http://spacebombardment.blogspot.com...and-clock.html

Propulsion System ISP (Hours)
AM-Beam MAX..................2,834
H-Fe Fusion MAX.............1,417
H-He Fusion MAX...............850
IC-Fusion MAX ................283
ORION MAX ....................278
NSWR 90% UTB MAX...............133
AIM ..........................17
VASIMR (high gear) .............8
Mini-Mag Orion .................6
ORION Low Altitude ..............4
1959 ORION 2nd Gen...............3
ORION Fusion ...................2
ORION Fission ..................1
1959 ORION 1st Gen...............1
Space Shuttle x3 SSME............0
Saturn-V first stage ............0
Single Saturn-V F-1 .............0
Space Shuttle x2 SRB.............0