For every 25 kg of a fully-fueled launch vehicle, only 1 kg is payload to low earth orbit (LEO). For every 1 kg sent to Mars, there is 100 kg of launch vehicle mass. You want to get back from Mars? That’s another topic. With orbital refueling, it is possible to raise the payload ratio from one percent back to four percent, quadrupling the mass of the vehicle sent to Mars. Unfortunately, LEO is a risky place to have spacecraft lingering for long periods with large amounts of propellant on board. Fortunately, there’s a lot of progress being made recently in all these areas.
