it would be a three-person landing team or that the CSM would rendezvous with an orbiting module were considered. Evolution The following phases were considered: Phase 1: 1969-1971: This "Apollo Phase" commenced with the first lunar landing and continued for four missions, or until sufficient experience had been achieved to allow the next phase to commence. As actually flown by NASA, these missions corresponded to Apollo 11 to Apollo 14. Phase 2: 1972 to 1973: This Lunar Exploration Phase would commence about two years after Apollo and consisted of four flights of the Extended Lunar Module (ELM), a modification of basic Apollo Lunar Module hardware. ELM missions extended lunar stay time to 3 or 4 days with landed payloads approaching 450 kg. This scenario corresponded to Apollo 15 to Apollo 17 as flown. Phase 3: 1974: A single Lunar Orbital Survey Mission was indicated after the Lunar Surface Exploration phase and would be the end of the initial buy of Apollo spacecraft. This 28-day lunar polar orbit mission would be flown after the Apollos and ELMs, in order to have several "ground-truth" sites. Phase 4: 1975-1976: This Lunar Surface Rendezvous and Exploration Phase nominally consisted of two dual-launch missions. A Lunar Payload Module (LPM - essentially the LM Truck of earlier studies) would be delivered by an uncrewed cargo carrier to the surface and provide a rendezvous target for a crewed ELM that would arrive up to 3 months later. The Apollo LM Shelter was essentially an Apollo LM with ascent stage engine and fuel tanks removed and replaced with consumables and scientific equipment for 14 days' extended lunar exploration. Associated vehicles The Apollo LM Taxi was essentially the basic Apollo LM modified for extended lunar surface stays. This was expected to be the workhorse of both Apollo Applications Extended Lunar Surface Missions beginning in 1970 and to larger Lunar Exploration System for Apollo in the mid-to-late 1970s. The Apollo LM Shelter was essentially an Apollo LM with ascent stage engine and fuel tanks removed and replaced with consumables and scientific equipment for 14 days' extended lunar exploration. The MOBEV F2B was a multi-person surface-to-surface flying vehicle. LESA (Lunar Exploration System for Apollo) Lunar Base The basic Apollo hardware would evolve into AES (Apollo Extension Systems), followed by ALSS (Apollo Logistics Support System), and then LESA (Lunar Exploration System for Apollo). The result would be ever-expanding permanent stations on the