Spacecraft Operations Glossary

Housekeeping telemetry

The measurements a spacecraft sends about its own health: voltages, currents, temperatures, wheel speeds, memory error counts. It is sampled on a schedule, arrives in gaps, and is the first place an anomaly shows.

Standard: ECSS-E-ST-70-41C (the Packet Utilization Standard) defines the housekeeping service.

In Jantar: Every telemetry citation in an investigation names a window of these channels. A gap is recorded as a gap, never filled in.

Telecommand

An instruction sent from the ground to the spacecraft: switch a heater, change a mode, load a table. Many deviations in telemetry are the expected response to a telecommand, not a fault.

Standard: ECSS-E-ST-70-41C defines telecommand packets and their services.

In Jantar: Jantar reads command history. At A0, the default, it constructs no command candidate; A1 staging is an opt-in, off unless a deployment enables it, and no route transmits. A deviation that follows a related command is suppressed before anyone is paged.

TT&C (telemetry, tracking and command)

The link and the ground systems that carry telemetry down, commands up, and the ranging used to track the spacecraft. When a pass returns less than it should, the fault can sit anywhere along it.

In Jantar: Jantar Ground scores each pass against its link budget and asks whether the ground or the spacecraft explains a poor one.

Space packet

The unit most spacecraft use to carry telemetry and telecommands: a short header naming the application process that produced it, a sequence count, and the data.

Standard: CCSDS Space Packet Protocol (133.0-B-2).

FDIR (fault detection, isolation and recovery)

How a spacecraft and its operators notice a fault, find where it is, and recover. On board, it reacts in seconds and often puts the craft into safe mode. On the ground, engineers own the hours after: understanding what happened and deciding what to do.

Standard: ECSS-E-ST-70-11C (space segment operability) sets the requirements.

In Jantar: Jantar works on the ground side of that handover. It investigates and proposes; it has no part in on-board fault handling.

FMECA (failure modes, effects and criticality analysis)

An engineering analysis, written during design, of how each part can fail, what each failure does to the rest of the spacecraft, and how much it matters. It is the operator’s own record of what can go wrong.

Standard: ECSS-Q-ST-30-02C.

In Jantar: A root cause in Jantar must cite a failure mode from the operator’s FMECA. Jantar never drafts an FMECA; without one, it declines to name a cause.

Safe mode

A minimal state a spacecraft enters when on-board protection trips: usually power-positive, often sun-pointing, with non-essential loads off. It keeps the craft alive while the ground works out what went wrong.

In Jantar: A safe-mode entry is where many investigations start. Jantar’s recovery procedure is a draft for a human to review, never an exit command.

Out of family

A reading outside the range the same channel showed under the same conditions before. It is not yet a fault: it is the question an investigation starts from.

Root cause

The failure that explains the observed deviations, as opposed to the symptoms it produced. A good root-cause statement names the part, the failure mode and the evidence for it.

In Jantar: Every claim in a Jantar root cause cites the knowledge graph, a document section or a telemetry window. A claim the evidence does not support is marked ungrounded and blocks release.

Link budget

The accounting of signal gains and losses between transmitter and receiver, which says what a pass should deliver at each elevation. A pass that falls short of it points at the antenna, the RF chain, interference or the spacecraft.

In Jantar: Jantar Ground scores pass quality against the link budget, not against a fixed limit.