By comparison , Soviet nuclear weapons were much heavier , and the powerful R - 7 rocket was developed to carry them .
Advances in US nuclear weapon technology had led to smaller , lighter warheads , and consequently , rockets with smaller payload capacities .
Soviet nuclear weapons were much heavier , and the powerful R - 7 rocket was developed to carry them .
Advances in US nuclear weapon technology had led to smaller , lighter warheads , and consequently , rockets with smaller payload capacities .