We covered, in previous articles, the five artificial objects that are leaving or have left the solar system. Today we will start another series on the various probes and objects sent to different celestial bodies of our solar system.
We will start with the Sun.
Helios-A and Helios-B (also known as Helios 1 and Helios 2) were a pair of probes launched into heliocentric orbit to study solar processes. This article will be on Helios-A.
Helios-A was launched on December 10, 1974, from Cape Canaveral Air Force Station Launch Complex 41 in Cape Canaveral, Florida. This was the first operational flight of the Titan IIIE rocket. The probe was placed in a heliocentric orbit of 192 days with a perihelion of 46,500,000 km (28,900,000 mi; 0.311 AU) from the Sun. During the first perihelion in late February 1975, the spacecraft came closer to the Sun than any previous spacecraft. The temperature of some components reached more than 100 °C (212 °F), while the solar panels reached 127 °C (261 °F), without affecting probe operations. During the second pass on September 21, however, temperatures reached 132 °C (270 °F), which affected the operation of certain instruments.
Trajectory: Check out the video to understand the trajectory followed by both Helios-A and Helios-B.
Source of Power: Electrical power is provided by solar cells attached to the two truncated cones. To keep the solar panels at a temperature below 165 °C (329 °F) in the proximity of the Sun, the solar cells are interspersed with mirrors, covering 50% of the surface and reflecting part of the incident sunlight while dissipating the excess heat. The energy supplied by the solar panels is a minimum of 240 watts when the probe is in the farthest part of its orbit from the Sun. The power whose voltage is regulated to 28 volts DC is stored on a silver-zinc battery of 8 Ah. The battery was only used during launch.
The primary mission of each probe spanned 18 months, but they operated much longer. Helios-A continued to function normally, but with the large-diameter DSN antennae not available, data was collected by small diameter antennae at a lower rate. By its 14th orbit, its degraded solar cells could no longer provide enough power for the simultaneous collection and transmission of data unless the probe was close to its perihelion. In 1984, the main and backup radio receivers failed, indicating that the high-gain antenna was no longer pointed towards Earth. The last telemetry data was received on February 10, 1986.
In the next article, we will cover Helios-B and other technical aspects of both the probes.