Nanotechnology

Problems with Large Satellites

Typical satellites deployed in the early twenty-first century weigh more than 1,000 kilograms (2,200 pounds). To qualify as a nanosatellite, the device must weigh less than 20 kilograms (or 44 pounds); a picosatellite less than 1 kilogram (2.2 pounds). Such small nanoor picosatellites could address two of the major problems involved with traditional satellite technology:

1. Cost. The major expense of deploying a traditional satellite lies in transportation costs. A ride on the shuttle averages $6,000 per pound, so the lighter the better. Tiny satellites could possibly be launched using small rockets or electromagnetic railguns, bypassing the expensive shuttle ride altogether.
2. Failure due to one faulty system. If the communications system of a traditional satellite fails, or if the satellite is damaged during deployment, the whole mission might be scrapped, at a loss of millions of dollars. But nano-and picosatellites could be designed with distributed functions in mind: Some may be responsible for navigation, some for communication, and some for taking photographs of target sites. Should a problem develop in one of the units, others in the group with the same function would take over. Distributed functions and built-in redundancy would save the mission.

Early Attempts: OPAL

Thanks to the miniaturization of off-the-shelf computer components, satellites the size of a deck of cards have already orbited Earth, performing simple tasks, and sending signals back to interested parties on Earth. These include groups of college students at Stanford University in California, who designed and built a satellite "mothership" called OPAL (Orbiting Picosatellite Automatic Launcher) as part of their master's degree program; a group called Artemis at Santa Clara University in California, who designed three of the picosatellite "daughterships" for the mission; and a group of ham radio operators from Washington, D.C., whose StenSat picosatellite was also included aboard the mothership. The Aerospace Corporation in El Segundo, California, manufactured the final two picosatellites for the mission to test microelectromechanical systems (MEMS) technology.

OPAL was launched onboard a JAWsat launch vehicle on January 26, 2000, from the Vandenberg Air Force Base in California. It consisted of a hexagonal, aluminum mothership 23 centimeters (9 inches) tall, weighing 23 kilograms (51 pounds), and containing the six small daughter satellites described earlier, weighing about 0.45 kilograms (1 pound) each. When it reached its orbiting altitude of 698 kilometers (434 miles) above Earth, the picosatellite daughterships were deployed by a spring-launching device.

Once free of the mothership, the picosatellites went into operating mode. One of the three Artemis satellites began transmitting the group's web site address in morse code, while the other two measured the field strength of lightning strikes. StenSat's transponder sent telemetry signals to ham radio operators around the world. The two satellites from the Aerospace Corporation were tethered together, and communicated with each other and the engineers on Earth using MEMS switches that selected between various experimental radio frequencies for transmission. OPAL was still operating a year after launch.

Micro-and Nanotechnologies

The technology that made OPAL possible is as near as one's laptop computer or personal digital assistant. Computing power that used to require a mainframe computer in a room of its own can now fit into a laptop, thanks to innovative engineers who continually cram more and more memory onto smaller and smaller silicon chips. The student engineers used a Motorola microcontroller with 1 MB of onboard RAM operating at 8.38 MHz as OPAL's central processing unit. It was powered by commercially available solar panels, and backed-up by rechargeable nickel cadmium batteries.

But off-the-shelf components, while sufficient for student projects, will not survive at the cutting edge of nanosatellite technology; other technologies will be necessary to keep the smaller-and-smaller trend going. MEMS are tiny devices—gears, switches, valves, sensors, or other standard mechanical or electrical parts—made out of silicon. The technology arose out of the techniques used by microchip designers: pattern a wafer of pure silicon with the dimensions of the transistors, resistors, logic gates, and connectors required for the chip, etch away the material surrounding the pattern, and one has the beginnings of an electronic circuit. So why not do the same for mechanical systems? Lay out a pattern for a tiny gear on a silicon wafer, etch away the surrounding material, including the material underneath that holds the gear to the wafer and to its axle, and one has a working gear that can mesh with other gears. By making sandwiches of different materials and etching them in a carefully controlled manner, scientists have been able to make gears, valves, pumps, switches, and sensors on a very small scale—the microscale. MEMS technology is often called a "top-down" approach: start with a large wafer of silicon and make microcomponents out of it.

To reach the even smaller nanoscale requires a "bottom-up" approach. Using instruments such as an atomic force microscope that can manipulate individual atoms, engineers can build tiny devices an atom at a time. Or, by understanding how atoms tend to bond together naturally, scientists can create conditions where nanoscale devices "self-assemble" on a patterned surface out of the atoms in a vapor. Such precise control will enable them to build nanostructures 1,000 times smaller than MEMS devices. This level of structural control will be necessary for the next generation of sophisticated nano-and picosatellites currently in the planning stages.

What Is Next?

The National Aeronautics and Space Administration's (NASA) Space Technology 5 (ST5) mission is scheduled to launch three nanosatellites into low orbit in 2003. The ST5 nanosatellites will be small octagons about 43 centimeters (17 inches) in diameter and 20 centimeters (8 inches) high—about the size of a big birthday cake. They will be complete systems in themselves, each having navigation, guidance, propulsion, and communications abilities. In addition, the ST5 nanosatellites will be test platforms for new space technologies. One of these, called A Formation Flying and Communications Instrument is a communications system designed to monitor the positions of small spacecraft relative to each other and the ground—a first attempt at making satellites fly in formation. Other technologies to be tested on ST5 include a lithium-ion power system that can store two to four times more energy than current batteries, an external coating that can be tuned to absorb heat when the spacecraft is cold or to emit heat when it is too warm, and a MEMS chip that makes fine attitude adjustments to the spacecraft using 8.5 times less power than 2002 devices.

By 2020 NASA hopes to deploy ANTS to the asteroid belt between Mars and Jupiter. ANTS stands for Autonomous Nano Technology Swarm. Each tiny spacecraft would weigh about 1 kilogram (2.2 pounds) and have its own solar sail to power its flight. After a three-year trip, the swarm would spread out to cover thousands of asteroids. The swarm would have a hierarchy of rulers, messengers, and workers. Each satellite would carry one type of instrumentation to perform a specific function: measure a magnetic field, detect gamma rays, take photographs, or analyze the surface composition of an asteroid. Messengers would relay instructions from the rulers to the workers, and also inform the rulers of important information collected by the workers. The rulers could then decide to reassign some of the workers to explore the more promising areas. In the end, a small number of messengers would return to the space station to deliver the data to scientists; the rest of the swarm would perish in space, having finished their duties. Scientists hope to obtain valuable information about the mineral resources of the asteroid belt, which could be a source for metals and other raw materials needed to build colonies in space.

Future Prospects

Nano-and picosatellites will also be useful in Earth orbit in situations where information from a large area is needed simultaneously. Traditional satellites can only be in one place at a time, but picosatellites can be everywhere, if enough of them are deployed. A swarm of picosatellites equipped with cameras and communications links could gather vital information from a battlefield on Earth, relaying enemy positions and troop counts to generals behind the lines. Or an array of satellites could be launched to gather atmospheric information that could help to predict the formation of hurricanes and tornadoes in time to warn the population. The Earth's entire magnetic field might be captured in one instantaneous "snapshot" by widely scattered swarms of satellites.

Projecting far into the future, perhaps a picosatellite could be made that would travel as far as possible into space, then manufacture a copy of itself before its mechanisms failed. This second generation robot/satellite could then travel as far as it could before making another replica, and so on. By sending out millions of tiny, affordable, self-replicating satellites, humankind's reach might one day extend to the farthest parts of the solar system.

SEE ALSO MINIATURIZATION (VOLUME 4); ROBOTIC EXPLORATION OF SPACE (VOLUME 2); ROBOTICS TECHNOLOGY (VOLUME 2); SATELLITES, TYPES OF (VOLUME 1).

Tim Palucka

Bibliography

Booth, Nicholas. Space: The Next 100 Years. New York: Orion Books, 1990.

The Editors of Time-Life Books. Spacefarers. Alexandria, VA: Time-Life Books, 1990.

Internet Resources

Orbiting Picosatellite Automated Launcher. Stanford University.<http://ssdl.stanford.edu/opal/>.

Space Technology 5 (ST5). New Millennium Program.<http://nmp.jpl.nasa.gov/st5>.