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"It's exciting to be in a position where you know you're
going to stumble onto things you didn't suspect were there,"
said Dr. Dennis Gallagher at NASA's Marshall Space Flight Center.
That's because in the 41 years that scientists have been studying the magnetosphere - the immense cloud of ionized gas formed by Earth's magnetic field - scientists have never gotten a picture of it. Somewhat like being in a massive fog, they have taken countless measurements throughout the magnetosphere, and taken pictures of its effects on the upper atmosphere. But the overall shape of the magnetosphere can only be inferred from those data.
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Feb. 16, 1999:
A unique camera that will take some of the first pictures
of Earth's invisible magnetic shield is being prepared for flight
on Feb. 15, 2000. The mission, called IMAGE, will explore a region
of space where the aurora is energized.
Stepping back for a better view
Gallagher is a co-investigator for the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite scheduled for launch from Vandenberg Air Force Base, Calif., on Feb. 15, 2000. IMAGE will be the first satellite that will let scientists step back and take pictures of the magnetosphere as it changes shape. The Earth's magnetic field acts as a buffer between the terrestrial environment and the solar wind. The two best known effects of the magnetosphere are the aurora borealis and the Van Allen radiation belts. The aurora is caused by electrons and ions zinging back and forth along the magnetic field lines and reversing course when they hit a "mirror" point. When energized by a solar storm, these particles can punch through the mirror points and hit the outer atmosphere, causing the aurora's enchanting glow. The Van Allen belts, named for discoverer James Van Allen, can disrupt the electronics of satellites.
These solar-terrestrial effects can also disrupt communications, cause massive power outages, and even corrode long-distance pipelines. As a result, the magnetosphere has been studied closely since Van Allen's discovery in 1958. Knowing the shape of the magnetosphere and how it changes in response to the solar wind will help scientists in predicting what the effects will be here on Earth. IMAGE's objectives are:
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Left: IMAGE
will be placed in an orbit that loops high above the Northern
Hemisphere to provide wide views of the aurora borealis and the
inner magnetosphere. The elliptical orbit will precess during
the 2-year mission.|
Right: A cutaway diagram of the magnetosphere illustrates how IMAGE will observe the magnetosphere. Assembling an IMAGEAmong the instruments will be the Wideband Imaging Camera (WIC) provided by NASA/Marshall. Science and engineering teams at NASA/Marshall recently completed testing and calibrating the WIC and sent it to the University of California at Berkeley which integrated it into the full collection of far-ultraviolet cameras. That assembly now is at Southwest Research Institute in San Antonio, Texas, for integration onto the instrument deck plate and more testing. Finally, the assembly will be sent to Lockheed Martin in Sunnyvale, Calif., for final assembly of the spacecraft, and then to Vandenberg Air Force Base, Calif., for launch. "The WIC is an unusual instrument," Gallagher said. "We here at Marshall and at the University of Alabama in Huntsville have a great deal of expertise in ultraviolet optics and experience in auroral imaging." |
To do that, IMAGE
will be launched into an orbit that loops from a low point of
1,000 km (600 mi) to a high point of almost 45,000 km (almost
27,000 mi). From that vantage point, IMAGE's instruments will
look back and be able to see the inner structure of the magnetosphere,
including the magnetopause, the boundary where the magnetosphere
meets interplanetary space.
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WIC builds on the team's experience with the Ultraviolet Imager (UVI) now operating aboard the Polar spacecraft. UVI provides images of the aurora borealis on both night and day sides of the northern hemisphere. The WIC will be sensitive to light in the 140-160 nm range (visible light spans 300-700 nm). It will have a 17x17-degree field of view (about 34 times the apparent diameter of the Moon) so it can see the entire Earth. WIC is one of three cameras in the far-ultraviolet instrument. The Spectrographic Imager will measure different types of aurora and remove the bright geocorona emissions from the images. The Geocorona Photometers will observe the distribution of the geocorona emissions to derive the magnetospheric hydrogen content responsible for neutral atom generation in the magnetosphere. |
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Left: The Wideband Imaging Camera shortly after it completed testing. An open treasure chestUnlike most other science missions, all the data from IMAGE's instruments will be made available to anyone as soon as it arrives. Traditionally, NASA has given the principal investigator exclusive use of the data for up to a year after it arrives.
CD-ROMs containing high-resolution data (cleansed of noise and formatted for use) will be sent to the principal investigators and to the National Space Science Data Center at NASA's Goddard Space Flight Center in Greenbelt, Md. Any scientist can access IMAGE data to explore the magnetosphere. "It's going to be an exciting time," Gallagher said. "Every time you figure out a new way to measure your environment, whether it's the universe or microscopic, you see things you didn't think would be there. You learn. That's what research is about. You learn more about the environment in new ways." |
Three other types
of instruments will be on IMAGE. A battery of three neutral atom
imagers will detect the presence of atoms by recording the light
given off when they collide with hydrogen atoms. A Radio Plasma
Imager will make cross-sectional images somewhat like a medical
CT-scan, by using the echoes from radio pulses broadcast by the
satellite. And the extreme-ultraviolet (EUV) imager will take
pictures at 30.4 nm of sunlight scattered by helium ions in the
plasmasphere, a donut-shaped region mostly containing hydrogen,
helium, and oxygen ions.|
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