Radiometer effect in space missions to test the equivalence principle

Nobili, A. M.; Bramanti, D.; Comandi, G. L.; Toncelli, Raffaella; Polacco, E.; Catastini, G.

doi:10.1103/physrevd.63.101101

Cited by 20 publications

(18 citation statements)

References 5 publications

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“…In this configuration disturbances along the cylinders' axes, such as the radiometer effect, are not a limitation. In 1D sensors the radiometer effect, caused by the residual gas in combination with temperature gradients across the axes of the cylinders, is a well known differential systematic effect competing directly with the violation signal which sets severe requirements ( [38] [39]).…”

Section: The Ideas Behind Ggmentioning

confidence: 99%

‘Galileo Galilei’ (GG): space test of the weak equivalence principle to 10 ⁻¹⁷ and laboratory demonstrations

Nobili

Shao

Pegna

et al. 2012

Class. Quantum Grav.

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The small satellite ‘Galileo Galilei’ (GG) will test the universality of free fall and hence the weak equivalence principle which is the founding pillar of general relativity to 1 part in 1017. It will use proof masses whose atoms differ substantially from one another in their mass energy content, so as to maximize the chance of violation. GG will improve by four orders of magnitude the current best ‘Eöt-Wash’ tests based on slowly rotating torsion balances, which have been able to reach their thermal noise level. In GG, the expected violation signal is a relative displacement between the proof masses of ≃ 0.6 pm caused by a differential acceleration aGG ≃ 8 × 10−17 ms−2 pointing to the center of mass of the Earth as the satellite orbits around it at νGG ≃ 1.7 × 10−4 Hz. GG will fly an innovative acceleration sensor based on rapidly rotating macroscopic test masses weakly coupled in 2D which up-converts the signal to νspin ≃ 1 Hz, a value well above the frequency of natural oscillations of the masses relative to each other νd = 1/Td ≃ 1/(540 s). The sensor is unique in that it ensures high rotation frequency, low thermal noise and no attenuation of the signal strength (Pegna et al 2011 Phys. Rev. Lett. 107 200801). A readout based on a very low noise laser interferometry gauge developed at Jet Propulsion Laboratory (≃ 1 pm Hz−1/2 at 1 Hz demonstrated) allows the short integration time to be fully exploited. A full scale sensor with the same degrees of freedom and the same dynamical features as the one to fly in GG has been setup on ground (GGG). The proof masses of GGG are affected by acceleration and tilt noise acting on the rotating shaft because of ball bearings and terrain microseismicity (both absent in space). Overall, by means of appropriate 2D flexure joints, these noise sources have been reduced by a factor almost 105 down to a differential acceleration between the proof masses of ≃ 7 × 10−11 m s−2 (at 1.7 × 10−4 Hz up-converted by rotation to ≃ 0.2 Hz). The corresponding noise in the relative displacements of the proof masses, read by co-rotating capacitance bridges, is ≃ 180 pm, which is 300 times larger than the target in space. GGG error budget shows that it can reach a differential acceleration sensitivity aGGGgoal ≃ 8 × 10−16 m s−2, not limited by thermal noise. This value is only a factor 10 larger than what GG must reach in space to meet its target, and slightly smaller than the acceleration noise of the torsion balance. It can be achieved partly by means of weaker joints and an optimized mechanical design—so as to improve the attenuation factor—and partly by replacing the current ball bearings with much less noisy air bearings (also used in torsion balance tests) so as to reduce input noise. A laser gauge readout with noise level rlaser-ro ≃ 30 pm Hz−1/2 at 0.2÷3 Hz will be implemented.

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Section: The Ideas Behind Ggmentioning

confidence: 99%

‘Galileo Galilei’ (GG): space test of the weak equivalence principle to 10 ⁻¹⁷ and laboratory demonstrations

Nobili

Shao

Pegna

et al. 2012

Class. Quantum Grav.

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“…Appearing parallel to Brownian disturbances, the anomalous fluctuations in microbalance weight measurements [9] and precise testing of the equivalence principle carried out in space missions [10] due to the seemingly omnipresent temperature inhomogeneities in the ambient residual gas and along the surfaces of the measuring devices are other implications of thermal transpiration.…”

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confidence: 99%

Thermal Transpiration at the Microscale: A Crookes Cantilever

et al. 2003

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Local temperature inhomogeneities in systems containing micron and submicron objects can result in unexpected consequences. If the mean free path of the host gas constituents is comparable to a characteristic length of the system, then a net exchange of momentum occurs between the constituents and the involved surfaces. For a given temperature gradient and a given pressure range, this results in the presence of Knudsen and Knudsen-like forces (KF). The pressure dependence of these forces has been studied using a microelectromechanical system composed of a microcantilever near a substrate surface. Nano-Newton scale KF are observed by the bending of the microcantilever as monitored by the charge variation on the microcantilever-substrate assembly in a capacitive mode.

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“…Were such a spurious effect, at some point, detected above thermal noise in SUEP, the ratio (10) in favor of SUREF would not prevent its separation from the signal unless the observed ratio between the two effects is as theoretically expected. Another disturbance competing with the signal, that questions the use of SUREF as a zero-check sensor is the radiometer effect, which is proportional to the residual pressure around the test cylinders and to the temperature gradient between the two ends of its sensitive/symmetry axis [30].…”

Section: Thermal Noise Systematic Errors and The "Zero-check" Smentioning

confidence: 99%

Testing the equivalence principle in space after the MICROSCOPE mission

Nobili

Anselmi

2018

Phys. Rev. D

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Tests of the Weak Equivalence Principle (WEP) can reveal a new, composition dependent, force of nature or disprove many models of new physics. For the first time such a test is being successfully carried out in space by the MICROSCOPE satellite. Early results show no violation of the WEP sourced by the Earth for Pt and Ti test masses with random errors (after 8.26 d of integration time) of about 1 part in 10 14 , and systematic errors of the same magnitude. This result improves by about 10 times over the best ground tests with rotating torsion balances despite 70 times less sensitivity to differential accelerations, thanks to the much stronger driving signal in orbit. The measurement is limited by thermal noise from internal damping in the gold wires used for electrical grounding, related to their fabrication and clamping. This noise was shown to decrease when the spacecraft was set to rotate faster than planned. The result will improve by the end of the mission, as thermal noise decreases with more data. Not so systematic errors. We investigate major nongravitational effects and find that MICROSCOPE's "zero-check" sensor, with test masses both made of Pt, does not allow their separation from the signal. The early test reports an upper limit of systematic errors in the Pt-Ti sensor which are not detected in the Pt-Pt one, hence would not be distinguished from a violation. Once all the integration time available is used to reduce random noise there will be no time left to check systematics. MICROSCOPE demonstrates the huge potential of space for WEP tests of very high precision and indicates how to reach it. To realize the potential, a new experiment needs the spacecraft to be in rapid, stable rotation around the symmetry axis (by conservation of angular momentum), needs high quality state-of-the-art mechanical suspensions as in the most precise gravitational experiments on ground, and must allow multiple checks to discriminate a violation signal from systematic errors. The design of the "Galileo Galilei" (GG) experiment, aiming to test the WEP to 1 part in 10 17 unites all the needed features, indicating that a quantum leap in space is possible provided the new experiment heeds the lessons of MICROSCOPE.

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Radiometer effect in space missions to test the equivalence principle

Cited by 20 publications

References 5 publications

‘Galileo Galilei’ (GG): space test of the weak equivalence principle to 10 ⁻¹⁷ and laboratory demonstrations

‘Galileo Galilei’ (GG): space test of the weak equivalence principle to 10 ⁻¹⁷ and laboratory demonstrations

Thermal Transpiration at the Microscale: A Crookes Cantilever

Testing the equivalence principle in space after the MICROSCOPE mission

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Radiometer effect in space missions to test the equivalence principle

Cited by 20 publications

References 5 publications

‘Galileo Galilei’ (GG): space test of the weak equivalence principle to 10 −17 and laboratory demonstrations

‘Galileo Galilei’ (GG): space test of the weak equivalence principle to 10 −17 and laboratory demonstrations

Thermal Transpiration at the Microscale: A Crookes Cantilever

Testing the equivalence principle in space after the MICROSCOPE mission

Contact Info

Product

Resources

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‘Galileo Galilei’ (GG): space test of the weak equivalence principle to 10 ⁻¹⁷ and laboratory demonstrations

‘Galileo Galilei’ (GG): space test of the weak equivalence principle to 10 ⁻¹⁷ and laboratory demonstrations