Explorer 9, known as S-56A before launch, was an American satellite which was launched in 1961 to study the density and composition of the upper thermosphere and lower exosphere.[1] It was a reflight of the failed S-56 mission, and consisted of a 7-kilogram (15 lb), 3.7-metre (12 ft) balloon which was deployed into a medium Earth orbit.[2] The mission was conducted by NASA's Langley Research Center.
Explorer 9 was launched from Launch Area 3 at the Wallops Flight Center, atop a Scout X-1 rocket with the serial number ST-4. It was the first spacecraft launched from Wallops Island to achieve orbit, with one previous attempt having failed. The launch occurred at 13:05:00 UTC on 16 February 1961, and resulted in Explorer 9 being deployed into a orbit with an apogee of 2,581 kilometres (1,604 mi), a perigee of 635 kilometres (395 mi), 38.8 degrees of inclination and a period of 118.4 minutes.[3] It was assigned the Harvard designation 1961 Delta 1.[4]
The second of six identical air density research satellites to be launched, Explorer 9 was the first to successfully reach orbit. It was still operational when the next satellite, Explorer 19, was launched, allowing simultaneous readings to be taken and compared.[5] It decayed from orbit on 9 April 1964.[3]
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- Italics indicates probes that failed to deploy or otherwise malfunctioned
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Payloads are separated by bullets ( · ), launches by pipes ( | ). Manned flights are indicated in bold text. Uncatalogued launch failures are listed in italics. Payloads deployed from other spacecraft are denoted in brackets.
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