Sergio Nozzoli

Methodology and instrumentation for testing the weak equivalence principle in stratospheric free fall

The use of the GiZero free-fall facility for testing the weak equivalence principle is discussed in this article. GiZero consists of a vacuum capsule, released from a balloon at an altitude of 40 km, which shields an experimental apparatus free falling inside the capsule itself. The expected residual acceleration external to the detector is 10−12 g (with g the Earth’s gravitational acceleration) for the 30 s free fall. A common-mode rejection factor of about 10−4 reduces the residual noise differential output to only 10−16 g. The gravity detector is a differential accelerometer with two test masses with coincident center of masses (i.e., zero baseline) with capacitive pick ups. Preparatory experiments have been conducted in the laboratory with a precursor detector by measuring controlled gravity signals, at low frequency, and by observing the Luni-Solar tides. The estimated accuracy in testing the weak equivalence principle, with a 95% confidence level, is 5×10−15 in a 30 s free fall. When compared to orb...

The high sensitivity Italian Spring Accelerometer (ISA) for fundamental physics in space

Abstract Many space experiments in fundamental physics require accelerometers of high sensitivity. We present here the “Italian Spring Accelerometer” (ISA), operating at low frequencies (10−4 ÷ 1 Hz), whose sensitivity is expected to be better than 10 −12 g Hz . An ISA prototype has been completed and used for ground tests. We describe ISA and report the results obtained from the exprimental measurements. We have conceived a differential accelerometer based on the same physical principles as ISA which, if operated at low temperatures, could reach a sensitivity better than 10 −14 g Hz and be of interest for testing the Weak Equivalence Principle in short-time free fall conditions.

Developments of the general relativity accuracy test (GReAT): a ground-based experiment to test the weak equivalence principle

Some future tests of the weak equivalence principle (WEP) with laboratory-size proof masses are likely to be conducted in freefall conditions in order to improve the test accuracy substantially. Some years ago the authors of this paper proposed to test the WEP in a vertical freefall inside a capsule released from a high-altitude balloon. The estimated accuracy in testing the WEP, with a 95% confidence level, is a few parts in 1015 in a 30 s freefall. When compared with other proposed orbital freefall experiments and ground-based tests, the vertical freefall retains some key advantages of the former without some of the disadvantages of the latter. Moreover, a two orders of magnitude increase in the accuracy of testing the WEP could be achieved with an affordable experiment that allows us to recover the detector and repeat the launches at short time intervals.

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 10(15) 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 ∼ 10(5)) 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.

Observations of mount etna seismicity during the 2002–2003 eruption based on deep-sea gravimeter data

This paper concerns observations made by a broadband deep-sea gravimeter installed on the plat-form of the SN-1 multiparameter seafloor observatory. The observatory was deployed at a distance of 25 km from the east coast of Sicily in southern Italy at a depth of 2105 m and was operated in a self-contained mode from October 2002 to February 2003 (134 days). The proximity to Mount Etna and the period of eruptive activity starting in late October 2002 lent added interest to this experiment. The seismic activity of Mount Etna, as recorded by the gravimeter, is characterized by the presence of two signal types, viz., a long-period volcanic tremor of variable amplitude and volcano-tectonic earthquakes. The bulk of energy in the long-period tremor occurs in the spectral interval between 2 and 5 s. The long-period seismic signals due to volcanic and global earthquakes were used to estimate resonant characteristics for Etna’s heterogeneous structures.

Testing deviations from the inverse square law with a freely falling gravity gradiometer at Balloon altitudes

SummaryWe discuss a null experiment to search for the fifth force at ranges around 10 km. It is proposed to use a three-axis gravity gradiometer to measure the trace of the Earth gravity tensor from a freely falling elevator dropped by a balloon. The main error sources are considered to some extent.

Testing the Weak Equivalence Principle with a free-fall experiment from a balloon

The paper describes a free-fall facility, called enhanced g-zero, to be dropped from a balloon at an altitude of 40–45 km for testing the Equivalence Principle. The free-fall duration is 30 s for a non-propelled capsule. Present estimates indicate that this facility provides an acceleration noise, away from the walls of the evacuated capsule, not to exceed 10−12 g during the fall. The envisaged technique for testing the Equivalence Principle involves the measurement of differential accelerations between two test masses of different materials that are part of a high-sensitivity detector. The detector is housed inside an instrument package cooled at the temperature of liquid helium. This package is first spun about a horizontal axis at a frequency of typically 1 Hz, for providing gyroscopic stabilization and modulating the gravity signal, and then released inside the falling capsule. The estimated accuracy in testing the Equivalence Principle, with 95% confidence level, is 5 parts in 1015 in a 30-s free fall.

GiZero: A free falling capsule for short term low gravity experiments

Abstract Results from the feasibility study of the “GiZero” free falling capsule are reported. GiZero is a capsule designed to perform experiments in free fall from ballooning at stratospheric altitude. It is shown that the residual gravitational disturbances inside GiZero during 20 s of free fall are smaller than 10 −12 g Hz . The study has been funded by ASI (Agenzia Spaziale Italiana) for the capsule to be operated at the balloon launching site of the Agency in Trapani-Milo (Sicily, Italy). GiZero is a vacuum capsule to be released from balloon at an altitude of about 40 km; it shields from air drag and solar radiation an experimental platform which can be released from the top of the capsule and recaptured at the opposite side after 20 s of free fall. We also describe in brief how GiZero could be used for experiments in fundamental physics, for applied sciences in microgravity conditions and for technological tests of hardware later to be flown in space.

ISA — An Accelerometer to Detect the Disturbing Accelerations Acting on the Mercury Planetary Orbiter of the BepiColombo ESA Cornerstone Mission to Mercury: on Ground Calibration

To reach the ambitious goals of the Radio Science Experiment of the BepiColombo space mission to Mercury, among which the planet structure and rotation and test Einstein’s theory of General Relativity (GR) to an unprecedented accuracy, an accelerometer has been selected to fly on‐board the MPO (Mercury Planetary Orbiter), the main spacecraft of the two to be placed around the innermost planet of our solar system around 2017. The key role of the on‐board accelerometer is to remove from the list of unknowns the non‐gravitational accelerations that disturbs the pure gravitational orbit of the MPO spacecraft in the strong radiation environment of Mercury. In this way the “corrected” orbit of the MPO may be regarded as a geodesic in the field of Mercury. Then, thanks to the very precise tracking from Earth, the possibility to study Mercury’s center‐of‐mass around the Sun and estimate several parameters related to the planet structure and verify the theory of GR. The selected accelerometer named ISA (Italian Sp...

The BepiColombo Radio Science Experiment and the Non‐Gravitational Perturbations to the Mercury Planetary Orbiter orbit: key role of the Italian Spring Accelerometer

The advantages of an on‐board accelerometer are outlined in the case of the Bepi‐Colombo mission to Mercury with respect to the modeling of the non‐gravitational perturbations at work in the strong radiation environment of Mercury. The readings from the Italian Spring Accelerometer guarantees a very significant reduction of the non‐gravitational accelerations impact on the space mission accuracy, especially of the strong direct solar radiation pressure.