From the expected scientific applications to the functional specifications, products and performance of the SABRINA missions

AIAA Guidance, Navigation, and Control Conference

Grassi

2010

This paper deals with the GPS-based relative navigation of LEO formations. Specifically, we consider applications characterized by two co-flying satellites with a large and highly variable separation, which are relevant to next generation monostatic/bistatic Synthetic Aperture Radar missions. In these applications, both scientific goals and control needs require the determination of the relative state with high accuracy. To this end, an Extended Kalman Filter is developed that processes double-difference pseudorange and carrier phase measurements on L1 and L2 frequencies. To preserve accuracy and robustness of the integer solution problem against large variations of the baseline, an original approach is developed in which, for each receiver, the Vertical Total Electron Content is included in the filter state. In addition, the double-difference ambiguities are re-estimated by the filter at each time step. A major technical problem of a filter processing double-differences is re-organizing the filter state when the pivot satellite changes. This is solved by an original and effective procedure that speeds up the filter convergence. Once the floating point estimates of the double-difference ambiguities have been produced by the dynamic filter, their integer values are extracted with the Least-Square Ambiguity Decorrelation Adjustment method and processed within a kinematic filter to estimate the relative position with high accuracy. Filter robustness and performance are evaluated by means of Monte Carlo simulations performed on the reference orbital scenario identified within the Italian SABRINA mission study. Results show that the integer ambiguities are always resolved, allowing to achieve a centimeter-level accuracy in all the simulated conditions.

Section: Filter Validationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

GPS-based Relative Navigation of LEO formations with Varying Baselines

Tancredi

AIAA Guidance, Navigation, and Control Conference

Grassi

2010

“…With specific reference to Low Earth Orbit (LEO) missions, remote sensing applications based on using Synthetic Aperture Radars (SAR) are meaningful examples of formation flying. Cross-Track Interferometry (XTI) and Large-Baseline Bistatic (LBB) SAR applications rely on processing radar images of the same scene produced by two or more physically separated antennas [1]- [3], which shall be distributed on different spacecraft following specific relative orbital paths in order to realize the desired separation.…”

Section: Introductionmentioning

confidence: 99%

“…The size of the physical separation, i.e. the baseline, depends on the considered application, and can range from a few hundreds of meters in XTI applications [1], [2] to a few hundreds of kilometers in LBB SAR missions [3]. Depending on the application, the knowledge of the inter-satellite separation up to the millimeter level may be required also over very long baselines (i.e.…”

Section: Introductionmentioning

confidence: 99%

Real-Time Relative Positioning of Spacecraft over Long Baselines

Tancredi

Journal of Guidance, Control, and Dynamics

Grassi

2014

This paper deals with the problem of real-time onboard relative positioning of low-Earth-orbit spacecraft over long\ud baselines using the Global Positioning System. Large intersatellite separations, up to hundreds of kilometers, are of\ud interest to multistatic and bistatic synthetic-aperture radar applications, in which highly accurate relative positioning\ud may be required in spite of the long baseline. To compute the baseline with high accuracy, the integer nature of dualfrequency,\ud double-difference carrier-phase ambiguities can be exploited. However, the large intersatellite separation\ud complicates the integer-ambiguities determination task due to the presence of significant differential ionospheric\ud delays and broadcast ephemeris errors. To overcome this problem, an original approach is proposed, combining an\ud extended Kalman filter with an integer least-square estimator in a closed-loop scheme, capable of fast on-the-fly\ud integer-ambiguities resolution. These integer solutions are then used to compute the relative positions with a singleepoch\ud kinematic least-square algorithm that processes ionospheric-free combinations of debiased carrier-phase\ud measurements. Approach performance and robustness are assessed by using the flight data of the Gravity Recovery\ud and Climate Experiment mission. Results show that the baseline can be computed in real time with decimeter-level\ud accuracy in different operating conditions

Bistatic Synthetic Aperture Radar

Moccia

Distributed Space Missions for Earth System Monitoring

2012

Bistatic Synthetic Aperture Radar represents an active research and\ud development area in radar technology. In addition, Bistatic and Multistatic SAR concepts are tightly related to formation flying and distributed space missions that also represent the new space-based remote sensing and surveillance frontiers. This chapter introduces Bistatic SAR, in particular by comparing its peculiarities, operation and performance with respect to conventional monostatic SAR. Some\ud basic concepts of bistatic SAR image formation and the main elements of bistatic SAR geometry are preliminary presented. Performance parameters are then analyzed, including geometric resolution, radiometric resolution and bistatic radar equation. Special emphasis is placed on analytical methods to evaluate the effects of bistatic SAR geometry on image resolution. Further implementation issues, such\ud as footprint, time and phase synchronization are also pointed out. The analysis of past bistatic radar and bistatic SAR experiments and proposed spaceborne bistatic SAR missions supplies essential information to understand how these issues have been faced and can be potentially solved in ongoing and future operational systems.\ud Finally, several scientific applications of bistatic SAR are outlined taking advantages of different techniques and methods