快猫短视频

A COUPLE of sundials is all it takes to ensure that the solar panels of small
satellites are always pointing at the Sun. 快猫短视频s at NASA鈥檚 Jet Propulsion
Laboratory in Pasadena, California, have shown that sensors working on the
sundial principle will keep a satellite鈥檚 solar panels working at maximum
efficiency.

Satellites that weigh less than 10 kilograms, known as 鈥渘anosatellites鈥�,
cannot carry huge on-board power supplies, says Richard Blomquist, who works on
nanosatellites at Carnegie Mellon University in Pittsburgh. 鈥淭hey largely depend
on solar power, so it鈥檚 extremely important they know where the Sun is,鈥� he
says.

To build the satellite鈥檚 sundials, Carl Christian Liebe and Sohrab Mobasser
took a 0.5-centimetre-square wafer of silicon and drilled hundreds of holes in
it. They fixed another silicon sheet containing a grid of light-sensitive
charge-coupled devices 0.75 millimetres beneath it. 鈥淭he idea is that depending
on where the Sun is, as it hits the top wafer it鈥檒l cast a shadow on the CCD,鈥�
says Liebe. 鈥淔rom where the shadow falls, you can work out where the Sun
颈蝉.鈥�

Liebe tested the device in a room fitted with a 鈥渉eliostat鈥� in its roof, a
device that directs a beam of sunlight down into the room below. By moving the
sensor and monitoring the image on the light-sensitive wafer, Liebe was able to
calculate the angle of the Sun to within a few minutes of a degree.

鈥淵ou鈥檙e absolutely going to need something like this,鈥� says Blomquist. But he
says that nanosatellites will need more than one sensor. 鈥淚f your satellite
takes a tumble, you can鈥檛 risk the sensor ending up on the wrong side of the
satellite,鈥� he says.