The drop went off on schedule at 6:04 a.m. Pacific Time from the mission's Orbital Sciences L-1011 jetliner, flying south-southwest over the Pacific Ocean off the California coast. At the moment the Pegasus first-stage engine ignited, the announcer at Vandenberg said the mission was away "to demonstrate that good science can come in small packages."

Pegasus performed as designed, with its second stage igniting about two minutes into the mission, after the rocket reached an altitude of 120 miles at a speed of about 12,000 miles (19,000 kilometers) per hour. After five minutes, the third stage motor kicked in and at seven minutes the spacecraft achieved orbital speed of 18,000 miles (28,000 kilometers) per hour and reached 200 miles in altitude, and one-by-one released its triple micro-sat payload.

The ST5 mission is part of NASA's New Millennium project, which was established to test the concept of using low-cost micro-sats, and to validate new technologies for future low-cost science missions. The three ST5 spacecraft are designed to collect data on Earth's magnetic field for at least 90 days and study the relationship between the magnetic field and the formation of auroras.

One test device included in the mission is a tiny heat radiator with components so small they are visible only under a microscope. The radiator employs shutters so small that several abreast are narrower than the width of a single human hair.

Scientists at Johns Hopkins University's Applied Physics Laboratory in Laurel, Md., attached the device to the skin of one of the ST5 satellites, to demonstrate how the technology can be used to regulate the temperature of a satellite or one of its instruments.

"This is the first time a fully space-qualified device of this type has ever been flown, and the first to be flown on the outside of a satellite," said APL team member Ann Darrin. "It's also the first demonstration of MEMS technology used to actively control temperature."

In a 4-inch-square section atop one of the micro-satellites, tiny comb-shaped motors powered by electrostatic charges open and close microscopic shutters to regulate the temperature of that area of the satellite. "When a satellite's in space, you need to keep its temperature constant," Darrin explained. "As we shrink the size of satellites and their onboard systems, it becomes harder to regulate and maintain a constant temperature. By putting these devices on the outside or skin of a satellite you can change its emissivity.

She said when the satellite is facing the Sun the device can cool the satellite by closing the shutter doors and reflecting the heat. Or, to warm the spacecraft, the shutters can be opened.

The 4-inch square radiator contains 36 chips, each about the size of a single key on a computer keyboard. Under a microscope, there are 72 shutter segments, each driven back and forth by six tiny motors controlled from an electrostatic charge-based power source located inside the satellite.

To protect the tiny devices from dust and condensation, which could hinder their operation, the team encased the devices in a window using a clear material known as CP-1, a polymer rugged enough to sit on the outside of a satellite during space-based operations, and more cost-effective than materials like single-crystal sapphire.

"Often people associate small with being frail," Darrin said, "but our tiny shutters, which don't touch when they close, are exceptionally strong, particularly when operating in space without gravity, weight or resistance forces to wear or degrade moving parts."

She said the small lightweight devices could shave off numerous pounds from a micro-sat, resulting in smaller radiators, for example, and making the overall micro-sat more efficient and cost-effective.

On March 15, controllers aborted an attempt to launch the ST5 mission after a locking pin failed to retract aboard the Pegasus just prior to the rocket's release from the L-1011 lifting aircraft.

Related Links
ST5
Pegasus
New Millennium
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