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Ed Kyle

KING OF GODS:  The Jupiter Missile Story
Fifth in a Series Reviewing Jupiter's Place in Space Age History
by Ed Kyle, Updated 7/16/2011

am11s.jpg (9039 bytes)Juno II:  Jupiter to Orbit

AM-11, the First Juno II, Fueled for Launch as Gantry Rolls Back

In November 1957 JPL head William Pickering suggested to General Medaris that the planned Redstone-based Jupiter C satellite launch vehicle be named “Juno”.  In Roman mythology, Juno was the sister/wife of Jupiter.   During the same month, Pickering proposed a Jupiter-based satellite launch vehicle for a lunar exploration project named “Red Socks”.  Thus the Jupiter-C that in early 1958 orbited Explorer I, the first U.S. satellite, was identified as a “Juno I” while “Juno II” was the name assigned to the Jupiter-based launcher.   Initially, both were U.S. Army launch vehicles. 

At the same time, Pickering also presented plans for “Juno III”, similar in design to Juno II but with more powerful upper stage solid motors from Grand Central Rocket Company.  Juno III would be able to lift about 20% more payload than Juno II.  JPL proposed to use Juno III to launch a satellite to photograph the far side of the Moon. 

During February 1958, Wernher von Braun traveled to JPL’s Pasadena, California facility for a “Juno Meeting”.  There Pickering, von Braun and others discussed plans to fly Juno II before year’s end, and to fly Juno III soon thereafter.  Both lunar and earth-orbiting missions were contemplated.

Juno launchers with JPL upper stage clusters provided limited payload capacity, making it difficult to deploy instruments and, especially, cameras, on satellites.  On March 20, 1958, Medaris asked JPL to investigate the use one or two liquid storable propellant upper stages atop Jupiter.  The new configuration, capable of lifting perhaps five times as much payload as Juno II/III, was named “Juno IV”.

On March 27, 1958, newly-formed Advanced Projects Research Agency (ARPA) announced its "Operation Mona" program to aim U.S. satellites toward the Moon.  ARPA’s program funded three Thor-Able and two Juno II launches, which would take place as soon as possible.  The effort was clearly part of a “race” with the Soviet Union to get something, anything, to the vicinity of Moon.  Juno III was not included, which effectively ended all plans for Juno III development.

am19gus.jpg (13213 bytes)Design

AM-19G High Speed Stage Shroud

While JPL continued to study and even began developing Juno IV during 1958, Juno II was quickly developed.   

Juno II was a four stage launch vehicle that used the same upper stage cluster developed by JPL for Jupiter-C/Juno I.  On Juno II, unlike Juno I, the upper stages were hidden within a payload shroud.

A modified Jupiter IRBM, stretched by 0.914 meters (3 feet) to accommodate about 6.2 tonnes (13,700 pounds) more propellant, served as the first stage.  The extra propellant extended the S-3D main engine burn time to a bit more than 180 seconds.  A set of retrorockets were added to the aft section of the Jupiter stage to ensure a clean stage separation.

Juno II’s JPL “high speed stages”, consisted of a spin-stabilized cluster of 15 solid rocket motors housed in a “launching tub”.  The stages were mounted to the top of the guidance and instrumentation compartment (essentially the IRBM’s “aft unit”).  This section had a “spatial attitude” control system that fired cold gas through eight jet nozzles positioned “tangentially” on four finlike tabs on its aft end.   The instrument compartment also housed the events programmer and the cluster drive motors.

The upper stage cluster, housed within the 1.23 meter (48.4 inch) diameter shroud, was spun up by a pair of electric motors before lift-off.   The motors continued to spin the cluster up to 400 rpm until the ignition of Stage 2.

pioneers.jpg (10398 bytes)Juno II Pioneer Launch Sequence

The second stage was a 331 kg (730 pound) circular cluster of eleven scaled-Sergeant solid rocket motors that produced an average of 9,131 kgf (20,130 pounds) thrust for 5.52 seconds.  JPL had developed the motors as one-fifth scale test versions of the Sergeant missile it was developing for the Army.   The 84.8 kg (187 pound) third stage, nestled within the second, used three scaled-Sergeants to produce 2,490 kgf (5,490 pounds) of average thrust for 5.52 seconds. The fourth stage was a single scaled-Sergeant mounted above the third stage.  It weighed 29.7 kg (65.4 pounds) loaded, burned 21.87 kg (48.21 pounds) of solid propellant, and produced an average of 830 kgf (1,830 pounds) of thrust during its 5.5 second burn.

A small payload mounted to the top of the fourth stage motor.  Juno II could lift 45 kg (99 pounds) to low earth orbit or 6.8 kg (15 pounds) to escape velocity. 

After the first stage shut down and separated  the upper stage cluster and the guidance and instrumentation compartment coasted for about 60 seconds.  The shroud covering the top of the upper stage cluster was jettisoned about 12.5 seconds after separation.   The instrumentation compartment’s “spatial attitude” cold gas jet control system maintained attitude during the coast. 

Beginning about 240 seconds after liftoff, with the timing depending on the mission and determined by the instrument compartment’s guidance system, the three upper stages fired in quick succession to provide the final acceleration to orbit. 

On May 1, 1958, ARPA effectively gained control of Juno I, II, and IV – and soon Juno V, beginning the transition of orbital launch programs away from the U.S. Army.   That process would move apace when NASA began operations on October 1, 1958.  At that time, NASA decided that it would continue the Juno II program in the short term, once that program was transferred from ARPA.  JPL itself joined NASA on December 3, 1958, only three days before the first Juno II launch.   ABMA remained an Army organization for the time being. 

am14s.jpg (3874 bytes)Shooting the Moon

AM-14 with Pioneer 4

By the time the first Juno II lifted off, the U.S. Air Force had already performed its three Thor-Able launch attempts, the latter two under NASA auspices for a program that it named "Pioneer".  None of the attempts reached orbit, though Pioneer 1, the second attempt, was boosted into a 43 hour, 17 minute long suborbital trajectory with a 113,854 km (70,700 mile) apogee on October 11, 1958.   Although Pioneer 1 didn't reach the Moon, it performed unprecedented measurements of the Earth's radiation belt.

ABMA and JPL had their go at the Moon beginning with the first Juno II, vehicle AM-11, launched from Cape Canaveral Launch Complex 5 at 05:44:52 GMT on December 6, 1958.  Atop the fourth stage was a tiny, 6.67 kg (14.7 pound) cone-shaped battery-powered spacecraft named “Juno IIA” by ABMA/JPL.  The intricately designed satellite, flown for the new NASA, would subsequently be known as “Pioneer 3”. 

Launch operations were much different in 1958 than they are today.  The upper stage cluster was mated to the rocket five days prior to launch, but Pioneer 3 itself was not attached until only a few hours before liftoff.  The remainder of the countdown was similar to a Jupiter IRBM test launch.

Liftoff was clean and the rocket climbed on its planned trajectory over the Atlantic.  The first stage cut off, the instrument section coasted and controlled attitude, the shroud separated, and the upper stages fired as planned.  It soon became apparent, however, that Pioneer 3 was flying with slightly less velocity than it needed to escape Earth’s gravity.  The satellite rose into space, reaching an altitude of 108,700 km (63,500 miles), before beginning its inevitable descent.  It reentered nearly 30 hours after liftoff, but provided hours of telemetry from Geiger-Mueller tube radiation detectors and from an optical trigger device during its flight, helping map the outer Van Allen radiation belts.  Giant dish antennas, such as the one at Goldstone, were used to pick up signals from Pioneer 3’s tiny 180 milliwatt, 960 MHz transmitter.

Juno II AM-11’s first stage had cut off 3.6 seconds earlier than expected, at X+176.2 seconds, due to a failure in the propellant depletion circuit.  The precise cause of the failure was never identified.  The upper stages had also behaved in an unexpected manner, wobbling slightly like a top, resulting in a slightly miss-aimed trajectory.   The satellite de-spin system also failed.

am14gos.jpg (4506 bytes)AM-14 Ignition on LC 5

ABMA installed new depletion switch components prior to the next attempt.  An additional arming circuit was added that prevented cutoff prior to 177.6 seconds, enough time to at least ensure an orbit.  The de-spin system was redesigned. 

The USSR’s Luna 1 was launched on January 2, 1959.  Luna 1 passed within about 6,000 km of the Moon and became the first satellite to escape Earth’s gravity and enter solar orbit. 

 Juno II had one more shot.  Following a scrubbed March 1 launch attempt, the second Juno II, vehicle AM-14, lifted off from LC 5 at 05:10:56 GMT on March 3, 1959.  This time the first stage burned for 183.1 seconds.  The instrument compartment separated six seconds later.  The payload shroud jettisoned 201.8 seconds after liftoff.  The upper stages began firing at 242.6 seconds and finished at X+268.8 seconds.  Pioneer 4 (Juno IIA-Prime), a close copy of Pioneer 3, separated 276.6 seconds after liftoff, de-spun itself by releasing weights, and was on its way.        

The fixes worked.  Pioneer 4 became the first U.S. satellite to enter solar orbit.   It passed within 60,000 km (37,000 miles) of the Moon on March 4 and was tracked for 82 hours until its batteries died when it was nearly 656,500 km (407,000 miles) from Earth.  It transmitted radiation, light sensor, and temperature data, and proved the capability of the ground tracking network to receive signals from deep space.  The satellite’s optical trigger was designed to detect the presence of the Moon if it passed within 32,258 km (20,000 miles), but Pioneer 4’s aim was slightly off, preventing that detection.

The first “Moon Race” ended emphatically when the Soviets hit the Moon with Luna 2 during September 1959 and photographed its far side one month later with Luna 3.

am16-1s.jpg (12576 bytes)LEO Success, and Failure

AM-16 Liftoff

Juno II now shifted to earth orbiting satellite launches.  The first such launch attempt created one of the most spectacular failures ever seen at the Cape.

Vehicle AM-16, with a 42 kg multipurpose scientific satellite named Explorer S-1, lifted off from LC 5 during daylight on July 16, 1959.  At liftoff the S-3D engine gimbaled full stop and the rocket turned hard toward the west (uprange).  Soon it was parallel to the ground and still turning hard.

The white rocket nearly turned upside down before the Range Safety Officer transmitted cutoff and destruct commands about 5 seconds after liftoff.  The nearly fully-fueled rocket plummeted to the ground in pieces and exploded in a massive fireball.  Ground impact was about 76 meters (250 feet) northwest of the pad and 91 meters (300 feet) southwest of the blockhouse, where the stunned launch crew watched upper stage solid motors burn on the ground.   

An investigation found that a short circuit had occurred between two diodes in a power supply inverter voltage regulator.  The short had cut off power to the guidance system, causing a full gimbal.  Future circuit boards of this type would use conformal coating to reduce the chances for a recurrence.

am16-2s.jpg (6223 bytes)AM-16 Just Before Destruction

Launch failures were common at the time.  In the midst of the Cold War space race, no thought was given to halting the program for an extended round of blue ribbon panel investigations.  Instead, ABMA and JPL simply stacked the next Juno II and payload on nearby LC 26B.

Vehicle AM-19B lifted off on August 14, 1959 with 11.6 kg (25.5 pound) Beacon 2, the inflatable sphere experiment.  This Juno II flew a northeast trajectory on a 48 degree azimuth, aiming for a low earth orbit.  Beacon 2, which was designed to sense the density of the atmosphere in the 30 to 150 km altitude range, did not require a fourth stage. 

Liftoff occurred at 1931:00:7 EST.  Juno II cleared the launch complex without incident, but soon ran into trouble.  Investigators had asked for a series of tracking flares to be ejected from the guidance compartment beginning 180 seconds after liftoff, at about the time of first stage cutoff.  The first flare fired, but no additional flares were seen.  The guidance compartment, now separated from the first stage, depressurized 203 seconds after liftoff.   

Tracking flares had likely ignited within the compartment.  The guidance and control system failed, causing the upper stages to fire in the wrong direction.  Beacon 2 fell short of orbit.

am16-3s.jpg (7194 bytes)AM-16 Destruct Commanded

Three Juno II failures had now occurred in four attempts, but the AM-19B failure was not caused by the launch vehicle.  Instead, it was caused by a flawed decision to add tracking flares to the guidance compartment. 

Juno II redeemed itself on October 13, 1959, when AM-19A launched 41.3 kg (91.15 pound) Explorer 7 into a 556 x 1,088 km x 50.3 deg orbit.  Explorer 7 was a copy of the satellite lost during the spectacular AM-16 failure three months earlier.  This multipurpose satellite had solar cells and rechargeable batteries to provide an extended duration mission.  It returned magnetic field and solar flare data for nearly two years. 

The AM-19A launch was delayed by 12 days when the vehicle suffered slight damage from the failure of Jupiter Missile AM-23, launched from LC 26B on September 15, 1959.   Jupiters and Redstones and Juno IIs all flew from the busy ABMA pads during 1959.   AM-23 was the ninth Jupiter missile launch of the year but was the first outright failure.  Like AM-16, it flew out of control near the launch pad and had to be destroyed 13 seconds after liftoff. 

Several months would pass before Juno II flew again.  Vehicle AM-19C lifted off on March 23, 1960 on an unsuccessful attempt to place Explorer S-46, a 10.2 kg (22.5 pound) “Van Allen” payload, into a highly elliptical orbit meant to sound the radiation belts.  

The Jupiter stage performed well, but the second stage cluster fired off axis, 19 degrees down and 5 degrees right.  It was determined that one of the 11 second stage motors had not ignited, creating off-axis thrust and inadequate velocity to reach orbit. 

juno2rs.jpg (17769 bytes)Juno II Review Committee

Juno II in Hanger R at Cape Canaveral

ABMA joined NASA on July 1, 1960, becoming NASA's George C. Marshall Space Flight Center.   NASA commissioned a Juno II Review Committee to study Juno II’s frustrating reliability issues.  By that date, Juno II had only managed to orbit two satellites in six attempts.  Four more Juno II rockets were available.  NASA wanted to know if it was worthwhile to fly them.

The Committee noted that Juno II was a “closed-end program”, with no plans for future use beyond the four vehicles.  It noted that many of the personnel who designed Juno II had already been transferred to other work, and that design information for the vehicle was already difficult to obtain.  The ABMA and JPL teams involved in Juno II were said to be separated, both from each other and from NASA in general.

The investigation found that failures had been caused by "varied and isolated reasons", indicative of poor quality control and vehicle checkout.  Every vehicle component in the design represented a potential single-point of failure.

am19as.jpg (6078 bytes)AM-19A Provided a Rare Success by Orbiting Explorer 7

Moral among team members was suspect, largely due to the fact that the program was dead-ending.   JPL was said to have become “uninterested" in Juno II after the Pioneer IV launch.  Pickering’s group was even said to have tried to end its involvement in the program after payload responsibility was reassigned by NASA.

JPL’s original Juno II payloads only weighed 15 pounds.  The subsequent non-JPL payloads weighed as much as 94 pounds, complicating the cluster design and reducing the expectation of success among team members.  Those involved in the project predicted that two out of the final four launches might succeed.

In the end, the Committee recommended flying the final four Juno II vehicles, essentially accepting that two out of four successes was a risk worth taking, given that the vehicles were already bought and paid for.  Two out of four would be the result.

The Final Four

Juno II AM-19D successfully lifted 92.5 pound Explorer 8 into a 370 x 2,341 km x 49.9 deg orbit on November 3, 1960.  All four of the final Juno II vehicles flew from LC 26B.   Explorer 8 measured charge accumulation on the surface of the satellite and measured the frequency, momentum, and energy of micrometeorite impacts.  A support cylinder was added to the stage 3 cone to support the heavier satellite.

Vehicle AM-19F flew next, on February 24, 1961.  This was a failed attempt to orbit the 75-1b Explorer S-45 ionosphere beacon satellite, a spacecraft meant to measure the ionospheres’ effect on radio signals.  First stage performance was normal, but something went wrong shortly after the stage separated from the guidance compartment.  The most likely failure mode was thought to be a sensor cable coming loose from the side of the payload shroud and wrapping itself around the spinning high speed stage cluster. Stage 4 and the payload were likely ripped free from the cluster and the stage 3 and 4 firing timer was likely damaged.  Although the instrument compartment regained control of the cluster, only the second stage fired and no orbit was attained.

am19es.jpg (6641 bytes)AM-19E Launches Explorer 11

On April 27, 1961,]uno II AM-19E successfully orbited Explorer 11, an 39.6 kg (85 pound) gamma-ray astronomy satellite.  Juno II performed as expected and Explorer 11 entered a 497 x 1,793 km x 28.49 deg orbit. Its gamma ray counter functioned until mid-December 1961.  

The final Juno II launch on May 24, 1961 provided an almost predictable, exasperating failure. Vehicle AM-19G attempted to launch Explorer S-45, another ionosphere beacon.  First stage flight was normal, as was instrument compartment separation.  During the coasting phase, however, the instrument unit power supply failed.  The second stage was not ignited and the final JPL high speed stage cluster spun its way down to impact the Atlantic Ocean.

Juno II passed into history just under three weeks after the ex-ABMA team had successfully launched Alan Shepard on his suborbital flight from LC 5 and was making preparations to fly its first Saturn rocket from a new, big launch complex up the coast.  By Juno II’s finale, NASA’s new Thor-Delta launcher had scored three consecutive successes and Lockheed’s new Agena upper stage had begun proving itself in nearly two dozen flights atop Thor and Atlas launchers. 

Juno II was done, but Jupiter’s moment in history was still to come.


History of the Jupiter Missile System, James Grimwood, Frances Stroud, U.S. Army Ordnance Missile Command, July 27, 1962.

A Reliability Review of the Juno II Vehicle, NASA Juno II Review Committee, July 13, 1960.

Juno Final Report, Volume II, Allen E. Wolfe, JPL, September 1960.

Juno Final Report, Volume III, C. F. Mohl, June 1962.

Project Ranger - A Chronology, R. Cargill Hall, JPL, April 1971.


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