My friends and I did some math on #ForAllMankind's Pathfinder shuttle and came to the conclusion that, to be able to reach orbit from an airlaunch, have the propellant fit inside its hull, and be light enough for a C-5 Galaxy to lift it, it needs to have a Liquid Core NTR. From an airplane launch, let us assume you need around 8.8 km/s of ΔV.
A NERVA engine has an Exhaust Velocity of about 8.25 km/s.

Using Tsiolkovsky's rearranged to find the mass ratio, we get that:
e^(8.8/8.25) ≈ 2.9

1/?

@galaxy_map I've been working on trying to map Star Trek to real stars on-and-off for a few years now, with the ultimate goal of perhaps plotting out the course taken by the Enterprises on their respective series.

The scale of the show is, partly, due to the speed of warp (1/?) @galaxy_map Warp travel obviously doesn't exist, and the writers have played loose with it, but *originally* it actually had a very specific range:

In TOS, the speed of a ship in warp is given by

Speed (in xC) = (WarpFactor)^3

So the TOS Enterprise normally pulls of 7^3 = 343c (2/?)