WHY Return to the Moon?
Mans existence in space is dependent on life support and radiation protection. The Moon has no atmosphere and Mars very little. Radiation impact on biologics and electronics is immediate. That impact increases with distance from the Earth, the solar cycle (solar maximum through solar minimum through solar maximum) and Galactic Cosmic Radiation (GCR). We need new technology for radiation protection and that is just one reason to learn what we must from the Moons environment - it is a very big reason considering our planets magnetosphere is in constant change.
The hurdles we face with going to the Moon are much the same hurdles we'd face in going to Mars or asteroids. Let's use the Moon and lunar environment to learn what it takes for humans to survive. Life support and fuel for spacecraft have been well addressed to our current operations. As we press beyond LEO they will become more demanding.
Solutions lead to overcoming issues..
What would the primary objectives be? I submit:
"The Moon is a Harsh Mistress" is the title of a book by Robert Heinlein (one of my favorites). Use of the title is not connected to the book. The lunar environment is the most dangerous space environment close to the Earth for humans to be in...what better place to learn from?
We know what exists on the Moon includes: water-ice; hydrogen; helium-3; silicon; iron; magnesium; calcium; aluminum; manganese; sodium and titanium. Foun in trace amounts are carbon; uranium, thorium and potassium. All of thse can be used for mans survival and transport through space. The technology to obtain and refine these resources just for space purposes will result in a wealth in patents and useable products.