‘Tumbling End Over End’: Gemini VIII, 1966Posted: January 20, 2015
Dave Scott (left) and Neil Armstrong breathe the fresh air of Earth as the hatches of Gemini VIII are opened after splashdown. Photo Credit: NASA
Ben Evans writes: Gemini VIII astronauts Neil Armstrong and Dave Scott accomplished a key goal in America’s bid to land a man on the Moon by successfully rendezvousing and docking with an unmanned Agena target vehicle in Earth orbit. As noted in part 1 AmericaSpace article, it was the first time that a manned vehicle had achieved physical contact with another target in space. However, the situation aboard Gemini VIII was far from perfect. A distinct lack of available tracking stations across the flight path had already resulted in decidedly “spotty” communications with the Mission Operations Control Room (MOCR) in Houston, Texas.
“We have serious problems here. We’re tumbling, end over end. We’re disengaged from the Agena.”
— Dave Scott
In fact, only two ship-based stations were supporting the flight, the Rose Knot Victor and the Coastal Sentry Quebec, together with a land site in Hawaii. Shortly before one loss of contact, at around 6:35 p.m. EST on 16 March 1966, Capcom Jim Lovell radioed the Gemini VIII crew. If problems arose, he told them, they should immediately deactivate the Agena with Command 400 and assume manual control with the Gemini. It was a standard call. Lovell could hardly have imagined that a potential disaster would soon engulf the mission.
Half an hour after docking with the Agena, Dave Scott instructed the target to roll them 90 degrees, and Neil Armstrong, in the commander’s seat, told Lovell that it had “gone quite well.” The call came a few seconds before Gemini VIII passed out of radio contact with the ground. Alone, the astronauts electronically activated the Agena’s tape recorder. Shortly thereafter, their attitude indicator showed that they were in an unexpected, and almost imperceptible, roll of about 30 degrees.
“Neil,” called Scott, “we’re in a bank.” Were the Agena’s attitude controls misbehaving? Or was it a problem with the target vehicle’s software? Certainly, Gemini VIII’s own thrusters were now switched off and the assumption could safely be made that the Agena was at fault. What they did not know was that one of their thrusters—the No. 8 thruster—had short-circuited and stuck into its “on” position. Unaware, Scott cut off the Agena’s thrusters, whilst Armstrong reactivated the Gemini’s thrusters in an attempt to stop the roll and bring the combination under control.
For a few minutes, his effort succeeded.
Gradually, the craft stabilized. Then, as Armstrong started to reorient them into their correct position, the unwanted motions resumed … albeit much faster than before and along all three axes. Perplexed, the men jiggled the Agena’s control switches, then those of the Gemini, on and off, in a fruitless attempt to isolate the problem. Glancing at his instrument panel, Scott noticed that their craft’s attitude propellant had dropped to just 30 percent. At this stage, it dawned on the astronauts that the fault was with their craft. “We had to disengage from the Agena,” Scott later wrote in his memoir, Two Sides of the Moon, “and quickly.”
“Television stations began interrupting their programmes—Batman and, ironically, Lost in Space—to provide live coverage. Original plans had called for Gemini VIII to splash down in the Atlantic and be recovered by the aircraft carrier U.S.S. Boxer, but the emergency guided them instead to a point in the western Pacific, 500 miles east of Okinawa.“
This posed its own problems, since both craft were rapidly rotating and could hit each other. Quickly, Scott set the Agena’s recording devices to allow flight controllers to remotely command it; a crucial step, since, after undocking, the target would otherwise be dead. “No one would ever know what the problem had been or how to fix it,” he wrote. His prompt action saved the Agena and preserved it not only for subsequent investigations, but also for a remarkable “double rendezvous” on the Gemini X mission in July.
Armstrong and Scott were still out of radio communications with the ground. They duly undocked from the Agena and fired a long burst of the Gemini’s thrusters to pull away … whereupon their craft, now free, began to spin much more violently, in roll, pitch, and yaw axes. Since the stuck-on No. 8 thruster was no longer turning the entire combination, the oscillations were correspondingly worse than before. At length, high above southeast Asia, they came into contact with the Coastal Sentry Quebec. Controllers were stunned at 6:58 p.m. when Dave Scott’s urgent call came through.
“We have serious problems here,” he reported. “We’re tumbling, end over end. We’re disengaged from the Agena.”
Jim Fucci, the communicator aboard the ship, was stunned and asked them about the problem. Quickly, and characteristically calm, Armstrong reported that they were continuously increasing in a left roll and unable to turn anything off. Fucci, an old NASA hand with great experience, alerted Houston that Gemini VIII was suffering from “pretty violent oscillations.” The resultant three-way conversation with the MOCR meant that several seconds elapsed before Flight Director John Hodge picked up all the details; Fucci had to repeat that Armstrong was “in a roll and he can’t stop it.”
In orbit, Armstrong threw circuit breakers to cut electrical power and hence the flow of propellant to the attitude thrusters, including troublesome No. 8. However, with no friction or counter-firing thrusters to halt it, the spinning continued … reaching a horrifying 60 revolutions per minute. Checklists, flight plans, and procedural charts were flung around Gemini VIII’s cabin by the resultant centrifugal force, and the unfiltered sunlight blazed through the astronauts’ windows with startling regularity. To Dave Scott, it was like a constant strobe light, hitting them square in the face. Added to this, the rotation was such that the astronauts were close to physically blacking out and they struggled to read their instruments. Physiologically, Armstrong and Scott were suffering from a complete loss of orientation…(read more)
This is part of a series of history articles, which will appear each weekend, barring any major news stories. Next week’s article will focus on the flight of Gemini 3 in March 1965, the first piloted mission of Project Gemini … a voyage forever associated with the corned beef sandwich.
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