September 20 – HEAO-3

Two and a half tonnes of HEAO-3, the last of its kind, were sent 486 kilometres in a generally upwards direction on top of an Atlas-Centaur launch vehicle on this day in 1979, on a planned 6 month mission, which eventually stretched to 21 months, to study x-rays, gamma rays and cosmic rays. HEAO stands for High Energy Astronomy Observatory.

Launch of HEAO-3 (image credit: NASA)

Launch of HEAO-3 (image credit: NASA)

HEAO-3 carried three experiments, described very briefly below:

1) The High Resolution Gamma Ray Spectrometer could have had an even longer name, as it was designed to study x-rays as well. Its purpose was to perform an all-sky survey, looking for x- and gamma-rays within a certain energy range.

2) The Cosmic Ray Isotope Experiment, whose primary purpose was to measure the isotopic composition of cosmic ray nuclei, as part of the drive to better understand the nature and propogation of cosmic rays.

3) The Heavy Nuclei Experiment did exactly what it said on the tin. It searched for heavy (and so-called super heavy) nuclei in cosmic rays.

So, here we are, 34 years later, and we still don’t quite understand how, why and where cosmic rays originate. But at least we’ve sorted one problem out: we know they’re not rays.

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ALSO TODAY . . . .

Launch of Surveyor 2 from Cape Kennedy, 1966, headed for Sinus Medii, but which crashed at or near crater Copernicus three days after launch, following a spin caused by a faulty thruster.

Model of Surveyor 2. (Photo credit: NASA.)

Model of Surveyor 2. (Photo credit: NASA.)

The purpose of Surveyor 2 was fairly simple.  It was a flying camera, designed to image the lunar surface, and possibly perform a “lunar bounce” (basically, fire up the engines to jump up and down on the Moon to test the surface consistency).

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1969  –  Discovery of comet 67P Churyumov-Gerasimenko by Kim Ivanovich Churyumov and Svetlana Ivanova Gerasimenko in the Soviet Union. “Chury” is a Jupiter-family comet with an intriguing shape. You will, of course, be familiar with it from the recent visit by the Rosetta probe. Research carried out since the discovery of the two-lobed shape of this comet by scientists at the University of Bern (Journal of Astrophysics, November 2016) has concluded that it is probably the result of a more conventionally shaped comet undergoing a gentle collision, creating two large fragments which then re-attached under their mutual gravitational attraction.

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