Ranger 4 was a spacecraft of the

Ranger program The Ranger program was a series of uncrewed space missions by the United States in the 1960s whose objective was to obtain the first close-up images of the surface of the Moon. The Ranger spacecraft were designed to take images of the lunar su ...

, launched in 1962. It was designed to transmit pictures of the lunar surface to

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

stations during a period of 10 minutes of flight prior to crashing upon the

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

, to rough-land a

seismometer A seismometer is an instrument that responds to ground displacement and shaking such as caused by quakes, volcanic eruptions, and explosions. They are usually combined with a timing device and a recording device to form a seismograph. The out ...

capsule on the Moon, to collect gamma-ray data in flight, to study radar reflectivity of the lunar surface, and to continue testing of the Ranger program for development of lunar and interplanetary spacecraft. An onboard computer failure caused failure of the deployment of the

solar panel A solar panel is a device that converts sunlight into electricity by using photovoltaic (PV) cells. PV cells are made of materials that produce excited electrons when exposed to light. These electrons flow through a circuit and produce direct ...

s and navigation systems; as a result the spacecraft crashed on the far side of the Moon without returning any scientific data. It was the first spacecraft of the

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to reach another

celestial body An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists within the observable universe. In astronomy, the terms ''object'' and ''body'' are of ...

and the first of any nation to reach the surface of the far side of the Moon.

Spacecraft design

Ranger 4 was a Block II Ranger spacecraft virtually identical to Ranger 3. The basic vehicle was , high and consisted of a lunar capsule covered with a balsawood impact-limiter, in diameter, a mono-propellant mid-course motor, a thrust retrorocket, and a gold- and chrome-plated hexagonal base in diameter. A large high-gain dish antenna was attached to the base. Two wing-like solar panels ( across) were attached to the base and deployed early in the flight. Power was generated by 8,680 solar cells contained in the solar panels which charged an 1 kWh capacity AgZn launching and backup battery. Spacecraft control was provided by a solid-state computer and sequencer and an Earth-controlled command system. Attitude control was provided by Sun and

sensors,

gyroscope A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining Orientation (geometry), orientation and angular velocity. It is a spinning wheel or disc in ...

s, and pitch and roll jets. The telemetry system aboard the spacecraft, consisting of two 960

MHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose formal expression in terms of SI base u ...

transmitters, one at 3 W power output and the other at 50 mW power output, the high-gain antenna, and an omnidirectional antenna. White paint, gold and chrome plating, and a silvered plastic sheet encasing the retrorocket furnished thermal control. Because heat sterilization was suspected to have caused the malfunction of Ranger 3's computer, this procedure was dropped on Ranger 4. The seismometer capsule was also painted with a sawtooth pattern for better thermal protection. The experimental apparatus included: (1) a vidicon television camera, which employed a scan mechanism that yielded one complete frame in ten seconds; 2) a gamma-ray spectrometer mounted on a boom; (3) a radar altimeter; and (4) a seismometer to be rough-landed on the lunar surface. The seismometer was encased in the lunar capsule along with an amplifier, a 50-milliwatt transmitter, voltage control, a turnstile antenna, and six silver-cadmium batteries capable of operating the lunar capsule transmitter for 30 days, all designed to land on the Moon at . The radar altimeter would be used for reflectivity studies, but was also designed to initiate capsule separation and ignite the retro-rocket.

Mission

Atlas 133D and Agena 6004 arrived at Cape Canaveral in March and began preflight checkouts. Unlike with previous Ranger launches, no serious difficulties were encountered in readying the launch vehicle for flight and the probe also passed all systems tests with ease. On April 20, Ranger 4 was stacked atop the booster and liftoff took place at 3:50 pm EST on April 23. Launch proceeded perfectly this time and there were no anomalies with either the Atlas or the Agena, which performed its second burn to send Ranger 4 on a translunar trajectory. After separation from the Agena, it was apparent that something was seriously amiss when tracking stations picked up Ranger 4's radio transmitter, but there was no telemetry data being returned or any response when commands were sent to the computer. Without telemetry, it could not be confirmed that the probe's solar panels had unfolded, but the fluctuating radio transponder indicated that Ranger 4 was tumbling and that the solar panels and high-gain antenna were not deployed either. The Atlas and Agena had both performed perfectly, in fact so well that Ranger 4 would not even need a midcourse correction burn to impact the Moon. However, this was all futile if the spacecraft was inoperative. Ground controllers sent commands to the probe to unfurl the solar panels and high-gain antenna and manually use the attitude control system to stop the rolling motion it was in, but the probe was unresponsive. The Spacecraft Data Analysis Team at JPL concluded that the main timer in Ranger 4's computer had stopped, which disabled the telemetry system, preprogrammed events such as

deployment, and also made the probe completely unresponsive to manual commands. Even though lunar impact would occur as planned, the mission was for all intents and purposes a failure. Making it a more bitter pill to swallow was the nearly-flawless launch vehicle performance. The booster problems that affected Rangers 1-3 had been resolved, only for the probe itself to completely fail, as unlike the previous missions, Ranger 4 did not return any useful data. Finding the cause of the timer malfunction could also be difficult since it had occurred during the coasting phase prior to trans-lunar injection when Ranger 4 was passing between tracking stations in the

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and

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. Without solar power, Ranger 4's batteries ran down on the morning of April 26 and the radio transponder ceased operating. The tiny transmitter in the seismometer capsule continued sending out a 50-milliwatt signal. According to the NASA, Ranger 4 impacted the far side of the

(229.3 degrees E, 15.5 degrees S) at at 12:49:53 UT on April 26, 1962, after 64 hours of flight. However, the coordinates were ″guesstimated" and the crater of the impact could not be identified by high-resolution images of the

Lunar Reconnaissance Orbiter The Lunar Reconnaissance Orbiter (LRO) is a NASA robotic spacecraft currently orbiting the Moon in an eccentric Polar orbit, polar mapping orbit. Data collected by LRO have been described as essential for planning NASA's future human and robotic ...

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

officials tried to put a positive spin on the mission, noting that it was the first time an American spacecraft had reached the surface of the Moon and that the probe was "far more sophisticated" than the

Soviet The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...

Luna 2 ''Luna 2'' (), originally named the Second Soviet Cosmic Rocket and nicknamed Lunik 2 in contemporaneous media, was the sixth of the Soviet Union's Luna programme spacecraft launched to the Moon, E-1 No.7. It was the first spacecraft Moon landi ...

space probe in 1959, which had been little more than a pressurized sphere designed to deposit pennants on the surface at impact. The excellent performance of the Atlas-Agena booster had also raised morale. This spacecraft, similar in design to Ranger 3, was the first American spacecraft to reach another celestial body. It was also the first spacecraft to impact the far side of the Moon. Although the spacecraft did not achieve its primary objective, the Atlas-Agena-Ranger combination performed without fault for the first time.

References

External links

Lunar impact: A history of Project Ranger (PDF) 1977Reuters.com
Planned lunar missions
Reuters.com
Chronology – Five key dates in the race to the Moon {{Use American English, date=January 2014 4 Spacecraft launched in 1962 Spacecraft that impacted the Moon 1962 on the Moon

Spacecraft design

Mission

See also

References

External links