Metaphor, he's comparing darts to segregation.
He claims that the exploration of space is in the definite future and America needs to join in to stay a powerful nation.
Answer: The answer is:
Justice and righteousness
Explanation:
As part of his great speech he said:
“There are those who are asking the devotees of civil rights, ‘When will you be satisfied?’ We can never be satisfied as long as our bodies, heavy with the fatigue of travel, cannot gain lodging in the motels of the highways and the hotels of the cities. We cannot be satisfied as long as the Negro’s basic mobility is from a smaller ghetto to a larger one. We can never be satisfied as long as a Negro in Mississippi cannot vote and a Negro in New York believes he has nothing for which to vote. No, no, we are not satisfied, and we will not be satisfied until justice rolls down like waters and righteousness like a mighty stream.”
