50 years after Explorer 1

50 years after Explorer 1

50 years after Explorer 1

Bad Astronomy
The entire universe in blog form
Jan. 31 2008 9:00 AM

50 years after Explorer 1

Today marks the 50th anniversary of the launch of America's first satellite, Explorer 1.

This was a response to Sputnik, launched by Soviets a few months before. The whole story is actually a bit complicated (Clavius.org has a nice synopsis, and AstroProf has more too); but ironically the Americans could have had the first satellite in orbit had they not been reluctant to use a rocket built for the Army and based on German technology.

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  


Explorer 1 was equipped with an X-ray detector that was basically a fancy Geiger counter. Built by a team led by James van Allen, it was lofted up to see what the radiation environment of space was. The team was astonished to discover that near-Earth space was tremendously radioactive; their detector saturated.

And thus the basis of the Moon Hoax was born.

Too bad; if the hoax believers had some basic science education they'd understand the problem. What Explorer 1 discovered were the van Allen radiation belts: regions around the Earth where the magnetic field of our planet has captured subatomic particles. Moving at high speed, when these slam into the metal walls of a satellite they are decelerated. This process produces X-rays (called Bremsstrahlung -- German for "braking" -- radiation), and that's what the Explorer 1 detector detected. Moon hoaxers get terribly confused about this, saying there are deadly X-rays in space. They're wrong: the X-rays are a by-product of the subatomic particles screeching to a halt inside metal. Unless the Sun is flaring, there is very little X-radiation in near-Earth orbit. It's the subatomic particles that are dangerous, but they can be stopped by various substances like glass and insulation without creating X-rays.

Try explaining that the hoax believers. You might as well speak in Klingon to them.

Anyway, Explorer 1 was a fantastic achievement. Not only was it the US's first satellite, it also broke through a new frontier in science. We learned that the Earth's magnetic field has ramifications for space flight, and eventually led to a better understanding of how we are coupled with our nearest star, the Sun.

Mind you, these guys had no clue what they'd find. That's why they put the X-ray detector in Explorer 1 in the first place! And look what happened.

I salute the pioneers of the space age, and of the space science age. We owe you folks a lot.