Forty-nine years ago today, the United States successfully launched Orbiting Solar Observatory No. 1 (OSO-1) into Earth orbit. This robotic spacecraft provided the first detailed scientific examination of the Sun from space.
The 1960’s was a time of both rapid growth and spectacular achievements in space exploration. Indeed, weather satellites, communications satellites and surveillance satellites were new inventions. Robotic space probes were sent to orbit and land on the Moon. Other autonomous spacecraft visited the inner planets of the Solar System. Men orbited the Earth. Still others landed on and returned from the Moon.
Space probes were also employed to good effect in an effort to learn more about our Sun. NASA’s Orbiting Solar Observatory (OSO) Program was America’s first attempt to acquire detailed solar physics data using orbital spacecraft. A total of eight (8) OSO space probes were launched into Earth orbit between 1962 and 1975.
The fundamental objective of the OSO Program was to monitor and measure solar electromagnetic radiation levels over an 11-year sun spot cycle. The idea was to map the direction and intensity of Ultraviolet, X-Ray and Gamma radiation throughout the celestial sphere over the long solar cycle. Onboard scientific instrumentation included a solar spectrometer, scintillation detector, proton electron analyzer and various flux monitors
OSO satellites were relatively large and complex for their time. Spacecraft attitude had to be tightly controlled since onboard instrument systems needed to be continuously trained on the solar disk. The probe’s solar physics data could be transmitted to ground receiving stations in real-time or recorded on tape for later transmittal.
OSO-1 was the first solar observatory orbited by the United States. Launch from Cape Canaveral’s LC-17A took place on Wednesday, 07 March 1962 at 16:04:00 UTC. A Thor-Delta 301/D8 launch vehicle placed the 458-lb OSO-1 satellite into a near circular Earth orbit (291-nm x 275-nm). The orbital period of 94.7 minutes meant that OSO-1 orbited the Earth 15.2 times each day.
OSO-1 performed well until its second onboard tape recorder gave up the ghost. This anomaly occurred on Tuesday, 15 May 1962. The loss of its last functional data recorder meant that all subsequent measurements had to be transmitted in real-time.
OSO-1 would continue making and transmitting solar physics measurements until May of 1964. At that time, the spacecraft power supply died when its solar cells failed. Although dormant, OSO-1 would continue to orbit the Earth for another seventeen (17) years. The spacecraft reentered the Earth’s atmosphere on Thursday, 08 October 1981.
OSO-1 and all succeeding OSO satellites contributed significantly to progress in the realm of solar physics. The OSO Program laid the foundation for more sophisticated and detailed study of our Sun through the auspices of such solar probes as SOHO, Ulysses and Skylab. Indeed, NASA’s Solar Probe Plus probe, currently scheduled to fly within the Sun’s coronal region sometime in the 2015/2016 period, will continue the legacy begun long ago by OSO-1.