NASA Successfully Launches Science Satellite Quintet

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Five THEMIS Probes To Track Geomagnetic Substorms

NEW YORK — Five NASA probes blasted into space Feb. 17, kicking off a two-year mission to hunt down the source of some of Earth’s most colorful auroral displays.

After two delayed attempts, a United Launch Alliance Delta 2 rocket successfully hauled the five THEMIS probes into orbit for NASA from Pad 17B at Florida’s Cape Canaveral Air Force Station.

“It was a very smooth count and it was a very good payout after yesterday’s tough one,” NASA launch director Chuck Dovale said following the launch.

Poor weather prevented preparations for a Feb. 15 THEMIS launch, only to be followed by high upper-level winds that thwarted a Feb. 16 launch attempt just minutes before the mission’s planned liftoff.

“Upper air winds were not an issue,” Dovale said. “The count was very quiet.”

The THEMIS launch has been delayed since October due to booster issues, NASA officials said.

THEMIS, short for Time History of Events and Macroscale Interactions During Substorms, marks the most spacecraft ever launched at one time for the space agency, NASA officials said.

The mission’s first probe — dubbed Probe A — popped free of its carriage about 73 minutes after launch as planned, with its four counterparts deploying like flower petals about three seconds later.

The five 128-kilogram THEMIS probes are nearly identical and designed to track the origin of powerful geomagnetic substorms within the Earth’s magnetic field.

Substorms occur when charged particles belched from the Sun crash into the Earth’s magnetic field, where they are funneled along magnetic field lines to the Earth’s North Pole to spur undulating ribbons of multi-colored hues in the aurora borealis, also known as the Northern Lights.

Without substorms, auroras would appear as a static sheet of greenish illumination, researchers said.

By pinpointing substorms, researchers hope to develop a better understanding of space weather — such as the high-energy particles produced by the Sun in solar flares — which can interfere with satellite communications and even endanger astronauts flying in Earth orbit. But researchers are still unclear on where substorms originate.

“Finding the elusive substorm point of origin is a question almost as old as space physics itself,” THEMIS principal investigator Vassilis Angelopoulos, of the University of California, Berkeley, told reporters in a Jan. 17 teleconference. “[The mission] is a stepping stone towards understanding space weather phenomena that affect our lives.”

The speed of the substorms makes tracking their starting point impossible with a single spacecraft, mission researchers said.

“By tracking those energy releases from one satellite to the other, [THEMIS] will be able to detect for the first time where those releases emanate,” Angelopoulos said before the Feb. 17 launch. “Really it’s an analogous system to what meteorologists use on the ground.”

Angelopoulos added that he hopes the THEMIS mission will shed new light on predicting space weather in the future. THEMIS draws its name from the Greek goddess of justice and wisdom.

First identified in the 19th century, geomagnetic substorms are recurring phenomena spawned by a sudden release of charged particles — collected from the Sun’s solar wind — in the Earth’s magnetic field. The high-energy particles follow the Earth’s magnetic field lines until they strike the upper atmosphere, giving a boost to the Northern Hemisphere’s aurora borealis, researchers said.

While a substorm’s aurora amplification seems like a limited visual effect, a series of such storms can occur during major space weather events that interfere with communications satellites or pose risks to astronauts in orbit, Angelopoulos said.

The $200 million THEMIS mission stems from a partnership between UC Berkeley and NASA’s Goddard Space Flight Center in Greenbelt, Md.

Built by UC Berkeley and Swales Aerospace, the five THEMIS probes are designed to take up stations in ever-higher orbits ranging between one-sixth and half the distance between the Earth and Moon. Every four days, the probes are expected to align with one another and ground stations on Earth to provide a curtain of sensors to scan for substorm activity for at least two years.

Only four THEMIS satellites are required to complete a primary two-year mission. After reaching orbit, two of the probes will be sent on a trajectory that carries them about one-sixth of the way to the Moon while two others take up stations about halfway to the Moon. The fifth THEMIS satellite is a spare in case one of its counterparts fails during the initial two-year mission.

“We’re flying five to increase our reliability,” Angelopoulos said.