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ASI - Agenzia Spaziale Italiana - Mission and Projects ASI - Agenzia Spaziale Italiana - Mission and Projects


Testing General Relativity

Main Theme Testing General Relativity
Mission Responsibility -  ASI
Launch Date tbd
End of Mission tbd
Current phase Phase A



Galileo Galilei (GG) is a small Italian mission aimed at testing the equivalence principle with an accuracy which has thus far never been achieved. The mission involves the development of a differential accelerometer to be put on board a satellite in Earth orbit in order to measure the acceleration relative to two testing masses with different composition in free-fall in the Earth's gravitational field. In order to demonstrate the feasibility of the accuracy required of the measurement in flight it is necessary to simulate the experiment on Earth; for this purpose a differential accelerometer that reproduces the project of the in-flight experiment, except for the presence of gravity, has been in operation for several years at the Pisa Section of the INFN (currently undergoing improvements). It has already achieved significant results.


The project was developed in close partnership with the Istituto Nazionale di Fisica Nucleare (National Institute of Nuclear Physics - INFN). ASI and INFN have subscribed to a framework agreement for several projects they collaborate in and, in the subsequent phases of the GG programme, will sign a specific agreement that will define the various contributions to the mission.


Scientific Objectives
GG falls into the context of testing basic principles of physics.  Its scope is to obtain an accuracy which has up to this time never been achieved to test the equivalence principle, one part in 1017. The method chosen is to test that all bodies in motion in free fall are subject to the same acceleration, independently of their mass and composition, the direct consequence of the equivalence principle. GG will carry out the best testing of the equivalence principle in the near future.


Italian Contribution
GG is a small Italian mission. The principal investigator is Anna Nobili, of the INFN, Pisa Section, and the Department of Physics of the Università di Pisa (University of Pisa).  International contributions are under definition.