The Skylark of Space - E. E. Smith

The novel begins with the accidental discovery, in a Government laboratory in Washington D. C., of a form of clean nuclear power. Our hero, Dr. Richard Seaton, uses this power to build first a flying belt and then an interstellar spaceship. He later discovers that the process operates by generation and manipulation of gravity fields.When his government coworkers do not believe him, Seaton acquires rights to his discovery from the government and commercializes it with the aid of his friend, millionaire inventor Martin Crane. A former colleague, Dr. Marc DuQuesne, joins with the unscrupulous World Steel Corporation to try to steal Seaton's invention. The resulting conflict escalates, as Seaton and Duquesne develop greater and greater technical capabilities and enlist more and more powerful alien races as allies.. (Summary by Wikipedia)