Subject: Radiometer effect in the microscope space mission Date: Fri, 11 Jan 2002 16:03:18 +0100 From: Anna Nobili To: Dr Pierre Touboul CC: Dr Richard Bonneville , Dr Francois Mignard , Dr Gilles Metris , Prof Stefano Vitale , Prof Roberto Battiston , Prof Giovanni F Bignami , "Prof M. Grewing" , Prof Bo Andersen , Prof David Southwood To: Pierre Touboul, ONERA CC: R. Bonneville, CNES F. Mignard, G. Metris, CERGA S. Vitale, R. Battiston, FPAG G.F. Bignami, ASI M. Grewing, SSAC Bo Andersen, SPC D. Southwood, ESA Subject: Radiometer effect in the Microscope space mission Dear Pierre: In your message to me dated December 10 you mentioned a forthcoming careful answer to the manuscript "Radiometer effect in the Microscope space mission". I wish to inform you that in the meantime this manuscript has been revised (PDF file enclosed). We have become aware of the LISA requirement on fluctuations of the temperature difference across the proof mass cavity, and this information has allowed us to make a quantitative comparison between LISA and Microscope. We conclude that, in the most favorable assumption that Microscope will meet the LISA requirements, the radiometer effect will still be twice as large as the target signal of an equivalence principle (EP) violation to 1 part in 10^15. If only the residual pressure will not be as required in LISA, but 10 times larger --as you in fact expect in Microscope-- the radiometer effect will exceed the signal by a factor 20. Since it is a systematic effect (not noise), with the same frequency and phase as the signal, it could be interpreted as an EP violation to 2 parts in 10^14, not far from torsion balance experiments on the ground which have already ruled out any violation larger than about 1 part in 10^13. Moreover, the Pt-Pt accelerometer, supposedly to be used for checking purposes, will not check for the radiometer effect because in its current design it is insensitive to it. I would appreciate it very much if you could respond to the issues raised in this manuscript with high priority. They are directly relevant to the Announcement of Opportunity recently issued by CNES/ESA for science contributions to Microscope. The AO is centered on the single scientific goal of testing the equivalence principle to 1 part in 10^15, a goal that we argue cannot be achieved, unless evidence is provided that thermal gradients will be controlled well enough for the radiometer effect to be smaller than the signal. This may be possible, but you should show how and to what level. Microscope is going to be the first mission in fundamental physics in Europe to fly on a dedicated satellite. And with direct ESA involvement. Coming short of its scientific target, and announcing a wrong result on such a relevant matter as the validity of General Relativity, would inevitably weaken our community. At times in which resources are diminishing and competition is increasing, that would be a serious threat for future missions in this field. I hope this makes it clear why I am concerned. Best regards, Anna ************************************************************************** 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_revised.pdf radiometer_microscope_revised.pdf Type: Acrobat (application/pdf) Encoding: base64