MSFC team
studies Earth's
magnetic
field

Up to now, trying to understand the Earth's magnetic field has been like trying to understand a hurricane by standing on the beach.

Now, though, scientists from Marshall Space Flight Center are part of a team trying to get a better view from deep space.

Weather satellites like the Explorer 1 launched in 1958 gave scientists a bird's-eye view of hurricanes, but satellites in low earth orbit can't give the same view of the planet's magnetosphere, Marshall physicist Dr. Dennis Gallagher said.

The magnetosphere extends from 14,000 to 27,000 miles, he said. But most satellites orbit within a few hundred miles of Earth. They can measure particles at a given point, but scientists really need a satellite that can get above the magnetosphere to see large-scale features.

Scientists want to know as much about the space around the Earth as they would any other part of the planet's environment.

They already know that the interaction between the sun and the magnetosphere can cause beautiful auroras. The interaction, though, also can also induce unwanted currents in long-distance transmission lines and burn out transformers on Earth or scramble satellite computer codes and blow circuits in space.

Marshall scientists are part of a team that was selected to build a satellite called IMAGE - Imager for Magnetopause-To-Aurora Global Exploration. Their proposal was one of 44 for the next in a series of relatively inexpensive space science missions called Medium-Class Explorers, or MIDEX, that the space agency hopes to fly in coming years.

The 660-pound satellite is scheduled to be launched by unmanned rocket in January 2000 on a two-year mission, Gallagher said. Launched into an elliptical polar orbit some 45,000 miles at its highest point, it will be able to look down at the magnetosphere.

Gallagher is a co-investigator on a team led by principal investigator James Burch of Southwest Research Institute in San Antonio. Lockheed Martin will build the basic satellite. The institute will install the science instruments.

IMAGE will house seven science instruments: two auroral cameras, a plasma imager, three neutral atom cameras and a radio sounder. Marshall plans to design and build two of them - a high energy neutral atom camera and an electron auroral imager.

Scientists here also are performing the theory and computer modeling that will help scientists design their instruments and interpret the resulting data gathered.

The magnetosphere can't be seen directly, Gallagher said. Scientists get a picture of it by measuring the behavior of charged and neutral atoms, referred to as plasma, that follow magnetic field lines the same way other scientists study winds by watching cloud movements.

Artists drawings of the magnetosphere are "technically science fiction," Gallagher said. They are a best-guess picture, based on efforts to understand measurements at individual points.

"When you can't see the whole thing and don't have science instruments every kilometer in every direction, you have to assemble an impression of what's happening on a statistical basis," he said. "You have to infer things you don't see that you can't directly measure based on things you do directly measure."

Earth's magnetic field is shaped like a giant doughnut with holes at the north and south poles, scientists think. The charged particles of the solar wind, however, flatten out the field on the planet's daylight side and "blows" it out into a long tail on the nighttime side.

That unseen plasma contains a lot of power, anywhere from tens to hundreds of thousands of electron volts. It was that energy NASA's recent tethered satellite experiment tired to tap as a prelude to a possible source of power for future space stations.

Gallagher said the $42 million mission should show plasma locations, densities and movement within the magnetosphere.

Satellites since the first U.S. satellite, Explorer 1, have measured particles and fields around them, but scientists can't be sure whether the changes they have observed are actual changes in the field or changes caused by the satellite location, he said.

"Everybody's betting we see things we didn't anticipate," Gallagher said. "We'll be flying instruments to look at an environment we've become accustomed to, but in an entirely new way. It's going to provide a tremendous amount of insight."