Your Editorial and News Feature on the James Webb Space Telescope (JWST) correctly point out that large missions are difficult for NASA to accommodate during times of constrained budgets Nature 440, 127 and 140–143; 2006). But you do not explore what the community gives up if the largest missions such as JWST are sacrificed or delayed.
These ‘flagship’ missions are expensive because they are not merely large but scientifically transformational. One of the most intellectually significant, and humbling, scientific discoveries of our lifetime is that the atoms and forces of which we and our environment are made and that hold us together are but a trace contaminant of the true composition of the Universe, which is 96% dark matter and dark energy. These and similar discoveries simply could not have been made by a large number of low-cost space-science missions.
JWST has similar paradigm-breaking capabilities, in fields as diverse as the search for life-forming mechanisms on extra-solar planets and the birth of galaxies. In the era when it is scheduled to fly, all the current great observatories (Hubble, Chandra and Spitzer) will have completed their missions, or nearly so. A decision to give up on a small number of flagship missions is not merely a decision of economics and resource distribution, but a fundamental decision to avoid solving the grandest problems of science at a time when we know that they are within our reach.