National Center for Atmospheric Research NCAR P.O. Box 3000 Boulder, CO 80307

1984-4 For Release: April 6, 1984

ASTRONAUTS AIM FIRST SPACE REPAIR MISSION ON SOLAR MAX SATELLITE

BOULDER— When Space Shuttle flight number STS-41C lifts off from Kennedy Space Center this Friday, NASA astronauts will gear up for the first satellite repair mission ever in space. The target: the Solar Maximum Mission observatory, a 2.5-ton spacecraft which became partially disabled in the fall of 1980 when the attitude control system failed.

One of its payload of seven instruments for investigating solar flares also quit--a unique solar telescope known as the coronagraph/polarimeter. The instrument, conceived and designed by scientists with the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, with funding from NASA, took more than 30,000 images of the sun's outer atmosphere before its video camera system stopped.

"Reactivation of the telescope would mean that solar physicists could continue the mission's original purpose, to study the inner workings of the solar atmosphere," says Robert MacOueen, director of NCAR's High Altitude Observatory.

The NCAR telescope, constructed by Ball Aerospace in Boulder, was launched aboard the satellite in February 1980 to study the corona, or outer surface of the sun, during the most active part of the sun's 11-year cycle. The corona is a manifestation of processes governed by the solar magnetic field, which stretches from deep in the interior of the sun out past the earth and into the interplanetary medium.

Flares and other disturbances on the sun generate a stream of electron and proton particles— the solar wind— which flows along the magnetic field lines and interacts with the earth's magnetic field, causing geomagnetic storms. "Such -more-

The National Center for Atmospheric Research is operated by the University Corporation for Atmospheric Research under the sponsorship of the National Science Foundation. Space Repair Mission - Page 2

storms," explains MacOueen, "may tear holes in or wrinkle the ionosphere (the electrically charged portion of our atmosphere), resulting in disruptions to communication systems on earth. Furthermore," he states, "these storms and changes in the flow of the solar wind have been conjectured to be one of the causes of changes in climate or weather."

One advantage of repairing the telescope now, MacQueen says, is that it will allow scientists to compare new observations with data obtained a decade ago from the Skylab Mission, during the same phase of the previous solar cycle. In both instances, the observations cover a period near minimum activity, when the solar corona behaves very differently than at maximum activity.

According to Dr. Lewis House, principal investigator for NCAR's High Altitude Observatory experiment, the repair mission involves having the Space Shuttle dock with the satellite, which is in nearly circular orbit approximately 300 miles above the earth.

"An astronaut will leave the shuttle to stabilize the satellite," House explains. "Then the remotely controlled manipulator arm will be used to place the satellite in the shuttle cargo bay. The astronauts will replace the attitude control system containing the blown fuses and then, hopefully, the box of electronics for the telescope, and finally reinsert the satellite into orbit."

These repairs would restore the $77 million spacecraft to full operation.

"An early demonstration of satellite repair in space afforded by the Solar Maximum Mission situation would be important to those groups using satellites and would clearly indicate the U.S. space capabilities made possible with the shuttle," House adds. "And it would really be exciting to have the telescope coronagraph/polarimater again providing the images we need to study the sun's activity."

The National Center for Atmospheric Research is sponsored by the National Science Foundation.

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Joan Vandiver Frisch, Information Officer National Center for Atmospheric Research P.O. Box 3000 Boulder, Colorado 80307 (303) 497-8721 or 443-5011 NASA Background Information on SMM/Repair of NCAR's Coronagraph/Polarimeter

Date of Space Shuttle STS-41C Launch: April 5, 1984

Location of Launch: Kennedy Space Center, Florida

A new era in satellite operations--the era of orbital service and repair-- begins in the spring of 1984 on the Space Shuttle STS-41C mission. A team of astronauts will replace a faulty module on the Solar Maximum Mission satellite known as Solar Max. Repair is necessary because three small fuses in the attitude control system failed, leaving Solar Max unable to point its instruments precisely at targets of observation on the sun. The crew will also repair scientific instruments aboard the orbiting solar observatory, including NCAR's coronagraph/polarimeter.

The faulty attitude control module is one of three replaceable, box like units that control power, commanding, and positioning of the satellite. These units are part of the multimission modular spacecraft system, which makes up the lower portion of the Solar Max satellite. The upper portion, the observatory, contains seven different instruments for solar research.

Using a jet-powered backpack called a manned maneuvering unit, one Shuttle crewman will fly 90 meters (100 yards) from the Shuttle cargo bay to the slowly spinning spacecraft. When the astronaut reaches the satellite, he will capture it with an attachment device and stop its rotation by activating the maneuvering unit's thrusters. When Solar Max is stabilized, the shuttle will move 9 meters (10 yards) below it. Then the remote manipulator system arm will grasp the satellite and lift it onto a platform in the shuttle's cargo bay, the "workshop" for the repair operation.

After Solar Max is securely latched to the support platform, the astronauts will begin the repair tasks. They will use a special module service tool to replace the malfunctioning module with a new one, enabling scientists once again to point the sophisticated instruments of the solar observatory toward specific areas on the sun.

The astronauts will then repair two accessible scientific instruments on the satellite. They will first place a baffle, or cover, on the satellite's X-ray polychromator unit, which measures X-ray emission from solar flares and shows scientists how particles are moving and changing in the hot solar gases.

When the first repair operations are completed, the crew will store all equipment and go inside the orbiter. The mission team at the NASA-Goddard control center will turn on Solar Max's power and perform an eight-hour remote check-out of the satellite's systems. If the check-out indicates that the satellite's systems are functioning properly, the astronauts will repair NCAR's coronagraph/polarimeter, which is located near the bottom of the solar observatory.

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The astronauts will don their spacesuits again and move through the airlock into the cargo bay to repair the coronagraph/polarimeter. They will be replacing the main electronics box in the instrument that is used to study the sun's outer atmosphere or corona by creating artificial eclipses. The repair operation is estimated to take three hours and is more complicated than the removal of the faulty attitude control module.

The tool kit for this repair includes scissors, adhesive tape strips, a ratchet tool, and a battery-operated screwdriver to fuse on screws and bolts. The ratchet tool will be available as a substitute for the electric screwdriver.

To remove the electronics box, which is about the size of a briefcase, and install a new one, the astronaut will open a panel in the observatory shell at the location of the box. He must cut through the foil insulation and remove screws that secure a protective thermal blanket over the box. After taping the thermal blanket and insulation out of the way, he will install a hinge and remove the remaining screws to open the panel that covers the main electronics box.

Next, he will unplug cables from the electronics box, remove the box and pass it to his partner, who will hand him the replacement electronic box from the tool locker. The new box will be installed, all connectors will be remated, the door closed and secured, and the protective insulation reattached.

When the astronauts have completed this repair, specialists at NASA-Goddard control center will turn on Solar Max's power and perform a remote systems check for the last time. The manipulator arm will grapple Solar Max and move it outside the cargo bay, pointing it toward the sun.

When it is on the arm outside the Shuttle, mission teams at NASA-Goddard will remotely deploy the satellite's high gain antenna. This antenna will allow the satellite to send data back to Earth.

While the crew rests overnight, Solar Max will remain attached to the arm outside the cargo bay. On day six, the arm will release the satellite, and the shuttle will back away. The crew will spend the rest of this day performing checks on the support system and preparing to deorbit. On the seventh day, the shuttle will land at Kennedy Space Center with Solar Max's failed parts, which will be returned to NASA-Goddard for engineering analysis.

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