Satellite Attitude Information Research Articles

Exchanging satellite attitude quaternions for improved GNSS data processing consistency

The orientation of GNSS satellites in space is a key quantity in GNSS data processing. It is required to correctly apply several force models and observation corrections. Incorrect or insufficient modeling of satellite attitude can lead to inconsistencies both among providers of GNSS products and between providers and users, which negatively affects the quality of combined products and positioning solutions. Exchanging satellite attitude information in the form of quaternions helps to eliminate or reduce those inconsistencies. This study presents the first systematic exchange of attitude data in a common format (called ORBEX) within the International GNSS Service (IGS). A comparison of attitude auxiliary data from seven IGS analysis centers over a one-year period shows significant differences for GPS and GLONASS satellites, but not for Galileo. These differences are mostly confined to eclipse periods but can reach up to 180°. Considering the attitude differences between analysis center solutions in an experimental clock combination significantly improved the consistency of analysis center solutions during eclipse periods. A kinematic PPP analysis covering ten globally distributed stations over one week resulted in an almost unanimous improvement when using the provided satellite attitude instead of a nominal model, with an average RMS reduction of 50% in the east and up components. The results presented in this study show that satellite attitude is important GNSS auxiliary data and making it available benefits both providers and users.

Observation-Based Attitude Realization for Accurate Jason Satellite Orbits and Its Impact on Geodetic and Altimetry Results

For low Earth orbiting satellites, non-gravitational forces cause one of the largest perturbing accelerations. During a precise orbit determination (POD), the accurate modeling of the satellite-body attitude and solar panel orientation is important since the satellite’s effective cross-sectional area is directly related to the perturbing acceleration. Moreover, the position of tracking instruments that are mounted on the satellite body are affected by the satellite attitude. For satellites like Jason-1/-2/-3, attitude information is available in two forms—as a so-called nominal yaw steering model and as observation-based (measured by star tracking cameras) quaternions of the spacecraft body orientation and rotation angles of the solar arrays. In this study, we have developed a preprocessing procedure for publicly available satellite attitude information. We computed orbits based on Satellite Laser Ranging (SLR) observations to the Jason satellites at an overall time interval of approximately 25 years, using each of the two satellite attitude representations. Based on the analysis of the orbits, we investigate the influence of using preprocessed observation-based attitude in contrast to using a nominal yaw steering model for the POD. About 75% of all orbital arcs calculated with the observation-based satellite attitude data result in a smaller root mean square (RMS) of residuals. More precisely, the resulting orbits show an improvement in the overall mission RMS of SLR observation residuals of 5.93% (Jason-1), 8.27% (Jason-2) and 4.51% (Jason-3) compared to the nominal attitude realization. Besides the satellite orbits, also the estimated station coordinates benefit from the refined attitude handling, that is, the station repeatability is clearly improved at the draconitic period. Moreover, altimetry analysis indicates a clear improvement of the single-satellite crossover differences (6%, 15%, and 16% reduction of the mean of absolute differences and 1.2%, 2.7%, and 1.3% of their standard deviations for Jason-1/-2/-3, respectively). On request, the preprocessed attitude data are available.

A novel two-stage extended Kalman filter algorithm for reaction flywheels fault estimation

This paper investigates the problem of two-stage extended Kalman filter (TSEKF)-based fault estimation for reaction flywheels in satellite attitude control systems (ACSs). Firstly, based on the separate-bias principle, a satellite ACSs with actuator fault is transformed into an augmented nonlinear discrete stochastic model; then, a novel TSEKF is suggested such that it can simultaneously estimate satellite attitude information and actuator faults no matter they are additive or multiplicative; finally, the proposed approach is respectively applied to estimating bias faults and loss of effectiveness for reaction flywheels in satellite ACSs, and simulation results demonstrate the effectiveness of the proposed fault estimation approach.

Navigation of Chang’E-2 asteroid exploration mission and the minimum distance estimation during its fly-by of Toutatis

China’s space probe Chang’E-2 began its asteroid exploration mission on April 15, 2012 and had been in space for 243days before its encounter with Toutatis. With no onboard navigation equipment available, the navigation of CE-2 during its fly-by of the asteroid relied totally on ground-based Unified S-Band (USB) and Very Long Baseline Interferometry (VLBI) tracking data. The orbit determination of Toutatis was achieved by using a combination of optical measurements and radar ranging. On November 30, 2012, CE-2 was targeted at a destination that was 15km away from the asteroid as it performed its third trajectory correction maneuver. Later orbit determination analysis showed that a correction residual was still present, which necessitated another maneuver on December 12. During the two maneuvers, ground-based navigation faced a challenge in terms of the orbit determination accuracy. With the optimization of our strategy, an accuracy of better than 15km was finally achieved for the post-maneuver orbit solution. On December 13, CE-2 successfully passed by Toutatis and conducted continuous photographing of Toutatis during the entire process. An analysis of the images that were taken from the solar panel monitoring camera and the satellite attitude information demonstrates that the closest distance obtained between CE-2 and Toutatis (Toutatis’s surface) was 1.9km, which is considerably better than the 30km fly-by distance that we originally hoped based on the accuracies that we can obtain on the satellite and Toutatis’ orbits.

Impact of orbit modeling on DORIS station position and Earth rotation estimates

The high precision of estimated station coordinates and Earth rotation parameters (ERP) obtained from satellite geodetic techniques is based on the precise determination of the satellite orbit. This paper focuses on the analysis of the impact of different orbit parameterizations on the accuracy of station coordinates and the ERPs derived from DORIS observations. In a series of experiments the DORIS data from the complete year 2011 were processed with different orbit model settings. First, the impact of precise modeling of the non-conservative forces on geodetic parameters was compared with results obtained with an empirical-stochastic modeling approach. Second, the temporal spacing of drag scaling parameters was tested. Third, the impact of estimating once-per-revolution harmonic accelerations in cross-track direction was analyzed. And fourth, two different approaches for solar radiation pressure (SRP) handling were compared, namely adjusting SRP scaling parameter or fixing it on pre-defined values.Our analyses confirm that the empirical-stochastic orbit modeling approach, which does not require satellite attitude information and macro models, results for most of the monitored station parameters in comparable accuracy as the dynamical model that employs precise non-conservative force modeling. However, the dynamical orbit model leads to a reduction of the RMS values for the estimated rotation pole coordinates by 17% for x-pole and 12% for y-pole.The experiments show that adjusting atmospheric drag scaling parameters each 30min is appropriate for DORIS solutions. Moreover, it was shown that the adjustment of cross-track once-per-revolution empirical parameter increases the RMS of the estimated Earth rotation pole coordinates. With recent data it was however not possible to confirm the previously known high annual variation in the estimated geocenter z-translation series as well as its mitigation by fixing the SRP parameters on pre-defined values.

Magnetometer-only linear attitude estimation for bias momentum pico-satellite

Satellite attitude information is essential for pico-satellite applications requiring light-weight, low-power, and fast-computation characteristics. The objective of this study is to provide a magnetometer-only attitude estimation method for a low-altitude Earth orbit, bias momentum pico-satellite. Based on two assumptions, the spacecraft spherical symmetry and damping of body rates, a linear kinematics model of a bias momentum satellite’s pitch axis is derived, and the linear estimation algorithm is developed. The algorithm combines the linear Kalman filter (KF) with the classic three-axis attitude determination method (TRIAD). KF is used to estimate satellite’s pitch axis orientation, while TRIAD is used to obtain information concerning the satellite’s three-axis attitude. Simulation tests confirmed that the algorithm is suited to the time-varying model errors resulting from both assumptions. The estimate result keeps tracking satellite attitude motion during all damping, stable, and free rotating control stages. Compared with nonlinear algorithms, such as extended Kalman filer (EKF) and square root unscented Kalman filer (SRUKF), the algorithm presented here has an almost equal performance in terms of convergence time and estimation accuracy, while the consumption of computing resources is much lower.

Attitude Detection Method of Nano Satellite HIT-SAT by Fluctuation of Received Signal Strength

In recent years, many universities have already launched small satellite on-orbit. Attitude information is important for satellite operation. However, many nano-satellite communication systems used amateur radio by narrow bandwidth frequency segment. Therefore, down-link of attitude information is expected to require substantial time. In this paper, we propose establishment of the attitude estimation method by means of the received radio power. And, satellite attitude information being estimated from the fluctuation of the received power. Then, comparison of satellite data obtained from on-board sensors with ground experiment. One major problem in this approach is the effect of Earth's ionosphere. As the radio signal passes through the ionosphere, the polarization angle is rotated by the Faraday Effect. The detection of attitude by the radiation pattern has been assumed that inaccurate. However, we are get data the spin satellite of liner polarization antenna. As a result, we can estimate 0.12rad/s accuracy of angular velocity measurement. This method can be applied to the attitude detection of many small satellites.

Tycho Astrometry and Photometry

AbstractIn the Tycho project astrometric and photometric data of about 1 000 000 stars to a limit of B = 12 mag will be derived. The brightest 500 000 stars will obtain magnitudes in two colours BT and VT, the fainter 500 000 usually only one broad-band magnitude T. There is confidence that an accuracy will be achieved about 0.03 arcsec for positions and 0.03 mag for magnitudes, at B = 10.5 mag. The results are obtained by appropriate treatment of the continuous data records generated by the Hipparcos satellite’s star mapper (which provide simultaneous measurements in two spectral channels), based on predicted star transits using its own ‘Tycho Input Catalogue’. The data treatment is carried out by the Tycho Data Analysis Consortium (TDAC), using calibration and satellite attitude information from the two Hipparcos data reduction consortia. An overview of the data reductions is given. Raw observation data and their numerical treatment are described. This assessment is based on a small data set, i.e. 12 weeks spread over the first 8 months of the Tycho ‘revised mission’ where the satellite is in the elliptical transfer orbit, instead of the intended geostationary orbit.