Rocket fuel; not as expensive as you'd think

A few days ago, there was a discussion on Reddit on whether it would be affordable for a person living today to go into orbit in their lifetime. A number of people stepped in to claim authoritatively that it could never happen. Their reasoning was rather interesting; one claimed that the main constraint was energy, and that that was intrinsically very, very expensive; the other claimed that it took $10,000 of 'oil' (presumably kerosene) to put one pound in orbit. The first guy mentioned the $10,000/lb (really, who measures spacecraft in pounds?) figure as well. Both were highly upvoted, and so forth.

There's just one problem. It's not true.

Let us take a typical, not terribly efficient, but very old, much-used, and reliable rocket, the Soviet/Russian Soyuz. For the sake of argument, let us take the Soyuz-2, which is the current leading model. An aside. You might assume from the name that the Soyuz-2 is the second Soyuz. And you'd be wrong, oh so wrong. It's about the tenth. Russian rocket naming is, to say the least, odd. Rockets are generally named after the first thing they launch, so the Proton rocket was first used to launch a satellite called Proton (used to study high-energy particles), the Zenit rocket was used to launch Zenit spy satellites, and so forth. The Soyuz rocket, then, was first used to launch the Soyuz spacecraft, originally supposed to be the Soviet lunar craft, and these days used to ferry people to the space station. The name stuck; there have been over 2,000 Soyuz launches, of which only about 150 carried people. Variants included the Soyuz, Soyuz-FG, Soyuz-U, Soyuz-U2, and now the Soyuz-2. There were plans for a Soyuz-3, but it's been scrapped in favour of something new.

Anyway. A Soyuz-2 can put a payload of 7.5 tonnes in orbit. Its market cost is $40 million per launch. That's $5,333 per kg. So already the $10,000/lb figure looks a bit silly. That's about the cost of launching something on a Titan IV, a rocket which existed solely to give the US a fully independent launch capability which wasn't an explodey shuttle, and generally considered the most expensive rocket ever.

But how much of that is fuel? Well, a Soyuz-2 has a mass of 305 tonnes, of which 270 tonnes is fuel. The fuel is kerosene and liquid oxygen. I'm not totally sure of the proportions; let's say they're half and half.

The current price of aviation kerosene (very similar to the kerosene used in a Soyuz) is about $700 per tonne. That's 70cent per kilo. Liquid oxygen is harder to find pricing for, but it was 21 cent per kilo in 2001. So, we're assuming 135 tonnes of each; that is, $94,500 worth of kerosene and $28,350 worth of liquid oxygen, totalling $122,850. So, the cost of fuel per kg payload for a Soyuz 2 is $16. $16/kg, not $20,000/kg.

The real cost of launching things into space is more down to labour, launch sites, manufacture of rockets and spacecraft, and so forth. This is a good thing! If these claims of $10,000 of fuel per kg launched were accurate, then launching things would indeed be intrinsically very expensive, with little hope of getting cheaper. Fortunately, this is not the case. All of these costs can be dealt with through automation, mass production, a shift to reusable craft when technology (especially materials technology) makes that practical, and so forth.

By the way, it should be very obvious that the $10,000 figure for fuel is silly. If it were accurate, then a Soyuz would, based on its payload, weigh about 300,000 tonnes, bigger than an aircraft carrier.

Some rocket fuel is more expensive, of course. In particular, the extremely poisonous UDMH used in the Proton and Titan rockets, and in most satellite stationkeeping systems, works out to about $50 per kilo, mostly because it is unsafe to handle. It's hard to get a proper figure on liquid hydrogen, though it's probably cheaper than kerosene in bulk. And solid fuel rockets are special; the fuel is the rocket, and processing costs are very high. But the point is that fuel need not be a blocking issue.

One more thing. The Soyuz has a payload of 7,500kg, using 270 tonnes of fuel. A Boeing 737-700 has a payload of 20,000kg, using 20 tonnes of fuel. So, it's a big difference, but it's not a totally mad, staggering difference.