E-Book Overview
Aerospace craft operate in three dimensional space, and thus must control for complex motions and dynamics. They also have challenging communication, navigation, and automation requirements. For these reason, sensors are absolutely critical to proper aerospace fight and function. This authoritative survey of all major classes of sensors used in aerospace vehicles and support systems will quickly bring the reader up to date on the most recent advances in types of sensors, their uses, and how they can be integrated with one another for total system controls. "Aerospace Sensors" offers invaluable guidance to both practicing aerospace engineers as well as engineering students in aerospace, mechanical electronics, and systems engineering. The reader will find valuable guidance on: principles of operation, design and performance for major classes of aerospace sensors - from gyroscopic inertial navigational systems to accelerometers, to electronic compasses; coverage on radio-altimeters and other autonomous radio sensors for motional parameters; an introduction satellite navigation systems and their aerospace applications, including GPS, GLONASS and GALILEO; and designing for sensor integration, including important facets of sensor system choice, integrated measuring system optimization and the simulation of sensor integration by appropriate algorithms.
E-Book Content
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%0) 3 m but is negligible for ten-metre waves. However, the troposphere allows the passage of long radio waves (l ≅ 3 cm and l ≅ 8 mm) and essentially absorbs waves of l < 3="" cm,="" where="" molecules="" of="" water="" vapor="" and="" oxygen="" have="" resonances.="" in="" hard="" rain="" and="" fog="" the="" conductivity="" falls,="" especially="" at="" l="">< 5="" cm.="" radio="" noise="" invariably="" reaches="" an="" antenna="" along="" with="" any="" useful="" signal,="" and="" may="" be="" atmospheric="" or="" galactic.="" at="" l="">< 10="" cm="" atmospheric="" noise="" is="" more="" powerful="" than="" galactic="">
INTRODUCTION • 13
Two varieties of atmospheric noise are especially intense at l = 1.35 cm and l = 0.5 cm, where the resonance radiation of vapor and oxygen molecules takes place. The ionosphere reflects short radio waves, which is why this band can be used for longdistance radio communication on Earth. Unfortunately, the top of the atmosphere acts as a lens for radio waves and forces them to spread when they are deflected. This affects all signals sent from satellites and other space vehicles to aircraft.
1.2.6
GEOMAGNETISM
The Earth’s magnetic field can be thought of as a simple dipole located at the center of Earth and at 11° to the axis of rotation. This inclination accounts for the displacement of the magnetic pole from the geographical pole. However, some small-scale and large-scale anomalies are superimposed on this main geomagnetic field. The most significant large-scale anomalies are located in the areas above Siberia (increasing) and the Atlantic side of South America (decreasing). They strongly influence the motion of charged particles in the belts of radiation up to heights of thousands of kilometres above the Earth. Detailed maps of the geomagnetic field have been obtained through experimentation, but this field is unstable for many reasons. Electric currents in the upper atmosphere (ionosphere and higher) cause the values of some components of the field to vary, and become especially large during auroras, when geomagnetic storms take place. Slow geological processes also cause the values of the main components of the field to vary. The magnetic field of the Earth is always compressed on the side toward the Sun due to the stream of solar plasma (solar wind). T