Explorer 6

Did You Know?

• On 13 October 1959, the Bold Orion anti-satellite missile used Explorer 6 as a target, passing within 6.4 km of the satellite.
• The Bold Orion missile intercepted Explorer 6 at a range of less than 3.5 km and an altitude of 252 km.
• The ASAT test launch took place from the Atlantic Missile Range Drop Zone at 11,000 m altitude, 29° North and 79° West.

Experiments

A fluxgate magnetometer was intended to measure the magnetic field component parallel to the spin axis, but permanent multipole disturbances within the vehicle saturated the instrument, yielding no data. Only the search coil magnetometer and aspect indicator provided information. A Neher-type integrating ionization chamber and an Anton 302 Geiger–Müller tube measured radiation; the ion chamber responded to electrons above 1.5 MeV and protons above 23.6 MeV, while the GM tube responded to electrons above 2.9 MeV and protons above 36.4 MeV. Counts and pulses were accumulated in separate registers and telemetered via analog and digital systems, though very little digital data were transmitted. The ion chamber operated from launch through 25 August 1959, and the GM tube through 6 October 1959. A micrometeorite momentum spectrometer using piezoelectric crystal microphones detected pulses but returned no scientifically useful data. A triple-coincidence omnidirectional proportional counter telescope observed protons above 75 MeV and electrons above 13 MeV in the trapped radiation region, aiming to determine properties of high-energy radiation and the proportion of X-ray versus particle counts.

Mission

Launched from Cape Canaveral on August 7, 1959, Explorer 6 rode a Thor-Able rocket into a highly elliptical orbit stretching from 250 to 42,500 kilometers. It spun at 2.8 rotations per second, with its axis fixed at a right ascension of 217 degrees and declination of 23 degrees. Four solar paddles near its equator were meant to recharge its batteries, but only three fully deployed, and that happened during spin-up instead of before it, cutting initial power to 63 percent of normal. That shortfall worsened over time, lowering the signal-to-noise ratio and degrading most data, especially near apogee. On August 14, 1959, while over Mexico at about 27,000 kilometers altitude, it captured the first satellite image of Earth, showing the north central Pacific Ocean and transmitting it to a Hawaii ground station over 40 minutes. One VHF transmitter failed on September 11, 1959, and contact ended on October 6, 1959, when solar charging current dropped too low. The mission yielded 827 hours of analog and 23 hours of digital data. Its orbit decayed on July 1, 1961.