SpaceX’s plan calls for everything to be new: a new engine (the Raptor), a new rocket (the ITC), a new spacecraft, new material composites and processes, in-orbit refueling, precision landing and same-day turnaround of a massive first-stage of its rocket, etc.

NASA’s Space Launch System rocket uses a different approach. It uses upgraded Space Shuttle Main Engines, the RS-25s; upgraded Shuttle-era solid rocket boosters, the upper stage will use existing engines (the RL-10s), the infrastructure is upgraded Shuttle infrastructure, and so on. These decisions weren’t made out of the blue, they were, in fact, mandated by Congress in the 2010 NASA Authorization Act. NASA was given the pieces and told to solve the problem of human spaceflight.

This is the conservative approach taken by aerospace companies when funding is limited: avoid making new stuff. Just look at nearly every recent Mars exploration architecture concept (such as the orbit-first concept we highlighted from a study team at NASA’s Jet Propulsion Laboratory or Lockheed-Martin’s Mars Base Camp). These Mars exploration architectures use existing NASA field centers and contractor workforces, piece together the parts of existing NASA programs, use as much flight-proven hardware as possible. Again, when funding is tight, particularly year-to-year funding, the best practice is avoid the risk of creating new hardware.

That’s because creating new, reliable space hardware is historically the source of cost and schedule overruns. NASA has been dogged by this problem over the decades, overselling and under delivering on its initial goals. But it’s not unique to NASA. Every institution (and every human) struggles with this all of the time—it’s called optimism bias. We assume the best possible outcome and downplay the negative ones. But it is impossible to anticipate all of the unknown unknowns that arise from the multitudinous interactions of complex systems. NASA has been burned by this many times, driving the conservative approach to hardware program and risk to prevent undue attention from a prickly Congress.

SpaceX doesn’t work for Congress. It’s a privately-held company, so they don’t have to answer to shareholders. SpaceX has the luxury to choose its own workforce, choose its own production sites, and use its own funding to develop any hardware it wants. The company has a clear vision that informs every aspect of their work.

It’s fun to design on the blank slate. Everything works perfectly, everything happens on time and on budget. But designing on a blank slate is risky since the real world has a nasty way of throwing problems your way. There will be engineering, political, and economic complexities that will disrupt this plan.

So perhaps the most important—and most revealing—moment came in the middle of Elon Musk’s presentation to the International Aeronautical Congress, when he said that the reason he is personally accumulating assets is to fund his Mars colonization plan. This is his life’s work. So when we talk about schedules, feasibility, and cost, balance that out with the fact that this is Musk’s life work. Elon Musk wanted to colonize Mars to save humanity, so he grabbed a blank piece of paper, worked backward, and founded SpaceX.