Moon. LESA (Lunar Exploration System for Apollo) represented the last lunar base concept studied by NASA prior to the cancellation of further Saturn V production. LESA would use a new Lunar Landing Vehicle to land payloads on the lunar surface and extended CSM and LM Taxi hardware derived from the basic Apollo program would allow crews to be rotated to the ever-expanding, and eventually permanent, lunar base. A nuclear reactor would provide power. Phases: 2 men/2 days - Apollo 2 men/14 days - AES - LM Shelter (2050 kg surface payload - LEM Shelter) 2 men/14 to 30 days - ALSS with shelter or MOLAB (4100 kg surface payload) 2-3 men/14 to 30 days - ALSS with a LASSO shelter or larger MOLAB (7900 kg surface payload) 3 men/90 days - LESA I (10,500 kg surface payload) 3 men/90 days - LESA I + MOLAB (12,500 kg surface payload) 6 men/180 days - LESA II with shelter and extended-range roving vehicle (25,000 kg surface payload) Lunar Escape Systems To support longer stays on the Moon, NASA also studied a number of simple Lunar Escape Systems as a means of returning two astronauts from the lunar surface to an orbiting CSM if the Lunar Module ascent-stage engine failed to ignite. Manned Venus Flyby Another plan for Apollo-based extended-duration crewed spaceflight would use a Saturn V to send three men on a Manned Venus Flyby, using the Saturn S-IVB stage as a "wet workshop". First the S-IVB would boost itself and the Apollo CSM on a trajectory that would pass by Venus and return to Earth, then any remaining fuel would be vented to space, after which the astronauts would live in the empty fuel tanks until they separated from the S-IVB shortly before reentry on their return to Earth. Development When procurement of Saturn Vs other than those required for the lunar landing was stopped in 1968, focus shifted to AAP. Aside from attempting to show that Apollo presented value for money, NASA and the main contractors of Boeing, Grumman, North American Aviation and Rockwell also hoped to put off the inevitable scaling down of staff and facilities following the completion of the first Moon landing. Three AAP proposals were selected for development: The Apollo Telescope Mission would be an Earth-orbiting mission for solar observation. The telescope would be based on a modified Lunar Module ascent stage, and launched using a