Which description best corresponds to the 'space' functional element of GPS?

• A. The ground-based monitoring network
• B. The satellites in orbit
• C. The control segment and master station
• D. The user receiver

Answer: (B)

The space element of GPS is the satellites in orbit. These satellites carry very precise atomic clocks and continuously transmit signals that include the navigation message and ephemeris data describing their exact orbits. A receiver uses the time it takes for those signals to reach it—combined with the satellite’s broadcast data—to determine pseudorange distances to multiple satellites. With signals from at least four satellites, the receiver can solve for its own position and clock error.

The other parts of the system live on the ground or in the user’s hands: the ground-based monitoring network and master control station make up the control segment that track and manage satellites, updating orbital and timing information; the user receiver is the portion that processes the signals to compute your location. Since this question focuses on which part is in space, the satellites in orbit are the correct description.