Which dataset provides the detailed trajectory of a spacecraft over time?

Which dataset provides the detailed trajectory of a spacecraft over time?

• A. TLEs
• B. Ground station logs
• C. Ephemeris data
• D. Propellant usage records

Answer: (C)

Ephemeris data provide the spacecraft’s position and velocity as a function of time, i.e., its trajectory over time. These datasets are generated from orbit determination using tracking measurements and encode time-tagged state vectors (and sometimes higher-order derivatives), giving a detailed path the spacecraft is expected to follow. TLEs offer a compact, epoch-based orbital representation used for approximate propagations but do not deliver a continuous, detailed trajectory. Ground station logs capture when and what measurements were made during passes, not a ready-to-use trajectory. Propellant usage records track fuel mass changes and maneuvers, not the path through space. So the detailed trajectory over time comes from ephemeris data.