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Atlantic Anomaly. Boosted by the Agena's thrust, the Gemini-Agena combination reached a maximum height of 476 miles, carrying Astronauts Young and Collins to the highest altitude ever reached by man—well above the 354-mile record set by Russian Cosmonauts Aleksei Leonov and Pavel Belyayev during the 1965 flight of Voskhod II. In its lofty elliptical orbit, Gemini-Agena passed several times through the "South Atlantic Anomaly," an area where the lower portion of the Van Allen radiation belt dips to within a few hundred miles of the earth. Though the astronauts were exposed to radiation, it was only one-twentieth the strength that NASA scientists had expected and well within safe limits.
The high, far-flung orbit also placed the coupled craft in position to begin a rendezvous with a second target: Agena 8, lifeless but still riding on a nearly circular orbit after its role in the aborted Gemini 8 mission four months earlier. At first, last week's Gemini-Agena was 3,220 miles ahead of Agena 8; during the next several hours, the dead target ship—revolving around the earth every 99 minutes, compared to 101 minutes for Gemini-Agena—slowly passed the sleeping astronauts.
After they had awakened, Young and Collins swung their craft into position and burned Agena's large thruster for eleven seconds. Again the astronauts felt the kick of the big engine. "It may be only one g.," said Young, "but it's the biggest one g. we ever saw." Because the thrust was against the direction of flight, it had a braking effect, reducing Gemini-Agena's velocity and cutting the apogee of its orbit from 476 to 245 miles. A final maneuver placed the astronauts in a 240-mile circular orbit slightly inside the path of Agena 8, now 1,245 miles ahead.
Ultraviolet Photography. While they waited to catch up, Young and Collins turned to their scheduled EVA (extravehicular activity). After securing their helmet face plates, they switched to their space-suit oxygen systems, and depressurized Gemini's cabin. Then Astronaut Collins swung open his hatch and stood up, sticking out into space from his waist up.
Using a camera loaded with ultraviolet-sensitive film, he shot spectrograms of several stars. Because ultraviolet is largely absorbed by the earth's atmosphere, the spectrograms could give astronomers a good look at the stars' composition and behavior and provide added information about their origin. As Gemini-Agena passed into daylight, Collins mounted a plate marked with colored patches of red, yellow, blue and grey, shot a series of test pictures that should help determine how the conditions of space affect color photography.