Wikipedia says that: Atmospheric and gravity drag associated with [space] launch typically adds 1.3 to 1.8 km/s to the launch vehicle delta-v required to reach normal LEO orbital velocity of around 7.8 km/s (28,080 km/h). Does anyone know, or know how to calculate/estimate/simulate the delta-v required to overcome atmospheric and gravity drag (excluding the 7.8 km/s for orbital velocity) if you were launching from 13km altitude? ie a commercial jetliner. I'm guessing it would be a lot less since its already only around 0.1 atm pressure up there. I also suspect its very difficult to work out.