|Mission type||Earth science|
|Launch date||April 3, 1963 at 01:55:00 UTC|
|Mission duration||1,325 days|
|Orbital decay||November 24, 1966|
|Homepage||NASA NSSDC Master Catalog|
|Semimajor axis||6963.64 km|
|Orbital period||96.39 m|
|Main instruments||Pressure gauges, mass spectrometers, electrostatic probes|
Explorer 17 (also known as Atmosphere Explorer-A (AE-A) and S6) was a United States satellite, launched at Cape Canaveral from LC-17B on a Delta-B booster, on April 3, 1963, to study the Earth's upper atmosphere. It was the first satellite of five Atmosphere Explorers.
Technical specifications 
Explorer 17 was a spin-stabilized sphere 0.95 m in diameter. The spacecraft was vacuum sealed in order to prevent contamination of the local atmosphere. Explorer 17 carried four pressure gauges for the measurement of total neutral particle density, two mass spectrometers for the measurement of certain neutral particle concentrations, and two electrostatic probes for ion concentration and electron temperature measurements. Battery power failed on July 10, 1963. Three of the four pressure gauges and both electrostatic probes operated normally. One spectrometer malfunctioned, and the other operated intermittently.
The successful launch and operating of Explorer 17 allowed scientists for the first time to obtain instantaneous atmospheric density measurements using several independent measuring systems, to measure the atmosphere during a single day under nearly constant local time conditions and geomagnetic activity, and to compare direct measurements of density with those inferred from measurements of perturbations in the satellite period orbit.
The spacecraft decayed from orbit after 1,325 days on November 24, 1966.
- Newton, George P.; Horowitz, Richard; Priester, Wolfgang (July 1965). "Atmospheric Density and Temperature Variations from the Explorer XVII Satellite and a Further Comparison with Satellite Drag". Planetary and Space Science (fee requiredBibcode:1965P&SS...13..599N. doi:10.1016/0032-0633(65)90042-5.) 13 (7): 599–616.