| | Explorer Spacecraft Series |
 | | This was so because even the early Explorers performed a large variety of scientific missions ranging from energy particle exploration through atmospheric and ionospheric studies to investigations of micrometeroids, air density, radio astronomy, geodesy, and gamma ray astronomy--not to mention interplanetary and solar monitoring. |
 | | The one constant amidst this diversity was that the early "Explorers" were smaller, simpler, and less costly than the orbiting observatories also used in scientific exploration of physical and astronomical phenomena. |
 | | The listing at the end of this narrative shows the satellites that clearly belong in the "Explorer" series because they were relatively small and uncomplicated, performed a scientific mission, and -- until quite recently -- appeared in satellite situation reports and post-launch reports under the name "Explorer," accompanied by a mission number. |
| www.hq.nasa.gov /office/pao/History/explorer.html (390 words) |