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.

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.