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Juno I
Juno I awaiting launch with Explorer I
FunctionOrbital launch vehicle
ManufacturerChrysler for the ABMA
Country of originUnited States
Height21.2 m (70 ft)
Diameter1.78 m (5 ft 10 in)
Mass29,060 kg (64,070 lb)
Payload to LEO
Mass11 kg (24 lb)
Launch history
Launch sitesLC-5 and 26A,
Cape Canaveral Missile Annex, Florida
Total launches6
First flight1 February 1958,
03:47:56 GMT
Last flightOctober 23, 1959
First stage – Redstone (stretched)
Powered by1 Rocketdyne A-7
Maximum thrust42,439 kgf (416.18 kN; 93,560 lbf)
Specific impulse235 s (2.30 km/s)
Burn time155 seconds
Second stage – Baby Sergeant cluster
Powered by11 Solid[1]
Maximum thrust7,480 kgf (73.4 kN; 16,500 lbf)
Specific impulse220 s (2.2 km/s)
Burn time6 seconds
PropellantPolysulfide-aluminum and ammonium perchlorate (Solid)
Third stage – Baby Sergeant cluster
Powered by3 Solid
Maximum thrust2,040 kgf (20.0 kN; 4,500 lbf)
Specific impulse236 s (2.31 km/s)
Burn time6 seconds
PropellantPolysulfide-aluminum and ammonium perchlorate (Solid)
Fourth stage – Baby Sergeant
Powered by1 Solid
Maximum thrust680 kgf (6.7 kN; 1,500 lbf)
Specific impulse249 s (2.44 km/s)
Burn time6 seconds
PropellantPolysulfide-aluminum and ammonium perchlorate (Solid)

The Juno I was a four-stage American space launch vehicle, used to launch lightweight payloads into low Earth orbit. The launch vehicle was used between January 1958 to December 1959. The launch vehicle is a member of the Redstone launch vehicle family, and 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. In 1958, a Juno I launch vehicle was used to launch America's first satellite, Explorer 1.


Developed as a part of the Explorer Project, the original goal for the launch vehicle was to place an artificial satellite into orbit. Following the Soviet Union's launch of Sputnik 1 on October 4, 1957 (and the resulting "Sputnik crisis") and the failure of the Vanguard 1 launch attempt, the program received funding to match the Soviet space achievements. The launch vehicle family name was suggested in November 1957 by Jet Propulsion Laboratory (JPL) Director Dr. William Pickering, who proposed the name Juno, after the Roman goddess and queen of the gods, as well as for its position as the satellite-launching version of the Jupiter-C. The fourth stage for the Juno I launch vehicle was derived following the September 1956 test launch of a Jupiter-C for the Army Ballistic Missile Agency, which could have been the world's first satellite launch, had a fourth stage been loaded and fueled. A fourth stage would have allowed the nose cone to overshoot the target and enter orbit.[2]

The first launch of a Juno I launch vehicle was in early 1958, with the successful launch of Explorer 1 satellite on February 1, 1958, at 03:47:56 GMT, after the Soviet Union's Sputnik 1 on October 4, 1957.[2] The launch had been scheduled for January 29, 1958, but was scrubbed twice. Explorer 1 was the first U.S. satellite, and it confirmed the existence of the Van Allen radiation belt. Following the first successful launch, five more Juno I launch attempts occurred with two successes and three failures. The final launch attempt was on October 23, 1958, from Cape Canaveral Launch Pad 5, which ended in failure.[3]

Launch vehicle

Juno I diagram

The Juno I consisted of a Jupiter-C first stage, based on the Redstone missile; with three additional solid fuel stages based on the Sergeant missile to provide the added impulse to achieve orbit.[4] The fourth stage was mounted on top of the "tub" of the third stage, and fired after third-stage burnout to boost the payload and fourth stage to an orbital velocity of 8 km/s (5.0 mi/s), with an acceleration of 25–51 g. The tub along with the fourth stage were set spinning while the launch vehicle was on the launch pad to provide gyroscopic force in lieu of a guidance system that would have required thrust vectoring, vernier thrusters, or a reaction control system. The booster guidance package (with the tub attached) separated from the first stage after burnout to provide attitude control until second stage ignition.[2] 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. It was the simplest method for putting a payload into orbit but having no upper-stage guidance, the payload could not achieve a precise orbit. Both the four-stage Juno I and three-stage Jupiter-C launch vehicles were the same height (21.2 m (70 ft)), with the added fourth-stage booster of the Juno I being enclosed inside the nose cone of the third stage.

Launch history

Juno I was launched six times by ABMA in 1958, intending to place satellites in LEO.[4][5]

Following the successful launch of Explorer 1 on February 1, 1958, the first U.S. satellite, Juno I made five more launches before being retired in favor of Juno II.[4] Although Juno I's launch of the Explorer 1 satellite was a huge success for the U.S. space program, only two of its remaining five flights were successful, Explorer 3 and Explorer 4,[1] giving the Juno I vehicle a mission total success ratio of 50%.[4] The Juno I vehicle was replaced by the Juno II in 1959.

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.

Juno I launches[4][5]
Flight No. Date / time (GMT) Rocket Launch site Payload Payload mass Outcome Comments
1 February 1, 1958
Juno I RS-29 (UE) LC-26A Explorer 1 22 kg Success Maiden launch of Juno I. First American satellite launched. 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.
2 March 5, 1958
Juno I RS-26 (UV) LC-26A Explorer 2 23 kg Failure Fourth stage did not ignite.
3 March 26, 1958
Juno I RS-24 (UT) LC-5 Explorer 3 23 kg Success Decay from orbit on June 28, 1958.
4 July 26, 1958
Juno I RS-44 (TT) LC-5 Explorer 4 29 kg Success Decay from orbit on October 23, 1959.
5 August 24, 1958
Juno I RS-47 (TI) LC-5 Explorer 5 29 kg Failure Booster collided with second stage after separation, causing upper stage firing angle to be off.
6 October 23, 1958
Juno I, RS-49 (HE) LC-5 Beacon 1 23 kg Failure Five stage version, Second stage separated prematurely from booster.


See also


  1. ^ a b Boehm, J.; Fichtner, H.J.; Hoberg, Otto A. Explorer satellites launched by Juno 1 and Juno 2 vehicles (PDF) (Report). US: NASA.Public Domain This article incorporates text from this source, which is in the public domain.
  2. ^ a b c Bello, Francis (1959). "The Early Space Age". Fortune. Archived from the original on November 3, 2013. Retrieved June 5, 2012.
  3. ^ "JUNO I FACT SHEET". Spaceline. Retrieved August 1, 2021.
  4. ^ a b c d e "Juno-1". Gunter's Space Page. Retrieved October 15, 2023.
  5. ^ a b "Juno-1 (5 stage)". Gunter's Space Page. Retrieved October 15, 2023.