Explorers have made breakthroughs in many fields of astrophysics. The science
from both these missions contributed to three Nobel Prizes - Giacconi (2002),
Mather, and Smoot (2006). Explorers have: marked the definitive beginning of
precision cosmology, discovered that short gamma-ray bursts are caused by
compact star mergers and have measured metalicity to redshifts z>6. NASA
Explorers do cutting-edge science that cannot be done by facility-class
instruments. The Explorer program provides a rapid response to changing science
and technology, to enable cutting-edge science at moderate cost. Explorers also
enable innovation, and engage & train scientists, managers and engineers,
adding human capital to NASA and the nation. The astrophysics Explorer launch
rate now being achieved is 1 per 3 years, and budget projections are in the
$150M/year range for the next five years. A newly Vigorous Explorer Program
should be created to: 1. Reach the long-stated goal of annual astrophysics
launches; 2. Find additional launch options for Explorers and actively
encourage cost savings in launchers and spacecraft, such as new commercial
vehicles and innovative partnerships. 3. Mitigate risk via stronger technical
development and sub-orbital programs, and through longer, more thorough, Phase
A programs, potentially reducing the need for a 30% contingency; 4. Strive to
protect the funding for missions that have reached Phase B, to prevent
significant launch slips and cancellations, with a goal of 4 to 5 years from
Phase B to launch; 5. Review the project management procedures and requirements
to seek cost reductions, including the risk management strategy and the review
and reporting process; 6. Review and possibly modify the cost caps for all
Explorer classes to optimize scientific returns per dollar. [ABRIDGED]
