Alexw, the rest of us define it by the number of launches required. No gray areas there.Did anyone put out proposals for asteroid defense? I know that we have already some coordinated efforts to identify potentially threatening objects; is there any possibility about doing something with 70MT to orbit, and maybe propellent depots? This is blue sky, and we'd better not need it before 2017, but still, is there anything we reasonable do about it with SLS capability?
Back in 2010, they thought SLS would be cheaper and more sustainable. Today, it is not. It has become too expensive to launch more than once a year. Solids are expensive and not reusable. They cost as much to refurbish as new ones. Hydrogen is not a good booster fuel. Is expensive and only good for upper stages. All the new rockets are using methane, Starship/superheavy, Vulcan, New Glenn, and some small startups. Clean, more power than hydrogen, and is great for reusable engines as there is no coking like kerosene. SpaceX has proven you can land a booster which is the largest and most expensive part of getting to orbit. Now we have to reuse upper stages/spacecraft. NASA did not go this route because of congress who appropriates the money.
Back in 2010, they thought SLS would be cheaper and more sustainable.