Explorer 7

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Explorer 7
Installing Explorer VII.jpg
Mission type Earth science
Operator NASA
Harvard designation 1959 Iota 1
SATCAT no. 22
Mission duration 2 years
Spacecraft properties
Manufacturer Jet Propulsion Laboratory
Launch mass 41.5 kilograms (91 lb)
Start of mission
Launch date October 13, 1959, 15:30:04 (1959-10-13UTC15:30:04Z) UTC[1]
Rocket Juno II
Launch site Cape Canaveral LC-5
End of mission
Last contact August 24, 1961 (1961-08-25)
Orbital parameters
Reference system Geocentric
Regime Low Earth
Semi-major axis 6,982.76 kilometers (4,338.89 mi)
Eccentricity 0.015834
Perigee 501 kilometers (311 mi)
Apogee 722 kilometers (449 mi)
Inclination 50.28 degrees
Period 96.78 minutes
RAAN 48.57 degrees
Argument of perigee 215.06 degrees
Mean anomaly 186.76 degrees
Mean motion 14.87
Epoch 17 December 2013, 05:12:52 UTC[2]
Revolution no. 87,055

Explorer 7 was launched October 13, 1959 at 10:36 a.m. Eastern Time by a Juno II rocket from Cape Canaveral Air Force Station to an orbit of 573 km by 1073 km and inclination of 50.27°.[3] It was designed to measure solar x-ray and Lyman-alpha flux, trapped energetic particles, and heavy primary cosmic rays. Also Secondary objectives included collecting data on micrometeoroid penetration and molecular sputtering and studying the Earth-atmosphere heat balance.

Cutaway of Explorer 7

Launch was originally scheduled for late September 1959, but the mission was delayed for a week after a Jupiter IRBM test on an adjacent pad failed shortly after liftoff, causing flying debris to hit Explorer 7's launch vehicle. However, the damage to the booster was minor and could be easily repaired.

Significantly, it also carried Verner Suomi's flat-plate radiometer, improved with the help of Robert Parent, that took the first Earth radiation budget measurements from space and initiated the era of satellite studies of the climate. Using both satellite observations of the Earth's heat balance and atmospheric cooling rates measured by net flux radiosondes, Suomi established the important role played by clouds in absorbing radiated solar energy. These observations established that Earth’s energy budget varies markedly due to the effect of clouds, the surface albedo, and other absorbing constituents. Using these instruments, Suomi and his team discovered that the Earth absorbed more of the Sun's energy than originally thought and demonstrated that it was possible to measure and quantify seasonal changes in the global heat budget.

The satellite weighed 41.5 kg, was 75 cm high and 75 cm wide. Powered by solar cells it also carried 15 nickel-cadmium batteries around its equator.

It transmitted data continuously through to February 1961 and went dead on August 24, 1961. It is still in orbit.[4]


  1. ^ McDowell, Jonathan. "Launch Log". Jonathan's Space Page. Retrieved 17 December 2013. 
  2. ^ "EXPLORER 7 Satellite details 1959-009A NORAD 22". N2YO. December 17, 2013. Retrieved December 17, 2013. 
  3. ^ "50th Anniversary of Explorer 7 Launch". Space and Science Engineering Center. University of Wisconsin. Retrieved 13 February 2010. 
  4. ^ "U.S. Space Objects Registry". Archived from the original on October 30, 2007. Retrieved 2011-11-29.