Cost of transportation

The cost estimates for transportation to Mars cover a large span. From extremely expensive (200 000$/kg) for one way scientific missions, to a more recent estimate of 500$/kg for the SpaceX Mars plans, and even less for future transportation systems.

The main cost parameter for launch systems cost is the number of flights per vehicle. Up till recently that number was one, but re-sibility seems to be achievable soon, and should be expected for any large scale plan for Mars colonization.

Propellant production costs

As far as propellant for launch vehicles is concerned, oxygen, hydrogen, kerosene and methane are all commercially available processes and are considered commodity goods for our purpose. The costs that were considered are in the following table:

Propellant	Density (kg/m3)	Cost ($/kg)	References
Oxygen	1140	0,16	NASA paid 67 cents per gallon for the shuttle, so about $0.16 per kg
Hydrogen	70	3	Hydrogen Production Cost Using Low-Cost Natural Gas, DOE projection, 2012
Kerosene	800	0,4	Commodity price for jet fuel, july 2016
Methane	420	0,2	0,1$/kg natural gas + delivery, refining and liquefaction
Propellant costs for launch vehicles, 2016

Cost to LEO

The main cost of transportation is for the phase from Earth surface to LEO.

	Launch cost economics
Launch cost economics is a complex subject, source of endless debates.  We present a simplified analysis here, for transportation to LEO, using the following equation:
Pc	Payload cost  ($/kg)	Pc= (De+Co*Vg+In+Vg*Vf*(Ma+Fu))/Pm*Vg*Vf
De	Development	Research, management and testing.  Safety requirements for crewed vehicles.  Flight proofing.
Ma	Materials and manufacturing	person hours, testing.
Co	Construction of the vehicle	Materials and manufacturing, person hours, testing.
In	Infrastructure	Manufacturing plants, tooling and launch sites for a series of vehicles
Ma	Maintenance cost per flight	Clean up, repair, upgrades, fueling, set up on pad.
Fu	Fuel cost per flight
Vg	Vehicles per generation	Number of vehicles built per design generation.
Vf	Vehicle flights	Number of flights a vehicle can do.
Pm	Payload mass (kg)
Environmental impact is not included as a cost but needs to be taken into account in the overall analysis. This parameter doomed fission pulsed propulsion and exotic fuels using fluorine, and might become an issue at high flight rates. The table below gives the results for the above equation.  It is based on the requirements of a 20 000 tonne starship such as Icarus Firefly.

Comparison of various launch systems:

Vehicle	Development	Construc- tion	Infra- structure	Flights	Fuel cost per flight	Mainten- ance/flight	Vehicles per generation	Payload	Payload cost
	Billions	millions	billions		millions	millions		kg	$/kg
Delta IV	0,5	300	0,2 B$	1	0,5	2	20	22 000	15 000
Falcon Heavy	0,3	70	0,2 B$	5	0,5	0,5	20	54 000	1 700
Falcon Heavy recoverable	0,7	90	0,2 B$	5	0,5	0,5	20	30 000	520
SpaceX Starship	10	600	2 B$	100	1,25	.5	20	300 000	40
REL Skylon	12	250	0,5 B$	200	0,1	0,1	200	15 000	48
Space gun	0,5	-	2 B$	20 000	0,05	0,01	20 000	1000	925
To achieve these figures ITS and Skylon need to transport, on average, ten times the mass required for the starship, so the minimum ‘size’ of the space economy would need to be ten times larger than what is required for the construction of the starship.  The firing rates requires for the space canon are very high and might not be achievable. These are base costs, without financing, subsidies, insurance or profit. The recoverable Falcon heavy is entirely speculative.

Cost from LEO to Mars

The same analysis that was used to show the gains of reusability can be used for orbital transfer.  Following the radical reduction in cost possible with high volume reusable launchers, the cost of moving to a higher orbit goes down significantly.  The solar electric or nuclear electric thrusters are clearly the most economical solution for the volumes needed for the development of a martian settlement.  

Vehicle	Development (billion$)	Construction (million$)	Infrastructure (billion$)	Flights per vehicle	Fuel cost per flight (million$)	Flights required	Payload per flight (tonnes)	Vehicles required	Total Flight costs (billion$)	Payload cost ($/kg)
Chemical one way	1.0	10.0	0.0	1.0	0	16,667	6	16,667	2,666	26,657
ITS with refuelling	0.0	0.0	0.0	100.0	0	556	180	6	39	389
Beamed power Skylon()	0.0	0.0	1.0	200.0	0.0	6,667	15	33	57	567
Solar electric()	2.0	300.0	0.2	100.0	0	556	180	6	15	151
Nuclear thermal	4.0	300.0	0.0	20.0	0	556	180	28	24	243
Orbital transfer vehicles Costs for 100 000 tonnes to high orbit. 2016$. The chemical one way is paired with the Delta IV vehicle.  For the purpose of this table solar electric is the same as nuclear electric. The payload  cost includes the cost of the Launcher flights required to carry up the propellant.

As for the launch vehicles, the orbital transfer vehicles are unmanned. This reduces cost and complexity tremendously, since there is no need to transport a crew and their living environment.  Docking, fuel and cargo transfer operations may be supervised and teleoperated, and the OTVs are provided with robot arms moving on rails, or similar active elements, that can be used for inspection and repair.  

Low thrust vehicles follow very different trajectories than high thrust vehicles.  They cannot profit from the Oberth effect, and therefore require much higher deltaV for the same mission.  Despite this, their reduced fuel use makes them more economical than high thrust vehicles. At least for most situations that concern the long term occupation of Mars.

	The Oberth effect, the gain from thrust deep in a gravity well
Δveff= Δv·√(2VE/Δv) where Δv= ve·ln(mo/mf)
Δveff	Effective Velocity change (m/s)
VE	Escape velocity (m/s)	Escape velocity of the body around which the vehicle is doing the Oberth maneuver
mo	Initial mass (kg)	Propellant, payload and vehicle structure
mf	Final mass (kg)	Payload and vehicle structure+remaining propellant

Cost to LMO

Propellant production on Mars is mostly a factor of the cost of electrolysis of water.

Propellant	Density (kg/m3)	Cost ($/kg)	References
Oxygen	1140	0,16	Oxygen is a byproduct of hydrogen separation
Hydrogen	70	3	Hydrogen from Electrolysis
Methane	420	0,2	Methane from Sabatier reaction and hydrogen from Electrolysis
Propellant costs for launch vehicles, 2016