|Slide from Elon Musk's BFR presentation at the IAC conference in Adelaide 2017|
Costs increase from left to right -- should prolly be a log scale. Click to enlarge.
In his presentation to the International Aeronautical Conference in Adelaide, Musk said something significant which I didn't get, first time round. He said that the cost per launch of the BFR/BFS combo, because the BFR and BFS will be fully reusable, would be cheaper than the cost per launch of the Falcon 1. The published cost of a Falcon 1 launch was $8.5 million.
Let's assume $1 million for fuel and another $1 mill for refurbishment every launch, which leaves $6.5 million to cover capital costs/depreciation and profit. The booster (BFR) will be used again and again, perhaps 100 times (Musk thinks it could be 1000 times), but it's more complicated with the ship (the BFS) because it will be used for different purposes. As a spaceship used only to reach Mars, its likely total number of uses will be limited, because Mars and Earth are only in opposition every 26 months. On the other hand, it could be used far more often on the moon run (only 3 days away) and for point-to-point fights on Earth. SpaceX would prolly use a Mars spaceship for moon missions and point-to-point flights in the 20 months between Mars missions, provided it could be unloaded it quickly enough on Mars for it to return to Earth before Mars and Earth moved too far apart. So it's feasible that you could use the BFS almost as often as the BFR.
Let's use Sam Dinkin's capital cost from my earlier stab at estimating costings, $185 million for the BFR and $150 million for the BFS. Let's assume just 50 launches for the BFS to allow for time taken to and from Mars (6 months) and some period spent on Mars loading and refuelling. That means the capital cost per launch of the combo would be ($185/100)+($150/50) or roughly $5 million per launch. Add our assumptions for fuel and maintenance and you get $7 million.
So how much would it cost to send one mission to Mars? $7 million for the BFR/BFS combo, plus 5 refuelling launches which would each cost about $4 million ($7 million just takes the BFS to LEO -- low Earth orbit) That's a total cost of $27 million. Add in additional costs for the first mission, such as the two cargo ships containing equipment the first settlers will need, plus a cargo ship to accompany the spaceship, and that totals $100 million or so, still 3 orders of magnitude less than any competing proposal. NASA's estimated cost for a mere handful of astronauts is $100 billion.
It all hinges on re-usability. If the BFR and BFS are re-usable even just 100 times, space travel becomes cheap. Satellites launches, trips to the ISS, trips to the moon to start a moon base, colonising Mars, mining the asteroid belt: all become economically feasible. When Musk first said that he would make his rockets re-usable everybody fell about laughing. No one else has managed it, they chortled. Now SpaceX routinely lands the Falcon 9 first stage and re-uses it. He now says he will be able to re-use his rockets 1000 times, and we all doubt him, even me. Perhaps we shouldn't.