What could be achieved

The thread on having to leaving Earth within 25 years got me thinking.
What would be achievable? This is a useful policy question, as
sometimes it helps to see the obstacles. When reengineering a process,
you can sometimes struggle to make a 5% improvement. Then you hear
that a competitor has made a 90% improvement. Just this knowledge
alone suddenly clarifies the way forward.

So what could be achieved?

Is launch capacity a serious obstacle. If America had to, it could
launch 1 shuttle C per day at a unit cost of $100 million. That would
be $36 billion for 36,000 tons to orbit per year. Much cheaper than
the Defence budget.

But what would be the next obstacle?
- We still don't know how to build closed system life support gear.
- For really large colonies we would still need to process lunar or
NEO material
- To do so we would need to manufacture solar panels in space

What else?

Once we know what could be achieved, we ask, apart from money, what's
stopping us.