To See the Sun

The sun in a clear sky could hardly be more visible, its light and heat beating down apparently unhindered. But scientists know that the earth's atmosphere stops most of the radiation in the sun's long spectrum, which runs all the way from gamma rays to radio waves. Now at last U.S. scientists are getting a steady, unhampered look at the sun's radiation.

The precious data come from a 440-lb. satellite observatory launched last week from Cape Canaveral into an orbit averaging 355 miles high. The satellite, called OSO (for Orbiting Solar Observatory), is a gadget-lovers' dream, the most complex object launched into space so far. Yet at last report it was working perfectly.

Drum & Sail. The heaviest part of OSO is a nine-sided drum containing batteries, radio equipment and position-control apparatus (see diagram). Mounted on a shaft running through the center of the drum is a semicircular "sail" covered on one side with solar cells to make electric power out of sunlight. While OSO was getting its final push from the launching rocket's third stage, both drum and sail were spinning rapidly. After it was fully in orbit, three arms carrying spherical tanks of high-pressure nitrogen swung outward, and small nitrogen jets reduced the spin to a steady 30 r.p.m.

OSO has more eyes (electrical light sensors ) than any spider. When it went into orbit, some of the eyes searched for the sun. and nitrogen discharged from a bottle in the drum moved the drum's axis until it was perpendicular to the sun's direction. Next, a motor on the central shaft started turning the sail so that its solar cells pointed steadily at the sun.

OSO gets gyroscopic stability from the spinning drum, while the solar cells on the pointing sail are always in the right position to develop maximum power.

Mounted on the sail, and pointed accurately at the center of the sun by a special set of eyes, are five of the 13 observing instruments that OSO carries. An X-ray spectrometer measures the wave length and strength of X rays coming from the sun. A photomultiplier tube looks for powerful gamma rays that are believed to come from electrons and positrons annihilating each other in the sun's churning gas. A dust counter watches the sun to find out whether microscopic dust particles are coming from its direction.

Send on Signal. Other instruments mounted on the drum record radiation from both sun and sky as the drum spins, and a neutron counter catches neutrons bounced up from the earth's atmosphere by the impact of cosmic rays. All the readings are recorded on tape during each orbit. When OSO passes over a Minitrack radio station, it is given a signal that makes the tape reverse its motion and quickly send its data down to earth.

It will take months for scientists to interpret all the new information that OSO is sending about the sun. Every instrument on the complicated satellite is apparently doing its duty. OSO is expected to function as a solar observatory for about six months, when its supply of compressed nitrogen will be exhausted.

By then, science will have an enormously deeper understanding of the sun, the earth's own star, which is the origin of all life on earth.

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