families in sub-Saharan Africa are likely to rely on dangerous and expensive diesel or kerosene for fuel, but while solar power would be a good alternative the upfront costs are often just impossible to meet. Indigo is a way to get around that problem, with a pay-as-you-go system. Local kiosks that sell prepay phone cards also sell scratch cards that allow users to buy a week's worth of electricity for about half the cost of the kerosene they'd usually buy. The user enters a code into the Indigo controller and the system works until the credit expires. After about 18 months users can pay a bit extra to unlock the controller or to upgrade to a bigger system. The solar controllers can charge cellphones and provide lighting for two lamps for 8 hours each night. Timely help: a brilliant system.


TIME A LITTLE LIGHT: Time of Flight cameras send light towards an object and measure how long it takes to bounce back. That reveals how far away the object is. In real life though things like fog, motion, transparency and other factors create multiple reflections, making it difficult to determine which is the correct measurement. A team at MIT though has come up with some sophisticated calculations to work out which is the true object. Their nano-camera probes a scene with a continuous-wave signal that oscillates at nanosecond periods, all using low cost off-the-shelf LEDs. Then an algorithm untangles the signals. Their nanophotography model could be used in medical imaging, collision-avoidance detectors for cars, and interactive gaming. It's all in the algorithm.

FLIPPING ROBOTS: Underwater shipwrecks can be very dangerous places, but the U-CAT underwater robot, designed to work inside shipwrecks, has flippers that allow it to swim through them. The robot can swim forward and backward, up and down and turn on the spot in all directions, making it totally manoeuvrable. An onboard camera allows its controllers to observe the whole journey. The robot will help archaeologists and others to explore shipwrecks without putting divers in dangerous positions. Tallinn University of Technology.

Miraz Jordan,