here, we discussed post-World War II history and linked it to two aspects of Robert Heinlein's Future History:
the interregnum of space travel;
the likelihood or otherwise of a religious dictatorship in the United States.
Since this discussion had been initiated by references to Poul Anderson's future history, Tales Of The Flying Mountains (New York, 1984), let's look at Flying Mountains history. One historical succession comprises:
the United States of America;
the Asteroid Republic;
the spaceship Astra.
The purposes of the Constitution of the Astra are:
to accomplish man's first venture beyond the Solar System;
to guarantee survival;
to maintain justice and tranquility;
to promote the common welfare;
to procure liberty for the first generation and their posterity.
The Constitution is established for the governance of ship and personnel until the completion of their mission. The voyage will take over forty years, thus two generations. Many who embark will not arrive at Alpha Centauri. Some will be born and die en route. Therefore, the Astra is a "generation ship" (slower-than-light, multi-generation, interstellar spaceship), like those in Heinlein's Future History and Anderson's Psychotechnic History. For the latter, see here.
After exploring the Centaurian system, the Astra might depart for somewhere other than Sol. Thus, "...an unknown number of generations..." (p. 10) would continue to live in the ship. There is both an elected Congress with a president and an Advisory Council. Engineering and Navigation are described as nonelective departments on p. 11. We might have a few posts on the sociopolitical structure within the Astra.