Given the question: Extract the answer to the question from the following context. Question: What is the position of Compass-M1 compared to the Earth? Context: Compass-M1 is an experimental satellite launched for signal testing and validation and for the frequency filing on 14 April 2007. The role of Compass-M1 for Compass is similar to the role of the GIOVE satellites for the Galileo system. The orbit of Compass-M1 is nearly circular, has an altitude of 21,150 km and an inclination of 55.5 degrees.
The answer is:
altitude of 21,150 km