The staff's problem was to appraise the spacecraft components' lifetime in terms of the ability of each system to perform two or three times longer than the operating limits originally built into them. Flight rules so far had specified an almost continuous operation of the automatic stabilization and control system, which caused a heavy drain on the spacecraft's electrical power supply. Also critical were oxygen reserves, reaction control fuel supplies, and increased recovery requirements. The tracking and communications network, built for three-orbit coverage, would require extensive modification if the tracking criteria applied to three orbits should apply to six or seven.
The three-orbit Mercury spacecraft, with all its electrically powered systems in action, consumed about 7,080 watt-hours of battery power from a total of about 13,500 watt-hours available. Thus a seven-orbit mission, obeying previous flight rules, would consume about 11,190 watt-hours, leaving a reserve supply of only 6.7 percent. Mercury Project Office engineers insisted there should be at least a 10 percent postlanding reserve as a safety factor and suggested at least two conservation methods to attain and surpass this amount. One was drawn from an earlier recommendation presented by McDonnell designers and planners; they had outlined possibilities for an 18-orbit mission, proposing that some of the systems be turned off during a substantial portion of the flight. In addition to this, the MSC engineers recommended switching telemetry transmitter and radar beacon operations to ground command. These measures, they felt, would raise the reserve power levels to about 15 percent.
After studying the spacecraft's environmental control system, the project engineers at MSC concluded that about 4.4 pounds of oxygen would be consumed during a seven-orbit flight, taking pilot usage and cabin leakage rates into consideration. By prevailing mission rules, this would leave an insufficient supply to meet possible contingencies of abnormal recovery. A supply of 8.6 pounds would meet the requirement, but the system carried only two 4-pound capacity bottles. So, either the rules had to be relaxed or the system had to be modified. The MSC study group recommended the modification possibility, adding that a strenuous program to reduce cabin leakage rates to 600 cubic centimeters per minute should be started. Formerly up to 1,000 cubic centimeters had been within design specifications. To cover the increase in carbon dioxide production from the longer flight, the project office planners pointed out that the canister carried in the three-orbit spacecraft could be filled with lithium hydroxide to its 5.4 pound capacity. This amount represented an increase from the 4.6 pounds that had been carried on the three-pass flights and should be sufficient extension of the C02 removal capability.
At the same time that these efforts were being made to provide the spacecraft systems with all the power they needed and the astronaut with enough breathable oxygen, some NASA and McDonnell engineers were wrestling with more advanced problems of tripling, quadrupling, and even raising by factors of six and eight the capabilities of the Mercury spacecraft to orbit Earth. But at this stage, planning for the day-long, 18-orbit mission depended heavily on some positive proof  from MA-8 that man and machines could tolerate, over a longer period and with larger margins for pilot safety and mission success, the vacuous, weightless, hot-cold extremes of space.
The most critical problem in preparations for the extended mission was providing enough hydrogen peroxide fuel to power the capsule's reaction control system. A seven-orbit mission operating in the fully automatic control mode would consume about 28 pounds of fuel, providing the systems were functioning normally. The Mercury Project Office suggested alternating a combination of automatic and manual modes to provide safer fuel reserves at the end of the flight. Such a procedure would expend 23 pounds of automatic and 18 pounds of manual fuel, leaving reserves of 12 and 15 pounds, respectively. Then, in case of malfunction in one of the control modes, the astronaut would be assured of an adequate fuel supply in the other mode.
Recovery procedures changed considerably for the proposed seven-orbit mission. The fourth, fifth, sixth, and seventh sinusoidal curves of the orbital ground trace passed over geographical points that almost intersected, while the fifth and sixth orbits did intersect in the northern Pacific about 275 miles northeast of Midway Island. This pattern shifted to the Pacific Ocean the optimum recovery area that had been in the Atlantic for MA-4 through MA-7. Kleinknecht's staff pointed out that a once-an-orbit primary recovery capability could be maintained with only a slight increase in the recovery forces. The primary landing area during the seventh orbit could be covered easily by Navy vessels moving to the zone from their base at Pearl Harbor, but some of the aircraft staging bases for past contingency landing areas would have to be relocated.
Then Sigurd A. Sjoberg, Robert F. Thompson, and other mission and recovery planners discovered a slight flaw in the seven-orbit flight profile. A hard mission rule required a contingency recovery capability within 18 hours after landing. This requirement could be easily met for a six-orbit mission, but adding a seventh orbit required additional recovery forces to satisfy that mission rule. So NASA decided to make MA-8 a six-orbit flight.5
During August 1962 the MA-8 mission planners continued to wrestle with many other operational considerations. But within the month they were able to issue the mission rules, data acquisition plan, a slight revision to the flight plan, recovery requirements and procedures, and the mission directive, only to find on some occasions that closer study of engineering preparations revealed new constraints, requiring minor changes to most of their guidebooks.6
4 Kenneth S. Kleinknecht, interview, Houston, May 3, 1965; "Mercury Seven-Orbit Mission Capability," memorandum report, Mercury Project Office, March 5, 1962.
5 "Mercury Seven-Orbit Mission Capability."
6 "MA-8 Mission Rules-Preliminary," Aug. 3, 1962; Revision A, Aug. 20, 1962; Revision B, Sept. 24, 1962; "MA-8 Data Acquisition Plan," Aug. 21, 1962; "MA-8 Technical Information Summary" [Aug. 20, 1962]; "Flight Plan for MA-8/16, Revision A," Sept. 10, 1962; "Mission Directive for Mercury-Atlas Mission No. 8 (MA-8-Spacecraft 16)," NASA Project Mercury working paper No. 228, Aug. 31, 1962; "Calculated Preflight Trajectory Data for Mercury-Atlas Mission 8 (MA-8) (Spacecraft No. 16-Atlas 113-D)," NASA Project Mercury working paper No. 229, Sept. 7, 1962; "MA-8 Recovery Requirements," Aug. 15, 1962; "MA-8 Recovery Procedures," Aug. 30, 1962.