Harvard Outpost Watches Sun

After two months in orbit 300 miles above the earth, an automatic telescope designed and assembled at the Harvard College Observatory is working perfectly. The ultra-violet light experiment aboard Orbiting Solar Observatory VI (OSO-VI) "is meeting 100 per cent of our expectations," said William H. Parkinson, lecturer on Astronomy and co-director of the project. "We've got a winner."

The 640-pound satellite was launched from Cape Kennedy on August 9. Besides the Harvard telescope, it contains 6 other experiments designed to measure solar emissions such as x-rays, ultraviolet light and neutrons that are ordinarily blocked from view by the upper layers of the earth's atmosphere. When ever the satellite emerges from the earth's shadow, two of these devices, including Harvard's telescope, constantly scan different portions of the sun's disc and record the intensity of the sun's radiation in varying sections of the spectrum.

Leo Goldberg, Director of the Harvard College Observatory, proposed the telescope project some 10 years ago. Since 1961, Parkinson and Edmond M. Reeves, lecturer on Astronomy, have been the project's co-directors.

NASA has so far provided $30 million to build the Harvard ultra-violet experiment and to process the results.

Ultra-violet measurements, like these, are important because ultra-violet rays from the sun occasionally interfere with earth's radio communications, and the energy from these invisible light waves supplies much of the solar heat that determines the earth's weather. Astronomers use slight, variations in the sun's ultra-violet spectrum as clues to the chemical and physical reactions goingon at various depths in the sun. By comparing satellite measurements of invisible radiation with earth-bound records of the sun's visible light, scientists should be able to predict some of these reactions and their effects on earth's weather and communications. Space travelers also need accurate forecasts to warn them of outburst of dangerous radiation.

The astronomers have aimed their telescope at several features on the sun, including "active regions"-the eruptions of hot material that appear against the "cooler" regions of the sun's surface. Active regions increase and decrease over an 11-year cycle. "This year is supposed to be a solar maximum-a period of maximum solar activity-but in spite of that, the sun has been notoriously quiet," Reeves said. "But this week the sun has perked up again."

"We haven't discovered any outstanding new phenomena," Reeves added, "but a great many observations that had been qualitative are now quantitative. Now you can start calculating the sun's behavior."

Besides observing the sun, the OSO-VI telescope has measured the absorption of ultraviolet light by the earth's upper atmosphere an important factor in the earth's weather.

The Harvard experiment is contained in a 40-inch box that is open at one end. The box is plated with gold to distribute heat evenly. A cluster of 13 light detectors-much like the electric eye on a camera-keeps the box pointed at the sun. A small telescope mirror collects solar rays coming through the open end of the box and then reflects them onto a diffraction grating, a row of closely-scaped lines that breaks the light up into a spectrum. This spectrum constantly changes as different chemical reactions occur on the sun.

The visible light region of this spectrum would show up as color bands, but the invisible ultra-violet rays can be detected only by a special electric tube. In the experiment, this tube acts like a television camera, converting the ultra-violet rays to electric impulses that are transmitted to earth.

A small motor moves the diffraction grating to examine any one of 10,000 different wavelengths or areas of the spectrum. A second motor keeps the telescope aimed at a single point, or else it shifts the entire telescope back and forth to scan small areas of the sun. It thus obtains a television picture in a particular type of ultra-violet light.

No one knows exactly how long OSO-VI and its Harvard experiment will continue to operate. OSO satellites are designed to last six months, but one earlier OSO has been working for nearly two years.

Since Goldberg first proposed the OSO telescope, the project here, like most satellite experiments, has run into major technical problems.

In 1965 and 1967, OSO satellites carried Harvard telescopes similar to this one. But the first telescope aboard OSO-II failed only seconds after being switched on, and a surge of electric power from a faulty transformer ruined the telescope on OSO-IV after six weeks of operation. However, the data from those six weeks has kept astronomers here more than busy for two years.

So far the best explanation for the OSO-IV failure is that a small bubble of gas was trapped in a plastic coating that surrounds the transformer's wire coils. As the gas slowly leaked out it caused a surge of electric current that burnt out the experiment's electric system.

To prevent such a failure from happening again, the Observatory scientists checked the OSO-VI transformer for gas bubbles while keeping it sealed in a vacuum chamber for a month. They also added an extra circuit that automatically turns the telescope off when too much electric power is produced. The satellite can be turned back on again once the danger is past.

The telescope that was originally slated for OSO-VI was a more advanced model, but a shortage of time and funds prevented it from flying. When the astronomers realized that the advanced version would not be ready in time, an extra copy of the earlier OSO-IV telescope was pressed into service (the Observatory had built a prototype, a flight instrument, and a spare for that satellite). This instrument was overhauled and improved in less than a year-an unusually short time for space hardware.

Harvard astronomers are particularly proud of OSO's flexibility. "An ordinary satellite takes the same type of data continuously," said Martin S. Huber, a Research Associate who calibrated the experiment. "But we have a real observatory with an almost infinite number of observation possibilities." The telescope can view the sun in one of 10,000 different wavelengths of ultra-violet light and can aim at a single point, take a picture of the entire sun, or scan an area only 1/15 the size of the sun's visible disc. Where earlier OSO satellites were able to take only one picture of the entire surface every 5 minutes, this telescope can also map a small region every 30 seconds. This allows the astronomers to follow very fast solar reactions in greater detail.

To take advantage of this flexibility, six Harvard scientists decide each observation schedule on a day-to-day basis. The six include Robert W. Noyes, lecturer on Astronomy, and Andrea K. Dupree and George L. Withbroe, Research Fellows at the Observatory, as well as Huber, Parkinson, and Reeves. One of the six, called the "duty scientist," is on 24-hour call each day to care for OSO, and the group meets every day at noon to discuss OSO's latest result.

They examine the duty scientist's report, a photograph of the sun taken that morning from the roof of the Observatory building, and a forecast of the sun's activity from the federal Environmental Science Services Administration. They then determine the most promising wave-lengths and sections of the sun to observe during the next day. The duty scientist sends these instructions to NASA's Goddard Space Flight Center near Washington, D.C., which then transmits the instructions to the satellite via a convenient tracking station.

Goddard Space Center also serves as middle man for data coming from OSO to the Observatory. During each of its 15 daily orbits, the satellite records its observations on a 100 minute long tape. When it passes over a tracking station, the ground controller orders the satellite to replay the entire tape in about five minutes. The tracking station then relays the broadcast to Goddard which sends the data to the duty scientist at 60 Garden Street through a special teletype machine. Tracking stations also ship magnetic tapes of each transmission a week later, and these tapes are eventually analyzed by computers here.

The six major tracking stations are located in Florida, North Carolina, South Africa, Australia, Ecuador, and Chile.

During roughly 10 percent of OSO's observation time, according to Reeves, ground-based observers take simultaneous measurements for later comparison with the satellite's data. Most of these cooperating astronomers have worked from the U.S.A., but scientists in Russia, Israel, and several other nations have also coordinated their observation schedules with OSO's.

The OSO experiment is closely connected with several other projects at the Observatory:

A sounding rocket called the Acrobee 150 was launched on September 11 to measure a section of the sun's ultra-violet spectrum very close to the region measured by OSO-VI. The rocket's readings actually overlapped OSO's in one small region, and the two instruments thus double-checked each other's operation. After four minutes of observation above White Sands, New Mexico, the rocket parachuted back to earth. "It was recovered so well that to a casual glance, you could not really be sure it had been launched," Parkinson said. The rocket will be repaired and flown again sometime next year.

The same group of scientists maintains a laboratory to duplicate the sun's heat for a few millionths of a second. By studying gases' spectra on earth at these high temperatures (roughly 10,000 F.), they can interpret the sun's spectra detected by the Harvard telescope.

Two of the solar telescope experiments scheduled for NASA's manned. Apollo Applications Program were designed at the Observatory and will add to the data gained from OSO-VI.

"The major observatories of the next ten years will be connected with the manned space program," Reeves said. An astronaut will sit in front of a television screen equipped with a set of cross-hairs. As he watches the sun on the screen, he will aim the cross-hairs at any areas that seem interesting, and the cross-hairs will electronically aim a telescope located outside the orbiting space station. This ability to follow sunspots, active regions, and other events immediately will be a great improvement over the present generation of automated telescopes which must be programmed a day ahead of time, Reeves said.

The Apollo telescope project will also permit detailed photographs to be taken and returned to earth by the astronauts. The flight instruments for this 1972 mission will arrive here in January for testing.