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Beacon 2



The second and final launch of the Beacon project, Beacon 2 was launched using a Juno 2 rocket. It was a thin plastic sphere (12-feet in diameter inflated) launched to study the upper atmosphere. Premature fuel depletion in the first stage combined with an upper stage guidance system malfunction resulted in failure of the mission. The major objective of the Beacon project was to place a 12-foot diameter inflatable sphere in orbit to study atmospheric density at various levels through visual observations. A secondary objective was to place a third stage instrumented payload casing in orbit.

Mission Profile

Beacon 2 (Jupiter AM-19B) was launched on 15 August 1959 at 00:31:00.7 UT (14 August, 7:31 p.m. EST) from the Atlantic Test range at Cape Canaveral, Florida. The fuel flow was determined to be about 4.5 kg (10 lb) per second higher than precalculated, resulting in early fuel depletion and cutoff of the first stage burn at 176.8 seconds after launch. This was about 4 seconds earlier than planned, and resulted in a velocity 5% to 10% below nominal. The first tracking flare was fired at about 180 seconds, and stage separation occurred at 183.8 seconds. At 203 seconds, telemetry indicated a sudden drop in pressure in the guidance compartment, resulting in loss of guidance control. The second stage continued to fire until cutoff at 656.1 seconds, but sub-nominal velocity and loss of guidance meant the vehicle could not achieve orbit. The last signal was received about 1000 seconds after launch, and no other flares were fired.

A review panel concluded two unrelated mishaps were responsible for the failure. The exact cause of the fuel depletion could not be resolved, but the most likely cause was determined to be fuel leakage through cracks in the tubes in the thrust chamber. The loss of pressure in the guidance compartment was concluded to be due to an explosion, probably one of the tracking flares malfunctioning.

Spacecraft and Subsystems

The payload was held in an 18 cm (7 in) diameter, 80 cm (31.5 in) long stainless steel cylinder mounted on top of the third stage. Total mass of the payload including the casing was 11.6 kg (25.5 lbs). The inflatable 3.66 meter (12 ft) diameter sphere was made of laminated mylar polyester film, 1 mil (25 micrometers) thick, coated on both sides with a microthin (0.45 mil, 11 micrometer) highly reflective aluminum foil and was uninstrumented. Uninflated, it folded into a cylindrical package with a mass of 4.2 kg (9.26 lbs) that was held in the top of the payload casing. Below the sphere package was an inflation and release valve and a bellows and piston assembly. The radio transmission assembly was mounted in the bottom of the cylinder. It comprised an rf transmitter, telemetry subcarrier oscillator, battery pack, and antenna. The transmitter was a crystal controlled transistorized oscillator operating at approximately 54 MHz. The oscillator fed a transistorized power amplifier serving as a frequency doubler to bring the transmission frequency to 108.03 MHz. Beacon power was greater than 50 mW. The battery pack held 12 mercury cells (Mallory RM12-RT2). Besides acting as a beacon, the transmitter could telemeter the transistor temperature, the sphere ejection, and the squib firing activating the pressure valve by using frequency step functions. Both the casing and the sphere, which was to be inflated and ejected from the casing, were to go into orbit.

Launch Vehicle

The Juno 2 launch vehicle was typically launched with four stages, but for Beacon 2 (AM-19B) only three stages were used. The first stage was a modified Jupiter booster with an NSAAS-3D power plant burning kerosene (RP-1) and liquid oxygen. It also held an instrument and guidance compartment which housed the spatial attitude control, the events programmer tracking devices, and cluster drive motors. It produced 150,000 lb (~670,000 N) thrust at sea-level. The engine had a gimbal mechanism operating in two planes to control pitch and yaw. The second stage consisted of eleven scaled down Sergeant motors arranged in an annulus about a center tube. Each motor contained approximately 23 kg (50 lbs)of T17-E2 solid propellant composed of polysulfide fuel and an ammonium perchlorate oxidizer. The third stage comprised a bundle of three scaled down Sergeant motors using polysulfide JPL136 solid propellant. A conical support structure at the end of the third stage held the payload. Total height of the rocket was 23.2 meters (76 ft) with a base diameter of 2.67 meters (8.75 ft).

Alternate Names

  • Beacon2

Facts in Brief

Launch Date: 1959-08-15
Launch Vehicle: Juno 2 (Juno II)
Launch Site: Cape Canaveral, United States
Mass: 4.2 kg

Funding Agency

  • NASA-Office of Space Science Applications (United States)


  • Space Physics

Additional Information

Questions and comments about this spacecraft can be directed to: Dr. David R. Williams



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