[skorgu]

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

[dalke]

If there's only one engine then that's 236 mN thrust according to your [1]. Lets call it 4.12 N - put a few thrusters on or improve the technology.

The station mass is 419,455 kg. F = ma so the acceleration is 1 µ G.

It will take a very long time to get to Mars that way.

[skorgu]

About 18 years assuming I'm using the right formula:

http://www.wolframalpha.com/input/?i=acceleration+formula&ra...