The energy curve is the story
A spacecraft with nonzero rest mass can approach the speed of light but cannot be accelerated to it with finite energy. In an inertial frame its kinetic energy is K = (γ − 1)mc², where γ = 1/√(1 − β²) and β = v/c.
The calculator uses these expressions to compare ideal scenarios. It includes neither an engine efficiency nor the mass of an energy source. The kinetic energy displayed is a lower-level physical requirement, not electrical input energy or a spacecraft design estimate.
Two clocks, one trip
For a constant-speed cruise over distance L measured in the departure/destination frame, the coordinate travel time is L/v and the traveler’s elapsed proper time is L/(γv). The shorter traveler time does not make the spacecraft locally faster than light.
The example distance is an editable 4.24 light-years. This is a simplified distance scale, not an ephemeris or a navigable route. Acceleration, deceleration, target motion and gravity are omitted. A real mission would integrate the full trajectory and its clock history.
Arrival is part of the energy budget
A fast flyby and a rendezvous are different missions. Stopping relative to the destination requires a momentum and energy exchange of its own. A launch beam behind the spacecraft is not automatically a braking system at the destination.
Use the calculator to interrogate a claim: what mass, what speed, whose clock and which energy boundary? Then return to engineering. The controls stop below c because there is no finite output for a massive spacecraft at c within this model.
Questions worth asking
Does time dilation let the ship exceed light speed?
No. It changes elapsed time between frames; it does not let a spacecraft outrun light in its local inertial frame.
Does the energy result include braking?
No. It is the ideal kinetic energy of the cruise state in the chosen frame. Propulsion losses, acceleration history and braking are excluded.
SOURCES & SCOPE / REVIEWED 23 OCTOBER 2026
- DOE Explains Relativity ↗Institutional explanation of special and general relativity.
- Relativistic spacecraft propelled by directed energy — Kulkarni, Lubin & Zhang ↗Published theoretical treatment; not Metric Flight hardware.
External research is not Metric Flight performance. Concept images and diagrams are illustrative. This project introduces no new company experimental result.
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