A few notes on the Engine -
Ludicrous ISP (5,200,000) - But this matches the performance figures given in the short story The Drive - http://www.syfy.com/theexpanse/drive/ , matched up with further details from Atomic Rockets website http://www.projectrho.com/public_html/rocket/enginelist.php#epstein
Runs on "efficiency" - Just kidding - Fuel is 99.8% water, .1% Lithium6 and .1% Deuterium.
Requires power to start. Generates a modest amount of electricity when running (alternator module) but can also generate power when idle (reactor mode) Currently does not generate MJ
Works with tweakscale - Prefab sizes of 1.25m, 2.5m, 3.75m, 5m, 7.5m, 10m, 15m, 20m, 30m, 40m
Here are some screenshots of the Epstein Engine (in its 2.5m size) in action propelling a 'Yatcht' consisting of a 3 Kerbal pod with a ~1/3 vehicle mass fuel load.
Note the total Delta V is roughly 6% c
Engine effects still need work.
Note - Note the 7 G thrust - Unlike other high ISP engines, this one is totally unbalanced as it also provides a high TWR
I'm still not totally happy with the texture maps, but it's a start.