Spacecraft measure onboard acceleration and gravity using sensitive accelerometers.
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Peer-reviewed literature and mission documentation report that spacecraft use sensitive onboard accelerometers and inertial sensors to measure acceleration, non-gravitational forces, and gravity field effects for navigation and geodesy.
A simplified gravitational reference sensor (S-GRS) is an ultra-precise inertial sensor for future Earth geodesy missions. These sensors measure or compensate for all non-gravitational accelerations of the host spacecraft to remove them in the data analysis and recover spacecraft motion due to Earth’s gravity field. Low–low satellite-to-satellite tracking missions like GRACE-FO that use laser ranging interferometers (LRI) are limited by the acceleration noise performance of their electrostatic accelerometers and temporal aliasing associated with Earth’s gravity field. The current accelerometers, used in the GRACE missions, have a limited sensitivity of ∼10-10\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim \,10^{-10}$$\end{document} m/s2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{2}$$\end{document}/Hz1/2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{1/2}$$\end{document} around 1 mHz. The S-GRS is estimated to be at least 40 times more sensitive than the GRACE accelerometers and over 500 times more sensitive if operated on a drag-compensated platform. This improvement is enabled by increasing the mass of the sensor’s test mass, increasing the gap between the test mass and its electrode housing, removing the grounding wire used in GRACE, and replacing it with a UV LED-based charge management system. This allows future missions to take advantage of the sensitivity of the GRACE-FO LRI in the gravity recovery analysis. The S-GRS concept is a simplified version of the flight-proven LISA Pathfinder (LPF) GRS. Performance estimates are based on models vetted during the LPF flight and the expected spacecraft environment based on GRACE-FO data. The relatively low volume (∼104\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim \,10^4$$\end{document} cm3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^3$$\end{document}), mass (∼\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim $$\end{document} 13 kg), and power (∼\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim $$\end{document} 20 W) enable the use of S-GRS on microsatellites, reducing launch costs and allowing more satellite pairs to improve the temporal resolution of gravity field maps. The S-GRS design and analysis, as well as its gravity recovery performance in two candidate mission architectures, are discussed in this article.
Inertial navigation is an essential technology for space applications due to its autonomy from external signals and references. In space, inertial navigation systems utilize accelerometers and gyroscopes to measure changes in velocity and orientation, enabling a spacecraft to determine its trajectory independently, assuming the gravitational accelerations are well known. While conventional accelerometers onboard space missions often suffer from a large drift in the frequency range below 10–3 Hz, quantum accelerometers can provide highly stable and drift-free measurements of non-gravitational acceleration and consequently improve the spacecraft orbits. This work evaluates the performance of a 3-axis quantum accelerometer for space navigation. In this paper, we analyze the performance of such sensors onboard a spacecraft in a parking orbit around Earth in two scenarios of maintaining a nadir-looking orientation and having an inertially fixed spacecraft. To achieve this goal, we simulate a spacecraft in the low Earth orbit using gravitational and non-gravitational accelerations, and we develop an in-orbit performance model for Mach- Zehnder-type quantum accelerometers capable of calculating the detection noise, quantum projection noise, laser frequency noise, wavefront aberration bias, and contrast loss, together with external effects such as the impact of rotation, and gravity gradient for each individual measurement. Using this modeling and based on the propagated orbit, we simulate the measurements of a 3-axis quantum accelerometer along the orbit in two different scenarios: first, we assume the spacecraft to maintain a nadir-pointing orientation, and then we consider another scenario in which the spacecraft is assumed to be inertially- fixed. The results demonstrate that the nadir-pointing orientation introduces more noise, particularly in the along-track and radial directions, due to uncompensated rotation. However, in both the nadir-pointing and inertially fixed scenarios, quantum sensors still produce white noise, consistent with their drift-free measurement capabilities. Furthermore, the findings emphasize the critical role of sensor placement within the spacecraft. Positioning the quantum accelerometer along the main axis of rotation is optimal, as it reduces the impact of centrifugal forces and improves measurement accuracy. This is especially important for spacecraft in nadir-pointing orientations or during maneuvers. This research is the simulation and implementation of a low-Earth orbit, undertaken as a proof-of-concept. In the future, we implement this modeling for a trajectory from Earth to the Moon. We discuss the challenges, limitations, and potential solutions.
<p>In the frame work of HERA mission, the gravimeter for small solar system objects (GRASS) has been developed to measure the local acceleration vector on the surface of the moonlet of the binary asteroid, Dimorphos. GRASS will be onboard Juventas CubeSat which is one of the two daughtercraft of ESA&#8217;s Hera spacecraft. Launched in 2024 it will arrive in the binary system in 2026. Following the soft-landing of the Juventas CubeSat, GRASS will record the temporal variation of the surface gravity vector.</p><p>The average gravitational force expected on the Dimorphos surface is around 5 x 10<sup>-5</sup> m s<sup>-2</sup> (or 5 mGal). Apart from the self-gravitation of the body, centrifugal forces and the acceleration due to the main body of the system contribute to the surface acceleration. The temporal variations of local gravity vector at the landing site will be used to constrain the geological substructure (mass anomalies, local depth and lateral variations of regolith) as well as the surface geophysical environment (tides, dynamic sloped and centrifugal forces).</p><p>We will present the GRASS science objectives in the Hera mission the operational concept that is foreseen to reach these objectives, its current status of development including first test results and the by simulation estimated performances of the instrument.</p><p>&#160;</p>
ended in 2022. The Atmospheric Structure Investigation used sensitive onboard accelerometers to deduce the in situ atmospheric density of Mars during
The Mars Reconnaissance Orbiter (MRO) is a spacecraft designed to search for the existence of water on Mars and provide support for missions to Mars, as part of NASA's Mars Exploration Program. It was launched from Cape Canaveral on August 12, 2005, at 11:43 UTC and reached Mars on March 10, 2006, at 21:24 UTC. In November 2006, after six months of aerobraking, it entered its final science orbit a
During the cruise phase, the MRO also used the Ka band Telecommunications Experiment Package to demonstrate a less power-intensive way to communicate with Earth.
The Optical Navigation Camera images the Martian moons, Phobos and Deimos, against background stars to precisely determine MRO's orbit. Although this is not critical, it was included as a technology test for future orbiting and landing of spacecraft. The Optical Navigation Camera was tested successfully in February and March 2006. It was subsequently turned off, but was turned back on in 2022 to collect data for a potential NASA-ESA Mars Sample Return mission.
Two additional science investigations are also on the spacecraft. The Gravity Field Investigation Package measures variations in the Martian gravitational field through variations in the spacecraft's speed. Speed changes are detected by measuring doppler shifts in MRO's radio signals received on Earth. Data from this investigation can be used to understand the subsurface geology of Mars, determine the density of the atmosphere and track seasonal changes in the location of carbon dioxide deposited on the surface. Due to decreased budgets, data collection ended in 2022.
The Atmospheric Structure Investigation used sensitive onboard accelerometers to deduce the in situ atmospheric density of Mars during aerobraking. The measurements helped provide greater understanding of seasonal wind variations, the effects of dust storms, and the structure of the atmosphere.
The original finding aid described this as: Description: Close up detail views of the Space Acceleration Measurement System Experiment set up in the mid deck showing the instrumentation and the electrical hook ups. The experiment's purpose is to determine to what extent the momentary vibrations of crew movement, equipment operation and spacecraft maneuvers act like gravitational forces on experiments. Another purpose is to measure the quasi-steady accelerations caused by the constant drag and rotation of the orbiting vehicle. Subject Terms: STS-50, COLUMBIA (ORBITER), MIDDECK, RECORDERS, SPACE
The original finding aid described this as: Description: Close up detail views of the Space Acceleration Measurement System Experiment set up in the mid deck showing the instrumentation and the electrical hook ups. The experiment's purpose is to determine to what extent the momentary vibrations of crew movement, equipment operation and spacecraft maneuvers act like gravitational forces on experiments. Another purpose is to measure the quasi-steady accelerations caused by the constant drag and rotation of the orbiting vehicle. Subject Terms: STS-50, COLUMBIA (ORBITER), MIDDECK, RECORDERS, SPACE
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