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 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.
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.