What about ion engines? I'm extremely not sure I have this math right but NEXT claims 4190 second ISP [0]. Plugging that into the rocket equation I get: iss_

What about ion engines? I'm extremely not sure I have this math right but NEXT claims 4190 second ISP [0]. Plugging that into the rocket equation I get: iss_mass = 419600 sep_isp = 4190 delta_v = 5748 htv_payload = 3310 falcon_launch_cost = 62000000 total_mass = iss_mass * math.exp(delta_v / (9.8 * sep_isp)) fuel_load = total_mass - iss_mass dragon_launches = math.floor(fuel_load / htv_payload) total_cost = dragon_launches * falcon_launch_cost I get: Total vehicle mass: 482,646.89 kg Fuel to add: 63,046.89 kg Dragon 2 launches: 19 Total cost: $1,178,000,000.00 Not what you'd call cheap but at least in the realm of the possible. I'm assuming the ISS' solar panels (~120 kW [1]) is sufficient to power the thruster, that a dragon launch costs no more than a falcon launch (certainly false), and that the ion engine is already on board the station. [0] https://en.wikipedia.org/wiki/NEXT_(ion_thruster) [1] https://en.wikipedia.org/wiki/Electrical_system_of_the_International_Space_Station