> it only takes 1000 KwH of energy to lift an average
> sized man out of the Earth's gravitational field

I guess this is a calculation of potential gravitational energy, which is given by the formula PE=mgh. This is the minimum theoretical energy that can do the job, if there are no losses other than doing work against gravity.

Suppose the astronaut is 72 kilograms in mass. Approximate gravity as 10m/s^2. Raise the astronaut to low earth orbit (say 100km). Multiply those together and you get 20 kilowatt hours, so I guess it's reasonable that 1000kWh would be enough to leave the earth's gravitational field (for all practical purposes).