Istituto Nazionale Di Astrofisica Istituto di Fisica dello Spazio Interplanetario V. Iafolla, E. Fiorenza, C. Lefevre, D.M. Lucchesi, A. Morbidini, S. Nozzoli, R. Peron, M. Persichini, A. Reale, F. Santoli ISA on the Moon: possible use of ISA on the Moon: possible use of accelerometers for in-orbit and on- accelerometers for in-orbit and on- ground measurements ground measurements 9th ILEWG International Conference on Exploration and Utilisation of the Moon (ICEUM9/ILC2007) Istituto di Fisica dello Spazio Interplanetario (IFSI/INAF), Roma, Italy Istituto di Fisica dello Spazio Interplanetario (IFSI/INAF), Roma, Italy
Transcript
Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario
V. Iafolla, E. Fiorenza, C. Lefevre, D.M. Lucchesi, A. Morbidini, S. Nozzoli, R. Peron, M. Persichini, A. Reale, F. Santoli
ISA on the Moon: possible use of accelerometers ISA on the Moon: possible use of accelerometers for in-orbit and on-ground measurementsfor in-orbit and on-ground measurements
9th ILEWG International Conference on Exploration and Utilisation of the Moon (ICEUM9/ILC2007)
Istituto di Fisica dello Spazio Interplanetario (IFSI/INAF), Roma, ItalyIstituto di Fisica dello Spazio Interplanetario (IFSI/INAF), Roma, Italy
Andreas Cellarius, Harmonia Macrocosmica, plate 19
The renewed interest for the exploration of our natural satellite opens the way for a series of experiments useful to constrain its formation, evolution and present composition. Improved satellite models of the lunar gravitational field will give a better global view of its internal structure; selenoseismology, with in-situ measurements, can complement this picture. An accelerometer like ISA (Italian Spring Accelerometer) can contribute in a fundamental way in supporting both types of measurements – in-orbit and on-ground – improving the quality of the range data by a removal of non-gravitational perturbations in the first case, and making a direct measurement of seismic waves in the second case. Both scenarios are discussed in the framework of possible future missions.
Iafolla, V. and Nozzoli, S., Plan. Space Sci. 49, 1609 (2001)
Iafolla, V. et al., Adv. Space Res. 38, 639 (2006)
Iafolla, V. et al., Celest. Mech. Dyn. Astr. 97, 165 (2007)
Abstract
Some references
Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario
Importance of Moon gravitational field knowledge…Importance of Moon gravitational field knowledge…
Knowledge of lunar gravitational field gives constraints on formation, evolution and present state of the Moon.Spherical harmonics expansion (resolution 5458 / l km)
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sincoscos1)(l
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mSmCPr
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GMrU
Degree variance
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Konopliv et al. (2001)
Mascons
Compare with Earth!
……and how to measure itand how to measure it
A measurement of the gravitational field can be obtained by an high-precision tracking of a spacecraft orbiting around it. The different harmonic terms of the field induce perturbations on the orbit that can be used via a numerical integration and orbit determination procedure to get an estimate of the harmonic coefficients.
The quality of the determination depends however on the modeling of spacecraft dynamics: this does not always reach the requirements.
Measuring their effects directly can substantially
help the gravity field determination!
Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario
ISA accelerometerISA accelerometer
ISA is a three-axis accelerometer with an intrinsic noise of 9.8∙10-10 m s-2 Hz-1/2 in the frequency band of 3∙10-5 – 10-1 Hz. It enables a fine measurement of the perturbations of non-gravitational origin acting on a spacecraft.
The displacements of a proof–mass due to a perturbing acceleration are detected by means of capacitive transducers in a bridge configuration, followed by a low noise amplifier
The capacitive bridge (CB) is biased at high frequency ( fp = 10 kHz ) so that accelerations at frequencies fs produce their unbalance
At the output of the CB the signals are seen as a modulation of the bias voltage at the two side–bands f = fp fs in the frequency domain
Due to the characteristics of the instrument, measuring its performances on-ground (subject to Earth gravity field) is not easy. Thermal and seismic noise constitute a sort of “background” that could be removed employing two accelerometers in a differential configuration: Common Mode Rejection.
The attained level of rejection in the relevant bandwidth is remarkable. It is an important reference for future development.
The experience gained in developing the accelerometer for the BepiColombo mission can be used for applications in a number of scenarios in Solar System exploration.
Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario
Scm
ACa SunRSun
ˆ
ISA around the Moon…ISA around the Moon…
There is space for
improvement!
An analysis of recent lunar gravity field models shows that its knowledge at high orders can be improved. ISA can support this improvement.
Photo Apollo 11
……and other ideasand other ideas
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Tempo giorni dal 2001
Misure GEOSTAR
Earthquakes 13 gen 2001 17:33:29:22Off Coast of Central AmericaRegistrazione Gravimetro Geostar Ustica
