NAA completed a preliminary requirement outline for spacecraft docking. The outline specified that the two spacecraft be navigated to within a few feet of each other and held to a relative velocity of less than six inches per second and that they be steered to within a few inches of axial alignment and parallelism. The crewman in the airlock was assumed to be adequately protected against radiation and meteoric bombardment and to be able to grasp the docking spacecraft and maneuver it to the sealing faces for final clamp.

A study was made by NAA to determine optimum location and configuration of the spacecraft transponder equipment. The study showed that, if a single deep space instrumentation facility transponder and power amplifier were carried in the command module instead of two complete systems in the service module, spacecraft weight would be reduced, the system would be simplified, and command and service module interface problems would be minimized. Spares in excess of normal would be provided to ensure reliability.

NAA investigated several docking methods. These included extendable probes to draw the modules together; shock-strut arms on the lunar excursion module with ball locators to position the modules until the spring latch caught, fastening them together; and inflatable Mylar and polyethylene plastic tubing. Also considered was a system in which a crewman, secured by a lanyard, would transfer into the open lunar excursion module. Another crewman in the open command module airlock would then reel in the lanyard to bring the modules together.

Two aerospace technologists at MSC, James A. Ferrando and Edgar C. Lineberry, Jr., analyzed orbital constraints on the CSM imposed by the abort capability of the LEM during the descent and hover phases of a lunar mission. Their study concerned the feasibility of rendezvous should an emergency demand an immediate return to the CSM.

Ferrando and Lineberry found that, once abort factors are considered, there exist "very few" orbits that are acceptable from which to begin the descent. They reported that the most advantageous orbit for the CSM would be a 147-kilometer (80-nautical-mile) circular one.

MSC directed North American to concentrate on the extendable boom concept for CSM docking with the LEM. The original impact type of docking had been modified:

1. The primary mode employed an extendable probe. It would establish initial contact and docking at a separation distance sufficient to prevent dangerous impact as a result of pilot error.
2. The backup mode consisted of free-flying the two modules together. Mean relative impact velocities established during free-flying docking simulation studies would be used as the design impact velocities.

At MSC, the Spacecraft Technology Division reported to ASPO the results of a study on tethered docking of the LEM and CSM. The technology people found that a cable did not reduce the impact velocities below those that a pilot could achieve during free flyaround, nor was fuel consumption reduced. In fact, when direct control of the spacecraft was attempted, the tether proved a hindrance and actually increased the amount of fuel required.

At a meeting of the Apollo Docking Interface Panel, North American recommended and Grumman concurred that the center probe and drogue docking concept be adopted.MSC emphasized that docking systems must not compromise any other subsystem operations nor increase the complexity of emergency operations. In mid-December, MSC/ASPO notified Grumman and North American of its agreement. At the same time, ASPO laid down docking interface ground rules and performance criteria which must be incorporated into the spacecraft specifications.

There would be two ways for the astronauts to get from one spacecraft to the other. The primary mode involved docking and passage through the transfer tunnel. An emergency method entailed crew and payload transfer through free space. The CSM would take an active part in translunar docking, but both spacecraft must be able to take the primary role in the lunar orbit docking maneuver. A single crewman must be able to carry out the docking maneuver and crew transfer.

Two astronauts took part in tests conducted by North American to evaluate equipment stowage locations in CM mockup 2. Working as a team, the astronauts simulated the removal and storage of docking mechanisms. Preliminary results indicated this equipment could be stowed in the sleeping station. When his suit was deflated, the subject in the left couch could reach, remove, and install the backup controllers if they were stowed in the bulkhead, couch side, or headrest areas. When his suit was pressurized, he had difficulty with the bulkhead and couch side locations. The subject in the center couch, whose suit was pressurized, was unable to be of assistance.

Grumman was studying problems of transmitting data if the LEM missed rendezvous with the CSM after lunar launch. This meant that the LEM had to orbit the moon and a data transmission blackout would occur while the LEM was on the far side of the moon. There were two possible solutions, an onboard data recorder or dual transmission to the CSM and the earth. This redundancy had not previously been planned upon, however.

North American submitted to ASPO a proposal for dynamic testing of the docking subsystem, which called for a full-scale air-supported test vehicle. The contractor estimated the program cost at $2.7 million for facilities, vehicle design, construction, and operation.

At North American, a mockup of the crew transfer tunnel was reviewed informally. The mockup was configured to the North American-proposed Block II design (in which the tunnel was larger in diameter and shorter in length than on the existing spacecraft). MSC asked the contractor to place an adapter in the tunnel to represent the physical constraints of the current design, which would permit the present design to be thoroughly investigated and to provide a comparison with the Block II proposal.

Remote operation of the CSM's rendezvous radar transponder and its stabilization and control system (SCS) was not necessary, ASPO told North American. Should the CSM pilot be incapacitated, it was assumed that he could perform several tasks before becoming totally disabled, including turning on the transponder and the SCS. No maneuvers by the CSM would be required during this period. However, the vehicle would have to be stabilized during LEM ascent, rendezvous, and docking.

In a letter on August 25, 1964, the LEM Project Office had requested Grumman to define the means by which CSM stabilization and rendezvous radar transponder operation could be provided remotely in the event the CSM crewman was disabled.

In another letter on October 16, the Project Office notified Grumman that no requirement existed for remote operation of either the rendezvous radar transponder or the stabilization and control system. The letter added, however, that the possibility of an incapacitated CSM astronaut must be considered and that for design purposes Grumman should assume that the astronaut would perform certain functions prior to becoming completely disabled. These functions could include turning on the transponder and the SCS. No CSM maneuvers would be required during the period in which the CSM astronaut was disabled but the CSM must remain stabilized during LEM ascent coast and rendezvous and docking phases.

MSC defined the requirements for visual docking aids on both of the Apollo spacecraft:

• At a range of 305 m (1,000 ft), the astronaut must be able to see the passive spacecraft and determine its gross attitude.
• From 61 m (200 ft) away, he must be able to judge the target's relative attitude and the alignment of his own vehicle.
• And from this latter distance - and still solely through visual means the pilot must be able to calculate the distance between the two spacecraft and the closing rate.

MSC approved North American's proposed location of the antenna for the radar transponder in the CSM, as well as the transponder's coverage. This action followed a detailed review of the relative positions of the two spacecraft during those mission phases when radar tracking of the LEM was required.

Perkin-Elmer Corp., Norwalk, Conn., and Chrysler Corp., Detroit, Mich., were authorized about $250,000 each to continue studies of optical technology for NASA. The nine-month extension of research by the two companies was to evaluate optical experiments for possible future extended Apollo flights. The proposed experiments included control of optical telescope primary mirrors, telescope temperature control, telescope pointing, and laser propagation studies.