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.
But with an upper stage, a crewed SLS should be capable of transporting the 20 tonne Orion plus an additional 10 to 20 tonnes of payload practically anywhere within cis-lunar space (the Lagrange points: L1, L2, L4, and L5 and lunar orbit). And as an unmanned vehicle, the SLS could eventually evolve into a system that could carry as much as 200 tonnes to LEO and 80 tonnes to L1 if it utilized up to four 5-segment SRBs plus and upper stage.
Right: crew launch vehicle with two 4-segment SRBs capable of transporting the Orion-MPCV to LEO ; left: crew launch vehicle with two 4-segment SRBs plus and upper stage (US) capable of transporting the Orion-MPCV anywhere within cis-lunar space
However, as a crew launch system could be much simpler, safer, and cheaper to operate if the SLS was launched without the SRBs. The only fatal crew launch accident ever to occur during the Space Shuttle era was due to a malfunction in the SRBs O-ring that allowed how gases and plumes to critically damage the adjacent cryogenically fueled external tank; the subsequent explosion destroyed the vessel and killed the crew. So in a new launch system, crew safety has to be a priority.
Shuttle derived LOX/LH2 core vehicle capable of launching a 20 tonne Orion-MPCV with a stretched SM with 8 to 9 tonnes of extra hypergolic fuel to LEO
A stretched shuttle derived LOX/LH2 without SRBs could send the Orion capsule to LEO by simply using the hypergolic fueled Service Module (SM) as an upper stage. An additional 8 to 9 tonnes of hypergolic fuel in a stretched SM with could transport 20 tonnes to LEO. Boeing Inc. has already conceived such a SLS derived crew launch vehicle without the SRBs.
Left: Cis-lunar crew launch vehicle, center: HLV cargo vehicle using two 4-segment SRBs, right: HLV cargo vehicle using three LOX/LH2 core vehicles
However, a stretched shuttle derived core vehicle with a large upper stage-- but still without SRBs-- could transport the 20 tonne Orion MPCV anywhere within cis-lunar space. If the upper stage is equipped with multiple RL-10 engines then the crew launch vehicle would have uber-safe engine-out capability in both first and second stages. This would allow NASA conduct simpler and safer manned cis-lunar missions to L1, L2, L4, L5, and lunar orbit almost immediately after the SLS becomes operational in 2016. And NASA is required by law to define near term manned missions for the SLS within cis-lunar space.
Orion-MPCV on cis-lunar mission to lunar orbit
Coupled with SRBs, the SLS would be the only vehicle capable of deploying the largest 65 tonne plus Bigelow space stations (BA-2100) to LEO or sending the smaller 25 tonne water shielded Bigelow space stations (BA 330) to the Lagrange points. While such Lagrange point space stations would still have too little shielding to provide astronauts with adequate protection against galactic radiation and especially potentially brain damaging heavy nuclei beyond a few weeks time, such stations would still contain enough water shielding to protect astronauts from the dangers of a major solar event.
As an orbital crew launch vehicle, the two stage LOX/LH2 vehicle might be capable of transporting the 20 tonne Orion plus 30 to 40 tonnes of payload to LEO. While this might seem like overkill, it should be remembered that transporting humans to an orbital space station requires more than just transporting the human body. Every human requires nearly one tonne of water, oxygen, and food per month in order to survive in space.
Once Americans return to the Moon again (which should still be NASA's priority, IMO), it has been suggested that a reusable LOX/LH2 lunar lander be developed that utilizes fuel mined from the lunar poles. Such a lunar transportation system would be able to transport humans and cargo from the lunar surface to L1 and back. This would greatly simplify and reduce the cost of sending humans to and from the lunar surface. And such a simpler and safer SLS combined with a reusable lunar shuttle might be very attractive to private commercial spaceflight companies seeking to expand the emerging space tourism industry all the way to the lunar surface.
Deriving Economically Sustainable Crew Launch Vehicles from the SLS