Four key research areas were listed for the next 3 decades.
The first key area is searching for evidence of cosmic inflation. From now to 2015 this is to be done by analysis of the cosmic microwave background. From 2015 to 2025 gravitational wave astronomy will be employed. Around 2025 the Big Bang Observer will continue by providing the next generation of gravitational wave astronomy.
The second issue is gaining a better understanding of black holes and related relativistic effects. From now to 2015 the Gamma-Ray Large Area Telescope will study the relativistic jets associated with black holes. The James Webb Space Telescope (JWST) will search for evidence of black hole growth and mergers in the early universe. Around 2015 gravitational wave astronomy will be used along with a new X-ray telescope (Constellation-X) to study black hole properties. After 2025 there will be an attempt to image matter falling into black holes.
The third issue is the investigation of dark energy. Up to 2025 this is to be done by studies of the distribution of visible and dark matter. After 2025 the Big Bang Observer will enable measurements of distances to binary systems consisting of neutron stars and black holes in order to better determine the geometry of the universe.
The fourth issue is the study of how galaxies, stars, and stellar planetary systems evolve. From now to 2015 the HST and the JWST will study stars in the earliest galaxies. From 2015 to 2025 Constellation-X will study the dispersal of heavy elements. After 2025 later instruments will study the evolution of nuclei, atoms and molecules.
All this depends, of course, on appropriate priorities being given to these objectives, so that solid science is not crowded out of the budget by ostentatious displays of national vanity in the form of manned junkets to the moon and Mars.
More information on NASA roadmaps is here and here.
Related documents include a report on Science in NASA's Vision for Space Exploration and the details about proposed cosmology research in Universe Exploration: From the Big Bang to Life.
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