 However, the detailed letter to Seamans, together with studies of the difficulties posed by the need for a massive rocket in a direct ascent and the problems associated with landing a large craft on the lunar surface following an earth orbit rendezvous, led Seamans and von Braun to support LOR by early 1962.While some aspects of Houbolt's initial estimates were off (such as a 10,000 pound Apollo Lunar Module which was ultimately 32,399 lb (14,696 kg)), his LOR package proved to be feasible with a single Saturn V rocket whereas other modes would have required two or more such rocket launches or a rocket much heavier than the Saturn V to lift enough mass into space to complete the mission

Leading up to the first mission of the Space Shuttle, STS-1, in 1981 Houboult co-wrote a letter with structural engineer Holt Ashley to Chris Kraft, director of Johnson Space Center, imploring him to delay the launch believing the orbiter would suffer major loss of thermal protection tiles, and potentially lose the vehicle.Of particular concern was a strut attaching the nose of the orbiter to the External Tank.