Make flight software respect the state

EgSA’s account emphasizes onboard software development. General small-spacecraft avionics handle commands, health reports, stored data and coordinated subsystem actions. Software must decide what an instruction means in the spacecraft’s present condition. The same camera request can be appropriate in one mode and inappropriate in another.

Use three invented modes: Protect, Ready and Image. Protect keeps the camera off; Ready permits an imaging request only when the defined power and pointing checks pass; Image collects a frame and then returns to Ready. These are original teaching states, not disclosed NExSat operating modes or commands.

In this fictional design, imaging is allowed when the battery estimate is at least 60 percent and a pointing-ready flag is true. At 59 percent with correct pointing, the request must be rejected. At exactly 60 percent with correct pointing, it satisfies those two stated conditions. At 80 percent with the flag false, it must still be rejected.

A test set should include the threshold, both sides of it, and combinations of the conditions. The battery percentage is invented; it is not a NExSat limit. A rule can be perfectly implemented yet inappropriate for a real battery or camera, so choosing and validating the requirement remains separate from testing its implementation.

A command depends on the present state

Suppose an invented control cycle must finish within 100 milliseconds. Reading inputs takes 25, calculating takes 45 and delivering outputs takes 20, totaling 90. Adding a 15-millisecond logging task inside that same serial cycle raises the total to 105 and misses the deadline. The extra feature needs a different schedule, more suitable resources or revised requirements justified by the mission.

Retain the software version, test inputs, timing measurements and observed state transitions. NASA’s open cFS framework is a separate example of reusable software: its maintainers explicitly leave mission-specific verification to each project. This does not mean NExSat uses cFS. Reusing components can save work while leaving the assembled mission’s behavior to be demonstrated.