Pioneer 12


A satellite shaped like a flat cylinder was launched using a launch vehicle called Atlas- Centaur Rocket on May 20th, 1978, drifting through space it finally encountered Venus on 4th December 1978. The Pioneer 12 satellite manufactured by Hughes Aircraft Company, California for NASA, it carried 17 different scientific experiments with it each having its own objectives to study Venus. All the 17 different experiments had a mass of about 45 Kilograms with the total satellite having a mass of about 452 Kgs.

As the satellite approached Venus, the satellite started orbiting Venus having an orbital period of 24 hours. It got as close as 142 Kilometres and as far as 2290 Kilometres from Venus. As any other object in space spins the satellite was spin stabilized at ~15 rpm. The stage was set for the scientific experiments to start working by stabilizing the altitude and orbit control using 7 thrusters, as it is necessary for the orbiter instruments to be in the atmospheric layers to study it.

Because of the orbit, the Pioneer 12 was permitted global mapping of the clouds, atmosphere and ionosphere, measurement of the upper atmosphere, ionosphere, and solar wind-ionosphere interaction and mapping of the planet’s surface by radar. It was the first spacecraft to study Venus using radar mapping.

Venus was always said to be a twin sister to Earth because the two are rough of the same size and there the similarity ends.  One significant difference is that Venus is covered by an opaque cloud layer that does not allow direct visualization of its surface. Pioneer Venus Orbiter which had a Polar Orbit around the planet, made observations which mapped approximately 90% of Venus at a resolution of about 10 kilometers. It mainly found out that the planet was almost perfectly spherical, unlike Earth which has a bulge at the equator. The radar imagery also found out that Venus has two large continents namely Ishtar Terra and Aphrodite Terra which are rough of about the sizes of the United States and Africa.

As the propellant began to run low, it caused the satellite to rise to about 2300 Km’s. By 1986 gravitational effects came into play putting the satellite lower than 2300 Km’s to finally allow the orbiter instruments to make direct measurement within the main ionosphere. The Venus Orbiter Radiometric Temperature Experiment, it was used to characterize the 3-D temperature field, the cloud structure which is very thick and mostly contains sulfuric acid droplets. The new discovery was a ‘dipole’ structure at high latitudes, with two hot spots rotating around the pole, surrounded by banks of cold cloud.  Mission scientists gave the name “Giant Vortex of surprisingly complex structure and behavior located in the middle atmosphere at the North Pole of the planet”. It’s the hottest spot in the planet’s upper atmosphere. Now there have been many theories for this strange phenomenon but thanks to the Venus Orbiter Radiometric Temperature Experiment which was manufactured by Jet Propulsion Lab.

The orbiter also had Ultraviolet Spectrometer by which it took an image of Venus in the ultraviolet, Viewed through a normal optical telescope, Venus is a dull, yellowish-white sphere without any other distinguishing features. However, in the ultraviolet, the picture changes significantly- dark and light areas appear on the planet, mostly reflecting the dynamics of the atmosphere. These dark lines over the planet mean that there is a substance in the atmosphere which is absorbing the Ultraviolet radiation, many of the scientists believed that sulfur particles were responsible for the absorption but it’s not the case.

The Pioneer’s UV Spectrometer is also famous for being the only one to observe the Halley Comet when it was not visible from Earth due to its close proximity to the Sun during February 1986. The UV Spectrometer observed the loss of water from the comet’s nucleus on February 9.

In the year 1992, Pioneer Venus began the final phase of its mission, in May the orbiter was held between 150 and 250 kilometers. The orbiter still working sent signals until 8 October 1992, eventually, the Pioneer Venus Orbiter disintegrated upon entering the atmosphere of Venus on October 22, 1992, burning like a bright meteor across the sky of Venus.

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