| |
New Astronomy, Vol. 8 (5) (2003) pp. 371-390
© 2002 Elsevier Science B.V. All rights reserved.
PII: S1384-1076(02)00233-6
a
Space Mechanics Group, Department of Mathematics, University of Pisa, I-56127 Pisa, ItalyReceived 19 August 2002; accepted 1 November 2002
Communicated by F. Melchiorri
We have proposed to test the equivalence principle (EP) in low Earth orbit with a
rapidly rotating differential accelerometer (made of weakly coupled concentric test
cylinders) whose rotation provides high frequency signal modulation and avoids severe
limitations otherwise due to operation at room temperature [PhRvD 63 (2001) 101101].
Although the accelerometer has been conceived for best performance in absence of weight,
we have designed, built and tested a variant of it at 1-g. Here we report the results of
measurements performed so far. Losses measured with the full system in operation yield a
quality factor only four times smaller than the value required for the proposed high
accuracy EP test in space. Unstable whirl motions, which are known to arise in the system
and might be a matter of concern, are found to grow as slowly as predicted and can be
stabilized. The capacitance differential read-out (the mechanical parts, electronics and
software for data analysis) is in all similar to what is needed in the space experiment.
In the instrument described here the coupling of the test masses is 24,000 times stiffer
than in the one proposed for flight, which makes it 24,000 times less sensitive to
differential displacements. With this stiffness it should detect test masses separations
of 1.5·10
2
µm, while so far we have achieved only 1.5 µm, because of large perturbations
due to the motor,
the ball bearings, the non-perfect verticality of the systemall of which, however, are absent in
space. The effects of these perturbations should be reduced by 100 times in order to
perform a better demonstration. Further instrument improvements are underway to fill this
gap and also to reduce its stiffness, thus increasing its significance as a prototype of
the space experiment.
PACS: 04.80.Cc;
07.10.h; 06.30.Bp;
07.87.+v
Keywords: Gravitation; Relativity; Instrumentation: detectors; Methods: laboratory; Methods: data analysis
*Corresponding author.
Copyright ©1996-2003 Elsevier Science B.V. All rights reserved.