OSO will allow scientists to check into sun’s corona Hughes News June 27, 1975 Transcribed by Faith Macpherson

 Because the sun’s energy gives life to earth, it’s little wonder that man seeks to learn more about an area that has mystified science for centuries.

Scientists will have a chance to scrutinize the sun’s atmosphere with the aid of the Orbiting Solar Observatory (OSO) launched by NASA from Cape Canaveral last Saturday.

The unmanned 2257-pound (1024 kg) spacecraft, designed and built by Space and Communications Group for NASA’s Goddard Space Flight Center in Greenbelt, MD, was launched by a Delta booster into a 343-mile-high (555 km) orbit to circle the earth every 96 minutes for the next year or so.

Primary scientific objective of the orbiting observatory called OSO-I, eighth spacecraft of a series launched since 1962, is to obtain a better understanding of the complex regions between the solar surface and the upper regions of the corona.

In this area, called the chromosphere-corona interface, the temperatures soar from 10,000 to more than 3 million degrees Fahrenheit, creating extremely hot gases that sweep out across 93 million miles of space to continuously immerse the earth and its sister planets in a tenuous solar wind that often creates auroral displays and sometimes disrupts worldwide radio communications.

Some NASA scientists believe the rise in temperature is due to continued agitation of the gases of the corona by shock waves heated and compressed, rising out of the boiling surface of the sun. These sharply defined shock waves, like a thunderclap or the sonic boom produced by aircraft, following one another in rapid succession, could create an accumulated heating effect to raise the temperature in the corona region considerably.

OSO-I will train telescopic instruments on the sun with a pointing accuracy of one arc second, or 1/3600 of a degree, an accuracy similar to a rifle marksman keeping a 10-foot target in his sights over the distance of Boston, MA, to Washington, DC, 400 miles or 643 km.

Pinpoint accuracy of this nature enables OSO to scan areas of the sun’s rim in 450-mile swaths – an area considered small because the sun’s diameter is 864,000 miles.

OSO consists of a spinning section, called the wheel and a stationary platform known as the sail. The sail contains solar cells to provide power and carries two pointing instruments able to scan the sun or point at any position on it. One, a spectrometer from the Centre National de la Recherche Scientifique (CNRS), France, will make fine structure studies of the chromosphere. The other, from the University of Colorado, will take high resolution ultraviolet spectrometer measurements.

Both instruments will scan the sun for other targets of opportunity, such as flares or sunspots.

Six additional instruments mounted in the spacecraft’s wheel, include experiments from Goddard Space Flight Center, University of Wisconsin, Lockheed Missiles and Space Company, Columbia University, and the U.S. Naval Research Laboratory. They will measure solar and celestial X-ray and ultraviolet radiation.

OSO-I is 10 ½ feet (3.2 m) high and 7.2 feet (2.18 m) in diameter. The spacecraft is designed for a one-year life in space.

The project is managed by Goddard, which is also responsible for OSO tracking and data acquisition and the Delta Launch vehicle.


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About Jack Fisher

Jack was a systems engineer at Hughes from 1961 to 1992. He contributed to various programs including Surveyor, Pioneer Venus, Galileo, Intelsat VI and innumerable proposals. He was the manager of of the Spacecraft Systems Engineering Lab until his retirement. Upon retirement Jack taught systems engineering at a number of national and international venues.