Juno I

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The Juno I was a four-stage American booster rocket which launched America's first satellite, Explorer 1, in 1958. A member of the Redstone rocket family, it was derived from the Jupiter-C sounding rocket. It is commonly confused with the Juno II launch vehicle, which was derived from the PGM-19 Jupiter medium-range ballistic missile.


The Juno I consisted of a Jupiter-C rocket, with a fourth stage mounted on top of the "tub" of the third stage, which was fired after third stage burnout to boost the payload and fourth stage to an orbital velocity of 18,000 mph (8 km/s). This multi-stage system, designed by Wernher von Braun in 1956 for his proposed Project Orbiter, obviated the need for a guidance system in the upper stages, proving to be the simplest and most immediate method for putting a payload into orbit; but as it had no upper-stage guidance, it could not inject the payload into a precise orbit. Both the four stage Juno I and three stage Jupiter-C launch vehicles were the same height (21.2 meters), with the added fourth stage booster of the Juno I being enclosed inside the nose cone of the third stage.


Although Juno I's Explorer 1 launch was a huge success for the U.S., only two of its remaining five flights were successful; launching Explorer 3 and 4. The American public was happy and relieved that America had finally managed to launch a satellite after the launch failures in the Vanguard and Viking series. With the relative success of the Juno I program, von Braun developed the Juno II, using a PGM-19 Jupiter first stage, rather than a Redstone.

The six launches of Juno I were:

  • January 31, 1958: orbited Explorer 1 weighing 30.66 lb (13.91 kg) with 18.35 lb (8.32 kg) of payload, perigee 224 mi (360 km), apogee 1,575 mi (2,535 km). Explorer 1 ceased transmission of data on May 23, 1958 when its batteries died, but remained in orbit for more than 12 years. It made a fiery reentry over the Pacific Ocean on March 31, 1970.
  • March 5, 1958: attempted orbit of Explorer 2, weighing 31.36 lb (14.22 kg) with 18.83 lb (8.54 kg) of payload, failed because fourth stage did not ignite.
  • March 26, 1958: orbited Explorer 3, weighing 31.0 lb (14.0 kg) with 18.53 lb (8.41 kg) of payload, perigee 119 mi (192 km), apogee 1,740 mi (2,800 km). Down June 28, 1958.
  • July 26, 1958: orbited Explorer 4, weighing 37.16 lb (16.86 kg) with 25.76 lb (11.68 kg) of payload, perigee 163 mi, apogee 1,373 mi (2,210 km). Down October 23, 1959.
  • August 24, 1958: attempted orbit of Explorer 5, 37.16 lb (16.86 kg) with 25.76 lb (11.68 kg) of payload. It failed after booster collided with second stage after separation, causing upper stage firing angle to be off.
  • October 23, 1958: attempted orbit of 12 ft (3.7 m) inflatable Beacon satellite 31.5 lb (14.3 kg) with 18.3 lb (8.3 kg) of payload. It failed when second stage separated prematurely from booster.


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