How small can satellites get and still be functional?

Look around—everything containing electronics is shrinking. So too with satellites. Currently, nanosatellites weighing as little as a kilogram (2.2 pounds) are available for orbital missions. The Stanford University and QuakeFinder of Palo Alto, California, in 2003, for example, consists of three four-inch-wide "Cubesats" weighing a mere 10 pounds combined. And pico-satellites as light as a cell phone (0.1 – 1 kg) are on the drawing board, says Young K. Bae, founder of the Bae Institute, currently under contract with the NASA Institute for Advanced Concepts to study ways to shrink satellite size.

How tiny can they get and still work?

Bae says two major factors limit how small satellites can get. The first is developing tiny thrusters to control them. "The attitude control of pico-satellites would require thrust on the order of tens of micro-newtons, while the femto-satellites (weighing less than one-tenth of a kilogram) may require thrust below micro-newtons." he says from his headquarters in Tustin, California. (A newton is the amount of force required to acclerate a mass of one kilogram by one meter per second, squared.) "Currently, there are no reliable micro-thrusters in this range, thus revolutionary new propulsion technologies may be required."

The second problem is the size of the sensors needed to do something useful in orbit. Bae laments that the laws of physics govern how far you can shrink telescope mirrors. To see something on Earth at a resolution of .3 meter (one foot) from an altitude of 500 kilometers, a telescope needs a mirror at least one meter in diameter. "Single pico- and femto- satellites would not be able to carry such large devices," he says. But multiple satellites flying in formation could form a virtual aperture or provide a frame for a membrane mirror.

Not surprisingly, that's what NASA has contracted him to study: ways of creating networks of small sats that can get big jobs done. If engineers can perfect these methods, Bae predicts clusters of satellites the size of ping-pong balls will soon be spinning in orbit.