New tools for the new millennium

Satellites will slice and dice the magnetosphere
to reveal its structure

Oct. 30, 1998: Over the past decade, space scientists have made great strides in understanding the mysterious mantle of electrified gas surrounding our planet. With the start of the new millennium - the theme of this workshop - they are ready to step out with a new range of tools that will ask more sophisticated questions in search of more definitive answers.

But first, they will extend the life of a winning team, the four spacecraft of the International Solar Terrestrial Physics (ISTP) program. Operations with Polar, Wind (both pictured above), Geotail, and the recently recovered Solar Heliospheric Observatory (SOHO) have been extended through 2002 to cover the upcoming solar maximum.

To date, the ISTP program has resulted in more than 800 professional papers, said Dr. Robert Hoffman, project scientist for Polar, and has significantly advanced our understanding of space physics from the dynamics of the sun to the origins of substorms in space around the Earth. More than 55 gigabytes of high-resolution data have been published on 81 compact disks.

All four spacecraft are in good shape although the extended mission will not be business as usual, Hoffman said. Polar's orbit is slowly shifting so it will have shorter views of the north polar region. But it will explore more of the magnetosphere at lower latitudes. It is expected to run out of propellant for attitude control around 2003.

Wind will shift from the L1 "halo" orbit 1 million km in front of the Earth into a "petal" orbit (pictured at right) taking it throughout the magnetosphere from November 1998 through April 1999. Geotail's instruments continue to work although it has run out of propellant to let it maneuver through the 2 million km-long (1.6 million mi) magnetic tail that is drawn out by the solar wind.

SOHO, also in the L1 position with a dozen special telescopes trained on the sun, continues to be reactivated after its near-death experience this summer.

"Almost miraculously, all the instruments appear to be working," Hoffman said.

The ISTP program originally included a quartet of European Space Agency spacecraft called Cluster, said Manuel Grande of ESA. They were destroyed when their launcher failed in 1995. The extended ISTP mission now will be joined by Cluster II (pictured at left) - built partly from spare parts - scheduled for launch in 2000 either on two Russian Soyuz launchers or an Ariane IV, depending on vehicle readiness.

The Cluster II spacecraft will fly in formation as tight as 200 km (120 mi) and as loose as 18,000 km (11,160 mi) as they orbit as far out as 10 times the diameter of the Earth. This way, scientists can measure small-scale turbulence in the magnetosphere and the solar wind. This will help scientists determine whether a set of conditions changing back and forth represents something like passing through the spiral arms of a storm or through separate storms.

Several spacecraft are scheduled to follow, starting with IMAGE (at right) - the Imager for Magnetosphere-to-Aurora Global Exploration - scheduled for launch in 2000 with on the ambitious mission of making visible the heretofore invisible magnetosphere. It will orbit as high as 45,000 km (28,000 mi) above the north pole to view the entire magnetosphere.

IMAGE will feature three unconventional "non-imaging" cameras. Instead of photons, they will collect neutral hydrogen, helium, and oxygen atoms. Because the energetic neutral atoms (ENA) are not controlled by the magnetic field, they fly in straight lines and can have starting points that are near or far. Nevertheless, with some complex equations to deconvolve the images, scientists will be able to build images that show heating regions that turned charged ions into neutralized atoms.

Dr. Thomas Moore of NASA's Goddard Space Flight Center said the Low-Energy Neutral Atom camera is crossing a couple of "final frontiers." First, taking "pictures" in this manner requires a little trickery, such as rejecting ions and electrons that would fool the detector, then ionizing the neutral atoms so they can be detected, and using filters to keep out light that would further cloud the view.

This makes the camera an ambitious, high-risk instrument. But if it works, it will also pay off in sampling the neutral interstellar and solar winds when the camera is pointing away from the Earth.

(Copies of the energetic neutral atom cameras will piggyback as TWINS - Two Wide-angle Imaging Neutral-atom Spectrometers - on two Department of Defense satellites in 2002 and 2004. Like a pair of eyes, they will give scientists a 3-D view of the large-scale structure and dynamics of the magnetosphere during 2004-06 when both spacecraft are operating.)

Radio, too, will be used somewhat like a camera with IMAGE's Radio Plasma Imager (RPI), described in yesterday's story, charting the magnetosphere like weather radar watching storms.

"The RPI is a revolutionary new instrument," said Dr. James Green, an RPI team member from NASA's Goddard Space Flight Center. "It will let us look at the dynamics of the magnetosphere as we never have before."

IMAGE will also carry more conventional cameras, like an Extreme Ultraviolet Imager that will observe helium ions trapped around the Earth. This was only done once before, when a special astronomy camera carried by Apollo 16 was aimed at Earth in 1972. IMAGE's EUVI is a triple camera that will see the energetic magnetosphere the light emitted by helium ions.

Other missions being developed or proposed include:

• TERRIERS - the Tomographic Experiment using Radiative Recombinative Ionospheric Extreme ultraviolet and Radio Sources - built by students at Boston University, will be launched in April 1999 to tale cross-sections of the ionosphere in conjunction with a radio observatory and other facilities in Massachusetts.
  
• The CAMEO mission - Conjugate Auroral and Magnetospheric Electrodynamic Observatory - proposed by NASA's Marshall Space Flight Center would orbit two identical spacecraft with imagers similar to those on Polar. One satellite would loop over the north pole in step with the other looping over the south pole. This would let scientists study the flow of energy and other effects between the northern and southern hemispheres.
  
• The Magnetospheric Multiscale Mission, planned for the 21st century, will comprise six satellites in groups dubbed microscope and telescope. With onboard propulsion to adjust their orbits, four spacecraft in "microscope" will fly in a pyramid formation ranging in width from a few kilometers to several times the size of the Earth. Of special interest to scientists will be measurements in boundaries between major sections of the magnetosphere. The two spacecraft in "telescope" will carry cameras to make images of large sections of the magnetosphere so data from "microscope" can be placed in context.
  
• By far, the most complex and ambitious of these missions is the Magnetospheric Constellation, several hundred satellites peppering the magnetosphere like so many weather balloons released all at once. It would make a series of highly detailed snapshots of the magnetosphere.
  
• MAGCaT, a proposed mission, would involve 16 spacecraft orbiting in the same plane and using radio to probe the magnetosphere. Using the same methods that CT-scans use to combine multiple X-rays into a cross-sectional image of a patient, MAGCaT would produce cross-sectional images of the magnetosphere. The resolution would be coarse by optical standards - the smallest features would be about half as wide as the Earth - but it would make a new images every 10 seconds, allowing scientists to watch the magnetosphere absorb the blows from the solar wind and then dump energy onto the Earth.

Sun-Earth connection - NASA's International Solar-Terrestial Physics mission

POLAR - mission page
WIND - mission page
GEOTAIL - mission page
SOHO - mission page

The Exploration of the Earth's Magnetosphere - Goddard's intro to the Earth's Magnetosphere
IMAGE - spacecraft home page (Launch in 2000)
More Space Science Headlines - NASA research on the web
NASA's Office of Space Science press releases and other news related to NASA and astrophysics

External links:
What is the Magnetosphere? - University of Michigan "Windows to the Universe," funded NASA
Windows to the Universe - University of Michigan
Primer/textbook of the magnetosphere University of Oulu, Finland
ESA Cluster II home page

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