Is that USA (United States of America) or UST (United States of Terra)? How bout USSSS (United States of Sol)? Hmmm, the USSSS Enterprise (United States of Sol Space Ship).
In the novels it was the United States of America. I am not sure whether you are familiar with the story, but Rhodan unites the planet to "Terra" and later does build a solar empire. So you are rather close.
I really loved the technical details about the story. Rhodans moon rocket was using NERVA engines for the 3rd stage while the first and second stage were chemical engines. One of the intitial authors was a physicist and that shows (the series has been running for more than 50 years now).
It is funny to hear the accounts of the authors nowadays. E.g. they were really upset that their hero made it to the moon "after" Neil Armstrong. They predicted in 1959 that the first moon landing would not happen until 1972. Their prediction for the political development was not quite correct either. E.g. they predicted an Asian federation from Russia and China (and probably other unnamed communist countries in the region). That never happened. Oddly enough though, it could happen now...
Sorry for the topic drift, it is just one of those childhood memories that I am very fond of