DESTINATION MOON: A History of the Lunar Orbiter Program
The End of the Operational Phase
[297] On September 2 Homer E. Newello Associate Administrator for Space Science and Applications, certified that the fifth mission was an unqualified success according to prelaunch objectives. Deputy Administrator Robert C. Seamans, Jr., concurred on September 6. Both NASA officials also assessed the whole program as successful; five missions had been flown out of five planned.48 Indeed the final Orbiter had capped an impressive effort by the Office of Space Science and Applications to bring man closer to stepping down upon the lunar soil and understanding where it was that he would be landing in the near future.
The status of the fifth Lunar Orbiter remained good following termination of readout early on the morning of [298] August 27. Lunar Orbiter II and III also continued to orbit the Moon and to provide extensive data on the lunar environment and its gravitational field. These three spacecraft served the Manned Space Flight Network as tracking targets for training personnel who would track Apollo.49
Lunar Orbiter II had sufficient attitude control gas to survive until early November. Ground control operators planned to impact it into the Apollo zone on the Moon's surface even though analysis of tracking data indicated that it could probably remain in orbit one or two years. longer. Once the spacecraft lost its attitude control gas, however, it would become a derelict in orbit, beyond the control of ground operations. Program officials deemed it necessary, therefore, to crash the spacecraft while they could, to avoid any potential communications interference in future manned missions. They also planned to lower Lunar Orbiter III's apolune to make its orbit as circular as possible for further training for Apollo tracking. However, expiration of its gas would soon mean that it, too, would have to be crashed.
The fifth Orbiter had just begun its extended mission late in August. Its orbit would be changed on October 10 so [299] that it might better survive the umbral eclipse of October 18. (Program engineer Leon J. Kosofsky and mission operators changed the orbit so that the spacecraft would pass through the eclipse and solar occultation by the Moon at the same time.) Apollo network trackers would continue to track the spacecraft as long as possible to increase their experience in preparation for manned lunar missions.50
On September 11 the Lunar Orbiter Program Office issued a statement of the plans for terminating the life of the three remaining Orbiters. It stated briefly:
The policy is to track the Orbiter spacecraft until the approach of loss of attitude control as indicated by the nitrogen pressure. While the spacecraft is still controllable, the engine will be fired so as to cause impact with the lunar surface. The impact will be made within the Apollo zone if feasible. At this time, it appears that Orbiter II will be impacted in early November, Orbiter III in mid October, and Orbiter V in mid summer 1968. Contact with Orbiter IV has been lost.51
Following the final acquisition of all Lunar Orbiter V photographic data, Lee R. Scherer issued a summary statement about the program's achievements. Among these he stressed that Lunar Orbiter II photography had led to the identification of the Ranger VIII impact point on the Moon. Orbiter III [300] photography had Identified Surveyor I on the Moon's surface. The locations of the other Surveyors were also determined by using Orbiter photography. The fifth Orbiter had photographed major lunar features of scientific interest at a resolution 100 times better than Earth-based telescopes could achieve under ideal observation conditions. All Orbiters combined had photographed the entire lunar surface at a better resolution by at least an order of magnitude than Earth-based telescopes could attain and had surveyed the heavily cratered far side of the Moon. The spacecraft had provided valuable data contributing to the determination of the Moon's gravitational field. Finally, one of the program's most significant accomplishments had been to advance the Apollo Program in a way other than photographic site certification.
Five Orbiters had enabled the Manned Space Flight Network to train personnel in tracking and to check out equipment and computer programs for the manned lunar missions beginning with Apollo 8 in December 1968 and including Apollo 10 through 17, of which all but Apollo 10 and 13 landed on the Moon. (Apollo 10 tested the complete spacecraft in lunar orbit and Apollo 13 aborted its landing mission because an onboard oxygen tank exploded in cislunar space.) The Office of Manned Space Flight could not have obtained the needed tracking experience at a timely date [301] if NASA had not flown the five Lunar Orbiter spacecraft.52
The chronology of the Lunar Orbiters concluded by the end of January 1968. On October 9, 1967, flight controllers commanded Lunar Orbiter III to impact on the Moon. On October 11 they commanded Lunar Orbiter II impact. They had lost communications with Lunar Orbiter IV on July 17, 1967, and assumed that its orbit had decayed sufficiently to permit it to crash onto the Moon late in October, but had no evidence confirming this. Lunar Orbiter V continued to fly its extended mission until, unexpectedly, it experienced an anomaly which threatened its orbit safety. A sudden loss of pressure in the nitrogen tank forced flight controllers to impact the spacecraft prematurely on the Moon to avoid losing it in orbit. They conducted this final maneuver on January 31, 1968, crashing Lunar Orbiter V near the equator on the Moon's western limb. The impact brought the operational phase of the Lunar Orbiter Program to a close.53