|Mission type||Lunar impactor|
|Harvard designation||1962 Alpha 1|
|Mission duration||2 days|
|Manufacturer||Jet Propulsion Laboratory|
|Launch mass||329.8 kilograms (727 lb)|
|Start of mission|
|Launch date||January 26, 1962, 20:30:00UTC|
|Rocket||Atlas LV-3B Agena-B|
|Launch site||Cape Canaveral LC-12|
|Lunar flyby (failed impact)|
|Closest approach||28 January 1962|
|Distance||36,800 kilometers (22,900 mi)|
Ranger 3 was a space exploration mission conducted by NASA to study the Moon. The Ranger 3 robotic spacecraft was launched January 26, 1962 as part of the Ranger program. Due to a series of malfunctions, the spacecraft missed the Moon by 22,000 mi (35,000 km) and entered a heliocentric orbit.
The Ranger 3 space probe was designed to transmit pictures of the lunar surface 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.
Ranger 3 was the first of the Block II Ranger designs. The basic vehicle was 3.1 m high and consisted of a lunar capsule covered with a balsa wood impact-limiter, 650 mm in diameter, a mono-propellant mid-course motor, a retrorocket with a thrust of 5080 pounds force (22.6 kN), 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 an 11.5 kg 1 kW·h 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 (code-named "Tonto") was encased in the lunar capsule along with an amplifier, a 50 mW 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 130 to 160 km/h (80 to 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 mission was designed to boost 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. A malfunction in the booster guidance system resulted in excessive spacecraft speed. Reversed command signals caused the spacecraft to pitch in the wrong direction and the TM antenna to lose earth acquisition, and mid-course correction was not possible. Finally, a spurious signal during the terminal maneuver prevented transmission of useful TV pictures. Ranger 3 missed the Moon by approximately 36,800 km on 28 January and is now in a heliocentric orbit. Some useful engineering data were obtained from the flight.
This was the first U.S. attempt to achieve impact on the lunar surface. The Block II Ranger spacecraft carried a TV camera that used an optical telescope that would allow imaging down to about 24 kilometers above the lunar surface during the descent. The main bus also carried a 42.6-kilogram instrument capsule that would separate from the bus at 21.4 kilometers altitude and then independently impact on the Moon. Protected by a balsa-wood outer casing, the capsule was designed to bounce several times on the lunar surface before coming to rest. The primary onboard instrument was a seismometer.
Around 140 seconds after liftoff, the guidance officer reported that he had lost his link on the Atlas. The antenna on the booster used to receive guidance commands had ceased working and the autopilot system reverted to its built-in backup program, but unfortunately this lacked the same precision as the ground guidance and the Atlas's staging and engine cutoff did not occur on schedule.The engines also over-accelerated and imparted excessive velocity into the Agena and probe, so that it entered a higher-than-planned parking orbit. Worse, equipment at a Florida tracking station malfunctioned and picked up Ranger 3's orbital parameters five minutes late. Meanwhile, the Agena restarted and sent the probe out of Earth orbit, but another error in its guidance program resulted in a further erroneous trajectory. This ensured that the spacecraft reached the Moon 14 hours early and missed it by 36,793 kilometers (22,862 miles) on 28 January.
Although impact with the Moon was no longer possible, Ranger 3 could still be used for deep-space studies. Commands were issued to unfurl the camera boom and on the 28th, a fixed-up computer program was uploaded. But midway through this maneuver, the probe's signal strength began to weaken and the computer system completely failed. The TV camera transmitted images, but as the antenna was now pointed away from Earth, they were extremely weak and noisy. It was possible to see the reference crosses on the camera lens, illuminated by reflected sunlight from the probe's chassis, but the Moon was not visible. With the computer dead, Ranger 3 became completely unresponsive to any ground commands and the earth and sun sensors were rendered useless. The gyroscopes continued to maneuver the probe and ground controllers momentarily reacquired a lock on the antenna, but without stable attitude control, they could not hold it steady. As they were unaware of the computer failure, they continued sending commands to Ranger 3 in vain. Sporadic tracking of the probe continued until January 31 when the attitude control thrusters exhausted their propellant supply, at which point the mission was officially terminated.
- "National Space Science Data Center - Ranger 3". National Air and Space Administration. Retrieved 19 June 2012.