Lunar Orbiter 4

Infobox Spacecraft
Name= Lunar Orbiter 4


Organization=NASA
Major_Contractors= Langley Research Center
Mission_Type=Orbiter
Satellite_Of= Moon
Launch= May 4, 1967 at 22:25:00 UTC
Launch_Vehicle= Atlas-Agena D
Decay= Impacted lunar surface no later than October 31, 1967, near 22--30 degrees W.
Mission_Duration= 180 days
Mass= 385.6 kg
NSSDC_ID= 1967-041A
Orbital_elements=yes
Semimajor_Axis= 6,152.5 km
Eccentricity= .28
Inclination= 85.5°
Orbital_Period= 721 minutes
Apoapsis= 6,111 km
Periapsis= 2,706 km
Orbits= 360

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 May 11, 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 maneuvers on each orbit to prevent light leakage into the camera which would ruin the film. On May 13 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 May 20 resulted in a decision to terminate the photographic portion of the mission on May 26. 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.

External links

* [http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770016195_1977016195.pdf DESTINATION MOON: A history of the Lunar Orbiter Program (PDF) 1976]