A Big Future For Tiny Birds
Russia's launch of the basketball-sized Sputnik I in 1957 stunned the world and ushered in the Space Age. But Sputnik was a behemoth compared with the two tiny satellites that sent their first signals back to Earth on Feb. 8. If Sputnik went "beep," these tiny birds went "chirp, chirp." Each one is smaller than a deck of cards and weighs less than half a pound. Yet the signals from these fledgling spacecraft, dubbed picosats, may herald another new era in communications and space research.
The experimental spacecraft, the tiniest ever placed in orbit, were built by Aerospace Corp. in El Segundo, Calif., for a consortium funded by the Defense Advanced Research Projects Agency (DARPA). Connected by a gossamer tether to prevent them from drifting apart, the two picosats talked to each other for a week--and to a third on the ground, mounted in the center of a dish antenna at SRI International in Menlo Park, Calif. Then the AA batteries that were the only source of power gave out. Their low-power radios were adapted from ordinary cordless phones. So the signals could be picked up only when SRI's big data-comm dish was aimed squarely at the satellites. To help track the pair, the tether contains gold wires, which return a strong radar echo.
Everything went so smoothly that today's huge, multibillion-dollar satellites could be getting lots of company in the not-too-distant future. Aerospace executives and others envision a chorus of inexpensive, mass-produced spacecraft that can be spewed from motherships on demand--and even soar off into deep space. "They are a harbinger of all kinds of miniature satellites," says Ernest Y. Robinson, a top engineer at Aerospace and co-author of a seminal paper that launched the concept of tiny spacecraft at a meeting of the International Astronautical Federation Congress in 1993. Since then, satellites have come to be classified by weight--picosats tipping the scales at less than 1 kilogram, or 2.2 pounds, for example (page 130J).
Packed into a mother satellite constructed by Stanford University space-engineering students, the picosats were lofted on a four-stage booster from Vandenberg Air Force Base on Jan. 26. The orbiting twins epitomize NASA's goal of building spacecraft that are smaller, lighter, and cheaper. And they are the closest thing yet to a satellite-on-a-chip.
Picosats rely on an advanced technology known as MEMS, for microelectromechanical systems. These systems integrate semiconductor circuits and minuscule mechanical devices carved from wafers of silicon. Earthbound examples of MEMS include air-bag release triggers in cars and tiny squirt-gun valves in ink-jet printer heads.
The primary goal of the present mission is to test various MEMS devices designed to be switched on and off remotely, via radio commands from the ground or a mothersat. This is a crucial step in demonstrating that MEMS chips are reliable enough to replace the bulky electronics boxes now used in satellites for navigation and orbital control, sensing, and computation. Last July the space shuttle Columbia carried into orbit a package of some 30 MEMS satellite components made by Rockwell Science Center in Thousand Oaks, Calif., including sensors and gyroscope controls. The tiny devices were closely monitored, and their performance was compared with that of the shuttle's own instruments. They passed with flying colors, leading to the current experiment.
MINIATURE THRUSTERS. Last year's shuttle mission was also the first test in space of a novel propulsion system designed to allow tiny satellites to maneuver in orbit. The device, developed by TRW, Aerospace, and California Institute of Technology under a $3.5 million DARPA contract, literally puts thousands of tiny rockets on a computer chip. Each thruster is a pinhead-size silicon box filled with a propellant. On command, microscopic heating elements in the boxes ignite the propellant. The burning fuel bursts through the thin outer face of the box, providing a tiny rocket-like thrust. Although each MEMS rocket can be used only once, arrays of thousands of thrusters might keep a small satellite on course for several years. Engineers estimate that almost a million thrusters could be packed into an area of just 16 square inches.
The thrusters will also be used to "de-orbit" little satellites at the end of their useful lives. That's so they won't add to the space junk already in orbit--floating debris that can pose a collision hazard. "That's a problem you have to address from Day One," says Siegfried Janson, an Aerospace scientist who invented the term nanosatellite.
When all MEMS components have been checked and rechecked and finally judged "space worthy," engineers intend to combine them in slightly larger satellites. These nanosat-size birds would be big enough to do really useful work in space and curb the need for costly monsters as big as cars. The mighty mites would be powered by solar cells and have the navigational skills to roam around space much more freely.
That's what appeals to the Defense Dept. Military planners and intelligence chiefs see great potential for nanosat spies. Mother birds packed with various types of special-purpose nanosats could be parked in orbit until their chicks are needed. Or it might be possible to shoot nanosats into low-earth orbit from a cannon or from high-flying jet planes. Either way, the Pentagon could quickly put a swarm of satellites over tomorrow's Kosovo, avoiding the protracted countdown required to launch a big rocket. The Lilliputian spies would provide a bird's-eye view of a battlefield--including details that might be missed by spy sats at much higher perches.
But Robinson and Janson see many other uses. A few small sats could pick up messages as they pass over one point on the globe, then download them to receivers at other locations. Or they could imitate, on the cheap, the Teledesic concept of a globe-circling constellation, with at least one sat always overhead. Janson says nanosats in contact with 10-meter-diameter ground antennas could handle data at the rate of 1 megabit a second. "One day we may see nanosatellite clusters used for Internet-in-the-sky applications," he says.
PONY EXPRESS. Scientific applications also abound. For astronomers, an array of nanosats could form a giant radio telescope in space that would dwarf ones on earth. Although nanosatellites will be limited to carrying optic systems with lenses no bigger than about 10 centimeters in diameter, that's sufficient to provide a ground resolution in the tens of meters. Suddenly, it could be affordable to continuously monitor agricultural, mineral, and water resources.
For its part, NASA already is planning to use nanosats to study the interaction of the earth's magnetic field with charged particles from the sun. In addition, future planetary probes might create a Pony Express relay back to Mother Earth by dropping off a trail of nansosats as they plunge into space. That would reduce the onboard power needed for distant probes to send reports back to earth, freeing up space for additional scientific instruments.
Scientists predict that the first full-fledged military and commercial nanosats will zip through the heavens in 8 to 10 years. It could happen sooner, thanks to the recent boost from President Clinton. His 2001 budget request includes an 84% increase in nanotechnology funding, with the Pentagon slated to get $110 million for projects such as MEMS--a 57% boost over its current allowance.
So construction of the huge International Space Station continues, and plans are still being drawn up for human bases on the moon and Mars. But a large part of the future may lie with the lightweights--minuscule spacecraft that will fit in an astronaut's pocket.