Space Cover #305: Viking 1, Arecibo and boulders on Mars Viking 1 was scheduled to land on Mars on the 200th anniversary date of the United States: July 4, 1976. However, the flight was delayed due to the Arecibo Radio Observatory in Puerto Rico's warning that there were 6 foot (two meter) boulders in the landing area. As a consequence, the landing of Viking 1 was delayed until July 20, 1976. I was curious how it was possible for a site on Earth able to determine that there were six foot boulders when the Viking Orbiters could not discern them.
To satisfy my curiosity, I sent a letter to the Director of the Arecibo Observatory, Dr. Harold Craft, who had been quoted in the newspapers about the decision. With my inquiry, I enclosed a cover for the landing of Viking 2 which still hadn't arrived at the Red planet.
Surprisingly, Dr. Craft wrote back to me and, in a words that a lay person could understand, told me that it was a result of the Doppler effect — the same thing that makes a train whistle sound different in tone as it gets closer and closer and again as it passes by and down the track. It is still hard to comprehend that this huge 306 meter (1000 ft) radio telescope could be so precise at a distance of 50 to 60 million miles away and the distance changing minute by minute.
When my cover for the landing of Viking 2 came back, Dr. Craft had signed it followed by his title. An image of a U.S. stamp which pictures this unique observatory is also shown herein.
posted 02-21-2015 02:20 PM
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