Trace a measurement through the onboard computer

A sensor produces a signal about a physical condition, such as temperature, rotation or light. The onboard system must acquire that signal, associate it with timing and interpret it using appropriate calibration. A stored number is a representation of the condition, with limits and possible errors.

Processing may combine several measurements into an estimate of the spacecraft’s state. That estimate can inform a decision, which is then sent through an interface to an actuator or another subsystem. A complete review follows the chain from measurement to physical response rather than stopping when a command is issued.

A value can be numerically plausible yet too old for the current decision. Imagine a fictional attitude-control task using a rotation measurement from ten seconds earlier while the vehicle is actively turning. The format may be valid, but the time relationship matters to how well it represents the present state.

A useful data interface therefore includes units, timing, validity and the meaning of unavailable values. Different subsystems need compatible definitions. Sending degrees into a calculation expecting radians is not corrected by a faster processor; it is an interface mismatch.

Follow the complete measurement chain

For a fictional sensor, physical value equals stored count times 0.5 plus 2. A count of 20 corresponds to 12 stated units. If the software applies the multiplier but omits the offset, it reports 10. The error is systematic in this example, not random noise that disappears through repeated sampling.

Trace one known input through acquisition, conversion, decision and output. Then test an invalid or stale input and inspect the defined response. These small cases help connect software behavior with the system requirement, while integrated testing must still establish that the real hardware and timing work together.