First, it should be noted that the objectives did not create the mission, but exactly the opposite: the mission created the objectives. If a mission had new or modified equipment, that created an objective to test it. Whatever scientific experiment were chosen would then create objectives to perform those experiments. There was not much structure to the process of picking objectives; in some cases, objectives were added during the mission. For example, Apollo 7 added the objective "Test pitch about Y axis" during the mission.
The type of mission (A through J) was a starting point for developing the objectives. Apollo 18-20 would have been type J missions like Apollo 15-17 had been, all of which had the same primary objectives:
- Perform selenological inspection, survey, and sampling of materials and surface features in a preselected area of the ___ region.
- Emplace and activate surface experiments.
- Conduct inflight experiments and photographic tasks from lunar orbit.
Being the first J-type mission, Apollo 15 had one additional objective:
- Evaluate the capability of the Apollo equipment to provide extended lunar surface stay time, increased EVA operations, and surface mobility.
The Apollo Spacecraft: A Chronology is a four-volume record of daily activities in the Apollo Program. Here is the entirety of the entries for Apollo 18 through 20:
1969 Jan 15
The Apollo Program Director expressed concern to the Director of MSC over the lack of guidelines of sufficient scope and depth for the lunar missions that would be flown after the first lunar landing and before the proposed lunar exploration program tentatively scheduled to begin in 1973.
He asked each of the manned space flight Centers to appoint a working group to define guidelines and to outline program objectives and content for the period of lunar exploration immediately following the first lunar landing. Areas requiring study were: scientific exploration, mission planning rationale, flight schedules and program impact, and vehicle
1969 July 29
NASA issued a tentative planning schedule for the Apollo program:
Flight Launch Plans Tentative Landing Area
Apollo l2 November 1969 Oceanus Procellarum lunar lowlands
Apollo 13 March 1970 Fra Mauro highlands
Apollo 14 July 1970 Crater Censorinus highlands
Apollo 15 November 1970 Littrow volcanic area
Apollo 16 April 1971 Crater Tycho (Surveyor VII impact area)
Apollo 17 September 1971 Marius Hills volcanic domes
Apollo 18 February 1972 Schroter's Valley, riverlike channel-ways
Apollo 19 July 1972 Hyginus Rille region-Linear Rille, crater area
Apollo 20 December 1972 Crater Copernicus, large crater impact area
1969 October 10
Major milestones were reached for extending astronauts' staytime on the moon and increasing their mobility for the Apollo 16-20 missions. Modifications in the A7L spacesuit incorporating improved waist mobility were authorized, and letter contract authority for the portable life support system/secondary life support system was approved.
1970 Jan 4
NASA had canceled the Apollo 20 mission and stretched out the remaining seven missions to six-month intervals, Deputy Administrator George M. Low told the press in an interview after dedication of the Lunar Science Institute (next to MSC in Houston). Budget restrictions had brought the decision to suspend Saturn V launch vehicle production after vehicle 515 and to use the Apollo 20 Saturn V to launch the first U.S. space station in 1972.
1970 Jan 7
NASA issued instructions for deletion of the Apollo 20 mission from the program (see January 4). MSC was directed to take immediate action to:
- Stop work on LM-14 and determine its disposition.
- Delete requirements for the Apollo 20 spacesuits and portable and secondary life support systems.
- Determine disposition of CSM 115A pending a final decision as to its possible use in a second workshop mission.
- Reevaluate orbital science experiments and assignments and prepare proposed revisions.
1970 Jan 16
An MSC meeting to realign the Apollo 16-19 lunar orbital science experiments recommended that the Sounding Radar Experiment, S-167, be deleted and the Lunar Electromagnetic Sounder, S-168, should be developed and flown. Scientific-value for the experiments was ranked in the following descending priorities for the various scientific disciplines: geochemistry, particles and fields, imagery and geodesy, surface and subsurface profiles, and atmospheres.
1970 Jan 29
Ground rules for service module design and integration, established during recent changes in the lunar orbital science program (see January 16), were reported. The Apollo LM experiment hardware would be installed and tested at KSC. A single scientific instrument module configuration was being proposed for Apollo 16-19 with modification kits developed, as required, to install Apollo 18 and Apollo 19 experiments. An expanded Apollo LM data system would be available for Apollo 16 (spacecraft 112).
The pages of Chronology corresponding to Feb 17 to Mar 7 are missing from both the scanned PDF and the online website. However, the index contains entries in this page range for "Apollo 18: redesignated Apollo 17" and "Apollo 19: mission deleted". Therefore, Apollo 18 and 19 were eliminated sometime between February 17 and March 7, 1970.
NASA has a webpage dedicated to Apollo 18-20. It says nothing about objectives or experiments. It does claim different landing sites:
J-3 (Apollo 18) Copernicus
J-4 (Apollo 19) Hadley
J-5 (Apollo 20) Tycho
It also speculates that the astronaut rotations would continue the pattern of a backup crew becoming the prime crew three missions later. This would result in the following crews:
- Richard Gordon, Commander
- Vance Brand, Command Module Pilot
- Harrison Schmitt, Lunar Module Pilot. When Apollo 17 became the last mission, geologist Schmitt replaced Joe Engle on Apollo 17. Had the original schedule been kept, it is likely that Engle would have stayed on 17 and Schmitt on 18.
- Fred Haise, Commander
- William Pogue, Command Module Pilot
- Gerald Carr, Lunar Module Pilot
- Charles Conrad, Commander. Conrad had already been to the moon, so perhaps Stuart Roosa would have taken his place as commander.
- Paul Weitz, Command Module Pilot
- Jack Lousma, Lunar Module Pilot