The ISS is primarily an engineering experiment, not a scientific experiment. This is lost on most of its critics. The objective was to build and operate a large space station for a prolonged period of time in order to study prolonged human space flight, closed circuit life support, in-space assembly and maintenance, etc., in order to practice for longer and further missions.
There's only so much you can do on the ground. At some point you have to "ship it" (pun intended?) and get real contact with the problem domain. That's when you find out about the unknown unknowns. (This is true for any engineering effort of any kind.)
This was done after the Apollo era because while we did make it to the moon the technology stack was far too immature for a robust space industry. It was horribly expensive, dangerous, and not suited for longer term missions. I've heard many Apollo engineers and astronauts remark that it's amazing we didn't lose anyone on those missions. We needed to develop and harden our space flight experience.
During the same period we also worked hard on reusable launch vehicles. The Shuttle was the first serious attempt and was lacking in many ways, but it demonstrated that you could use an orbiter repeatedly. The Falcon/Dragon stack is more practical and represents a re-framing of the problem. It builds on Shuttle experience and also on the Delta Clipper project:
I'm not sure how much direct engineering transfer occurred, but some indirect transfer certainly occurred as I'm sure people in SpaceX studied this and other related projects extensively before beginning their own work.
We now have the technology to send prolonged missions with better safety margins and very nearly have a reusable (and thus more economical) launch stack to launch them.
In addition to this, it's important to note a class of scientific experiments that cannot be done by satellites that the ISS has been at the forefront of: researching the prolonged effects of micro-gravity and space-flight on the human body. This will be very relevant if we intend to send people to Mars or back to the Moon.
There's only so much you can do on the ground. At some point you have to "ship it" (pun intended?) and get real contact with the problem domain. That's when you find out about the unknown unknowns. (This is true for any engineering effort of any kind.)
This was done after the Apollo era because while we did make it to the moon the technology stack was far too immature for a robust space industry. It was horribly expensive, dangerous, and not suited for longer term missions. I've heard many Apollo engineers and astronauts remark that it's amazing we didn't lose anyone on those missions. We needed to develop and harden our space flight experience.
During the same period we also worked hard on reusable launch vehicles. The Shuttle was the first serious attempt and was lacking in many ways, but it demonstrated that you could use an orbiter repeatedly. The Falcon/Dragon stack is more practical and represents a re-framing of the problem. It builds on Shuttle experience and also on the Delta Clipper project:
https://en.wikipedia.org/wiki/McDonnell_Douglas_DC-X
I'm not sure how much direct engineering transfer occurred, but some indirect transfer certainly occurred as I'm sure people in SpaceX studied this and other related projects extensively before beginning their own work.
We now have the technology to send prolonged missions with better safety margins and very nearly have a reusable (and thus more economical) launch stack to launch them.