Source: DESTINATION MOON: A History of the Lunar Orbiter Program, NASA TM-3487
 Even before Lunar Orbiter V flew, the Office of Space Science and Applications was entertaining the prospect of flying a sixth Orbiter mission. Boeing had nearly enough parts to assemble another spacecraft at an initial cost of about $13 million. A gamma-ray experiment also existed which scientists desired to fly on a sixth Orbiter. Its inclusion would raise the cost of the mission by about $3 million. However, the necessity to relocate personnel on the Lunar Orbiter team to other jobs presented a major problem blocking another mission.1
Lunar Orbiter Program officials estimated that if the mission of Lunar Orbiter V failed, the program would have to fly a sixth Orbiter. However, refurbishment of a sixth spacecraft required such parts as two new solar panels. The Lunar Orbiter Program Office examined the needs and the lead times required for a sixth mission during May and June 1967. By the beginning of July program management knew that OSSA soon had to make a commitment to another mission if it wanted  to avoid major shifts of personnel at Langley and Boeing following the photographic phase of Mission V. Known, too, was the simple fact that the longer NASA officials waited to approve the go-ahead for a new mission, the greater the costs and the more severely the management arrangements would impact on other NASA programs2
On July 5 Scherer issued a statement summarizing the objectives of the fifth mission and the rationale behind a sixth Orbiter flight. He pointed out that the total cost of each of the first five missions amounted to $40 million apiece. The sixth mission would cost less than one third of this. Even if the fifth mission successfully achieved all planned objectives, a sixth mission could accomplish very valuable and different goals. Briefly it could 1) perform a total survey of the far side of the Moon at 60 to 80 meters resolution, 2) take a concentrated look at the best Apollo Program sites as determined through analysis of photographic data from the fifth mission, and 3) closely survey additional areas of high scientific interest. If Mission E failed,3 a Mission F would be necessary according to Scherer.4
 The Lunar Orbiter Project Office at Langley sent a memorandum to Scherer’s Office on July 12 detailing the options open to OSSA for a sixth mission. The first option required a go-ahead decision by mid-July. The details were these: 1) that refurbishment and processing the spacecraft required four months and was the pacing item; 2) cost of launching Lunar Orbiter F late in November would amount to $12.75 million; 3) a launch by that time would retain the launch readiness capability of the previous launches; 4) this option provided the greatest retention of overall experience in the Lunar Orbiter team.5 The second option was the same as the first except that it allowed for cancellation of preparations for a sixth flight early in September. At that time, data from Lunar Orbiter V would be available. If the mission was successful and the need for another mission was insufficiently justified, then the Lunar Orbiter Program could cancel the additional mission at a cost of about $4 million.6
The third option was the least manageable. It required that NASA postpone the July go-ahead but authorize funds to hold the team and the hardware in readiness until evaluation of the Lunar Orbiter V mission results. This option would  extend the earliest possible launch date from late November 1967 to late January 1968 and raise the cost of a sixth mission to $16.5 million. It would also impact on the launch of OGO-E (Orbiting Geophysical Observatory satellite E) and would delay the Air Force takeover of Launch Complex 13 at Cape Kennedy. In view of these circumstances the Langley Lunar Orbiter Project Office recommended that only the first option be considered and that NASA Headquarters approve go-ahead before July 22, 1967.7
On July 14, 1967, Homer E. Newell sent NASA Deputy Administrator Robert C. Seamans, Jr., a summary of the alternatives for a sixth mission. He reiterated the three options which the Langley memorandum had specified and underlined Langley’s position in support of a July go-ahead for a late November launch. He stressed to Seamans that a delayed decision would affect management problems, costs, and schedules in the Office of Space Science and Applications.8
Seamans weighed the need for a sixth mission and decided that NASA funds would better support other activities. On July 24, 1967, Scherer officially informed Langley that NASA  Headquarters had decided against a sixth Lunar Orbiter mission. However, he stated in his telegram to Floyd L. Thompson that a remote possibility for a reversal existed if the fifth mission failed. He requested Langley to proceed to phase out the program but to retain mission-peculiar test, launch, and flight operations equipment until it had completed the photo readout of Mission V. This retention did not apply to personnel, and Langley was to commence reassignment.9
Because Lunar Orbiter V succeeded beyond expectations in carrying out its mission objectives, its Achievements proved that the cancellation of a sixth mission had been a prudent move. Moreover, the Apollo Program had virtually no need for the kind of data a sixth mission might have obtained; it would not have been decisive in mission planning. Indeed, at the Apollo Site Selection Board meeting on March 30s 1967, Apollo Program officials agreed that, “although further data from Lunar Orbiters D and E will be requested., the photography already received from Orbiters I. II, and III meets the minimal requirements of the Apollo Program for site survey for the first lunar landing.”10They arrived at this conclusion  by detailed screenings of Lunar orbiter data using the following steps:
1. Construct Lunar Module landing ellipses and radar approach templets from photo support data.
2. Outline reject areas on medium resolution photographs.
3. Scan remaining area where high-resolution coverage is also available.
4. Select better ellipse locations with favorable radar approaches. Identify obstacles.
5. Select best ellipse based on landing and radar obstacles, count craters, and compute ‘N’ number from medium-resolution photos. For most favorable sites continue evaluation with high-resolution photography.
6. Evaluate ellipses on high-resolution photography and compute ‘N’ number11
Chapter 11 notes
1. Lunar Orbiter Program Office, NASA, Comments on Seamans Draft Memo (Undated), June 26, 1967. See also memorandum from SL/Manager, Lunar Orbiter Program, to SL/Acting Director, Lunar and Planetary Programs, Subject: Lunar Orbiter 6, April 6, 1967.
3. NASA missions and spacecraft are denoted by capital letters (Mission E) during the prelaunch phase. After a successful launch, the mission and spacecraft are designated by numerals (Mission V).
4. Lunar Orbiter Program Office, NASA, Action Item Summary, Action Item 31, Lunar Orbiter: Review and report the neces sity for an additional Lunar Orbiter Mission, memo date June 16, 1967.
5. Memorandum from Lunar Orbiter Project Office to NASA, Code SL, Attention: Capt. L. R. Scherer, Subject: Lunar Orbiter Project Recommendation for Implementing an Additional Mission July 12, 1967.
6. Ibid., p. 2.
8. Memorandum from S/Associate Administrator for Space Science and Applications to AD/Deputy Administrator, Subject: Considerations related to decision on a sixth Lunar Orbiter, July 14, 1967.
9. Telegram., priority, unclassified, from Lee R. Scherer, Manager Lunar Orbiter Program, to Langley Research Center, Attention: Dr. F. L. Thompson., Mr. E. C. Draley, Mr. C. H. Nelson, July 24, 1967.
10. Memorandum from MA/Apollo Program Director, Subject: Minutes of the Apollo Site Selection Board Meeting, March 30, 1967, p. 5.
11. Ibid., Attachment– Steps in Lunar Orbiter Screening.
12. Memorandum from MA/Apollo Program Director, Subject: Minutes of Apollo Site Selection Board Meeting, March 16, 1966, document dated May 5, 1966.
13. Minutes of the Joint Meeting of the Apollo Site Selection Board and the Surveyor/Orbiter Utilization Committee., June 1, 1966, document dated July 1, 1966, pp. 1-2.
14. Ibid., p. 3.
15. Minutes of Apollo Site Selection Board., December 15, 1966, document dated March 7, 1967. Site II P 6 is located in the southwestern areas of Mare Tranquillitatis (approximately 23° east longitudes 2° north latitude). This site eventually became the Apollo 11 landing site, Tranquility Base. Site II P 2 is located east or the crater Maskelyne and northeast of the crater Censorinus (approximately 33° east longitudes 3° north latitude).
16. Ibid., Attachment G,, Preliminary Landing Site Analysis of Orbiter I, p. 2.