In the first half of 1969 the Office of Manned Space Flight (OMSF) had anticipated the requirements of the extended ("J") missions, Apollo 16-20, by ordering studies on modification of the lunar module and development of a powered lunar-surface vehicle [see Chapter 10]. After studies by the lunar module contractor, Grumman Aircraft Engineering Company, were reviewed by OMSF's Management Council, MSC authorized Grumman on June 9 to proceed with modifications on LM-10 and subsequent spacecraft. Changes to the landing module would allow it to carry additional payload (the lunar roving vehicle) to the lunar surface, return more lunar samples to earth, and provide consumables (oxygen, water, and electrical power) to support the crew on the moon for periods up to 78 hours. The first "extended" lunar module was to be delivered in time for launch in April 1971.41 Major changes included enlargement of the fuel and oxidizer tanks on both ascent and descent stages, extension of the descent engine nozzle to improve its efficiency, addition of batteries and solar cells to recharge them, and rearrangement of stowage space.42 At a critical design review in mid-September, MSC cut out some of the changes to minimize cost increases, discarding the solar cells and reducing the maximum duration of stays on the moon to 54 hours. The extended LM would weigh 36,000 pounds (16,330 kilograms), compared to 32,000 (14,515 kilograms) for earlier versions.43
A large part of this extra payload was the lunar roving vehicle, which would extend the astronauts' range on the moon. In May 1969 a surface-traversing vehicle was chosen rather than a flying unit as the most suitable means of carrying the astronauts and their tools to sites of scientific interest, and Marshall Space Flight Center was assigned responsibility for its development.44 That fall, the Boeing Company won the contract to develop the lunar roving vehicle (LRV or "rover"). The rover was to be a battery- powered vehicle weighing 400 pounds (181 kilograms), capable of carrying a 970-pound (440-kilogram) load as far as 120 kilometers (75 miles).45 Boeing's facility in Huntsville, Alabama, was to build the chassis and assemble the complete vehicle from components manufactured by Boeing in its Seattle plant and by AC-Delco Electronics. Development time was short: the schedule called for delivery of the first of four vehicles by April 1, 1971, for flight on Apollo 17, then scheduled for the following September.46
The weight increases necessary to extend the lunar missions forced a number of changes in the launch vehicle as well. Rocket engineers, whose experience had made them familiar with the tendency of payloads to grow, usually built their engines to a somewhat higher capacity than the design requirement, so that they could increase the thrust by making relatively minor changes. So it was with the Saturn V.47 In August 1969 MSC flight planners and Marshall engineers began discussing means of enabling the Saturn V to launch 106,500 pounds (48,310 kg).48 The F-1 engines on its first stage could be readjusted to a higher thrust level after acceptance firing. Timers could be reset to reduce the amount of unburned propellant left in the tanks at engine cutoff. These changes, plus modifications to the S-II second stage, would raise the payload by more than 700 kilograms (1,540 pounds). An equally significant change was reduction of the fuel reserves provided to make up for unpredictable variations in launch conditions and engine performance. Seven manned launches had given engineers enough performance data to indicate that these reserves could be reduced without affecting crew safety, adding another 700 kilograms of payload capacity.49
Changes in some launch constraints could increase the launch capability of the Saturn V as well. For example, lowering the earth orbit into which the spacecraft and S-IVB were initially injected (the parking orbit) by 10 nautical miles (11.5 statute miles, 18.5 kilometers) could allow another 300 kilograms (660 pounds) to be added to the spacecraft, at the cost of some slight additional heating of the spacecraft and a loss of some radar-tracking data. Finally, some 200 kilograms (440 pounds) of payload could be added by optimizing the azimuth on which the Saturn V was launched.50 After some months of analysis and discussion, several of these changes were made in preparation for Apollo 15, enabling the Saturn V to launch 107,000 pounds (48,535 kilograms).51
41. MSC to Grumman Aircraft Engineering Co. (GAEC), contract change authorization (CCA) no. 2002, Amendment no. 1, "LM Modifications Study for Extended Lunar Staytime," Mar. 13, 1969: Samuel C. Phillips, TWX to MSC, May 9, 1969; MSC to GAEC, CCA no. 2333, "LM-10 and Subsequent Modification Program," June 9, 1969.
42. GAEC LMA790-2, "Lunar Module Modification Program [LMMP], Vehicle Familiarization Manual," Aug. 28, 1969.
43. Joseph N. Kotanchik to Asst. Dir. for Chemical and Mechanical Systems, MSC, "Report on Attendance at LMMP CDR at GAC, September 12, 1969," Sept. 15, 1969; GAEC, "LMMP Critical Design Review Board Meeting Minutes, September 12, 1969," Sept. 17, 1969.
44. Lee R. Scherer to multiple addressees, TWX, May 27, 1969.
45. Saverio F. Morea, MSFC, to James A. McDivitt, "LRV Weight Growth," Nov. 6, 1969; McDivitt to Roy E. Godfrey, MSFC, Dec. 12, 1969.
46. McDivitt to multiple addressees, "Lunar Roving Vehicle," Nov. 1, 1969; George E. Mueller to Administrator, "Manned Space Flight Weekly Report - November 3, 1969," Nov. 3, 1969.
47. Roger E. Bilstein, Stages to Saturn: A Technological History of the Apollo/Saturn Launch Vehicles, NASA SP-4206 (Washington, 1980), pp. 376-77.
48. Donald C. Wade to multiple addressees, "August 12 Saturn V payload improvement meeting," Aug. 15, 1969; John D. Hodge to Phillips, "Increased Saturn V Payload Capacity," Aug. 29, 1969.
49. J. O. Cappellari, Jr., ed., "Where on the Moon? An Apollo Systems Engineering Problem," The Bell System Technical Journal 51(5) (May-June 1972): 1028-34; Rocco A. Petrone to multiple addressees, "Saturn V Performance Capability for Apollo 16-20," Nov. 24, 1969.
50. Cappellari, "Where on the Moon?", p. 1030.
51. Richard G. Smith, MSFC, to Petrone, "Use of 510 Launch Vehicle for 107,000 Pounds Payload Mission," July 22, 1970.