That's no moon...
Explorer IX was placed into Earth orbit on February 16, 1961 after a successful launch on a new Scout rocket. The satellite was designed to inflate after launch and test atmospheric densities in low orbit. Its aluminum foil layers on the skin functioned as the craft's antenna but it's tracking system failed after launch. The mission controllers used the craft's camera system to help keep track of the spacecraft. Power was supplied by solar cells placed around the outer skin.
The launch was notable for being the first successful launch of a satellite on a solid rocket motor (the Scout launcher), and for being the first successful launch from the Virginia Wallops Island facility.
Explorer IX would finally burn up in the atmosphere 50 months later. An entire series of probes like Explorer IX would eventually be designed for testing the properties of our outer atmosphere.