Lunar Orbiter 4 Mission

Alternate Names: Lunar Orbiter-D, 02772
Launch Date: 1967-05-04
Launch Vehicle: Atlas-Agena D
Launch Site: Cape Canaveral, United States
Mass: 385.6 kg
Nominal Power: 375.0 W
Launch/Orbital information for Lunar Orbiter 4
Experiments on Lunar Orbiter 4
Data collections from Lunar Orbiter 4

Description

Lunar Orbiter 4 was designed to take advantage of the fact that the three previous Lunar Orbiters had completed the required needs for Apollo mapping and site selection. It was given a more general objective, to "perform a broad systematic photographic survey of lunar surface features in order to increase the scientific knowledge of their nature, origin, and processes, and to serve as a basis for selecting sites for more detailed scientific study by subsequent orbital and landing missions. It was also equipped to collect selenodetic, radiation intensity, and micrometeoroid impact data. The spacecraft was placed in a cislunar trajectory and injected into an elliptical near polar high lunar orbit for data acquisition. The orbit was 2706 km x 6111 km with an inclination of 85.5 degrees and a period of 12 hours.


After initial photography on 11 May 1967 problems started occurring with the camera's thermal door, which was not responding well to commands to open and close. Fear that the door could become stuck in the closed position covering the camera lenses led to a decision to leave the door open. This required extra attitude control manuevers on each orbit to prevent light leakage into the camera which would ruin the film. On 13 May it was discovered that light leakage was damaging some of the film, and the door was tested and partially closed. Some fogging of the lens was then suspected due to condensation resulting from the lower temperatures. Changes in the attitude raised the temperature of the camera and generally eliminated the fogging. Continuing problems with the readout drive mechanism starting and stopping beginning on 20 May resulted in a decision to terminate the photographic portion of the mission on 26 May. Despite problems with the readout drive the entire film was read and transmitted. The spacecraft acquired photographic data from May 11 to 26, 1967, and readout occurred through June 1, 1967. The orbit was then lowered to gather orbital data for the upcoming Lunar Orbiter 5 mission.

A total of 419 high resolution and 127 medium resolution frames were acquired covering 99% of the Moon's near side at resolutions from 58 meters to 134 meters. Accurate data were acquired from all other experiments throughout the mission. Radiation data showed increased dosages due to solar particle events producing low energy protons. The spacecraft was used for tracking purposes until it impacted the lunar surface due to the natural decay of the orbit no later than October 31, 1967, between 22--30 degrees W longitude.

Spacecraft and Subsystems

The main bus of the Lunar Orbiter had the general shape of a truncated cone, 1.65 meters tall and 1.5 meters in diameter at the base. The spacecraft was comprised of three decks supported by trusses and an arch. The equipment deck at the base of the craft held the battery, transponder, flight progammer, inertial reference unit (IRU), Canopus star tracker, command decoder, multiplex encoder, traveling wave tube amplifier (TWTA), and the photographic system. Four solar panels were mounted to extend out from this deck with a total span across of 3.72 meters. Also extending out from the base of the spacecraft were a high gain antenna on a 1.32 meter boom and a low gain antenna on a 2.08 meter boom. Above the equipment deck, the middle deck held the velocity control engine, propellant, oxidizer and pressurization tanks, Sun sensors, and micrometeoroid detectors. The third deck consisted of a heat shield to protect the spacecraft from the firing of the velocity control engine. The nozzle of the engine protruded through the center of the shield. Mounted on the perimeter of the top deck were four attitude control thrusters.

Power of 375 W was provided by the four solar arrays containing 10,856 n/p solar cells which would directly run the spacecraft and also charge the 12 amp-hr nickel-cadmium battery. The batteries were used during brief periods of occultation when no solar power was available. Propulsion for major maneuvers was provided by the gimballed velocity control engine, a hypergolic 100-pound-thrust Marquardt rocket motor. Three-axis stabilization and attitude control were provided by four one-lb nitrogen gas jets. Navigational knowledge was provided by five Sun sensors, Canopus star sensor, and the IRU equipped with internal gyros. Communications were via a 10 W transmitter and the directional 1 meter diameter high gain antenna for transmission of photographs and a 0.5 W transmitter and omnidirectional low gain antenna for other communications. Both antennas operated in S-band at 2295 MHz. Thermal control was maintained by a multilayer aluminized mylar and dacron thermal blanket which enshrouded the main bus, special paint, insulation, and small heaters.

Results of the Lunar Orbiter Program

The Lunar Orbiter program consisted of 5 Lunar Orbiters which returned photography of 99% of the surface of the Moon (near and far side) with resolution down to 1 meter. Altogether the Orbiters returned 2180 high resolution and 882 medium resolution frames. The micrometeoroid experiments recorded 22 impacts showing the average micrometeoroid flux near the Moon was about two orders of magnitude greater than in interplanetary space but slightly less than the near Earth environment. The radiation experiments confirmed that the design of Apollo hardware would protect the astronauts from average and greater-than-average short term exposure to solar particle events. The use of Lunar Orbiters for tracking to evaluate the Manned Space Flight Network tracking stations and Apollo Orbit Determination Program was successful, with three Lunar Orbiters (2, 3, and 5) being tracked simultaneously from August to October 1967. The Lunar Orbiters were all eventually commanded to crash on the Moon before their attitude control gas ran out so they would not present navigational or communications hazards to later Apollo flights. The Lunar Orbiter program was managed by NASA Langley Research Center and involved building and launching 5 spacecraft to the Moon at a total cost of $163 million.

Original source: NASA - NSSDC

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