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Article ; Online: An Algorithm to Estimate the Power Spectral Density From Allan Deviation.

De Marchi, Fabrizio / Plumaris, Michael K / Burt, Eric A / Iess, Luciano

IEEE transactions on ultrasonics, ferroelectrics, and frequency control

2024 Volume 71, Issue 4, Page(s) 506–515

Abstract: Complex architectures for wireless communications, digital electronics, and space-based navigation interlink several oscillator-based devices such as clocks, transponders, and synthesizers. Estimators characterizing their stability are critical for ... ...

Abstract	Complex architectures for wireless communications, digital electronics, and space-based navigation interlink several oscillator-based devices such as clocks, transponders, and synthesizers. Estimators characterizing their stability are critical for addressing the impact of random fluctuations (noise) on the overall system performance. Manufacturers typically specify this as an Allan/Hadamard Variance (AVAR/HVAR) profile in the time domain. However, stochastic processes constituting the noise are more thoroughly described in the frequency domain by the power spectral density function (PSD). Both are second-moment measures of the time series, but it is only possible to translate unambiguously from the PSD to the AVAR/HVAR, not vice versa, except in the case of a single noise type, a rather unrealistic case. This note presents an analytical method to generate an approximated PSD expressed as a set of power-laws defined in specific intervals in the frequency domain, starting from an AVAR/HVAR expressed as a set of power-laws in the time domain. The proposed algorithm is straightforward to implement, applicable to all noise types (and combinations thereof), and can be self-validated by reconstructing the corresponding AVAR/HVAR by direct computation. Coupling with well-established algorithms relying on the PSD for power-law noise generation, the ensuing method encompasses the capability for generating multicolored noise in end-to-end simulations, as demonstrated hereby for NASA's deep space atomic clock. We also report on the limitations of the algorithm and analytical expressions of the continuous version of the algorithm.
Language	English
Publishing date	2024-03-28
Publishing country	United States
Document type	Journal Article
ISSN	1525-8955
ISSN (online)	1525-8955
DOI	10.1109/TUFFC.2024.3372395
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Book ; Online: Design and performance of a Martian autonomous navigation system based on a smallsat constellation

Molli, S. / Durante, D. / Boscagli, G. / Cascioli, G. / Racioppa, P. / Alessi, E. M. / Simonetti, S. / Vigna, L. / Iess, L.

2022

Abstract: Deciphering the genesis and evolution of the Martian polar caps can provide crucial understanding of Mars' climate system. The growing scientific interest for the exploration of Mars at high latitudes, and the need of minimizing the resources onboard ... ...

Abstract	Deciphering the genesis and evolution of the Martian polar caps can provide crucial understanding of Mars' climate system. The growing scientific interest for the exploration of Mars at high latitudes, and the need of minimizing the resources onboard landers and rovers, motivates the need for adequate navigation support from orbit. We propose a novel concept based on a constellation that can support autonomous navigation of different kind of users devoted to scientific investigations of those regions. We study two constellations, that differ mainly for the semi-major axis, composed of 5 small satellites (based on the SmallSats design being developed in Argotec), offering dedicated coverage of the Mars polar regions. We focus on the architecture of the inter-satellite links (ISL), the key elements providing both ephemerides and time synchronization for the broadcasting of the navigation message. Our concept is based on suitably configured coherent links, able to suppress the adverse effects of on-board clock instabilities and to provide excellent range-rate accuracies between the constellation's nodes. The data quality allows attaining good positioning performance for both constellations with a largely autonomous system. Indeed, we show that ground support can be heavily reduced by employing an ISL communication architecture.
Keywords	Physics - Space Physics
Subject code	629
Publishing date	2022-12-03
Publishing country	us
Document type	Book ; Online
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Book ; Online: The effect of Jupiter oscillations on Juno gravity measurements

Durante, D. / Guillot, T. / Iess, L.

2016

Abstract: Seismology represents a unique method to probe the interiors of giant planets. Recently, Saturn's f-modes have been indirectly observed in its rings, and there is strong evidence for the detection of Jupiter global modes by means of ground-based, ... ...

Abstract	Seismology represents a unique method to probe the interiors of giant planets. Recently, Saturn's f-modes have been indirectly observed in its rings, and there is strong evidence for the detection of Jupiter global modes by means of ground-based, spatially-resolved, velocimetry measurements. We propose to exploit Juno's extremely accurate radio science data by looking at the gravity perturbations that Jupiter's acoustic modes would produce. We evaluate the perturbation to Jupiter's gravitational field using the oscillation spectrum of a polytrope with index 1 and the corresponding radial eigenfunctions. We show that Juno will be most sensitive to the fundamental mode ($n=0$), unless its amplitude is smaller than 0.5 cm/s, i.e. 100 times weaker than the $n \sim\ 4 - 11$ modes detected by spatially-resolved velocimetry. The oscillations yield contributions to Juno's measured gravitational coefficients similar to or larger than those expected from shallow zonal winds (extending to depths less than 300 km). In the case of a strong f-mode (radial velocity $\sim$ 30 cm/s), these contributions would become of the same order as those expected from deep zonal winds (extending to 3000 km), especially on the low degree zonal harmonics, therefore requiring a new approach to the analysis of Juno data.
Keywords	Astrophysics - Earth and Planetary Astrophysics
Subject code	551
Publishing date	2016-10-02
Publishing country	us
Document type	Book ; Online
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Article: A way forward for fundamental physics in space.

Bassi, A / Cacciapuoti, L / Capozziello, S / Dell'Agnello, S / Diamanti, E / Giulini, D / Iess, L / Jetzer, P / Joshi, S K / Landragin, A / Poncin-Lafitte, C Le / Rasel, E / Roura, A / Salomon, C / Ulbricht, H

NPJ microgravity

2022 Volume 8, Issue 1, Page(s) 49

Abstract: Space-based research can provide a major leap forward in the study of key open questions in the fundamental physics domain. They include the validity of Einstein's Equivalence principle, the origin and the nature of dark matter and dark energy, ... ...

Abstract	Space-based research can provide a major leap forward in the study of key open questions in the fundamental physics domain. They include the validity of Einstein's Equivalence principle, the origin and the nature of dark matter and dark energy, decoherence and collapse models in quantum mechanics, and the physics of quantum many-body systems. Cold-atom sensors and quantum technologies have drastically changed the approach to precision measurements. Atomic clocks and atom interferometers as well as classical and quantum links can be used to measure tiny variations of the space-time metric, elusive accelerations, and faint forces to test our knowledge of the physical laws ruling the Universe. In space, such instruments can benefit from unique conditions that allow improving both their precision and the signal to be measured. In this paper, we discuss the scientific priorities of a space-based research program in fundamental physics.
Language	English
Publishing date	2022-11-02
Publishing country	United States
Document type	Journal Article ; Review
ZDB-ID	2823626-9
ISSN	2373-8065
ISSN	2373-8065
DOI	10.1038/s41526-022-00229-0
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Article ; Online: A rigid and weathered ice shell on Titan.

Hemingway, D / Nimmo, F / Zebker, H / Iess, L

Nature

2013 Volume 500, Issue 7464, Page(s) 550–552

Abstract: Several lines of evidence suggest that Saturn's largest moon, Titan, has a global subsurface ocean beneath an outer ice shell 50 to 200 kilometres thick. If convection is occurring, the rigid portion of the shell is expected to be thin; similarly, a weak, ...

Abstract	Several lines of evidence suggest that Saturn's largest moon, Titan, has a global subsurface ocean beneath an outer ice shell 50 to 200 kilometres thick. If convection is occurring, the rigid portion of the shell is expected to be thin; similarly, a weak, isostatically compensated shell has been proposed to explain the observed topography. Here we report a strong inverse correlation between gravity and topography at long wavelengths that are not dominated by tides and rotation. We argue that negative gravity anomalies (mass deficits) produced by crustal thickening at the base of the ice shell overwhelm positive gravity anomalies (mass excesses) produced by the small surface topography, giving rise to this inverse correlation. We show that this situation requires a substantially rigid ice shell with an elastic thickness exceeding 40 kilometres, and hundreds of metres of surface erosion and deposition, consistent with recent estimates from local features. Our results are therefore not compatible with a geologically active, low-rigidity ice shell. After extrapolating to wavelengths that are controlled by tides and rotation, we suggest that Titan's moment of inertia may be even higher (that is, Titan may be even less centrally condensed) than is currently thought.
Language	English
Publishing date	2013-08-29
Publishing country	England
Document type	Journal Article ; Research Support, U.S. Gov't, Non-P.H.S.
ZDB-ID	120714-3
ISSN	1476-4687 ; 0028-0836
ISSN (online)	1476-4687
ISSN	0028-0836
DOI	10.1038/nature12400
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Article ; Online: Measurement and implications of Saturn's gravity field and ring mass.

Iess, L / Militzer, B / Kaspi, Y / Nicholson, P / Durante, D / Racioppa, P / Anabtawi, A / Galanti, E / Hubbard, W / Mariani, M J / Tortora, P / Wahl, S / Zannoni, M

Science (New York, N.Y.)

2019 Volume 364, Issue 6445

Abstract: The interior structure of Saturn, the depth of its winds, and the mass and age of its rings constrain its formation and evolution. In the final phase of the Cassini mission, the spacecraft dived between the planet and its innermost ring, at altitudes of ... ...

Abstract	The interior structure of Saturn, the depth of its winds, and the mass and age of its rings constrain its formation and evolution. In the final phase of the Cassini mission, the spacecraft dived between the planet and its innermost ring, at altitudes of 2600 to 3900 kilometers above the cloud tops. During six of these crossings, a radio link with Earth was monitored to determine the gravitational field of the planet and the mass of its rings. We find that Saturn's gravity deviates from theoretical expectations and requires differential rotation of the atmosphere extending to a depth of at least 9000 kilometers. The total mass of the rings is (1.54 ± 0.49) × 10
Language	English
Publishing date	2019-01-17
Publishing country	United States
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	128410-1
ISSN	1095-9203 ; 0036-8075
ISSN (online)	1095-9203
ISSN	0036-8075
DOI	10.1126/science.aat2965
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Article ; Online: Juno spacecraft gravity measurements provide evidence for normal modes of Jupiter.

Durante, Daniele / Guillot, Tristan / Iess, Luciano / Stevenson, David J / Mankovich, Christopher R / Markham, Steve / Galanti, Eli / Kaspi, Yohai / Zannoni, Marco / Gomez Casajus, Luis / Lari, Giacomo / Parisi, Marzia / Buccino, Dustin R / Park, Ryan S / Bolton, Scott J

Nature communications

2022 Volume 13, Issue 1, Page(s) 4632

Abstract: The Juno spacecraft has been collecting data to shed light on the planet's origin and characterize its interior structure. The onboard gravity science experiment based on X-band and Ka-band dual-frequency Doppler tracking precisely measured Jupiter's ... ...

Abstract	The Juno spacecraft has been collecting data to shed light on the planet's origin and characterize its interior structure. The onboard gravity science experiment based on X-band and Ka-band dual-frequency Doppler tracking precisely measured Jupiter's zonal gravitational field. Here, we analyze 22 Juno's gravity passes to investigate the gravity field. Our analysis provides evidence of new gravity field features, which perturb its otherwise axially symmetric structure with a time-variable component. We show that normal modes of the planet could explain the anomalous signatures present in the Doppler data better than other alternative explanations, such as localized density anomalies and non-axisymmetric components of the static gravity field. We explain Juno data by p-modes having an amplitude spectrum with a peak radial velocity of 10-50 cm/s at 900-1200 μHz (compatible with ground-based observations) and provide upper bounds on lower frequency f-modes (radial velocity smaller than 1 cm/s). The new Juno results could open the possibility of exploring the interior structure of the gas giants through measurements of the time-variable gravity or with onboard instrumentation devoted to the observation of normal modes, which could drive spacecraft operations of future missions.
Language	English
Publishing date	2022-08-30
Publishing country	England
Document type	Journal Article
ZDB-ID	2553671-0
ISSN	2041-1723 ; 2041-1723
ISSN (online)	2041-1723
ISSN	2041-1723
DOI	10.1038/s41467-022-32299-9
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Book ; Online: Saturn's deep atmospheric flows revealed by the Cassini Grand Finale gravity measurements

Galanti, Eli / Kaspi, Yohai / Miguel, Yamila / Guillot, Tristan / Durante, Daniele / Racioppa, Paolo / Iess, Luciano

2019

Abstract: How deep do Saturn's zonal winds penetrate below the cloud-level has been a decades-long question, with important implications not only for the atmospheric dynamics, but also for the interior density structure, composition, magnetic field and core mass. ... ...

Abstract	How deep do Saturn's zonal winds penetrate below the cloud-level has been a decades-long question, with important implications not only for the atmospheric dynamics, but also for the interior density structure, composition, magnetic field and core mass. The Cassini Grand Finale gravity experiment enables answering this question for the first time, with the premise that the planet's gravity harmonics are affected not only by the rigid body density structure but also by its flow field. Using a wide range of rigid body interior models and an adjoint based thermal wind balance, we calculate the optimal flow structure below the cloud-level and its depth. We find that with a wind profile, largely consistent with the observed winds, when extended to a depth of around 8,800 km, all the gravity harmonics measured by Cassini are explained. This solution is in agreement with considerations of angular momentum conservation, and is consistent with magnetohydrodynamics constraints.
Keywords	Astrophysics - Earth and Planetary Astrophysics
Subject code	551
Publishing date	2019-02-12
Publishing country	us
Document type	Book ; Online
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Article ; Online: The depth of Jupiter's Great Red Spot constrained by Juno gravity overflights.

Parisi, Marzia / Kaspi, Yohai / Galanti, Eli / Durante, Daniele / Bolton, Scott J / Levin, Steven M / Buccino, Dustin R / Fletcher, Leigh N / Folkner, William M / Guillot, Tristan / Helled, Ravit / Iess, Luciano / Li, Cheng / Oudrhiri, Kamal / Wong, Michael H

Science (New York, N.Y.)

2021 Volume 374, Issue 6570, Page(s) 964–968

Abstract: Jupiter’s Great Red Spot (GRS) is the largest atmospheric vortex in the Solar System and has been observed for at least two centuries. It has been unclear how deep the vortex extends beneath its visible cloud tops. We examined the gravity signature of ... ...

Abstract	Jupiter’s Great Red Spot (GRS) is the largest atmospheric vortex in the Solar System and has been observed for at least two centuries. It has been unclear how deep the vortex extends beneath its visible cloud tops. We examined the gravity signature of the GRS using data from 12 encounters of the Juno spacecraft with the planet, including two direct overflights of the vortex. Localized density anomalies due to the presence of the GRS caused a shift in the spacecraft line-of-sight velocity. Using two different approaches to infer the GRS depth, which yielded consistent results, we conclude that the GRS is contained within the upper 500 kilometers of Jupiter’s atmosphere.
Language	English
Publishing date	2021-10-28
Publishing country	United States
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	128410-1
ISSN	1095-9203 ; 0036-8075
ISSN (online)	1095-9203
ISSN	0036-8075
DOI	10.1126/science.abf1396
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Article ; Online: A test of general relativity using radio links with the Cassini spacecraft.

Bertotti, B / Iess, L / Tortora, P

Nature

2003 Volume 425, Issue 6956, Page(s) 374–376

Abstract: According to general relativity, photons are deflected and delayed by the curvature of space-time produced by any mass. The bending and delay are proportional to gamma + 1, where the parameter gamma is unity in general relativity but zero in the ... ...

Abstract	According to general relativity, photons are deflected and delayed by the curvature of space-time produced by any mass. The bending and delay are proportional to gamma + 1, where the parameter gamma is unity in general relativity but zero in the newtonian model of gravity. The quantity gamma - 1 measures the degree to which gravity is not a purely geometric effect and is affected by other fields; such fields may have strongly influenced the early Universe, but would have now weakened so as to produce tiny--but still detectable--effects. Several experiments have confirmed to an accuracy of approximately 0.1% the predictions for the deflection and delay of photons produced by the Sun. Here we report a measurement of the frequency shift of radio photons to and from the Cassini spacecraft as they passed near the Sun. Our result, gamma = 1 + (2.1 +/- 2.3) x 10(-5), agrees with the predictions of standard general relativity with a sensitivity that approaches the level at which, theoretically, deviations are expected in some cosmological models.
Language	English
Publishing date	2003-09-25
Publishing country	England
Document type	Journal Article
ZDB-ID	120714-3
ISSN	1476-4687 ; 0028-0836
ISSN (online)	1476-4687
ISSN	0028-0836
DOI	10.1038/nature01997
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