Explorer 2 was an American unmanned space mission within the Explorer program. Intended to be a repetition of the previous Explorer 1 mission, which placed a satellite into medium Earth orbit, the spacecraft was unable to reach orbit due to a failure in the launch vehicle during launch.
Explorer 2 was launched from Cape Canaveral Missile Test Center of the Atlantic Missile Range (AMR), LC-26A in Florida on 5 March 1958 at 18:27:57 GMT by a Juno I launch vehicle. The Juno I had its origins in the United States Army's Project Orbiter in 1954. The project was canceled in 1955 when the decision was made to proceed with Project Vanguard.
Background
Following the launch of the Soviet Sputnik 1 on 4 October 1957, the Army Ballistic Missile Agency (ABMA) was directed to proceed with the launching of a satellite using the Juno I four-stage variant of the three-stage Jupiter-C, which had already been flight-tested in nose-cone re-entry tests for the Jupiter IRBM (intermediate-range ballistic missile). Working closely together, ABMA and Jet Propulsion Laboratory (JPL) completed the job of modifying the Jupiter-C and building Explorer 1 in 84 days.
Spacecraft
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 long, diameter cylinder and nosecone that comprised the fourth stage of the Jupiter-C launch vehicle. With a mass of , it was about heavier than Explorer 1. The spacecraft body was made of stainless AISI-410 steel, 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.
Micrometeorite Detector
Direct measurements of micrometeorites were made on Explorer 1 using two separate detectors: a wire grid detector and a crystal transducer. The parameters determined were the influx rates of each size interval, the impinging velocity, the composition, and the density of the micrometeorite.
The wire grid detector consisted of 12 cards (connected in parallel) mounted in a fiberglass supporting ring which in turn was mounted on the satellite's cylindrical surface. Each card was wound with enameled 17-micron-diameter nickel alloy wire. Two layers of wire were wound on each card to ensure that a total area of completely covered. A micrometeorite of about 10 microns would fracture the wire upon impact, destroy the electrical connection, and thus record the event.
Resistance Thermometers
The Explorer 2 satellite was equipped with four resistance thermometers that made direct temperature measurements, three external and one internal. The primary purpose of the experiment was to study the efficacy of passive thermal control (in this case, insulation and exterior coatings) on the exterior and interior of a satellite, and to document the temperature of the instrumentation to study its effect on instrument operation.
Thermometers
The thermometer designated external temperature gauge no. 1 was mounted on the outer hull at the bottom of the upper (instrumentation) section of the satellite. This measured the cylinder skin temperature over a range of -50 °C to +110 °C, with an accuracy of 4 °C over the range -10 °C to +80 °C. External temperature gauge no. 2 was mounted along the bottom of the nose cone to measure the nose cone skin temperature. It could cover a range of -50 °C to +220 °C. The accuracy was 16 °C at a temperature of 50 °C and 18 °C at 0 °C. External temperature gauge no. 3 was mounted at the top of the nose cone and measured the stagnation-point temperature. It covered from -50 °C to +450 °C with an accuracy of approximately 20 °C.
Launch vehicle
The launch vehicle was a Juno I, 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 launch vehicle. 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. 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 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.
See also
- Explorer 1
- Explorer program