In a recent edition of New Scientist, there is an headline which says that sundial principles are being applied to satellites.
In seems that for the new generation of micro-satellites designers want to avoid having lots of heavy on-board batteries, and so will rely on small solar panels to provide power at the time it is needed. With only a few small batteries to provide a reserve, it is important to have the solar panels aligned correctly to maximise power generation. The solution as described is a silicon chip, about 0.5 cm2 with hundreds of tiny cylindrical holes drilled though it. Below that is a light-sensitive pixel grid, like the CCD "eye" in a videocam. Dependant on the angle of incident sunlight, different combinations of CCD pixels are illuminated. Some additional circuitry analyses the pattern of illumination to calculate how the device is orientated relative to the sun, and thus can steer it to the best position. The answer is good to a few minutes of arc. The headline caught my attention, but after reading the article I don't think it is really like a sundial. It reminded me more of those sun-shadow devices for aligning dish antennae, or perhaps one of the digital sundials which uses a weird grid to make a number-shaped shadow. The article is only a few short paragraphs and doesn't say much more than my summary, but if you want to read it look in New Scientist for April 21st 2001, page 20. Steve --------------------------------------------------------- Want to know who's going to win in your constituency? Try my UK Tactical Voting Wizard at http://users.eastlink.ca/~srgl/election2001.htm
