Subject: Microscope Date: Tue, 04 Dec 2001 20:06:44 +0100 From: Anna Nobili To: Prof David Southwood CC: Prof Bo Andersen , "Prof M. Grewing" , Prof Giovanni F Bignami To: Prof David Southwood, Director of ESA Science Programme CC: Prof. Bo Andersen, Chairman of ESA Science Programme Committee Prof M. Grewing, Chairman of ESA Space Science Advisory Committee Prof G.F. Bignami, ASI Scientific Director Dear Professor Southwood: Enclosed is a manuscript on "Radiometer effect in the MICROSCOPE space mission". It will take some time for it to be published, but I think you should be informed of its conclusions at this point. Motivated by a recent paper published by the MICROSCOPE scientists (Touboul & Rodrigues, Class. Quantum Grav. 18, 2487, 2001) we have re-examined the radiometer effect for this experiment. We find that our previous evaluation (Nobili et al., Phys. Rev. D Rapid Communications, 63, 101101, 2001) is in agreement with the estimate made by the mission scientists; we point out that it is a systematic effect (not noise) and show why, for MICROSCOPE, it is far more relevant than it is for LISA despite the higher target sensitivity of LISA accelerometers. At present there is no experimental evidence that the thermal gradients which generate the radiometer effect in MICROSCOPE will be as small as required. For that reason we have addressed the issue as to how this disturbance can be distinguished from the signal. We found no way to separate the two. Indeed, it turns out that even the second MICROSCOPE accelerometer, with test cylinders both manufactured in Platinum for checking purposes, will not allow the radiometer effect to be separated, unless its design is substantially modified. The risk is that a well known, classical effect could be interpreted as a violation of the Equivalence Principle, which would invalidate General Relativity. I am aware that MICROSCOPE is mostly a French mission. However, I remember that during the Stockholm Workshop on small national missions in Europe and the role of ESA, you have stressed that ESA's contribution should be an endorsement of the scientific content and merit of the mission, not of the national interests. Best Regards, Anna Nobili ************************************************************************** Anna M Nobili tel +39 050 844252; fax +39 050 844224 Gruppo di Meccanica Spaziale mobile +39 347 2522634 Dipartimento di Matematica Universita' di Pisa Via Filippo Buonarroti 2 I-56127 Pisa, Italia nobili@dm.unipi.it "Galileo Galilei" (GG) Project Webpage: http://eotvos.dm.unipi.it/nobili PGB (Pico Gravity Box) Webpage: http://eotvos.dm.unipi.it/nobili/pgb Anna Nobili: http://eotvos.dm.unipi.it/nobili/homenobili.html ************************************************************************** --------------------------------------------------------------------- Name: radiometer_microscope.pdf radiometer_microscope.pdf Type: Acrobat (application/pdf) Encoding: base64