What is the difference between NLS, DIRECT v1.0, DIRECT v2.0, and DIRECT v3.0?
In the early 1990’s, NASA’s Marshall Space Flight Center (MSFC) designed a heavy lift launch vehicle to complement the Space Shuttle in constructing a space station. This vehicle, known as the National Launch System or NLS, successfully passed its Preliminary Design Review (PDR), which several Constellation components have yet to pass. However, the program went unfunded during the Clinton administration and the NLS was relegated to the filing cabinets. In 2006, Ross Tierney revitalized and updated NLS on NASASpaceflight.com as an alternative to the Ares launch vehicles, which were facing development problems. At the same time, TeamVision corporation concluded a similar study with a vehicle nearly identical to Tierney’s DIRECT. The proposals merged to create DIRECT v1.0, advocating a single launch vehicle to fulfill both the Crew and Cargo launch roles. In late 2006, Dr. Doug Stanley of MSFC criticized DIRECT’s use of a highly evolved version of the Delta IV’s RS-68 engine on DIRECT’s f
