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Valerio Iafolla David M. Lucchesi Sergio Nozzoli Francesco Santoli 《Celestial Mechanics and Dynamical Astronomy》2007,97(3):165-187
We have estimated a preliminary error budget for the Italian Spring Accelerometer (ISA) that will be allocated onboard the
Mercury Planetary Orbiter (MPO) of the European Space Agency (ESA) space mission to Mercury named BepiColombo. The role of
the accelerometer is to remove from the list of unknowns the non-gravitational accelerations that perturb the gravitational
trajectory followed by the MPO in the strong radiation environment that characterises the orbit of Mercury around the Sun.
Such a role is of fundamental importance in the context of the very ambitious goals of the Radio Science Experiments (RSE)
of the BepiColombo mission. We have subdivided the errors on the accelerometer measurements into two main families: (i) the
pseudo-sinusoidal errors and (ii) the random errors. The former are characterised by a periodic behaviour with the frequency
of the satellite mean anomaly and its higher order harmonic components, i.e., they are deterministic errors. The latter are
characterised by an unknown frequency distribution and we assumed for them a noise-like spectrum, i.e., they are stochastic
errors. Among the pseudo-sinusoidal errors, the main contribution is due to the effects of the gravity gradients and the inertial forces, while among the random-like errors the main disturbing effect is due to the MPO centre-of-mass displacements produced by the onboard High Gain Antenna (HGA) movements and by the fuel consumption and sloshing. Very subtle to be considered
are also the random errors produced by the MPO attitude corrections necessary to guarantee the nadir pointing of the spacecraft.
We have therefore formulated the ISA error budget and the requirements for the satellite in order to guarantee an orbit reconstruction
for the MPO spacecraft with an along-track accuracy of about 1 m over the orbital period of the satellite around Mercury in
such a way to satisfy the RSE requirements. 相似文献
2.
In this paper, modal parameters of a layered soil system comprising of a soft clay layer overlying a dense sand layer are identified from accelerometer recordings in a centrifuge test. For the first time, the subspace state space system identification (4SID) method was employed to identify the natural frequencies, damping ratios, and complex valued mode shapes while considering the non-proportional damping in a soil system. A brief review of system identification concepts needed for application of the 4SID techniques to structural modal identification is provided in the paper. The identified natural frequencies were validated against those estimated by transfer function spectra. The computed normal mode shapes were compared with closed-form solutions obtained from the one-dimensional shear wave propagation equation. The identified modal parameters were then employed to synthesize state space prediction models which were subsequently used to simulate the soil response to three successive base motions. The identified models captured acceleration time-histories and corresponding Fourier spectra reasonably well in the small and moderate shaking events. In the stronger third shaking event, the model performed well at greater soil depths, but was less accurate near the surface where nonlinearities dominated. 相似文献
3.
We have defined new algorithms for the data processing of a satellite geodesy mission with gradiometer (such as the next European
mission GOCE) to extract the information on the gravity field coefficients with a realistic estimate of their accuracy. The
large scale data processing can be managed by a multistage decomposition. First the spacecraft position is determined, i.e.,
a kinematic method is normally used. Second we use a new method to perform the necessary digital calibration of the gradiometer.
Third we use a multiarc approach to separately solve for the global gravity field parameters. Fourth we use an approximate
resonant decomposition, that is we partition in a new way the harmonic coefficients of the gravity field. Thus the normal
system is reduced to blocks of manageable size without neglecting significant correlations. Still the normal system is badly
conditioned because of the polar gaps in the spatial distribution of the data. We have shown that the principal components
of the uncertainty correspond to harmonic anomalies with very small signal in the region where GOCE is flying; these uncertainties
cannot be removed by any data processing method. This allows a complete simulation of the GOCE mission with affordable computer
resources. We show that it is possible to solve for the harmonic coefficients up to degree 200–220 with signal to error ratio
≥1, taking into account systematic measurement errors. Errors in the spacecraft orbit, as expected from state of the art satellite
navigation, do not degrade the solution. Gradiometer calibration is the main problem. By including a systematic error model,
we have shown that the results are sensitive to spurious gradiometer signals at frequencies close to the lower limit of the
measurement band. If these spurious effects grow as the inverse of the frequency, then the actual error is larger than the
formal error only by a factor ≃2, that is the results are not compromised. 相似文献
4.
The paper is focused on the estimate of the impact of the non-gravitational perturbations on the orbit of the Mercury Planetary Orbiter (MPO), one of the two spacecrafts that will be placed in orbit around the innermost planet of the solar system by the BepiColombo space mission. The key rôle of the Italian Spring Accelerometer (ISA), that has been selected by the European Space Agency (ESA) to fly on-board the MPO, is outlined. In the first part of the paper, through a numerical simulation and analysis we have estimated, over a time span of several years, the long-period behaviours of the disturbing accelerations produced by the incoming direct solar radiation pressure, and the indirect effects produced by Mercury’s albedo. The variations in the orbital parameters of the spacecraft, together with their spectral contents, have been estimated over the analysed period. The direct solar radiation pressure represents the strongest non-gravitational perturbation on the MPO in the very complex radiation environment of Mercury. The order-of-magnitude of this acceleration is quite high, about 10?6 m/s2, because of the proximity to the Sun and the large area-to-mass ratio of the spacecraft. In the second part of the paper, we concentrated upon the short-period effects of direct solar radiation pressure and Mercury’s albedo. In particular, the disturbing accelerations have been compared with the ISA measurement error and the advantages of an on-board accelerometer are highlighted with respect to the best modelling of the non-gravitational perturbations in the strong radiation environment of Mercury. The readings from ISA, with an intrinsic noise level of about $10^{-9}\,m/s^{2}/\sqrt{Hz}The paper is focused on the estimate of the impact of the non-gravitational perturbations on the orbit of the Mercury Planetary Orbiter (MPO), one of the two spacecrafts that will be placed in orbit around the innermost planet of the solar system by the BepiColombo space mission. The key r?le of the Italian Spring Accelerometer (ISA), that has been selected by the European Space Agency (ESA) to fly on-board the MPO, is outlined. In the first part of the paper, through a numerical simulation and analysis we have estimated, over a time span of several years, the long-period behaviours of the disturbing accelerations produced by the incoming direct solar radiation pressure, and the indirect effects produced by Mercury’s albedo. The variations in the orbital parameters of the spacecraft, together with their spectral contents, have been estimated over the analysed period. The direct solar radiation pressure represents the strongest non-gravitational perturbation on the MPO in the very complex radiation environment of Mercury. The order-of-magnitude of this acceleration is quite high, about 10−6 m/s2, because of the proximity to the Sun and the large area-to-mass ratio of the spacecraft. In the second part of the paper, we concentrated upon the short-period effects of direct solar radiation pressure and Mercury’s albedo. In particular, the disturbing accelerations have been compared with the ISA measurement error and the advantages of an on-board accelerometer are highlighted with respect to the best modelling of the non-gravitational perturbations in the strong radiation environment of Mercury. The readings from ISA, with an intrinsic noise level of about
in the frequency band of 3·10−5–10−1 Hz, guarantees a very significant reduction of the non-gravitational accelerations impact on the space mission accuracy, especially of the dominant direct solar radiation pressure. 相似文献
5.
Exploring the possibilities for star-tracker assisted calibration of the six individual GOCE accelerometers 总被引:1,自引:0,他引:1
P. N. A. M. Visser 《Journal of Geodesy》2008,82(10):591-600
A method has been developed and tested for estimating calibration parameters for the six accelerometers on board the Gravity
field and steady-state Ocean Circulation Explorer (GOCE) from star tracker observations. These six accelerometers are part
of the gradiometer, which is the prime instrument on board GOCE. It will be shown that by taking appropriate combinations
of observations collected by the accelerometers, by modeling acceleration terms caused by gravity gradients from an a priori
low-degree spherical harmonic expansion, and by modeling rotational acceleration terms derived from star-tracker observations,
scale factors of each of the accelerometers can be estimated for each axis. Simulated observations from a so-called end-to-end
simulator were used to test the method. This end-to-end simulator includes a detailed model of the GOCE satellite, its instruments
and instrument errors, and its environment. Results of the tests indicate that scale factors of all six accelerometers can
be determined with an accuracy of around 0.01 for all components on a daily basis. 相似文献
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