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Thermospheric Density and Wind Determination from Satellite Dynamics
This book covers advances in the algorithms used for processing satellite accelerometry and Two-Line Element TLE orbit data in the collection of data on atmosphere and wind. Coverage includes an extensive analysis of the resulting density and wind products. Wanderungen in die Erdgeschichte:. In reality, the transition is gradual and a tiny fraction of the atmophere gases is still present at the altitude of low orbiting satellites.
Currently, the U. Figure 3.
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Each black dot in this image shows either a functioning satellite, an inactive satellite, or a piece of debris. Although the space near Earth looks crowded, each dot is much larger than the satellite or debris it represents, and collisions are extremely rare. The consequences of a spacecraft collision with debris can range from performance degradation to failure and satellite fragmentation.
In LEO, debris as small as a few millimeters in diameter can puncture unprotected fuel lines and damage sensitive components, while debris smaller than 1 mm in diameter can erode thermal surfaces and damage optics. Although smaller objects can partly be mitigated through the use of meteor bumpers, such as on the ISS, the only way to mitigate larger objects impact is to maneuver the spacecraft to avoid collision.
Such maneuvers are expensive, impact the operation of sensitive experiments on board, and ideally should only be done if the chance of collision is high. To assess the risk, and mitigate the likelihood of collision, the SSN monitors these objects and predicts their orbits about three days ahead.
Orbit propagation models are used to determine the location of space objects in the relatively near-term typically over a period of a few days or less for purposes of collision avoidance or re-entry predictions, and also to make long-term predictions typically over a period of years about the debris environment. Since accurate orbit propagation models that include all forces acting on an orbiting object can be very computation intensive, most models take into account only the forces that most strongly affect the space objects in particular orbital regions.
The primary forces acting on a space object in LEO are atmospheric drag and gravitational attraction of the Earth . The largest uncertainty in determining orbits for satellites operating in low Earth orbit is the atmospheric drag. Drag is the most difficult force to model mainly because of the complexity of neutral atmosphere variations driven by the Sun, and the propagation from below of lower atmosphere waves [5, 6]. Atmospheric neutral density models routinely used in orbit determination applications are mainly empirical.
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These models are based on historical observations to which parametric equations have been fitted, representing the known variations of the upper atmosphere with local time, latitude, season, solar and geomagnetic activity [7, 8, 9]. First-principle or physics-based models can also provide information about the atmospheric density conditions. Unlike empirical models, first principles physics models seek to calculate a physical quantity starting directly from established laws of physics without making assumptions such as empirical or fitted parameters.
Taking into account the interactions between upper atmosphere winds, composition and densities, first-principle models are able to provide a realistic representation of neutral density in the upper atmosphere if the magnitude, spatial distribution, and temporal evolution of the solar sources can be defined with sufficient accuracy, especially in long-duration magnetic storm events . As the time progresses, the satellite will encounter denser air following the beginning of the magnetic storm starting around Universal Time. As the storm comes to end, atmospheric density slowly goes back to quiet conditions.
Fuller-Rowell, and M. Codrescu , Global Joule heating index derived from thermospheric density physics-based modeling and observations, Space Weather, 10, S, doi Crowther, R. London, Ser.
Atmospheric Remnants in the Low Earth Orbit Region around km Altitude
Alle Produkte. Steiner eds. After obtaining his diploma at Sint Maartenscollege in Maastricht, he started studying aerospace engineering at Delft University of Technology in His master's thesis, completed in August , was on the topic of nongravitational force modelling in the orbit determination of ESA's ERS and Envisat Earth observation satellites.
After graduation, he initially started work on several projects related to satellite radar altimetry and precise orbit determination of radar altimeter satellites. The year marked the start of a transition to a series of research projects performed for the European Space Agency ESA , aimed at the development and testing of algorithms for deriving thermospheric density from satellite observations, and the improvement of thermosphere density models.