Would the Juno program be more cost effective if the spacecraft took a direct flight to Jupiter rather than using gravitational pull from planets, which took nearly 5 years instead of say, 2 years? Yes, there are booster and other hardare costs, but the program would save 3 years of engineers and scientists costs (sorry guys from bean counters). Was that option considered in detail?
Was that option considered in detail?
Almost certainly not. This question is based on the false assumption that staffing levels remain more or less constant across all phases of flight. This is not the case. Staffing is very light during passive phases such as coast.
Requirements for communications mandate a large antenna. No matter how good we become at miniaturization, a large antenna will always be required; it's a matter of physics. There are miniaturization limits on the scientific instruments. Limitations of launch vehicles restrict how much energy can be applied to a payload. This energy translates to velocity, and the larger the payload mass, the smaller the velocity. Sophisticated missions such as Juno, along with most of missions to the outer planets, would not be possible without using gravity assists.
The probe was doing very little during the period it was cruising, and needed relatively little manpower for supervision. I think we can assume that the scientists waiting for it to arrive were not idle in the intervening time.
A direct flight would require a bigger rocket, bigger than the available ones. A direct flight with an available rocket would require a much smaller probe with less mass for instruments and more fuel. The mission designers tested a lot of different flight plans and looked for a good compromise between flight time and instruments mass. They did not have the option of using a very powerful and fast rocket which existed only in theory but not in practice.