used to image the surface, including the Descartes Highlands site being considered for Apollo 16, but it quickly developed a fault with the shutter that Roosa could not fix despite considerable help from Houston. Although about half of the photographic targets had to be scrubbed, Roosa was able to obtain photographs of Descartes with a Hasselblad camera and confirm that it was a suitable landing point. Roosa also used the Hasselblad to take photographs of the impact point of Apollo 13's S-IVB near Lansburg B crater. After the mission, troubleshooting found a tiny piece of aluminum contaminating the shutter control circuit, which caused the shutter to operate continuously. Roosa was able to see sunlight glinting off Antares and view its lengthy shadow on the lunar surface on Orbit 17; on Orbit 29 he could see the sun reflecting off the ALSEP. He also took astronomical photographs, of the Gegenschein, and of the Lagrangian point of the Sun-Earth system that lies beyond the Earth (L), testing the theory that the Gegenschein is generated by reflections off particles at L. Performing the bistatic radar experiment, he also focused Kitty Hawk VHF and S-band transmitters at the Moon so that they would bounce off and be detected on Earth in an effort to learn more about the depth of the lunar regolith. Return, splashdown and quarantine Antares lifted off from the Moon at 1:48:42 pm EST (18:48:42 UTC) on February 6, 1971. Following the first direct (first orbit) rendezvous on a lunar landing mission, docking took place an hour and 47 minutes later. Despite concerns based on the docking problems early in the mission, the docking was successful on the first attempt, though the LM's Abort Guidance System, used for navigation, failed just before the two craft docked. After crew, equipment, and lunar samples were transferred to Kitty Hawk, the ascent stage was jettisoned, and impacted the Moon, setting off waves registered by the seismometers from Apollo 12 and 14. A trans-earth injection burn took place on February 6 at 8:39:04 pm (February 7 at 01:39:04 UTC) taking 350.8 seconds, during Kitty Hawk 34th lunar revolution. During the trans-earth coast, two tests of the oxygen system were performed, one to ensure the system would operate properly with low densities of oxygen in the tanks, the second to operate the system at a high flow rate, as would be necessary for the in-flight EVAs