Image: THEMIS satellites
NASA
NASA's five THEMIS satellites are shown just after deployment in this artist's interpretation.
By Staff Writer
updated 2/16/2007 4:25:32 PM ET 2007-02-16T21:25:32

Five NASA probes aimed at unraveling mysteries surrounding Earth’s colorful auroras are set to launch Friday evening after a 24-hour weather delay.

A United Launch Alliance Delta 2 rocket carrying the five probes that make up the Time History of Events and Macroscale Interactions During Substorms mission is scheduled to liftoff at about Friday at Kennedy Space Center in Florida. The launch will set a new NASA record for the most number of scientific satellites ever launched into orbit aboard a single rocket.

“We’re complete through all of our readiness reviews,” launch director Chuck Dovale told reporters Thursday during a press conference. “The team is poised to start countdown tomorrow and we’re ready to go.”

The probes were originally set to launch on Thursday but thunderstorms and severe weather in the Cape Canaveral region the day before interrupted fueling of the rocket.

Weather forecasters are optimistic that winds tonight will not reach beyond about 29 mph (25 knots), which is the minimum requirement for a launch abort.

THEMIS consists of five identical probes, each about the size of a dishwasher and weighing nearly 300 pounds, that will spread out to form a unique constellation aimed at studying the aurora borealis and aurora australis — the colorful light shows that occur over Earth’s northern and southern polar regions, respectively.

Undulating like rainbow ribbons in the sky, auroras are visible manifestations of so-called “geomagnetic substorms” that occur in near-Earth space. These substorms are caused when electrically charged gas blown by the sun’s solar winds slam against Earth’s magnetic shield, called the magnetosphere.

THEMIS will help answer scientific questions about when and where the substorms start, but it could also have practical implications, said Dick Fisher, director of NASA’s Helios Division. For example, Fisher said, airlines currently require pilots flying over the North Pole to maintain constant communications. If communications is broken, as can occur during substorms, pilots are required to land their planes. Being able to predict when substorms might occur could thus help airlines better plan their routes.

“To get a jetliner on the ground and make it stay overnight costs a lot of money,” Fisher said.

When they begin data collection next winter, the five THEMIS probes will align over North America once every four days, allowing 20 ground stations in Canada and Alaska to monitor substorms for 15 to 20 hours at a stretch. Over the mission’s two-year lifetime, the probes are expected to observe some 30 substorms.

“We’re looking forward to the next challenge,” aid UC Berkley’s Peter Harvey, NASA’s THEMIS project manager, “which is synchronizing all five spacecraft over North America and keeping them humming along.”

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