Human spaceflight: diversify the portfolio, Alan Stern, Space Review

"The American people expect big things from our nation's human space flight enterprise. Tragically, however, for the past 20+ years, our country's civil human spaceflight effort hasn't been able to deliver big things, such as historic exploration milestones at far away destinations, or advancing the cause of easy human access to near-space locales. What we need now is more than just a flexible path. We need parallel paths. Instead, human spaceflight in the United States has struggled just to keep its sole domestic transportation system, the Space Shuttle, flying a few times per year, and to complete the assembly of its sole destination--the International Space Station."