Reactionless drive ships orbital flight in 3rd ed physics?

[Pursuivant]

Originally Posted by weby

In 3rd edition space there was a thing where low thrust ships with wings could fly to orbit on planets with atmosphere if they had a certain % of their mass as thrust.

I checked GURPS 3E Space 3rd Edition & I didn't see anything like what you're describing.

You might be thinking of ships built using modular ship design rules having to use a certain percentage of fuel/reaction mass to get into orbit. Streamlined/winged designs which generate lift would reduce the amount of fuel required, but not by a fixed percentage.

You might be thinking of some of the Transhuman Space books, where there were different formulas for fuel consumption, time, etc. required for operations in different atmospheres or Low, High, or Geosynchronous orbits.