The general thrust equation is force = propellant's mass per second X exhaust velocity, right? What if the propellant is highly relativistic? One gram of propellant expelled at 290,000,000 m/s should produce 290,000 N, according to the above equation. However, this doesn't take relativistic change into account.

What I want to know is how to calculate thrust when relativistic exhaust is involved.

The general thrust equation is $F = \frac{dm}{dt}\cdot v$, where $m$ is propellant's mass and $v$ is the exhaust velocity, is the equation right? What if the propellant is highly relativistic? One gram of propellant expelled at $290,000,000\ \text{m/s}$ should produce $290,000\ \text{N}$, according to the above equation. However, this doesn't take relativistic change into account.

What I want to know is how to calculate thrust when relativistic exhaust is involved.