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.