Jim Sahli                                                       May 17, 1996 Goddard Space Flight Center
Greenbelt, Md.
(301) 286-0697

POLAR STATUS REPORT #3

NASA SPACECRAFT STARTS SENDING SCIENTIFIC DATA 

        Three months into the Polar mission scientists working on this NASA 
mission are starting to receive data from all eleven instruments aboard the 
spacecraft.  Scientists plan to unveil the first images taken by the three imagers 
on the Polar spacecraft at a May 23 meeting of the American Geophysical Union 
in Baltimore.

        "Overall the spacecraft and instruments are performing exceptionally well," said
Dr. Bob Hoffman, who is the Polar Project Scientist at NASA'S Goddard Space Flight
Center in Greenbelt, Md.  "The imagers are providing some exciting new looks at the 
dynamic aurora, especially over the sunlit portion of the Earth.  We're now coordinating 
our science operations with those of other spacecraft and ground-based facilities."


        Polar was launched from Vandenberg AFB in California on Feb. 24 on a Delta II 
rocket.  Polar is in an elliptical orbit with an apogee of 32,000 statute miles and a 
perigee of 3,200 statute miles on a polar path inclined 86 degrees from the equator and 
circles the Earth about every 18 hours. Scientists are able to send their scientific data 
down to the ground several times each day.

        The only significant problem encountered to date is a slight wobble to the despun 
platform on which the imagers are mounted.  After erecting the long booms that hold 
instruments away from the main body of the spacecraft 
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and very long antennas for scientific measurements, the control engineers found that 
the spacecraft spin axis is tilted slightly from the axis around which it should be 
spinning, causing the imagers to wobble.

        Engineers at the spacecraft manufacturer, Lockheed Martin in East Windsor, N.J., 
and at Goddard are still trying to pinpoint the cause, though some evidence points to 
one of the six meter booms as the problem. For two of the three imagers onboard, the 
wobble is causing some smearing of the auroral images in one direction.  The scientists 
responsible for the imagers are reprogramming the onboard software that controls the 
acquisition of the images to minimize the effect of the wobble.

        Polar is the latest spacecraft in NASA's Global Geospace Science mission series, 
which is part of the International Solar-Terrestrial Physics program. Polar and a sister 
spacecraft, Wind, are performing simultaneous, coordinated measurements of key 
regions of Earth's space environment.  Included are observations of entry and transport 
of solar plasma over Earth's magnetic poles, imaging of the aurora (Northern and 
Southern lights) and investigations of solar wind properties.  Wind was launched in 
November 1994.

        The spacecraft is cylinder-shaped 7.9 feet in diameter and 6.9 feet high.
It includes a despun platform at one end to hold the imagers.  Dry weight is 2,200 
pounds, with an additional 660 pounds of hydrazine propellant for orbit and attitude 
control.  Its design life is three years.

        The 11 Polar spacecraft instruments were supplied by university and industry 
teams as well as NASA laboratories.  Data from the instruments will be used to study a 
vast range of phenomena from electromagnetic radiation to charged particles from very 
low to relativistic energies. Especially important on Polar are the three high resolution 
imagers looking down on the Earth's polar regions.  The instruments image at 
wavelengths from the visible to ultraviolet and into the X-ray region.

        Goddard is managing the Polar project for the Office of Space Sciences at NASA 
Headquarters in Washington, D.C.

        Information about the Polar mission and the ISTP are available on the Internet at 
the following locations:
Polar:        http://www-istp.gsfc.nasa.gov/ISTP/ggs_project.html ISTP:           
http://www-istp.gsfc.nasa.gov/

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