The United States entered the space race 50 years ago today (okay, I wrote this on the anniversary, but am posting a day late) with the successful launch of the Explorer 1 spacecraft. Although Explorer 1 was a modest 30 pounds and quite simple by the standards of today’s spacecraft, it made an important scientific discovery. The spacecraft was built at JPL, where I happen to be at this moment for a Cassini Project Science Group meeting, and where there is a distinctly festive air and displays of the history of JPL’s involvement in the U.S. space program. The key instrument on Explorer 1 was a Cosmic Ray Package that was essentially a Geiger counter for detection of charged particles. The flux of charged particles was much less than expected at high altitudes (>2000 km), but equal to the expected value at lower altitudes. James Van Allen, lead instrument scientist on Explorer 1, hypothesized that the instrument was saturated by radiation from charged particles trapped in the Earth’s magnetosphere at high altitudes. The confirmation of this by Explorer 3 a few months later earned these regions the name they are still known by: the Van Allen radiation belts. Because of the high energy of the particles in these toroidal regions around the Earth, they pose a hazard for astronauts as well as spacecraft electronics. The space shuttle and space station orbit safely beneath the belts. Pics of the festivities at JPL coming shortly.

Hmm. I think the pictures are on my phone, but they didn’t translate to my computer last time I synched.