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Explorer 2



The objective of Explorer 2 (1958 F02) was to put a second Explorer satellite in orbit to follow up on the studies of radiation and micrometeorites performed by Explorer 1. This Explorer launch failed on March 5, 1958.

Spacecraft and Subsystems

Explorer 2 was identical to Explorer 1 except for the addition of a tape recorder designed to enable playback of data. The satellite was a 2.03 m long, 0.15 m diameter cylinder and nosecone that comprised the fourth stage of the Jupiter-C launch vehicle. With a mass of 14.22 kg, it was about 0.25 kg heavier than Explorer 1. The spacecraft body was made of stainless AISI-410 steel, 0.058 cm thick. The case was heat-oxidized to a gold color and eight alternate stripes of white Rokide A (flame sprayed aluminum oxide) were used for temperature control.

The base of the cylinder held the Sergeant solid-fuel rocket motor. The sub-carrier oscillators and Mallory mercury batteries for the low power transmitter were in the upper part of the nose cone. Below these was the low power (10 mW, 108.00 MHz) transmitter for the carrier and sub-carrier signals, which used the stainless steel satellite skin as a dipole antenna.

Below the nose cone was the detector deck, holding the Geiger-Mueller counter tube for the cosmic ray experiment, the command receiver, for recorder interrogations, high power playback transmitter (60 mW, 108.03 MHz) for interrogation response, cosmic ray experiment electronics, Mallory mercury batteries for the high power transmitter, and a 0.23 kg, 5.7 cm diameter magnetic tape recorder. An acoustic micrometeorite detector was mounted to the inside of the spacecraft cylinder near the cosmic ray device. Near the bottom of the detector deck four circularly polarized turnstile stainless steel wire whip antennas protruded radially from the side of the spacecraft, equally spaced around the axis. A gap for the high powered antenna and a heat radiation shield were between the payload and the rocket motor. The micrometeorite detectors were arranged in a ring around the cylinder near the bottom of the spacecraft. Four temperature gauges were mounted a various locations in the spacecraft.

The launch vehicle was a Juno 1, a variant of the three-stage Jupiter-C with an added fourth propulsive stage, which in this case was the Explorer 2. The first stage was an upgraded Redstone liquid-fueled rocket. The second stage comprised a cluster of eleven Sergeant solid-fuel rocket motors and the third stage held three Sergeants. The booster was equipped to spin the fourth stage in increments, leading to a final rate of 750 rpm about its long axis.

Mission Profile

Explorer 2 launched from the Cape Canaveral Missile Test Center of the Atlantic Missile Range, pad 26A, on 5 March 1958 at 18:27:59 UT. The flight was nominal through third stage ignition. The fourth stage failed to ignite, making attainment of orbital velocity impossible. The spacecraft reentered the atmosphere and fell into the Atlantic Ocean near Trinidad, some 3000 km from the launch site.

The cause of the failure was believed to be due to failure of a light plastic cone, which held the igniter in place at the fourth stage nozzle, under the launch stresses. This allowed the igniter to fall out of position. The igniter support was strengthened for later flights.

Alternate Names

  • Explorer2
  • 1958-F02

Facts in Brief

Launch Date: 1958-03-05
Launch Vehicle: Jupiter C (Juno I)
Launch Site: Cape Canaveral, United States
Mass: 14.22 kg

Funding Agency

  • Department of Defense-Department of the Army (United States)


  • Space Physics

Additional Information

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



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