"GALILEO GALILEI" (GG) Pre Phase A Report, ASI (1996)
Overview
GALILEO GALILEI (GG) is a small satellite mission aimed at testing the Equivalence Principle to 1 part in 1017. The key feature of the mission is to modulate the signal of a possible violation of equivalence at high frequency by spinning both the spacecraft and the payload. The answer as to how fast spin can be compatible with an experiment that requires to be sensitive to extremely small forces can be found in classical mechanics and the absence of weight. GG is designed as a system of supercritical rotors in space, in fact very close to being ideal unconstrained rotors, with weak mechanical coupling to provide a number of advantages, discharging among them. A target accuracy one order of magnitude more ambitious than in all previous studies of GG derives from a deeper understanding of supercritical rotation and recent laboratory results obtained within the maiupp GALILEO GALILEI on the GROUND (GGG) experiment.
The GG bus can be regarded as part of the scientific payload itself because the entire satellite design, its attitude and orbit, are driven by the experiment that it carries. A general purpose platform would therefore be difficult to adapt. However, GG needs no new technology, except for one single item that becomes a goal on its own right: the technology of maiupp FIELD EMISSION ELECTRIC PROPULSION (FEEP) for fine compensation of non gravitational forces can be fully validated for the first time on GG.
A high accuracy test of the Equivalence Principle would be an outstanding scientific result -one way or another- which only space can provide. GG would fail by not getting close to its target sensitivity. If the target sensitivity is reached, this rules out violation to that level anyway, and it is a major achievement; whether or not the observed signal can be ascribed to a violation of equivalence will need confirmation in any case by another (possibly different) experiment before becoming a benchmark for fundamental physics of the next decades. The essence of science is repeatibility, and space science can be no exception. This is why GG has been designed with one experimental chamber only: to optimize the experiment, increase reliability, reduce complexity and cost .... and make it happen. All mission proposals for testing the Equivalence Principle in space have now focused on this scientific goal only, coming down in dimensions and cost; two different small missions can strengthen each other in the battle for funding, leaving competition to the scientific and technological issues, where it is highly beneficial. Nowadays this is commonplace for big scientific ground projects where repeatibility is a serious matter of concern regardless of the large amount of resources that big projects need.
In this spirit this Pre-Phase A Report is offered to ESA for a comparative assessment of GG versus MiniSTEP and GEOSTEP. Thanks are due to ESA Directorate of Science for the resourses it has devoted to the assessment process.
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(Anna Nobili- nobili@dm.unipi.it)
Last edited April 24, 1998