March 17 – Round and Round She Goes

Today’s Factismal: Vanguard 1 has orbited the Earth 223,000 times since its launch in 1958.

Quick! What’s roughly spherical, weighs three pounds, and goes around the Earth nearly eleven times a day? It’s Vanguard 1!

An engineering spare for the Vanguard 1 satellite (Image courtesy NASA)

An engineering spare for the Vanguard 1 satellite (Image courtesy NASA)

Launched on March 17, 1958, this was only the fourth satellite ever to make it into Earth orbit, and the first to be solar powered. It was supposed to last for just six years; fifty-six years later on, it is still in orbit (though the instruments have long since died).

Vanguard 1 had three main missions. The first, and most important, mission was restoring the nation’s confidence in their space program. Though the US had managed to launch a satellite into orbit (Explorer 1 on January 31), it had started to tumble almost right away. Worse, there had been several very public failures including one rocket explosion shown live on television. A successful launch was essential to demonstrate that the US could keep up in the “space race” that had developed.

Second, Vanguard was intended to bolster interest in science and engineering. In order to do that, it had two radio transmitters that broadcast on ham radio frequencies. Ostensibly, the beacons were intended to help geophysicists accurately determine the shape of the Earth by allowing them to measure the slight changes in Vanguard’s speed caused by changes in the topography below; practically, they encouraged young students to become engineers and scientists by allowing them to hear the satellite as it went overhead. (This mission is continued today with the AO-51, AO-27, and SO-50 satellites.)

The third mission was also the most counter-intuitive to non-physicists. Vanguard 1 was intended to allow scientists to measure the density of the atmosphere in outer space. Though most non-scientists believe that there is a hard boundary between outer space and the atmosphere, in truth it is more of a vaguely defined zone. As you go up, the atmosphere becomes less and less dense but never entirely stops. As a result, satellites that orbit close to the Earth (e.g., Vanguard 1, the International Space Station) are slightly slowed down by atmospheric drag. By measuring the amount of slowdown, physicists are able to determine the density of the upper atmosphere.

And the results were certainly surprising. Originally, the mission planners had thought that the upper atmosphere was so thin that the satellite would orbit for 2,000 years. Instead, it is dense enough that Vanguard 1 will fall to Earth after only 240 years (185 years from now). Those results have helped with the design of new satellites and even inspired one private space venture.

If you’d like to get a little inspiration of your own but don’t want to build a ham radio station, then why not use the SatCam app? This smartphone app uses pictures that you take of clouds to “ground-truth” satellite data so that scientists can get a better idea of what the satellites are really seeing. In return for your photos, the app shows you what the satellite saw as it passed overhead.

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