From Frontierpedia, the wiki for the Frontier Universe
The FENNEL engine is a Roman rocket engine based on technology deciphered from the Codex. It belongs to the propulsion technology used by the Roman Empire for spaceflight.
Its operating principle is classified. The Codex Administrative Council treats the engine as a strategic core technology and maintains strict control over the knowledge required to reproduce it.
Codex origin
The engine emerged from the organised interpretation of technical material preserved in the Codex. It is therefore recorded as a derived Roman technology rather than an independently developed conventional engine.
Public records identify the Codex as the source of the design but do not describe the mechanism by which the engine produces thrust. The absence of that detail reflects official secrecy, not an incomplete designation.
Name
The name refers to the tradition that Prometheus concealed fire inside a fennel stalk before giving it to humankind. Roman interpreters connected the recovered technical knowledge of the Codex with that earlier gift of fire.
A memoir attributed to the engine’s chief interpreter presents the FENNEL name as a declaration that humanity, carrying the gift in return, had become capable of travelling toward Prometheus.
Classification and control
The Codex Administrative Council designates FENNEL as one of the Empire’s strategic core technologies. Technical custody therefore rests with an imperial body responsible for the management of Codex-derived knowledge.
The Council restricts access to the engine’s operating principle and controls its transmission. The technology is not treated as open knowledge even within Roman technical institutions.
Records concerning the engine accordingly distinguish between facts that may be publicly named—its Codex origin, category, and controlling authority—and the classified engineering details needed for construction or operation.
Role and distinction
FENNEL belongs to the propulsion systems of Roman spacecraft. The engine concerns the movement of a vessel under its own power.
It is distinct from the Via Imperii, whose fixed gates create controlled passages between star systems. A ship may depend on both technologies during an interstellar voyage, but they remain separate systems with different functions.