First Pictures: Voyager 1 Portrait of the Earth & Moon – September 18, 1977

For space enthusiasts of a certain age like myself, the 1970s were a golden age of discovery with missions encountering all five planets known to ancient astronomers. Surely the greatest of these were NASA’s Voyager missions which returned spectacular images of the outer planets and their satellites over the course of a decade starting in 1979. But the very first image returned by Voyager 1 and subsequently released to the public stuck with me and gave a foretaste of what was to come. That image was the first portrait of the Earth and Moon as seen from Voyager 1 as it left its home for good.

The launch of Voyager 1 from Cape Canaveral on September 5, 1977. (NASA)

Voyager 1 was launched from LC-41 at Cape Canaveral on September 5, 1977 some 16 days after its slower moving twin, Voyager 2 (the spacecraft numbering was reversed from their launch order to avoid confusion later as the faster moving Voyager 1 reached Jupiter and Saturn first). On September 11 and 13, Voyager 1 made a pair of trajectory correction maneuvers to fine tune its trajectory and eliminate the minor errors remaining from launch. On September 18, Voyager 1 was instructed to acquire optical navigation images including a sequence of 54 images in the direction of the Earth – a trio of narrow-angle images each taken through different color filters for 18 different aiming positions. At the time these images were taken, Voyager 1 was 11.66 million kilometers away from the Earth directly above Mt. Everest at 25° north latitude on the dark side of the planet. At this range, the image scale was about 110 kilometers per pixel.

Here is a color image showing the Earth and Moon together for the first time as seen from a departing interplanetary spacecraft. Voyager 1 took this color image on September 18, 1977 from a range of 11.66 million kilometers which was subsequently released to the public on January 10, 1978. Click on image to enlarge. (NASA/JPL

Because the Earth was out of view of Voyager’s high gain antenna during the first weeks of the mission, these images were not transmitted back to Earth until October 7 and 10. The images were subsequently sent to JPL’s Image Processing Laboratory (IPL) for processing and the creation of a near-true-color image. Because the Moon is so much darker than the Earth, the Moon was artificially brightened by a factor of three relative to the Earth by computer enhancement so that both worlds would show clearly in the same image. The resulting color image was released to the public by JPL on January 10, 1978.

Diagram of the major components and instruments of the Voyager spacecraft. Click on image to enlarge. (NASA)

Each Voyager spacecraft carried a pair of vidicon-based slow scan television cameras attached on a pointable Science Scan Platform mounted on the end of one of the booms extending from the spacecraft’s bus. This would be the last NASA planetary mission to use vidicon-based imagers with improved solid state cameras employed on future missions. Despite the comparatively primitive nature of these cameras, JPL engineers used their 13 years of experience flying vidicon cameras on earlier Mariner and Viking missions to create highly sensitive and stable cameras suitable for use in the dim reaches of the outer solar system.

Diagram showing the layout of Voyager’s wide and narrow angle cameras. Click on image to enlarge. (NASA)

Each Voyager carried a wide and a narrow angle camera which employed 200 mm and 1,500 mm focal length lenses, respectively, to focus images on an 11 mm square vidicon plate. This resulted in 3.2° and 0.42° fields of view for these cameras – the equivalent of using 400 mm and 3,200 mm lenses on an old style 35 mm format camera. The images were subsequently read out as quickly as 48 seconds after being sliced into 800 lines consisting of 800 pixels each. Each pixel was digitized to 8 bits and could be transmitted live at a rate of as great as 115,200 bits per second or saved on a magnetic tape recorder with a 100-image capacity (the equivalent of about 61 megabytes of data). Each camera had its own eight-position filter wheel which included orange, green and blue filters that could be combined to create near true color images. Because of the low sensitivity of vidicon cameras at redder wavelengths, a wide-band orange filter was employed instead of a red filter which would normally be used to create true color images. Despite the comparatively primitive nature of these cameras, Voyager 1 returned tens of thousands of images over the following years providing some of the most spectacular views of Jupiter and Saturn we have today.

Voyager 1 took this color image of Jupiter and two of its satellites, Io and Europa, on February 13, 1979 at a range of 20 million kilometers about three weeks before closest approach. Click on image to enlarge. (NASA/JPL)

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Related Reading

“Voyager 1: The First Close Encounter with Titan”, Drew Ex Machina, November 12, 2015 [Post]

“Voyager 2: The First Uranus Flyby”, Drew Ex Machina, January 24, 2016 [Post]

“Finishing the Grand Tour: Voyager 2 at Neptune”, Drew Ex Machina, August 29, 2019 [Post]

General References

Michael M. Mirabito, The Exploration of Outer Space with Cameras, McFarland, 1983

Andrew Wilson, Solar System Log, Jane’s Publishing, 1987

Voyager to Jupiter and Saturn, NASA SP-420, 1977

Voyager Mission Status Bulletin No. 9, JPL/NASA, September 29, 1977

Voyager Mission Status Bulletin No. 10, JPL/NASA, October 20, 1977

Voyager Mission Status Bulletin No. 14, JPL/NASA, January 16, 1978