Sci-Fi book about the Moon being Stolen. It is in three parts. There is a male protagonist. Read late 1980's/early 1990's.

[Badseedgirl]

I think I read this book back in the late 80's early 90's. I'm sorry I can not be more specific.
Part One: The basic plot starts with the sun is stolen by aliens. The protagonist is born underground where a limited number of people sought shelter. I think it might have been a government think tank, but my memory is a little fuzzy about this. Anyway the young man spends his entire youth underground, but decides to escape. I think through some kind of air vent, again memory is vague, but I think I remember a scene with a fan. The young man escapes, and thinks he is going to die from the lack of O2 and cold on the surface.
Start of part 2: Turns out there were still people living on the face of the planet. The aliens were not trying to kill everyone, just most people. There were scientist on moon bases and they were able to do some kind of space hanky panky (sorry again my memory is vague) and started some kind of fusion from two planets, or Jupiter's moons or something. The young man falls in love with a woman who's parent (one of them) also escaped from below ground. The young woman id disgusted because they are like 3rd cousins or something. Turns out because there were so few people on the bases, the new society is scrupulous about keeping track on genealogy. Also the woman is the daughter of the leader of the survivors and lives on the moon bases. The young man doe snot give up and works going to the frozen remote parts of the world looing for artifacts under the tone of ice. Somehow he doesn't necessarily win the girl's heart, but does make himself valuable enough to become the husband and next heir apparent for Leader.
Part 3: So the Man has now worked himself up to being president and finds out that the aliens who stole the sun are still in contact with humans. They were "winnowing the wheat from the chaff" so to speak when they stole the sun. They only wanted people brave enough and smart enough to make the fusion to create the new sun. The aliens have been slowly providing help to the humans, so they will be worthy of space exploration. The Man, not president is horrified when finding this out and somehow over throws the aliens and makes plans to go and steal those same aliens sun.

This story line has stuck with me for 20+ years and I would really like to read this book again, but I have no idea of an author or title.

PLEASE HELP!

[Rainbowheart]

Anything on the Underground Cities list?

[Rosa]

Long shots: Underground Man?
The Rape of the Sun?