A lot of the focus is on the massive speed, distance, and power challenges.

We Are Crippled Because We Cannot Really Build in Space
The most technically feasible ways to start making much faster progress to making travel around the solar system routine and fast and then to build a foundation for interstellar flight is to build large and light space structures.

Fully reusable rockets are the game changer that SpaceX is creating now. The next steps are robotic construction capabilities and megawatt and gigawatt power. No matter what the large power source is we have to build large in space to radiate the heat from the large power systems.

Going 400 Times Faster to Get to 10% of the Speed of Light

To convey the challenge of reaching 10% lightspeed, consider the improvements between the 1977 Voyager and the 2011 Juno missions. In roughly three decades there was a four-fold increase in speed. At that rate, it would take another 130 years to reach 10% lightspeed. The gap between achieved speeds and the goal of 0.1c is a factor of 400 (Juno achieved 0.00025c). The technical challenge is to increase spacecraft ?V by at least 400 times more than presently possible with chemical rockets.