The stated goal of NASA is to go to Mars by the mid 2030s. The first of the vehicles that might take us there, the Space Launch System and Orion, won’t fly people until at least 2021 with the current budget realities. That is over seven years away, or nearly two presidential terms. The political landscape will be totally different by that time, so there is a risk of cancellation before hardware can even get to the launch pad. What NASA needs is a 10-year timeframe for a goal of going to Mars.
NASA’s proposed 2016 budget is just over $18.5 billion, but not all of that is spent on space exploration. Only $4 billion goes to developing exploration hardware, like SLS and Orion, and another $4 billion goes to the International Space Station. If it is assumed that all infrastructure in low earth orbit will be privatized, including ISS, that gives NASA $8 billion a year for deep space exploration. The reality is that NASA needs at least twice that amount to develop all the hardware needed to send humans to Mars.
Going to Mars in 10 years will give the economy a huge boost, much like what happened with the Apollo program in the 60s and 70s. To get to the moon by 1969, the country had to create whole new industries to get there. The economic gains from that program are still being felt today with microprocessors and satellite technology, but more importantly, Apollo inspired a generation of students to go into careers in science and engineering.
It can be expected that a Mars program will have similar results, only this time there is an emerging private spaceflight industry to help lower the cost of getting there. NASA can use the same partnership that is currently being used to promote a private human spaceflight industry to help sustain a human presence on the red planet.
The problem with saying that NASA is to go to Mars in 20 years is that the program can lose focus. If you have a 10-year timeline, you have to focus on what it takes to get there and little else. There’s no need to create a fancy solar electric propulsion system or “better radiation protection” when we already have the technology to get people to Mars safely. We only have to decide that it is time to go.