Explorer 7


Explorer 7
Installing Explorer VII.jpg
Mission typeEarth science
Harvard designation1959 Iota 1
COSPAR ID1959-009A
SATCAT no.22
Mission duration2 years
Spacecraft properties
ManufacturerJet Propulsion Laboratory
Launch mass41.5 kilograms (91 lb)
Start of mission
Launch dateOctober 13, 1959, 15:30:04 (1959-10-13UTC15:30:04Z) UTC[1]
RocketJuno II
Launch siteCape Canaveral LC-5
End of mission
Last contactAugust 24, 1961 (1961-08-25)
Orbital parameters
Reference systemGeocentric
RegimeLow Earth
Semi-major axis6,982.76 kilometers (4,338.89 mi)
Perigee altitude501 kilometers (311 mi)
Apogee altitude722 kilometers (449 mi)
Inclination50.28 degrees
Period96.78 minutes
RAAN48.57 degrees
Argument of perigee215.06 degrees
Mean anomaly186.76 degrees
Mean motion14.87
Epoch17 December 2013, 05:12:52 UTC[2]
Revolution no.87,055
Explorer program
S-46A →

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. Secondary objectives included collecting data on micrometeoroid penetration, 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. It made the first coarse maps of "the solar radiation reflected by the Earth and the infrared radiation emitted by the Earth".[4]

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. Explorer 7 was unable to detect solar x-rays due to its sensors being saturated by background radiation in the Van Allen Belts.[5]

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.[6]


  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. ^ Kidder, S.Q.; Vonder Haar, T.H. (1995). Satellite Meteorology: An Introduction. Elsevier Science. p. 2. ISBN 978-0-08-057200-0. Retrieved 2020-10-05.
  5. ^ Significant Achievements in Solar Physics 1958-1964. Washington D.C.: NASA. 1966. p. 63.
  6. ^ "U.S. Space Objects Registry". Archived from the original on October 30, 2007. Retrieved 2011-11-29.