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Papers by Alberto Anselmi

Planetary and Space Science, 2001

The paper presents the results of the deÿnition studies performed for the European Space Agency (... more The paper presents the results of the deÿnition studies performed for the European Space Agency (ESA) on system architectures and 7 enabling technologies for "BepiColombo", a Cornerstone class mission to be launched in the 2007-2009 time frame. The scientiÿc mission comprises 1-year observations by a Mercury Planetary Orbiter (MPO), dedicated to remote sensing, and a Mercury Magnetospheric Orbiter 9 (MMO), dedicated to particles and ÿelds, plus short-duration in situ analysis by a Mercury surface element (MSE). A exible approach to the programme has been developed, comprising two alternative launch scenarios. In the ÿrst option (2009), the 2500-kg class satellite 11 composite, including two propulsion modules and three scientiÿc modules, is launched by an Ariane-5. The trajectory design is based on Venus and Mercury gravity assists plus the thrust provided by a Solar Electric Propulsion Module (SEPM), that is jettisoned before 13 being captured into Mercury orbit. Capture and orbit insertion, executed by successive manoeuvres of a Chemical Propulsion Module (CPM), occur less than 2:5 yr after launch. In the second scenario, the mission is split into two launches of a small launch vehicle. Two 15 1200-kg class composites are launched either in the same one-month window or at an interval of 1:6 yr. One composite comprises the SEPM, CPM, MMO and MSE and the other comprises duplicate SEPM+CPM and the MPO. The trajectory design follows the same 17 principles as the Ariane-5 mission, with the SEPM thrust reduced by half and cruise duration ranging between 2.3 and 3:5 yr. Whatever be the implementation, the mission is expected to return about 1700 Gbit of scientiÿc data during the one-year observation phase. The 19 crucial aspects of the spacecraft design are associated with, and constrained by, the high-temperature and high-radiation environment. Basic feasibility has been demonstrated by an extensive design and analysis exercise, and the focus of the programme has now moved to 21 a 3-year preparatory programme dedicated for developing the enabling technologies.

Physics Letters A, 2003

The design of the satellite for the GG experiment was addressed in phase-A level studies in 1997-... more The design of the satellite for the GG experiment was addressed in phase-A level studies in 1997-2000, based on an equatorial orbit, and more recently re-addressed for sun-synchronous orbit (SSO). The mission consists of an experiment running uninterrupted with few operational modes, small telemetry rates, easily controlled by one ground station. The satellite is small, low-weight, with low power demand. The configuration, resembling a spinning top, is very compact and stiff. The main requirements are for thermal stability, drag-free control and spin rate control. The reconfiguration to SSO makes the mission suitable for a low-cost launch, and improves the thermal performance.

Classical and Quantum Gravity, 2012

The GG ("Galileo Galilei") satellite experiment aims to test the Equivalence Principle (EP) to 10... more The GG ("Galileo Galilei") satellite experiment aims to test the Equivalence Principle (EP) to 10-17 , an extremely ambitious goal (due to improve current best results by 4 orders of magnitude) that should tell us in a clear cut way whether we are in the presence of a new long-range physical interaction (violation) or not (confirmation). Either way, it would be a major result. An end-to-end space experiment simulator was constructed at TAS-I based on GOCE simulator and ASI (Agenzia Spaziale Italiana) funding. The resulting error budget is consistent with the mission goal, which can be realized in 4 years from the start of Phase B. In the lab, a full scale prototype has provided a 25 days continuous run with a sensitivity -in the field of the Sun, hence at diurnal frequency- of a few nanometers in the relative displacement of the proof masses, to be compared with the picometer level required in space for GG to achieve its goal. A passive suspended prototype is under completion in order to reduce ground platform noise by means of an appropriate cardanic suspension which has now been proved to be able to reduce diurnal terrain noise by a factor 104 . The crucial issue of thermal noise has been recently revisited and a major new insight has come thanks to M. Shao (JPL): in GG, by up-converting the frequency of an EP violation signal in the field of the Earth from its (low) orbital frequency of 1.7 · 10-4 Hz to the (high) rotation/modulation frequency of 1Hz -the highest ever in EP experiments- proof mass thermal noise is reduced by orders of magnitude, as the ratio of these frequencies squared. Instead, cooling the experiment to superfluid He temperature would only reduce thermal noise by a factor 10. This is a feature unique to GG. It now appears that, if equipped with an intrinsic differential transducer such as a SIM like laser gauge, GG may indeed aim to an EP test to 10-18 . The end-to-end GG simulator built at TAS-I in 2009 during GG Phase A-2 study is the crucial tool that allows this analysis to be performed in a reliable way and in a short time, at the very beginning of GG Phase B Study should ASI approve it.

Advances in Space Research, 2000

GALILEO GALILEI" (GG) is a proposal for a small, low orbit satellite devoted to testing the Equiv... more GALILEO GALILEI" (GG) is a proposal for a small, low orbit satellite devoted to testing the Equivalence Principle (EP) of Galileo, Newton and Einstein to 1 part in 10 17 . At the end of 1997 GG has been selected and funded by ASI (Agenzia Spaziale Italiana) for a 1-year Phase A study. The main novelty of GG is that the concentric hollow test cylinders whose relative motion (in the plane perpendicular to the spin axis) would be affected by an EP violation, spin together with the read-out capacitance sensors placed in between them. The nominal spin rate is 2 Hz, and this is the frequency at which the putative EP violation signal is modulated by the sensors. As compared to other experiments the modulation frequency is increased by more than a factor 10 4 , thus reducing 1/f (low frequency) electronic and mechanical noise. GG will have FEEP ion thrusters for drag compensation. The required amount of propellant is of a few grams only. The experiment works at room temperature. To demonstrate the feasibility of the space experiment a payload prototype for EP testing on the ground (GGG -GG on the Ground) is under development in the laboratories of Laben. The challenge in this field is to fly an experiment able to improve by many orders of magnitude the current best ground sensitivity (≅10 -12 ). This requires spurious relative motions of the test bodies to be greatly reduced, leaving them essentially motionless. Doing that with more than one pair of bodies appears to be an unnecessary complication. This is why GG is now proposed with a single pair of test masses. Information, research papers and photographs of the ground apparatus are available on the Web (http://tycho.dm.unipi.it/nobili/ ggproject.html).

Classical and Quantum Gravity, 1999

Test masses coupled by weak mechanical suspensions are sensitive to differential forces such as t... more Test masses coupled by weak mechanical suspensions are sensitive to differential forces such as the force due to a possible violation of the equivalence principle (EP). If in addition they are put in rapid rotation, the differential signal is modulated at high frequency, which is beneficial for noise reduction. Galileo Galilei (GG) is a proposed space experiment for testing the equivalence principle to 1 part in 0264-9381/16/4/032/img8 based on these concepts. A recent paper by Jafry and Weinberger (1998 Class. Quantum Grav. 15 481-500) claims that GG can only reach 0264-9381/16/4/032/img9. We show that the analysis of this paper is flawed (by several orders of magnitude) because of two misconceptions: one on the physical nature of mechanical damping and the other on active control methods for the stabilization of spinning bodies.

While the energy density of the Cosmic X-ray Background (CXB) provides a statistical estimate of ... more While the energy density of the Cosmic X-ray Background (CXB) provides a statistical estimate of the super massive black hole (SMBH) growth and mass density in the Universe, the lack, so far, of focusing instrument in the 20-60 keV (where the CXB energy density peaks), frustrates our effort to obtain a comprehensive picture of the SMBH evolutionary properties. HEXIT-SAT (High Energy X-ray Imaging Telescope SATellite) is a mission concept capable of exploring the hard X-ray sky with focusing/imaging instrumentation, to obtain an unbiased census of accreting SMBH up to the redshifts where galaxy formation peaks, and on extremely wide luminosity ranges. This will represent a leap forward comparable to that achieved in the soft X-rays by the Einstein Observatory in the late 70'. In addition to accreting SMBH, and very much like the Einstein Observatory, this mission would also have the capabilities of investigating almost any type of the celestial X-ray sources. HEXIT-SAT is based on high throughput (>400 cm2 @ 30 keV; >1200 cm2 @ 1 keV), high quality (15 arcsec Half Power Diameter) multi-layer optics, coupled with focal plane detectors with high efficiency in the full 0.5-70keV range. Building on the BeppoSAX experience, a low-Earth, equatorial orbit, will assure a low and stable particle background, and thus an extremely good sensitivity for faint hard X-ray sources. At the flux limits of 1/10 microCrab (10-30 keV) and 1/3 microCrab (20-40 keV) (reachable in one Msec observation) we should detect ~100 and ~40 sources in the 15 arcmin FWHM Field of View respectively, thus resolving >80% and ~65% of the CXB where its energy density peaks.

Planetary and Space Science, 2001

The paper presents the results of the deÿnition studies performed for the European Space Agency (... more The paper presents the results of the deÿnition studies performed for the European Space Agency (ESA) on system architectures and 7 enabling technologies for "BepiColombo", a Cornerstone class mission to be launched in the 2007-2009 time frame. The scientiÿc mission comprises 1-year observations by a Mercury Planetary Orbiter (MPO), dedicated to remote sensing, and a Mercury Magnetospheric Orbiter 9 (MMO), dedicated to particles and ÿelds, plus short-duration in situ analysis by a Mercury surface element (MSE). A exible approach to the programme has been developed, comprising two alternative launch scenarios. In the ÿrst option (2009), the 2500-kg class satellite 11 composite, including two propulsion modules and three scientiÿc modules, is launched by an Ariane-5. The trajectory design is based on Venus and Mercury gravity assists plus the thrust provided by a Solar Electric Propulsion Module (SEPM), that is jettisoned before 13 being captured into Mercury orbit. Capture and orbit insertion, executed by successive manoeuvres of a Chemical Propulsion Module (CPM), occur less than 2:5 yr after launch. In the second scenario, the mission is split into two launches of a small launch vehicle. Two 15 1200-kg class composites are launched either in the same one-month window or at an interval of 1:6 yr. One composite comprises the SEPM, CPM, MMO and MSE and the other comprises duplicate SEPM+CPM and the MPO. The trajectory design follows the same 17 principles as the Ariane-5 mission, with the SEPM thrust reduced by half and cruise duration ranging between 2.3 and 3:5 yr. Whatever be the implementation, the mission is expected to return about 1700 Gbit of scientiÿc data during the one-year observation phase. The 19 crucial aspects of the spacecraft design are associated with, and constrained by, the high-temperature and high-radiation environment. Basic feasibility has been demonstrated by an extensive design and analysis exercise, and the focus of the programme has now moved to 21 a 3-year preparatory programme dedicated for developing the enabling technologies.

Physics Letters A, 2003

The design of the satellite for the GG experiment was addressed in phase-A level studies in 1997-... more The design of the satellite for the GG experiment was addressed in phase-A level studies in 1997-2000, based on an equatorial orbit, and more recently re-addressed for sun-synchronous orbit (SSO). The mission consists of an experiment running uninterrupted with few operational modes, small telemetry rates, easily controlled by one ground station. The satellite is small, low-weight, with low power demand. The configuration, resembling a spinning top, is very compact and stiff. The main requirements are for thermal stability, drag-free control and spin rate control. The reconfiguration to SSO makes the mission suitable for a low-cost launch, and improves the thermal performance.

Classical and Quantum Gravity, 2012

The GG ("Galileo Galilei") satellite experiment aims to test the Equivalence Principle (EP) to 10... more The GG ("Galileo Galilei") satellite experiment aims to test the Equivalence Principle (EP) to 10-17 , an extremely ambitious goal (due to improve current best results by 4 orders of magnitude) that should tell us in a clear cut way whether we are in the presence of a new long-range physical interaction (violation) or not (confirmation). Either way, it would be a major result. An end-to-end space experiment simulator was constructed at TAS-I based on GOCE simulator and ASI (Agenzia Spaziale Italiana) funding. The resulting error budget is consistent with the mission goal, which can be realized in 4 years from the start of Phase B. In the lab, a full scale prototype has provided a 25 days continuous run with a sensitivity -in the field of the Sun, hence at diurnal frequency- of a few nanometers in the relative displacement of the proof masses, to be compared with the picometer level required in space for GG to achieve its goal. A passive suspended prototype is under completion in order to reduce ground platform noise by means of an appropriate cardanic suspension which has now been proved to be able to reduce diurnal terrain noise by a factor 104 . The crucial issue of thermal noise has been recently revisited and a major new insight has come thanks to M. Shao (JPL): in GG, by up-converting the frequency of an EP violation signal in the field of the Earth from its (low) orbital frequency of 1.7 · 10-4 Hz to the (high) rotation/modulation frequency of 1Hz -the highest ever in EP experiments- proof mass thermal noise is reduced by orders of magnitude, as the ratio of these frequencies squared. Instead, cooling the experiment to superfluid He temperature would only reduce thermal noise by a factor 10. This is a feature unique to GG. It now appears that, if equipped with an intrinsic differential transducer such as a SIM like laser gauge, GG may indeed aim to an EP test to 10-18 . The end-to-end GG simulator built at TAS-I in 2009 during GG Phase A-2 study is the crucial tool that allows this analysis to be performed in a reliable way and in a short time, at the very beginning of GG Phase B Study should ASI approve it.

Advances in Space Research, 2000

GALILEO GALILEI" (GG) is a proposal for a small, low orbit satellite devoted to testing the Equiv... more GALILEO GALILEI" (GG) is a proposal for a small, low orbit satellite devoted to testing the Equivalence Principle (EP) of Galileo, Newton and Einstein to 1 part in 10 17 . At the end of 1997 GG has been selected and funded by ASI (Agenzia Spaziale Italiana) for a 1-year Phase A study. The main novelty of GG is that the concentric hollow test cylinders whose relative motion (in the plane perpendicular to the spin axis) would be affected by an EP violation, spin together with the read-out capacitance sensors placed in between them. The nominal spin rate is 2 Hz, and this is the frequency at which the putative EP violation signal is modulated by the sensors. As compared to other experiments the modulation frequency is increased by more than a factor 10 4 , thus reducing 1/f (low frequency) electronic and mechanical noise. GG will have FEEP ion thrusters for drag compensation. The required amount of propellant is of a few grams only. The experiment works at room temperature. To demonstrate the feasibility of the space experiment a payload prototype for EP testing on the ground (GGG -GG on the Ground) is under development in the laboratories of Laben. The challenge in this field is to fly an experiment able to improve by many orders of magnitude the current best ground sensitivity (≅10 -12 ). This requires spurious relative motions of the test bodies to be greatly reduced, leaving them essentially motionless. Doing that with more than one pair of bodies appears to be an unnecessary complication. This is why GG is now proposed with a single pair of test masses. Information, research papers and photographs of the ground apparatus are available on the Web (http://tycho.dm.unipi.it/nobili/ ggproject.html).

Classical and Quantum Gravity, 1999

Test masses coupled by weak mechanical suspensions are sensitive to differential forces such as t... more Test masses coupled by weak mechanical suspensions are sensitive to differential forces such as the force due to a possible violation of the equivalence principle (EP). If in addition they are put in rapid rotation, the differential signal is modulated at high frequency, which is beneficial for noise reduction. Galileo Galilei (GG) is a proposed space experiment for testing the equivalence principle to 1 part in 0264-9381/16/4/032/img8 based on these concepts. A recent paper by Jafry and Weinberger (1998 Class. Quantum Grav. 15 481-500) claims that GG can only reach 0264-9381/16/4/032/img9. We show that the analysis of this paper is flawed (by several orders of magnitude) because of two misconceptions: one on the physical nature of mechanical damping and the other on active control methods for the stabilization of spinning bodies.

While the energy density of the Cosmic X-ray Background (CXB) provides a statistical estimate of ... more While the energy density of the Cosmic X-ray Background (CXB) provides a statistical estimate of the super massive black hole (SMBH) growth and mass density in the Universe, the lack, so far, of focusing instrument in the 20-60 keV (where the CXB energy density peaks), frustrates our effort to obtain a comprehensive picture of the SMBH evolutionary properties. HEXIT-SAT (High Energy X-ray Imaging Telescope SATellite) is a mission concept capable of exploring the hard X-ray sky with focusing/imaging instrumentation, to obtain an unbiased census of accreting SMBH up to the redshifts where galaxy formation peaks, and on extremely wide luminosity ranges. This will represent a leap forward comparable to that achieved in the soft X-rays by the Einstein Observatory in the late 70'. In addition to accreting SMBH, and very much like the Einstein Observatory, this mission would also have the capabilities of investigating almost any type of the celestial X-ray sources. HEXIT-SAT is based on high throughput (>400 cm2 @ 30 keV; >1200 cm2 @ 1 keV), high quality (15 arcsec Half Power Diameter) multi-layer optics, coupled with focal plane detectors with high efficiency in the full 0.5-70keV range. Building on the BeppoSAX experience, a low-Earth, equatorial orbit, will assure a low and stable particle background, and thus an extremely good sensitivity for faint hard X-ray sources. At the flux limits of 1/10 microCrab (10-30 keV) and 1/3 microCrab (20-40 keV) (reachable in one Msec observation) we should detect ~100 and ~40 sources in the 15 arcmin FWHM Field of View respectively, thus resolving >80% and ~65% of the CXB where its energy density peaks.