I think you make a good point in the foot print area, but isn't 2100 pretty close in human terms? We already have CNC machines, 3D printers, automated semi-conductor factories, etc. I for one would be very impressed if we could make a fully self replicating colony & factory in the next 90 years.

Also if you were hitchhiking you would need a massively plentiful source of fuel in the target environment because it doesn't have the sun pumping energy into it.