Well, the other way to check if I am right or wrong is to back calculate the rocket equation. Instead of relying what I say, what’s the payload mass to propellant mass of the BFR? Saturn V (the rocket equation is the same for the BFR, and it is using recoverable boosters and a compromise fuel (liquid CH4) so I expect it to perform slightly worse) it’s 6.5 million pounds total rocket mass, 85% payload, to 261,000 lbs to LEO. So 4% of the mass is payload, 85⁄4 = 21.25 kg of propellant for every kilogram of payload.
Ok, CH4 + 202 = CO2 + 2H20
1⁄3 of the mass is the CH4, while 2⁄3 is O2. That helps a lot as liquid oxygen is cheaper, only 16 cents per kilogram. So $2.26 for the liquid oxygen.
Well, how much does 7.08kg of liquid methane cost? (note that BFR needs purified methane and cannot use straight natural gas)
2.757 gge * 1.14 = 3.14 therm. Average prices presently per therm are $0.92. So $2.89 for the unpurified fuel. Then you need to purify it to pure methane (obviously with some loss of energy/gas/filter media) and liquify it. I am going to assume this raises the cost 50%. So $4.33 for the natural gas. Total cost per kg for the fuel is $4.33+2.26 = $6.59.
$10 a kg for payload to LEO, including the rocket, seems rather optimistic. Remember the rocket needs repair and will occasionally blow up. Helicopters and other much lower energy terrestrial machines, the maintenance + repairs are often either similar or more expensive than the price of the fuel. I would expect the real minimum cost per kg to be at least 3 times the cost of fuel: 2 units of repair/replacing exploded rocket parts for every kg of propellant. Or $19.78 per kg, which would be phenomenal results compared to today’s $2720 a kg (using spaceX now), and just half as good as Elon Musk’s promise.
Hard laws of nature here. I want to go to space as well but it takes a literal swimming pool of fuel under you to do it, and while SpaceX has made some impressive advances, it doesn’t change the basic parameters of the problem.
Well, the other way to check if I am right or wrong is to back calculate the rocket equation. Instead of relying what I say, what’s the payload mass to propellant mass of the BFR? Saturn V (the rocket equation is the same for the BFR, and it is using recoverable boosters and a compromise fuel (liquid CH4) so I expect it to perform slightly worse) it’s 6.5 million pounds total rocket mass, 85% payload, to 261,000 lbs to LEO. So 4% of the mass is payload, 85⁄4 = 21.25 kg of propellant for every kilogram of payload.
Ok, CH4 + 202 = CO2 + 2H20
1⁄3 of the mass is the CH4, while 2⁄3 is O2. That helps a lot as liquid oxygen is cheaper, only 16 cents per kilogram. So $2.26 for the liquid oxygen.
Well, how much does 7.08kg of liquid methane cost? (note that BFR needs purified methane and cannot use straight natural gas)
Well, 1.14 Therm = 1 gge = 5.660 lb. So 21.25kg = 15.61 pound, 15.61 pound/5.660 = 2.757 gge.
2.757 gge * 1.14 = 3.14 therm. Average prices presently per therm are $0.92. So $2.89 for the unpurified fuel. Then you need to purify it to pure methane (obviously with some loss of energy/gas/filter media) and liquify it. I am going to assume this raises the cost 50%. So $4.33 for the natural gas. Total cost per kg for the fuel is $4.33+2.26 = $6.59.
$10 a kg for payload to LEO, including the rocket, seems rather optimistic. Remember the rocket needs repair and will occasionally blow up. Helicopters and other much lower energy terrestrial machines, the maintenance + repairs are often either similar or more expensive than the price of the fuel. I would expect the real minimum cost per kg to be at least 3 times the cost of fuel: 2 units of repair/replacing exploded rocket parts for every kg of propellant. Or $19.78 per kg, which would be phenomenal results compared to today’s $2720 a kg (using spaceX now), and just half as good as Elon Musk’s promise.
Hard laws of nature here. I want to go to space as well but it takes a literal swimming pool of fuel under you to do it, and while SpaceX has made some impressive advances, it doesn’t change the basic parameters of the problem.