Integer ambiguity fixing is routinely applied to double-differenced GPS phase measurements to achieve precise positioning. Double-differencing is interesting because it removes most of the common errors between the different signal paths. However, if common errors can be estimated it becomes attractive to fix integer ambiguities on undifferenced measurements. Phase measurements then become pseudorange-like measurements with a noise level of a few millimeters.This paper introduces a new method for fixing dual-frequency GPS ambiguities on undifferenced phase measurements either locally or globally. The clocks for the GPS constellation obtained during this process can be used for precise point positioning of ground based receivers and for precise orbit determination of low Earth orbiting satellites. The resulting positioning precision is comparable to that of standard differential positioning without the need for a reference station. Ambiguity-fixed satellite orbits for the GRACE and Jason satellites are more precise than the most precise solution available today.
On the NASA 2020 rover mission to Jezero crater, the remote determination of the texture, mineralogy and chemistry of rocks is essential to quickly and thoroughly characterize an area and to optimize the selection of samples for return to Earth. As part of the Perseverance payload, SuperCam is a suite of five techniques that provide critical and complementary observations via Laser-Induced Breakdown Spectroscopy (LIBS), Time-Resolved Raman and Luminescence (TRR/L), visible and near-infrared spectroscopy (VISIR), high-resolution color imaging (RMI), and acoustic recording (MIC). SuperCam operates at remote distances, primarily 2–7 m, while providing data at sub-mm to mm scales. We report on SuperCam’s science objectives in the context of the Mars 2020 mission goals and ways the different techniques can address these questions. The instrument is made up of three separate subsystems: the Mast Unit is designed and built in France; the Body Unit is provided by the United States; the calibration target holder is contributed by Spain, and the targets themselves by the entire science team. This publication focuses on the design, development, and tests of the Mast Unit; companion papers describe the other units. The goal of this work is to provide an understanding of the technical choices made, the constraints that were imposed, and ultimately the validated performance of the flight model as it leaves Earth, and it will serve as the foundation for Mars operations and future processing of the data.
To achieve maximum benefit from the altimetric data collected by the French‐American TOPEX/POSEIDON spacecraft, radial orbit accuracy of 10 cm or better is required. This unprecedented requirement led the French Space Agency Centre National d'Etudes Spatiales (CNES) to develop a new high‐accuracy tracking system, Doppler orbitography and radiopositioning integrated by satellite (DORIS), and a new precision orbit production facility, the Service d'Orbitographie DORIS. A global effort produced new models and new orbit determination strategies. The result of these efforts has been assessed after 1 year of operation. The original goal has clearly been met, and the TOPEX/POSEIDON orbits produced by NASA and CNES agree to better than the 5 cm RMS level in the radial direction. At this level of accuracy, traditional techniques cannot correctly describe the actual orbit error, and some new procedures are proposed.
We show that the gravitational field equations derived from an action composed of i) an arbitrary function of the scalar curvature and other scalar fields plus ii) connection-independent kinetic and source terms, are identical whether one chooses nonmetricity to vanish and have non-zero torsion or vice versa.
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