Hartebeesthoek: keep a spacecraft connected

SANSA Space Operations provides tracking, telemetry — open definition and command services from Hartebeesthoek. Its heritage reaches back to NASA and JPL operations in the early 1960s. Today the programme describes support for geosynchronous, polar-orbiting and scientific spacecraft. A national space capability can therefore include helping operate missions owned by many different customers, as well as building domestic satellites.

The three terms describe different jobs. Tracking helps determine where a spacecraft is and how it is moving. Telemetry brings measurements of spacecraft condition and activity to the ground. Command sends instructions in the other direction. They work together: a team needs a useful pointing prediction to establish contact, then interpretable telemetry to understand whether an authorized command had the intended effect.

A low-orbiting spacecraft is visible from a particular station for only part of its orbit. Acquiring the signal and completing checks takes time within that opportunity. In an invented eight-minute contact, suppose acquisition and setup require two minutes, and the remaining six minutes carry usable data at a constant two megabits per second. The simplified capacity is 360 seconds multiplied by two, or 720 megabits.

That calculation deliberately assumes the stated rate is usable data after overhead and that there are no interruptions. If the two-megabit rate instead describes the raw radio channel, headers, coding and retransmission can reduce the delivered file volume. A larger antenna or a longer nominal visibility window is therefore not, by itself, a guarantee that every planned file will arrive. Operations planning needs compatible equipment, schedules and a realistic delivery budget.

Turn visibility into a usable data budget

Imagine a command asks a spacecraft to change a heater setting. A ground log saying sent establishes a transmission attempt. An onboard acknowledgment can establish receipt or acceptance, depending on the protocol. Later telemetry showing the new setting and expected behavior provides stronger evidence of execution. Keeping these stages separate makes a contact log useful when an operation does not go as planned.

A useful contact record includes the station, spacecraft, time interval, equipment configuration and results. Preserve unsuccessful attempts too: they can reveal whether a recurring gap follows a particular pass or setting. A photograph of an antenna cannot establish those operational details. SANSA’s programme description supplies the South African context; the engineering exercise explains why antennas, people and information handling all belong in a mission story.