Explorer 1,
the first American satellite, launched January 31, 1958. Explorer 1
discovered the Van Allen radiation belts around the Earth.
These radiation belts are a dominant source of background noise in X-ray
detectors.
The ASE-MIT experiment payload launched 1 minute before midnight on
18 June 1962 using a USAF Areobee 150 rocket. This rocket was above
80 km for a total of 5 min and 50 sec, and reached a maximum altitude
of 225 Km. As the spinning rocket climbed above 80 km the doors
opened and discovered the first evidence for cosmic X-ray radiation
from beyond our solar system. This flight discovered Sco X-1, the brightest
X-ray source in the sky and now known to be an X-ray binary system. The
flight also discovered an intense X-ray background, which is now believed
to be the superposition of many fainter extragalactic sources known as
active galactic nuclei (AGN).
