ABSTRACT
After an introduction to the ways in which objects’ gravitational fields may be used to probe their structures, the operating principles of accelerometers are described. Although they all act in much the same way (using the inertia of a test mass to detect the acceleration), their details vary from one instrument to another. The range of possible designs is examined by looking at the way specific instruments on spacecraft operate.
Gravity fields are also to be studied by mapping a spacecraft's orbit to high levels of precision. The methods used to measure the orbits and the information obtainable from those measurements are again examined through the use of exemplars.
