The task before the team at the JPL in 1957 was immense. They were to create a satellite that was technologically the equal of Sputnik, and get it into space as soon as possible. It was a task they accomplished in 3 short months. The satellite they put together was dubbed 'Explorer 1', and it weighed a mere 10kgs.
It carried with it a cosmic-ray detection package, an internal temperature sensor, three external temperature sensors, a nose-cone temperature sensor, a micrometeorite impact microphone, and a ring of micrometeorite erosion gauges. Which, I'm sure you'll agree, sounds adequate for the purposes.
Crudely speaking, the team at the JPL strapped all this to the top of a rocket, pointed it into the sky and on January 31st, 1958, the USA had caught up.