NASA had ambitious follow-on human spaceflight plans as it reached its lunar goal, but soon discovered it had expended most of its political capital to do so. A victim of its own success, Apollo had achieved its first landing goal with enough spacecraft and Saturn V launchers left for a total of ten lunar landings through Apollo 20, conducting extended-duration missions and transporting the landing crews in Lunar Roving Vehicles on the last five. NASA also planned an Apollo Applications Program to develop a longer-duration Earth orbital workshop (later named "Skylab") from a spent S-IVB upper stage, to be constructed in orbit using several launches of the smaller Saturn IB launch vehicle. But planners decided this could be done more efficiently by launching the workshop pre-fabricated on the ground using a single Saturn V, which immediately eliminated Apollo 20. Budget cuts soon led NASA to cut Apollo 18 and 19 as well. Apollo 13 encountered an in-flight spacecraft failure and had to abort its lunar landing in April 1970, returning its crew safely but temporarily grounding the program again. It resumed with four successful landings on Apollo 14 (February 1971), Apollo 15 (July 1971), Apollo 16 (April 1972), and Apollo 17 (December 1972).