February 10, 2000
Pint-Size Satellites Will Soon Be Doing Giant Jobs
With half-pound birds already in orbit, a new era in space exploration, military technology, and telecommunications is dawning
Russia's launch of basketball-sized Sputnik I in 1957 stunned the world and ushered in the Space Age. But Sputnik was a behemoth compared to the two satellites that sent their first signals back to Earth on Feb. 8. If Sputnik went "beep," these tiny birds -- smaller than a deck of cards and weighing less than half a pound -- are going "chirp, chirp." The signals from these fledgling spacecraft, dubbed picosats, may also be the wake-up call for a new era in communications, defense, and space research.
The experimental spacecraft, the tiniest ever placed in orbit, were built by Aerospace Corp. as part of a consortium funded by the Defense Adanced Research Agency (DARPA). Connected by a gossamer tether to keep them in radio range of each other, the picosats are now talking to each other as well as to a third picosat on the ground over communications systems adapted from conventional cordless telephones.
Their builders envision a not-too-distant day when huge, multibillion dollar satellites may have lots of company in orbit. They'll be joined by 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, who was co-author of a seminal paper that launched the concept of tiny spacecraft at a meeting of the International Astronautical Federation Congress in Graz, Austria, in 1993.
SMALLEST SATELLITE: Picosats launched on Jan. 26 weigh less than one-half pound each and measure 4 by 3 by 1 inches
CREDIT: Aerospace Corp.
Packed into a mother satellite constructed at Stanford University called OPAL, the picosats were lofted on a four-stage booster from Vandenberg Air Force Base on Jan. 26. The orbiting twins epitomize the National Aeronautics & Space Administration's goal of building spacecraft that are "smaller, lighter, and cheaper." And they are the closest that researchers have come to creating a "satellite-on-a-chip."
FROM THE MOTHERSAT.
Picosats rely on an advanced technology known as MEMS, for microelectromechanical systems. These systems integrate logic circuits and mechanical devices carved from wafers of silicon. Earthbound examples of MEMS include air-bag triggers and ink-jet printer heads.
The primary goal of the present mission is to test MEMS radio switches made by Rockwell Science Center in Thousand Oaks, Calif., and to demonstrate that miniature satellites can be released from a mothersat by a command from the ground, and then operate in space. Last July, the space shuttle Columbia carried into orbit a test package of some 30 MEMS satellite components, such as sensors and gyroscope control systems. The tiny devices were capable of such essential functions for any spacecraft as navigation and control, sensing, propulsion, computation, and thermal control.
The shuttle mission was the first test in space of a novel propulsion system designed to allow tiny satellites to maneuver in space. The device, developed by TRW, Aerospace, and the California Institute of Technology under a $3.5 million DARPA contract, literally puts thousands of tiny rocket motors on a computer chip. Each thruster is a silicon box that measures about 700 to 1,000 microns on a side and is filled with a propellant such as those used in automotive air bags.
ROCKET-ON-A-CHIP: Array of 19 tiny microthrusters (left) is drawfed by a penny. But each produces produces 100 watts of power for an instant when they are fired -- enough energy to maneuver a small satellite (right)
CREDIT: Aerospace Corp., Caltech
Microscopic heating elements in the boxes ignite the propellant in response to a control signal. The burning fuel bursts the thinner outer face of the box, providing a tiny thrust like a rocket motor. Although each rocket element can be used only once, arrays of thousands, even millions, of thrusters might keep a small satellite on course for a few years. The engineers estimate that almost a million thrusters could be packed into an area of just 16 square inches.
When all the components have been tested and judged "space worthy," the engineers intend to combine them in slightly larger satellites capable of useful work in space. Called nanosatellites and weighing from 2 to 20 pounds, they will be powered by solar cells and have navigational capability.
The Defense Dept., of course, sees a great potential for nanosats. Satellites packed with various types of nanosats could be placed in orbit until the small satellites are needed. For example, a swarm of miniature satellites could communicate with sensors on a battlefield and convey important surveillance and tactical information. Or they could be used to destroy incoming ballistic missiles.
But Robinson and his colleague Siegfried Janson, a senior scientist who coined the term nanosatellite at the Graz meeting in 1993, see many other uses. They could pick up messages as they pass over one part of the globe, then download them to a remote receiver. Networks of nanosats configured so there's always at least one overhead at any time could carry telephone calls and data. Janson says nanosats communicating with 10-meter diameter ground antennas could transmit and receive data at the rate of 1 megabit a second. And arrays of nanosats flying in formation could function as a giant antenna. "One day we may see nanosatellite clusters used for Internet-in-the-sky applications," he notes.
Scientific applications also abound. Even though nanosatellites will be limited to optics up about 10 centimeters in diameter, ground resolution will be tens of meters in the visible-light range. Agricultural, mineral, and water resources could be mapped and monitored continuously. Various nanosatellites could look at different parts of the visible and infrared spectrum to produce maps.
LIKE HANSEL & GRETEL.
For its part, NASA is already planning an experiment called the Magnetospheric Constellation 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 communications relay back to Mother Earth by dropping off trailing nansosat relays as they plunge into the distant reaches of the solar system.
The satellite scientists preduct that the first full-fledged military and commercial nanosats will be zipping through the heavens in 8 to 10 years. The effort just got a boost from President Clinton, who included an 84% increase in nanotechnology funding in his 2001 budget request. Of the $227 million earmarked as the National Nanotechnology Initiative, the Defense Dept. is slated to get $110 million in funding for projects such as MEMS -- a 57% increase over the current budget.
The drive to make satellites ever-smaller is hardly played out. Just when we've added picosat and nanosat to our vocabulary, along comes "smart dust." A group at the University of California at Berkeley has begun a DARPA-funded effort to create MEMS particles, each no more than a cubic millimeter in size, that could be lifted for brief intervals by microthrusters to monitor weather, air quality -- or a battlefield.
So construction of the huge orbiting International Space Station continues, and plans are drawn for establishing human bases on the Moon and Mars. But a large part of the future may lie with the lightweights -- minuscule spacecraft that would fit in an astronaut's pocket and perhaps be as tiny as grains of star dust.
For More Information:
Sound file of Sputnik's beeps
Background on small satellites
Description of MEMS technology from Sandia National Laboratories
By Alan Hall in New York
EDITED BY DOUGLAS HARBRECHT
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