On April 16-17, 1976, Helios-B made its closest approach to the sun, thereby setting a record for the closest flyby of the sun.

April is here and with it comes searing heat as the sun beats down heavily on most parts of India. You must be aware, however, that the sun, with its entire mass of glowing, boiling heat, is the source of all life on Earth. Our sun, in fact, influences how every object in the solar system is shaped and behaves.

Studying solar processes

This means that learning more about the sun and understanding it better has always been a priority. Apart from studying it from here on Earth, which is what we did for most of our history, we have also started sending spacecraft to explore its secrets. The Helios mission was one such mission, sending out a pair of probes into heliocentric orbit (an orbit around the sun) to study solar processes.

Following the success of the Pioneer probes, which formed a ring of solar weather stations along Earth’s orbit to measure solar wind and predict solar storms, the Helios mission was planned. While the Pioneer probes orbited within 0.8 AU (astronomical unit, mean distance between Earth and sun) of the sun, the Helios probes shattered that record within years.

A joint German-American deep-space mission to study solar-terrestrial relationships and many solar processes, it was NASA’s largest bilateral project up until then. The Federal Republic of Germany (West Germany) paid around $180 million of the total $260 million cost and provided the spacecraft, while NASA provided the launch vehicles.

Named Helios-A and Helios-B and equipped with state-of-the-art thermal control systems, the pair of probes were renamed Helios 1 and Helios 2 after their launches. Launched late in 1974, Helios 1 passed within 47 million km (0.31 AU) of the sun at a speed of 2,38,000 km per hour on March 15, 1975. While this was clearly the closest any human-made object had ever been to the sun, the record was broken again in a little over a year by its twin probe.

Even though Helios-B was very similar to Helios-A, the second spacecraft had improvements in terms of system design in order to help it survive longer in the harsh conditions it was heading for. Launched early in 1976, Helios 2 was also put into heliocentric orbit like its twin.

Achieves perihelion

Helios 2, however, flew 3 million km closer to the sun when compared to Helios 1. On April 16-17, 1976, Helios 2 achieved its perihelion or closest approach to the sun at a distance of 0.29 AU or 43.432 million km. At that distance, Helios 2 took the record for the closest flyby of the sun, a record that it didn’t relinquish for over four decades. It also set a new speed record for a spacecraft in the process, reaching a maximum velocity of 68.6 km/s (2.46.960 km/h).

Helios 2’s position relative to the sun meant that it was exposed to 10% more heat or 20 degrees Celsius more heat when compared to Helios 1. In addition to providing information on solar plasma, solar wind, cosmic rays, and cosmic dust, Helios 2 also performed magnetic field and electrical field experiments.

Apart from studying these parameters about the sun and its environment, both Helios 1 and Helios 2 also had the opportunity to observe the dust and ion tails of at least three comets. While data from Helios 1 was received until late 1982, Helios 2’s downlink transmitter failed on March 3, 1980. No further usable data was received from Helios 2 and ground controllers shut down the spacecraft on January 7, 1981.

This was done to avoid any possible radio interference with other spacecraft in the future as both probes continue to orbit the sun.

Parker Solar Probe gets closer and faster

After enjoying its position for over 40 years, Helios 2’s records were finally broken by NASA’s Parker Solar Probe. Launched on August 12, 2018 to study the sun in unprecedented detail, the probe became the first to “touch” the sun during its eighth flyby on April 28, 2021 when it swooped inside the sun’s outer atmosphere. Already holding both the distance and speed records, it is expected to further break them both during its 24 orbits of the sun over its seven-year lifespan. When it completed its 15th closest approach to the sun a month ago on March 17, it came within 8.5 million km of the sun’s surface.

Picture Credit : Google

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