Are Robert Grissom and Gus Grissom related?

No, Robert Grissom and Gus Grissom are not related. Gus Grissom, born in 1926, was an American astronaut and one of the original Mercury Seven astronauts. Robert Grissom is not a widely recognized figure in connection with Gus Grissom, and there is no known familial relationship between them.