by Marcel F. Williams
With the end of the Space Shuttle era, there has been much focus on the emerging commercial crew industry in America with the hope that these vehicles will be ready to transport humans into orbit by the middle of the decade. However, by law, NASA's new SLS (Space Launch System) must also be capable of launching humans into orbit and beyond while also serving as a backup system for delivering crew and cargo to the ISS if such missions cannot be met by the private commercial crew companies.
It has generally been assumed that the crew launch vehicle derived from a shuttle space launch system (SLS) will simply be composed of an inline LOX/LH2 rocket coupled with two 4-segment or 5-segment solid rocket boosters (SRBs). Such a system would be capable of carrying a 20 tonne Orion-MPCV (Multi-Purpose Crew Vehicle) to LEO plus perhaps an additional 40 to 50 tonnes of payload to orbit.
However, without an upper stage (US), such a crew launch vehicle would have very limited beyond LEO capabilities.