Short-haul vehicles (surface to orbit, out to 100 planetary diameters or nearby satellites) could have 180 G-hours endurance for bigger payload capacities.
So . . . when I give my Fireflyesque multi-function reaction engines enough on-board fuel endurance to handle 4 round trips to jump point and back from a typical planet for ~5% of ship volume, I'm in the right ballpark, physics-wise?
NOTE: "Multi-function" means these engines use atmosphere for thrust whenever it's available, only using tanked fuel (normally water) when outside a suitable atmosphere.
--
Richard Aiken
"Never insult anyone by accident." Robert A. Heinlein
"I studied the Koran a great deal. I came away from that study with the conviction there have been few religions in the world as deadly to men as Muhammed." Alexis de Tocqueville
"We know a little about a lot of things; just enough to make us dangerous." Dean Winchester (fictional monster hunter portrayed by Jensen Ackles)
"It has been my experience that a gun doesn't care who pulls its trigger." Newton Knight (as portrayed by Matthew McConaughey), to a scoffing Confederate tax collector facing the weapons held by Knight's young children and wife.