Bill Gerstenmaier, NASA chief of human spaceflight, is supporting the development of the multi-billion per year Space Launch System. The justification is that Falcon Heavy can deliver 18-22 tons to lunar orbit while SLS could deliver a bit more.
There are currently no payloads or missions that require the extra payload capacity to lunar orbit. Increasing the number of side-boosters from two sets of side boosters to four sets on a SpaceX Falcon Heavy would create a 100-ton payload capacity Falcon Super Heavy with two more side boosters can be created that would match any planned Space Launch System that could fly for the next ten years. All planned version of the Space Launch System will be vastly inferior to SpaceX BFR.
SpaceX will fly for $90 million per launch versus the planned $1 billion for Space Launch System.
The SpaceX Heavy not only cost $500 million to develop versus $11 billion already spent for no flights for the Space Launch System; Space Launch System will need another $5-10 billion to get close to where SpaceX Heavy is in launch capacity but still without reusability and for a system that will cost 10-20 times more to fly. Space Launch System will remain an embarrassing poster child for government waste and corruption. It is has been obvious for decades that the US government has corrupt and broken spending.
Space Launch System is costing over $2 billion per year and will not have its first launch until 2019 if the new schedule was kept. The initial system would only be able to launch 70 tons. It would not be able to launch 130 tons until 2029 if development schedule was kept. The SLS program would have increased costs when they actually starting launching rockets. Costs would ramp to over $4 billion per year from 2019. $11 billion has already been spent and after seven years there will be no launch for another two years.
The total cost of the actual 30-year service life of the space shuttle program through 2011, adjusted for inflation, was $209 billion. There were 135 Space Shuttle launches. The cost of the Space shuttle was over $1.5 billion per launch. The Space Shuttle was initially pitched as a reusable $5 million per launch system that would refly every week. These promises are all the things that SpaceX is on the way to actually delivering.