Small spacecraft missions—the US scene

Abstract

In current NASA terms a fully fuelled small spacecraft weighs less than 1000 kg. It may be recalled that the first US spacecraft (1958) weighed only 14 kg (virtually a NanoSat by today's standard) and by contrast the Hubble Space telescope (1990) is 10.8 tonnes and was carried aloft inside another spacecraft (the 80 tonne Shuttle). Since 1992 NASA has embarked upon a policy of limiting cost and schedule aspects for its smaller scientific spacecraft in order to promote a structured, but competitive, programme for more frequent research investigations. This marks a departure from the sporadic, expensive, annually reviewed missions of the past. Already this policy has met with success at a time when research budgets are shrinking. The role of these small spacecraft is often complementary to the infrequent class of large observatories and can serve to develop steadily technologies that are then made available to all US programmes. However, the development of low-cost launchers is lagging behind expectations and some short-cuts on spacecraft reliability are questioning the new philosophy. NASA is an organization consisting of many centres, which have to some extent overlapping or complementary programmes. This paper is an attempt to present the thread that runs through the everchanging NASA scene.