Melvin F. Brooks, the Agena systems monitor in Flight Control, immediately began conferring with the Lockheed engineers to figure out what had happened. They suspected that the vehicle's center of gravity had been miscalculated. How could they command the vehicle to offset this? On the next main engine burn, the center-of-gravity compensation attempt failed. Brooks and Lockheed engineers huddled again. What could be wrong now? They finally agreed that there also seemed to be trouble in the yaw hydraulics, allowing the engine to gimbal more than it should. The target's orbit now measured 211 by 476 kilometers.80
If this Agena were to become Gemini IX's or X's passive target, there were two major problems to contend with, and Flight Control had to decide what to do about them. There was definitely too much fuel aboard* and the orbit was still too high. Hodge and his controllers decided not to try any more plane-change maneuvers; they would simply try to get the vehicle to the altitude they wanted. The next firing, a retrograde maneuver, convinced them that they had the hang of operating the vehicle. So Flight Control concentrated on reducing the fuel supply in both the primary and secondary tanks.81
In all, ten maneuvers were made using the two propulsion systems, sometimes with both firing at once. This was considerably more than the five starts required by the contract. The Agena's command and communications system had accepted a total of 5,439 commands (45 from the Gemini VIII spacecraft). Lockheed's contract had only called for 1,000.82
Just before the Gemini VIII-Agena docking, Scott had commented that he "bet those Lockheed guys are just jumping up and down." And so they had been. Jubilation died quickly when the news came that the spacecraft was in trouble. Agena's solo maneuvers wiped away any suspicions of wrongdoing on its part.  Somebody else must shoulder the blame for Gemini VIII's early landing. Why had thruster No. 8 failed in the open position?
From its landing spot in the Pacific Ocean, the spacecraft had been hauled back to its place of birth - the McDonnell plant in St. Louis - so the engineers could analyze its problems. Set up in a controlled laboratory where the investigations could proceed unmolested, the spacecraft was checked over completely for more than a month. Only the most probable cause of the trouble could be identified. Scott Simpkinson's evaluation team decided that:
The valves on thruster 8 opening unintentionally was probably caused by an electrical short, . . . there were several locations in the spacecraft at which the fault could have occurred.To prevent a recurrence of the thruster problem, McDonnell changed the attitude control circuit switch so that when it was in the "off" position no power could go to the thrusters. Formerly, turning the power to the electronics packages did not stop power going to the thrusters. They could still fire.83
Thus, the Gemini VIII mission ended on a dissonant chord - high success (the first space docking), undeniable failure (abbreviation of the mission), and much relief (safe recovery of the astronauts from a dangerous situation). The timing of the failure was especially frustrating. Being out of communications left the flight controllers and engineers helpless. Time after time in later interviews they repeated: if that spacecraft had just been over a ground station, telemetry would have told them that thruster No. 8 was firing continuously; they could have told the crew what to do before the reentry control system was activated and it was too late. Although the Gemini team was chagrined that the crew had been forced to land early, the knowledge that docking could be achieved with relative ease somewhat assuaged their anguish. Moreover, the Agena solo had demonstrated the target vehicle could help fly more elegant missions. There would be no pause in the program.84
Press on to Gemini IX!
* The Agena's electrical system would be dead before a return visit by a spacecraft; with no way to control the target, a load of fuel was a hazard during any rendezvous attempt.
79 "Gemini VIII Agena Target Vehicle Flight Plan," February 1966, p. 1; memo, Whitacre to Mgr., GPO, "Post-rendezvous Gemini Agena target vehicle maneuvers," GV-66350, 8 March 1966; [Ertel], Gemini VIII; "Agena Press Conference," 24 March 1966, pp. 9-10; "Gemini Agena Target Vehicle 5003," LMSC-A817204, p. vii.
80 Letter, Mathews to Gardner, GV-66301, 5 Jan. 1966, with enclosures, (1) memo, Kraft to GPO, Attn: Whitacre, "Request for information for the generation of Propellant Remaining Computer Program," 21 Dec. 1965, and (2) memo, Kraft to Mgr., GPO, "SPS thruster alignment and Agena vehicle errors resulting from c.g. offsets," 21 Dec. 1965; "Agena Press Conference," pp. 10, 11; "Gemini VIII Mission Report," p. 1-3.
81 "Agena Press Conference," pp. 13, 14.
82 "Gemini VIII Mission Report," p. 5-187; "Gemini Agena Target Vehicle 5003," LMSC-A817204, p. A-1; TWX, Mathews to SSD, Attn: Gardner, "Commands to Agena Vehicle 5003 during the Gemini VIII Mission," GV-12397, 4 April 1966; TWX, Network Ops. to Walter H. Wood,"GT-8 Agena," 23 March 1966.
83 "Gemini VIII Voice," p. 63; "Gemini VIII Mission Report," p. 5-88; MSC Gemini News Center Release, "Short in Circuitry Blamed for Gemini 8 Mission Termination," 19 March 1966; Robert L. Sharp, interview, St. Louis, 14 April 1966; memo, Mathews to Chief, Flight Safety Office, "Control system modifications," GP-62154, 22 April 1966; "Gemini IX-A Mission Report," p. 3-8.
84 Gilruth, interview, Houston, 21 March 1968; Meyer, interview, Houston, 9 Jan. 1967; Mathews interview.