Ranger 4 was designed to transmit pictures of the lunar surface to Earth stations during a period of 10 minutes of flight prior to impacting on the Moon, to rough-land a seismometer 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 panels and navigation systems, the spacecraft impacted on the far side of the Moon without returning any scientific data.

Spacecraft and Subsytems
Spacecraft and Subsystems

Ranger 4 was a Block II Ranger spacecraft virtually identical to Ranger 3. The basic vehicle was 3.1 m high and consisted of a lunar capsule covered with a balsawood impact-limiter, 65 cm in diameter, a mono-propellant mid-course motor, a 5080-pound thrust retrorocket, and a gold- and chrome-plated hexagonal base 1.5 m in diameter. A large high-gain dish antenna was attached to the base. Two wing-like solar panels (5.2 m across) were attached to the base and deployed early in the flight. Power was generated by 8680 solar cells contained in the solar panels which charged a 11.5 kg 1000 W-hour 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 Earth sensors, gyroscopes, and pitch and roll jets. The telemetry system aboard the spacecraft consisted of two 960 MHz transmitters, one at 3 W power output and the other at 50 mW power output, the high-gain antenna, and an omni-directional antenna. White paint, gold and chrome plating, and a silvered plastic sheet encasing the retrorocket furnished thermal control.

The experimental apparatus included:
(1) a vidicon television camera, which employed a scan mechanism that yielded one complete frame in 10 s;
(2) a gamma-ray spectrometer mounted on a 1.8 m 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 6 silver-cadmium batteries capable of operating the lunar capsule transmitter for 30 days, all designed to land on the Moon at 130 to 160 km/hr (80 -100 mph). The radar altimeter would be used for reflectivity studies, but was also designed to initiate capsule separation and ignite the retro-rocket.



The telescopic vidicon television camera was designed to transmit closeup pictures of the lunar surface from 4000 to 47 km above the moon. The system contained an allelectrostatic deflection and focus vidicon which combined a target with rapid erase capability. The exposure time of 20 msec on the photoconductor surface was designed to prevent blurring of the optical image and to provide a closing of the optical system during the 13-sec scan and erase operation of the vidicon electronic system. The slowly decaying image and subsequent scanning yielded one complete frame in 10 sec. To achieve the desired resolution, 200 scanning lines were employed per frame. The video bandwidth for this system was approximately 200 cps. The optical system developed was a conventional cassegrain configuration astronomical telescope employing a primary concave parabolic mirror and a centrally located secondary convex hyperbolic mirror for reflecting the lunar image on the photoconductive image surface. The experiment failed due to major spacecraft malfunctions which prevented the cislunar termial maneuver.

Gamma Ray

A gamma-ray spectrometer that consisted of a detector, a 32-channel pulse height analyzer, and a high-voltage power supply was designed to measure the gamma radiation coming from the surface of the moon. The detector contained a beveled 7.62-cm diam cesium iodide crystal surrounded in a phoswich arrangement by a plastic scintillator of .317-cm thickness. This was coupled to a 7.62-cm diam photomultiplier tube. Pulses were passed into the analyzer, which was provided with storage for 2 to the 16th pulses in each channel. Reject circuitry was designed to block the analyzer when charged particles traversed the phoswich. The first 12 hr of data were obtained with the detector close to the main structure of the spacecraft. A telescoping boom then moved the detector to a position 6 ft from the main structure and data were taken for 6 hr. Although a vehicle malfunction caused the probe to miss the moon by approximately 36,579 km, data were received for more than 40 hr. Intermittent signals ended February 2, 1962, at 800,000 km range.

Radar Altimeter

A radar altimeter was included in the experiment package to initiate capsule separation and retrorocket ignition 19 to 25 km above the lunar surface and to measure the radar reflectivity of the lunar surface and study its properties. The instrument was a standard pulse-type radar with peak power output from the magnetron transmitter of between 150 and 400 W. The instrument had a frequency of 9400 mHz and a pulse repetition rate of 500 to 600 pps. The superheterodyne receiver bandwidth was 12 to 16 mHz, and its noise figure was 11 to 12 db. Antenna beamwidth was 4.5 deg. The altimeter was designed to begin measurements on command from earth at 198 to 55 km from the moon (nominally 137 km). The planned lifetime of measurement was 9 sec to 2 min. Because of a spacecraft failure that prevented lunar impact, no experiment data were returned.


A suspended magnetic seismometer was designed to determine the presence or absence of lunar seismicity and of a lunar crust, lava layers, or dust layers. The instrument was intended to collect data on the mechanical properties of lunar materials and to obtain preliminary information on the nature of the lunar core and on the depth and focus of moonquakes. The 3.36-kg instrument comprised a coil, a spring-suspended magnet, and an internal calibration device. The 1.70-kg seismic mass consisted of a permanent magnet suspended from the body of the instrument. It was suspended so as to maintain concentration of the seismic mass within the instrument body and to allow the siesmometer to operate at any inclination of its longitudinal axis from 0 to 90 deg. To damp the rapid movement of the seismic mass upon lunar impact, the instrument was vacuum-filled with a protective fluid. Upon impact, the survival package was intended to float into an upright position. The seismic caging fluid would then escape, and a pressure switch would initiate the experiment. A measurement lifetime of 30 days was planned. Preflight instrument calibration was performed in the laboratory, and inflight calibration was to be continued throughout the flight. Because of a spacecraft failure that prevented lunar impact, the experiment returned no data.

Launch-Orbit Information

Launch Information

Launch Date: 1962-04-23 at 20:50:00 UTC
Launch Vehicle: Atlas-Agena B
Launch Site: Cape Canaveral, United States
Decay Date: 1962-04-26
Mass: 331.1 kg kg Nominal Power: 135.0 W

Mission Profile

The mission was designed to boosted towards the Moon by an Atlas/Agena, undergo one mid-course correction, and impact the lunar surface. At the appropriate altitude the capsule was to separate and the retrorockets ignite to cushion the landing. Due to an apparent failure of a timer in the spacecraft's central computer and sequencer following launch the command signals for the extension of the solar panels and the operation of the sun and earth acquisition system were never given. The instrumentation ceased operation after about 10 hours of flight. The spacecraft was tracked by the battery-powered 50 milliwatt transmitter in the lunar landing capsule. Ranger 4 impacted the far side of the Moon (229.3 degrees E, 15.5 degrees S) at 9600 km/hr at 12:49:53 UT on April 26, 1962 after 64 hours of flight.

Total research, development, launch, and support costs for the Ranger series of spacecraft (Rangers 1 through 9) was approximately $170 million.