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Fifty-five years ago this month, the first Jupiter-C launch vehicle flew a suborbital mission in which it attained a maximum velocity of 16,000 mph.  The successful flight test was a significant step in the development of what would ultimately result in the United States’ first satellite launcher.

The Jupiter-C was a derivative of the Army’s Redstone Short Range Ballistic Missile (SRBM).  It was designed to test sub-scale models of the warhead reentry vehicle used by the Jupiter Intermediate Range Ballistic Missile (IRBM).  The “C” in Jupiter-C stood for Composite Reentry Test Vehicle.

The Jupiter-C launch vehicle was composed of three (3) separate stages.  The vehicle measured 68.5 feet in length and had a maximum diameter of 70 inches.   Lift-off weight was 62,700 lbs.  All Jupiter-C launches took place from LC-5 and LC-6 at Cape Canaveral, Florida.

The Jupiter-C first stage was a Redstone missile stretched by 8 feet to allow for increased propellant load capability.  Power was provided by a single Rocketdyne A-7 liquid rocket engine that burned alcohol and liquid oxygen as propellants.  The A-7 produced 78,000 lbs of thrust for about 150 seconds.

The Jupiter-C second and third stages consisted of clusters of Baby Sergeant solid rocket motors.  Specifically, the second stage clustered eleven (11) of these motors that generated a total thrust of 16,500 lbs for 6 seconds.  The third stage utilized a cluster of three (3) Baby Sergeants that produced a total thrust of 4,500 lbs for 6 seconds.  Propellants for the solids included polysulfide-aluminum and ammonium perchlorate.

The second and third stage solid rocket motors were housed in a large cylinder that sat atop the first stage.  This cylinder (referred to as the “tub”) was spun at a rotational velocity that varied from 450 to 750 RPM in flight.  The purpose in doing so was to mitigate the effects of thrust misalignments and provide gyroscopic stability during the  firing periods of the second and third stage solid rocket motor clusters.

The kinematic performance capability of the Jupiter-C was such that it could readily put a payload in orbit given a fourth stage.  However, the State Department strictly forbade any attempt to orbit a satellite with the Jupiter-C.  Even if that were to happen “accidentally”.  The philosophy at the time was that America’s first satellite would be orbited using a non-military booster.

The first Jupiter-C was launched from LC-5 at Cape Caneveral, Florida on Wednesday, 19 September 1956.  Launch time was 05:47 UTC.  (For the record, we note here that some historical sources quote the launch date as being Thursday, 20 September 1956.)  The vehicle did not carry a scaled Jupiter nose cone test article, but a dummy fourth stange and about 20 lbs of instruments in its stead.

The kinematic performance of the first Jupiter-C was impressive.  The vehicle reached a speed of 16,000 mph (1,500 mph less than orbital requirement) at third stage burnout.   Impact occurred in the Atlantic Ocean roughly 2,861 nm downrange of the launch site.  Apogee for the suborbital flight was 593 nm.

There were only two more Jupiter-C test flights after the inaugural mission.  These occurred on Wednesday, 15 May 1957 and Thursday, 08 August 1957, respectively.  Each vehicle carried a scaled Jupiter nose cone test article.  Surface temperatures exceeded 2,000 F and the ablative thermal protection system worked remarkably well.  So much was learned from these missions that further Jupiter-C flights were deemed unnecessary.

The addition of a live fourth stage rocket motor to the Jupiter-C was known as Juno I.  Indeed, using a single Baby Sergeant solid rocket motor and a small scientific payload constituted the Explorer I satellite.  History records that Explorer I was orbited by a Juno I launch vehicle on Friday, 31 January 1958.  Significantly, it was the first satellite to be orbited by the United States.

Posted in Aerospace, History

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