Manned Spacecraft Center notified Marshall Space Flight Center, Huntsville, Alabama (which was responsible for managing NASA's Agena Programs) that Project Gemini required 11 Atlas-Agenas as rendezvous targets and requested Marshall to procure them. The procurement request was accompanied by an Exhibit 'A' describing proposed Gemini rendezvous techniques and defining the purpose of Project Gemini as development and demonstrating Earth-orbit rendezvous techniques as early as possible. If feasible, these techniques could provide a practical base for lunar and other deep space missions. Exhibit B to the purchase request was a Statement of Work for Atlas-Agena vehicles to be used in Project Gemini. Air Force Space Systems Division, acting as a NASA contractor, would procure the 11 vehicles required. Among the modifications needed to change the Atlas-Agena into the Agena rendezvous vehicle were: incorporation of radar and visual navigation and tracking aids; main engines capable of multiple restarts; addition of a secondary propulsion system, stabilization system, and command system; incorporation of an external rendezvous docking unit; and provision of a jettisonable aerodynamic fairing to enclose the docking unit during launch. The first rendezvous vehicle was to be delivered to the launch site in 20 months, with the remaining 10 to follow at 60-day intervals.

Westinghouse Electric Corporation, Baltimore, Maryland, received a $6.8 million subcontract from McDonnell to provide the rendezvous radar and transponder system for the Gemini spacecraft. Purpose of the rendezvous radar, sited in the recovery section of the spacecraft, was to locate and track the target vehicle during rendezvous maneuvers. The transponder, a combined receiver and transmitter designed to transmit signals automatically when triggered by an interrogating signal, was located in the Agena target vehicle.

ACF Electronics Division, Riverdale, California, of ACF Industries, Inc., received a $1 million subcontract from McDonnell to provide C- and S-band radar beacons for the Gemini spacecraft. These beacons formed part of the spacecraft's tracking system. With the exception of frequency-dependent differences, the C-band beacon was nearly identical to the S-band beacon. Their function was to provide tracking responses to interrogation signals from ground stations.

McDonnell awarded a $26.6 million subcontract to International Business Machines (IBM) Corporation's Space Guidance Center, Owego, New York, to provide the computer system for the Gemini spacecraft. The digital computer was the heart of the spacecraft's guidance and control system; supplementary equipment consisted of the incremental velocity indicator (which visually displayed changes in spacecraft velocity), the manual data insertion unit (for inserting data into, and displaying readouts from, the computer), and the auxiliary computer power unit (to maintain stable computer input voltages). In addition to providing the computer and its associated equipment, IBM was also responsible for integrating the computer with the systems and components it connected with electrically, including the inertial platform, rendezvous radar, time reference system, digital command system, data acquisition system, attitude control and maneuver electronics, the launch vehicle autopilot, console controls and displays, and aerospace ground equipment.

McDonnell proposed to evaluate the Gemini redezvous radar and spacecraft maneuvering system on early flights by using a rendezvous evaluation pod to be ejected from the spacecraft in orbit. Manned Spacecraft Center (MSC) liked the idea and asked McDonnell to pursue the study. During the last week in June, McDonnell received approval from MSC to go ahead with the design and development of the rendezvous pod. It would contain a radar transponder, C-band beacon, flashing light, and batteries.

Gemini Project Office reported that a thorough study of the reentry tracking histories of the Mercury-Atlas 4, 5, 6 and 7 missions had been completed. The study indicated that a C-band radar tracking beacon should be integrated into the spacecraft reentry section in place of the planned S-band beacon. The change would improve the probability of tracking spacecraft reentry through the ionization zone.

Gemini Project Office directed McDonnell to provide spacecraft No. 3 with rendezvous radar capability and to provide a rendezvous evaluation pod as a requirement for missions 2 and 3. Four pods were required: one prototype, two flight articles, and one flight spare.

Manned Spacecraft Center directed McDonnell to study requirements for a spacecraft capable of performing rendezvous experiments on the second and third Gemini flights. The experimental package would weigh 70 pounds and would include an L-band radar target, flashing light, battery power supply, and antenna systems. On the second flight, a one-day mission, the experiment was to be performed open-loop, probably optically - the astronaut would observe the target and maneuver the spacecraft to rendezvous with it. On the third flight, a seven-day mission, the experiment was to be performed closed-loop, with spacecraft maneuvers controlled automatically by the data it received from its instruments.

Upon receipt at Cape Canaveral, the target vehicle would be inspected and certified. After this action, mechanical mate and interface checks with the target docking adapter would be accomplished. Agena-Gemini spacecraft compatibilty tests would then be conducted, and the Agena would undergo validation and weight checks. Subsequently, a joint checkout of the spacecraft and Agena would be conducted with tests on the Merritt Island radar tower.

Gemini Project Office discussed with contractors the establishment of a philosophy for the final phase of the rendezvous mission. They agreed on the following general rules: (1) when the launch was on time, the terminal maneuver would be initiated when the Agena came within range of the spacecraft's sensors, which would occur between spacecraft insertion and first apogee; (2) automatic and optical terminal guidance techniques would always back each other up, one method being selected as an objective for each mission and the other serving as a standby; (3) during early rendezvous missions, the terminal phase would be initiated by the third spacecraft apogee or delayed until the twelfth because of range radar tracking limitations; (4) for the same reason, no midcourse corrections should be made during orbits 4 through 11; (5) in case of extreme plane or phase errors, the Agena would be maneuvered to bring it within the spacecraft's maneuver capability; and (6) after such gross Agena maneuvers, the Agena orbit would be recircularized and two orbits of spacecraft catchup would precede the initiation of terminal rendezvous plan.

Testifying before the Subcommittee on Manned Space Flight of the House Committee on Science and Astronautics, D Brainerd Holmes, Director of Manned Space Flight, sought to justify a $42.638 million increase in Gemini's actual 1963 budget over that previously estimated. Holmes explained: 'This increase is identified primarily with an increase of $49.9 million in spacecraft. The fiscal 1963 congressional budget request was made at the suggestion of the contractor. The increase reflects McDonnell's six months of actual experience in 1963.' The subcommittee was perturbed that the contractor could so drastically underestimate Gemini costs, especially since it was chosen without competition because of supposed competence derived from Mercury experience. Holmes attributed McDonnell's underestimate to unexpectedly high bids from subcontractors and provided for the record a statement of some of the reasons for the change: 'These original estimates made in December 1961 by NASA and McDonnell were based on minimum changes from Mercury technology ..... As detailed specifications for subsystems performance were developed ....... realistic cost estimates, not previously available, were obtained from subcontractors. The first of these ....... were obtained by McDonnell in April 1962 and revealed significantly higher estimates than were originally used. For example: (a) In data transmission, it became necessary to change from a Mercury-type system to a pulse code modulation (PCM) system because of increased data transmission requirements, and the need to reduce weight and electrical power. The Gemini data transmission system will be directly applicable to Apollo. (b) Other subsystems have a similar history. The rendezvous radar was originally planned to be similar to ones used by the Bomarc Missile, but it was found necessary to design an interferometer type radar for low weight, small volume, and to provide the highest reliability possible. (c) The environmental control system was originally planned as two Mercury-type systems, but as the detail specifications became definitive it was apparent that the Mercury ECS was inadequate and, although extensive use of Mercury design techniques were utilized, major modifications were required.'

George M Low, Director of Spacecraft and Flight Missions, Office of Manned Space Flight, explained to the House Subcommittee on Manned Space Flight why eight rendezvous missions were planned. 'In developing the rendezvous capability, we must study a number of different possible ways of conducting the rendezvous ..... For example, we can conduct a rendezvous maneuver in Gemini by purely visual or optical means. In this case there will be a flashing light on the target vehicle. The pilot in the spacecraft will look out of his window and he will rendezvous and fly the spacecraft toward the flashing light and perform the docking. This is one extreme of a purely manual system. On the opposite end of the spectrum we have a purely automatic system in which we have a radar, computer, and stabilized platform and, from about 200 or 500 miles out, the spacecraft and the target vehicle can lock on to each other by radar and all maneuvers take place automatically from that point on. We know from our studies on the ground and our simulations that the automatic way is probably the most efficient way of doing it. We would need the least amount of fuel to do it automatically. On the other hand it is also the most complex way. We need more equipment, and more equipment can fail this maneuver so it might not be the most reliable way. The completely visual method is least efficient as far as propellants are concerned, but perhaps the simplest. In between there are many possible combinations of these things. For example, we could use a radar for determining the distance and the relative velocity between the two without determining the relative angle between the two spacecraft and let the man himself determine the relative angle. We feel we must get actual experience in space flight of a number of these possibilities before we can perform the lunar orbit rendezvous for Apollo.'

The Cape Gemini/Agena Test Integration Working Group met to define "Plan X" test procedures and responsibilities. The purpose of Plan X was to verify the Gemini spacecraft's ability to command the Agena target vehicle both by radio and hardline; to exercise all command, data, and communication links between the spacecraft, target vehicle, and mission control in all practical combinations, first with the two vehicles about six feet apart, then with the vehicles docked and latched but not rigidized; and to familiarize the astronauts with operating the spacecraft/target vehicle combination in a simulated rendezvous mission. Site of the test was to be the Merritt Island Launch Area Radar Range Boresight Tower ('Timber Tower'), a 65 x 25 x 50-foot wooden structure.

Representatives of Manned Spacecraft Center's Instrumentation and Electronics Systems Division and McDonnell met to coordinate the Gemini radar program. Gemini Project Office had requested an increased effort to put the rendezvous radar system in operational status.

Following up Gemini Project Office's request to bring the Gemini rendezvous radar system to operational status, Manned Spacecraft Center Instrumentation and Electronics System Division personnel met with Westinghouse at Baltimore to review the test program. Westinghouse had completed its radio frequency anechoic chamber test, but test anomalies could not be pinpointed to the radar system, since chamber reflections might have been responsible. An outdoor range test was planned to determine whether the chamber was suitable for testing the radar.

NASA Headquarters directed Gemini Project Office to take the radar and rendezvous evaluation pod out of Gemini-Titan (GT) missions 3 and 4. GT-4 would be a battery-powered long-duration flight. The pod would go on GT-5, and thus the first planned Agena flight would probably slip in the schedule.

At a meeting of the Gemini Project Office's Trajectories and Orbits Panel, members of Flight Operations Division described two mission plans currently under consideration for the first Agena rendezvous flight. One was based on the concept of tangential Agena and spacecraft orbits, as proposed by Howard W. Tindall, Jr., and James T. Rose when they were members of Space Task Group. The second plan, based on a proposal by Edwin E. Aldrin, Jr., then of Air Force Space Systems Division, involved orbits which were concentric rather than tangential. The most significant advantage of the second plan was that it provided the greatest utilization of onboard backup techniques; that is, it was specifically designed to make optimum use of remaining onboard systems in the event of failure in the inertial guidance system platform, computer, or radar.

Air Force Space Systems Division (SSD) accepted the first Agena D (AD-71) for the Gemini program. The Agena D was a production-line vehicle procured from Lockheed by SSD for NASA through routine procedures. Following minor retrofit operations, the vehicle, now designated Gemini Agena target vehicle 5001, entered the manufacturing final assembly area at the Lockheed plant on May 14. There began the conversion of the Agena D into a target vehicle for Gemini rendezvous missions. Major modifications were installation of a target docking adapter (supplied by McDonnell), an auxiliary equipment rack, external status displays, a secondary propulsion system, and an L-band tracking radar.

Representatives from Instrumentation and Electronics Division conducted preliminary rendezvous radar flight tests at White Sands Missile Range. Testing was interrupted while the T-33 aircraft being used was down for major maintenance and was then resumed on October 19. Flight testing of the rendezvous radar concluded December 8.

After its receiving inspection had been completed (January 6), the spacecraft was moved to the Merritt Island Launch Area Radar Range for a communications radiation test. This test, performed only on spacecraft No. 3 because it was scheduled for the first manned mission, exercised spacecraft communications in a radio-frequency environment closely simulating the actual flight environment. The test was run January 7, and the spacecraft then began preparations for static firing.

Gemini Program Office reported that during the missions of Gemini 4 and 5, skin-tracking procedures had been successfully developed. On these missions, the C-band radars were able to track the spacecraft in both the beacon and skin-track mode. It was, therfore, possible to obtain tracking data when the spacecraft was powered down and had no tracking beacons operating. As a result, the skin-tracking procedures were integrated into the network support for all remaining Gemini missions.

The augmented target docking adapter (ATDA) would serve as an alternative to the Gemini Agena target vehicle (GATV) if efforts to remedy the GATV problem responsible for the October 25 mission abort did not meet the date scheduled for launching Gemini VIII. Additional Details: here....