The Epstein Drive is an advanced VASMIR drive system that can provide continuous thrust. It was invented by Solomon Epstein one hundred and fifty years ago on Mars. The drive utilizes magnetic coil exhaust acceleration to increase drive efficiency (to approximately 0.1 kg*m^2), which enables spaceships to sustain thrust throughout the entire voyage. A ship fitted with the efficient Epstein drive is able to run the drive continuously for acceleration to its goal and then after flipping at about the halfway point is able to run the drive continuously during deceleration. Previous engine designs used propellant less efficiently and could not be run long enough to achieve the high velocities that the Epstein drive permitted.
However, running under continuous thrust causes wear and tear on a ship and its engine. The Thrust rating of a ship is its’ Maximum Continuous Thrust rating. However, running at that rate requires an Average (8+) Engineer(M-Drive) check once per day with a cumulative DM-1 for every day of running at that speed. So a ship with Thrust-1 would have to make a check at DM-1. On the second day the check is made at DM-2 and so on. When a roll is failed, roll 4D6 to determine how many hours into the day the ship made it before the breakdown (sometime between 4 to 24 hours). A breakdown (equivalent to a critical hit on the drive) can be temporarily patched using the normal repair rules on page 161 of the Main Rule Book).
In order to stress the engine less, ships usually run at less than full power. At ½ thrust the Engineer(M-Drive) check is only made once every 6 days (roll 1D6 to determine which day the breakdown occurs on if a failure occurs). But most ships usually travel at 1/3 of max thrust. At that speed the Engineer(M-Drive) check is made every 12 days (roll 2D6 to determine the breakdown day).
Typical thrust ratings for most large ships are Thrust-1 (1G Full, 0.5G Half, 0.33G Third), Thrust-2 (2G Full, 1G Half, 0.66G Third), and Thrust-3 (3G Full, 1.5G Half, 1G Third). Typically, only fighters and some small craft can have engines rated to go faster than Thrust-3 but they do not carry enough fuel for long flights.
Travel times and a rough fuel consumption can be determined using the Space Travel Calculator and entering the weight of the non-fuel/fuel tank parts of the ship as the payload.
Skill test summary:
- Running at Full Continuous Thrust: Average (8+) Engineer (M-Drive) check (4D x 1 hours, INT). DM-1 per Day cumulative.
- Running at 1/2 Continuous Thrust: Average (8+) Engineer (M-Drive) check (1D x 1 Days, INT). DM-1 per 6 Days cumulative.
- Running at 1/3 Continuous Thrust: Average (8+) Engineer (M-Drive) check (2D x 1 Days, INT). DM-1 per 12 Days cumulative.