NASA Administrator Charles Bolden speaks in front of Falcon 9 rocket in 2016. (credit: NASA)

Although some NASA officials such as then-deputy director Lori Garver were wary of the rocket’s costs—about $20 billion has now been poured into development of a launch vehicle based on existing technology—Bolden remained a defender of the large rocket, calling it a lynchpin of the agency’s plans to send humans beyond low-Earth orbit, perhaps to the Moon or Mars. He also dismissed the efforts of commercial space companies like SpaceX to build comparable technology.

When I sat down with Bolden for an interview in 2014 at Johnson Space Center, I asked why NASA was investing so much in the SLS rocket when SpaceX was using its own funds to develop the lower-cost Falcon Heavy rocket. His response at the time: “Let’s be very honest. We don’t have a commercially available heavy-lift vehicle. The Falcon 9 Heavy may some day come about. It’s on the drawing board right now. SLS is real.”