Turn an ambition into a testable requirement

A need describes an intended outcome. A requirement — open definition states a condition the system must satisfy. A constraint — open definition limits available solutions, such as a mass allocation, interface or approved operating environment. A design choice is one way of meeting the need within those limits. Mixing these categories can lock a project into a solution before alternatives are compared.

“Return a calibrated time series” describes an outcome more directly than “use this particular camera.” The camera may eventually be chosen, but its selection should follow from required performance and interfaces. Requirements should make the success criterion clear enough to evaluate.

“Send data quickly” is ambiguous. In a fictional exercise, “deliver the specified daily product within six hours of its final observation under the defined contact schedule” gives timing, scope and conditions. The team still needs definitions of product completeness and what happens outside the specified conditions.

Avoid adding precision unsupported by the scientific need. A requirement ten times tighter than necessary can impose major cost with little benefit. Conversely, a vague requirement can allow an implementation that technically passes a review while failing the intended use.

Imagine a detector provides values in one unit while the receiving software assumes another. Each component may work correctly on its own, yet the combined result is wrong. An interface — open definition requirement should define units, timing, meaning, formats and behavior at boundaries, not just the shape of a connector.

Traceability — open definition links each requirement back to a need and forward to the evidence that verifies it. If a proposed requirement has neither a purpose nor a verification — open definition approach, ask whether it is necessary or sufficiently defined. If a critical need has no supporting requirement, it can disappear during implementation.

Trace the interface as well as the parts

Suppose a tighter pointing requirement increases actuator power beyond an allocation. The team must revisit alternatives or the governing requirements through an accountable decision. Quietly ignoring either requirement creates a system whose documented design and actual behavior no longer agree.

Requirements evolve as teams learn, but changes need a rationale and impact review. Recheck connected software, operations and tests. The aim is a consistent set of statements that describe the intended mission and can be supported by evidence, not a long list whose internal contradictions are hidden.