Measurement of small forces in the physics of gravitation and geophysics

The measurement of weak forces or accelerations is of fundamental importance in a variety of problems in science and technology. This topic is addressed in this paper with particular attention to gravity measurements. A general review of the current gravity measurement techniques in geophysics, general relativity and gravitation is first presented. Then, a general description of the instruments used for gravitational measurements and a brief analysis of the noise sources are discussed

Tidal tilts observations in the Gran Sasso underground laboratory

A new tiltmeter, based on the technology for building a space-borne high-sensitivity accelerometer and manufactured at IFSI/CNR, has been operating during several years in the INFN Gran Sasso underground laboratory. The results of the analysis of a three-year data set, processed with the program package ETERNA, to estimate earthtidal parameters are reported. For the best series of data (1998) tide measurement accuracies are: 0.5–1% for the M2 (lunar principal) amplitude and 3–4% for the O1 (lunar declination) amplitude. The tiltmeter installed at a depth of 1400m shows no clear evidence of meteorological effects. Observed tidal parameters are compared with theoretical tidal parameters predicted for a non-hydrostatic inelastic Earth model and demonstrate good agreement for the M2 component. Due to the high accuracy of the tidal components prediction (better than 1%) tidal measurements were used to estimate the long-term stability of the instrument response

Experimental gravitation and geophysics

Seismic noise is the major obstacle to performing sensitive measurements of the gravitational field on the ground. The INFN (Istituto Nazionale di Fisica Nucleare) underground laboratory in Gran Sasso, L’Aquila(Italy), seems to be a favourable place from the environmental noise point of view. This paper describes briefly two, relatively low cost, gravity experiments that can be performed in the underground laboratory: a) A measurement of preferred-frame and preferred-location effects. b) A test of the equivalence principle. Preliminary experimental data of the seismic noise are also presented

Deep Sea Gravity Measurements: GEOSTAR-2 Mission Results

A new concept gravity meter with sensitivity close to Hz ms / 10 2 8 − − in the range of 10 -5 −1Hz intended for observation of the vertical component of the Earth gravity and teleseismic waves was implemented at the Istituto di Fisica dello Spazio Interplanetario (IFSI), CNR and successfully operated during the GEOSTAR-2 mission. The gravimeter has demonstrated a capability to operate for long time in an autonomous regime and a good reliability for operation in extreme environments; at the same time the experimental measurements gave the information for the further gravimeter’s implementation. Results of observation and data analysis included the registration of seismic waves excited by global earthquakes and the evaluation of the low frequency modes of free oscillations of the Earth are reported

Deep Sea Gravity Measurements: GEOSTAR-2 Mission Results

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The use of a cubesat to validate technological bricks in space

In the framework of the FP7 program FISICA (Far Infrared Space Interferometer Critical Assessment), we are developing a cubesat platform which will be used for the validation in space of two technological bricks relevant for FIRI. The first brick is a high-precision accelerometer which could be used in a future space mission as fundamental element for the dynamic control loop of the interferometer. The second brick is a miniaturized version of an imaging multi-aperture telescope. Ultimately, such an instrument could be composed of numerous space-born mirror segments flying in precise formation on baselines of hundreds or thousands of meters, providing high-resolution glimpses of distant worlds. We are proposing to build a very first space-born demonstrator of such an instrument which will fit into the limited resources of one cubesat. In this paper, we will describe the detailed design of the cubesat hosting the two payloads

Testing the Equivalence Principle in an Einstein Elevator: Detector Dynamics and Gravity Perturbations

We discuss specific, recent advances in the analysis of an experiment to test the Equivalence Principle (EP) in free fall. A differential accelerometer detector with two proof masses of different materials free falls inside an evacuated capsule previously released from a stratospheric balloon. The detector spins slowly about its horizontal axis during the fall. An EP violation signal (if present) will manifest itself at the rotational frequency of the detector. The detector operates in a quiet environment as it slowly moves with respect to the co-moving capsule. There are, however, gravitational and dynamical noise contributions that need to be evaluated in order to define key requirements for this experiment. Specifically, higher-order mass moments of the capsule contribute errors to the differential acceleration output with components at the spin frequency which need to be minimized. The dynamics of the free falling detector (in its present design) has been simulated in order to estimate the tolerable errors at release which, in turn, define the release mechanism requirements. Moreover, the study of the higher-order mass moments for a worst-case position of the detector package relative to the cryostat has led to the definition of requirements on the shape and size of the proof masses

Measurement of the quality factor of a new low-frequency differential accelerometer for testing the equivalence principle

A cryogenic differential accelerometer has been developed to test the weak equivalence principle to a few parts in 1015 within the framework of the general relativity accuracy test in an Einstein elevator experiment. The prototype sensor was designed to identify, address, and solve the major issues associated with various aspects of the experiment. This paper illustrates the measurements conducted on this prototype sensor to attain a high quality factor (Q ∼ 105) at low frequencies (<20 Hz). Such a value is necessary for reducing the Brownian noise to match the target acceleration noise of 10−14 g/√Hz, hence providing the desired experimental accuracy.AstronomyPhysic

TEPEE/GReAT (General Relativity Accuracy Test in an Einstein Elevator): Ready to start

TEPEE/GReAT is an experiment aimed at testing the principle of equivalence at a level of accuracy equal to 5 parts in 1015 by means of a differential acceleration detector free falling inside a co-moving, cryogenic, evacuated capsule, released from a stratospheric balloon. The detector is spun about a horizontal axis during the fall in order to modulate the equivalence principle violation signal at the spin frequency. Thanks to the recent funding of the Italian side, the project is ready to enter its second phase. The main activities related to detector prototype (both non-cryogenic and cryogenic versions) development and testing, free-fall tests, signal extraction from noise (in particular related to the common-mode rejection factor) and flight model requirements are discussed