The Orion Project, famously led by physicist Freeman Dyson in 1958, would have used atomic bombs to propel a spacecraft potentially to interstellar speeds. The project was, however, considered dead after 1963. Why was the project abandoned?

Select one:

a. The concept was considered technically infeasible by the team that researched the technological application of nuclear propulsion.

b. The Partial Test Ban Treaty of 1963 prohibited the use of nuclear weapons in space.

c. There was a lack of volunteers willing to make the sacrifice of a multi-generational one-way voyage into the unknown.

d. All of the above