What Rocket Am I?: Quiz 12

Clue 1: My payload to orbit was about 11 kg.
Clue 2: I am a four-stage rocket based on the Jupiter-C missile.
Clue 3: I was developed in the United States by the Army Ballistic Missile Agency.
Clue 4: I was first launched in 1958.
Clue 5: I helped discover the Van Allen radiation belts.
Clue 6: I launched the first American satellite, Explorer 1.
Clue 7: I stand 21.2 meters tall.

Yes, I am Juno I.

I was part of the International Geophysical Year efforts, marking America's entry into the space race.