Juno II was an American

space launch vehicle A launch vehicle or carrier rocket is a rocket designed to carry a payload (spacecraft or satellites) from the Earth's surface to outer space. Most launch vehicles operate from a launch pads, supported by a launch control center and syste ...

used during the late 1950s and early 1960s. It was derived from the

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...

missile, which was used as the first stage.

Development

Solid rocket motors derived from the

MGM-29 Sergeant The MGM-29 Sergeant was an American short-range, solid fuel, surface-to-surface missile developed by the Jet Propulsion Laboratory. The missiles were built by Sperry Utah Company. The Sergeant was the third and last in a series of JPL rockets fo ...

were used as upper stages, eleven for the second stage, three for the third stage, and one for the fourth stage, the same configuration as used for the upper stages of the smaller

Juno I 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 was a member of the Redstone launch veh ...

launch vehicle. On some launches to

low Earth orbit A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never mor ...

the fourth stage was not flown, allowing the launch vehicle to carry an additional nine kilograms of payload. Development of the Juno II was extremely fast due to being completely built from existing hardware. The project began in early 1958 and the first vehicle flew at the end of the year.

Chrysler Stellantis North America (officially FCA US and formerly Chrysler ()) is one of the " Big Three" automobile manufacturers in the United States, headquartered in Auburn Hills, Michigan. It is the American subsidiary of the multinational automoti ...

were responsible for the overall contract, while

Rocketdyne Rocketdyne was an American rocket engine design and production company headquartered in Canoga Park, California, Canoga Park, in the western San Fernando Valley of suburban Los Angeles, California, Los Angeles, in southern California. The Rocke ...

handled the first stage propulsion and

Jet Propulsion Laboratory The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, United States. Founded in the 1930s by Caltech researchers, JPL is owned by NASA an ...

handled the upper stage propulsion. The first three were converted Jupiter missiles, however all remaining boosters were built as Juno IIs from the beginning. The main differences between the Juno II and Jupiter were stretched propellant tanks for increased burn time (the first stage burn time was approximately 20 seconds longer than on the Jupiter), a reinforced structure to support the added weight of upper stages, and the inertial guidance system replaced with a radio ground guidance package, which was moved to the upper stages.

History

The Juno II was used for ten satellite launches, of which six failed. It launched

Pioneer 3 Pioneer 3 was a spin-stabilized spacecraft launched at 05:45:12 GMT on 6 December 1958 by the U.S. Army Ballistic Missile Agency in conjunction with the NASA, using a Juno II rocket. This spacecraft was intended as a lunar probe, but failed to ...

Pioneer 4 Pioneer 4 was an American spin-stabilized uncrewed spacecraft launched as part of the Pioneer program on a lunar flyby trajectory and into a heliocentric orbit making it the first probe of the United States to escape from the Earth's gravity. ...

Explorer 7 Explorer 7 was a NASA satellite launched on 13 October 1959, at 15:30:04 GMT, by a Juno II launch vehicle from Cape Canaveral Air Force Station (CCAFS) to an orbit of and inclination of 50.27°. It was designed to measure solar X-ray and L ...

Explorer 8 Explorer 8 was a NASA research satellite launched on 3 November 1960. It was intended to study the temporal and spatial distribution of the electron density, the electron temperature, the ion concentration, the ion mass, the micrometeorite di ...

, and

Explorer 11 Explorer 11 (also known as S-15) was a NASA satellite that carried the first space-borne gamma-ray telescope. This marked the beginning of space gamma-ray astronomy. Launched on 27 April 1961 by a Juno II, the satellite returned data until 17 ...

from

Cape Canaveral Launch Complex 5 Cape Canaveral Launch Complex 5 (LC-5) was a launch site at Cape Canaveral Space Force Station, Florida used for various Redstone and Jupiter launches. It is most well known as the launch site for NASA's 1961 suborbital Mercury-Redstone 3 flight ...

and Launch Complex 26B. The first launch of a Juno II,

on 6 December 1958, suffered a premature first stage cutoff, preventing the upper stages from achieving sufficient velocity. Pioneer 3 could not escape Earth orbit, but transmitted data for some 40 hours before reentering the atmosphere. A malfunction in a propellant depletion circuit was found to be the cause of the failure, although the exact nature of it could not be determined. The circuit was redesigned afterwards.

launched successfully on 3 March 1959, making for the only first-generation U.S. lunar probe to accomplish all of its mission goals, as well as the sole successful U.S. lunar probe until 1964. After Pioneer 4, NASA shifted their lunar efforts to the bigger

Atlas-Able The Atlas-Able was an American expendable launch system derived from the SM-65 Atlas missile. It was a member of the Atlas family of rockets, and was used to launch several Pioneer spacecraft towards the Moon. Of the five Atlas-Able rockets built ...

booster and decided instead to utilize the Juno II for Earth orbital launches. By removing the fourth stage, the payload capacity was nearly doubled. The attempted launch of an Explorer satellite on 16 July 1959 failed dramatically when the Juno II lost control almost immediately at liftoff, performing a cartwheel before the Range safety officer sent the destruct command. The almost fully fueled booster crashed a few hundred feet from the pad, blockhouse crews watching in stunned surprise at the upper stage motors burning on the ground. Cause of the mishap was quickly traced to a short between two diodes in a power inverter, which cut off power to the guidance system at liftoff and caused the Juno's engine to gimbal to full stop, flipping the vehicle onto its side before Range Safety action was taken. To prevent a recurrence of this failure mode, improved coatings were used on the circuit boards in the booster. On 15 August 1959, the next Juno II was flown, carrying the Beacon satellite. While first stage performance was nominal, the upper stages malfunctioned. One intended experiment on this mission was the ejection of four flares stowed in the interstage section which would be tracked and photographed during the launch. However, things went awry when the flare ejection failed to take place on schedule. The control system also malfunctioned and drove the upper stages into the

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

instead of orbit. It was concluded that one of the flares deployed inside the interstage section instead of outside like it was intended to, causing the guidance compartment to depressurize and cause loss of vehicle control.

was scheduled for launch in the last week of September 1959, but a Jupiter missile test on an adjacent pad failed just after liftoff on 15 September 1959 and the Juno II suffered minor damage from flying debris. This was quickly repaired and the launch performed successfully on 13 October 1959. Explorer 7 would be the last Juno II launch from LC-5 as the pad was then permanently reassigned to

Project Mercury Project Mercury was the first human spaceflight program of the United States, running from 1958 through 1963. An early highlight of the Space Race, its goal was to put a man into Earth orbit and return him safely, ideally before the Soviet Un ...

. On 23 March 1960, another Explorer satellite failed to reach orbit when one second stage motor failed to ignite, causing imbalanced thrust that sent the payload into the Atlantic Ocean. In mid-1960, with only two successful launches in six attempts, a NASA board conducted a thorough reevaluation of the Juno II as a launch vehicle. The failures were mostly traced to isolated component failures that occurred as a result of inadequate testing and checkouts. This was blamed on the program being close-ended, with no further plans for development of the booster, leading to low interest and apathy among those in the program. The JPL team who developed the Juno II had originally only intended it for the Pioneer lunar probes and their interest started waning as soon as NASA began Earth orbital launches with the vehicle. Even worse, most of the design team had been disbanded and its members reassigned to other projects, making it difficult to obtain technical information for the Juno II. The conversion of the booster for LEO launches also threw off the calibration of the spinning tub third stage which was designed for the tiny Pioneer probes and not the larger Explorer satellites. At this time, NASA had four Juno IIs remaining in their inventory. The review board predicted that two of them would launch successfully, but recommended that there was no reason not to fly the boosters since they had already been bought and paid for. Their assumptions proved correct.

was launched successfully on 3 November 1960, with the next attempt on 24 February 1961 a failure. A control cable came loose during ascent and wrapped itself around the spinning third stage tub, damaging the upper stages and payload. Second stage ignition occurred on time, but the third stage did not ignite and the satellite failed to orbit.

launched successfully on 27 April 1961, an event that raised NASA's morale during a mostly disastrous month characterized by Project Mercury failures and the Soviet launch of a man into space. On 24 May 1961, the final Juno II lifted from LC-26A carrying another ionospheric beacon satellite. The instrument unit lost power following first stage separation, resulting in no second stage ignition and the payload reaching the ocean floor instead of orbit. By this time however, the fast-rising

Thor-Delta The Thor-Delta, also known as Delta DM-19 or just Delta was an early American expendable launch system used for 12 orbital launches in the early 1960s. A derivative of the Thor-Able, it was a member of the Thor family of rockets, and the first ...

and Agena vehicles were on their way to take over as mainstays of the U.S. light and medium lift launch vehicle arsenal.

Launch history

Specifications

* Total length: 24.0 m * Orbit payload to 200 km: 41 kg * Escape velocity payload: 6 kg * First launch date: 6 December 1958 * Last launch date: 24 May 1961

References

External links