One thing that space enthusiasts keep hearing is frustration over why the Russians are the only ones able to launch people into space, forcing American and European astronauts to hitch rides.

Attached is a chart I threw together showing the five major spacefaring powers (the US, Russia, ESA, Japan, and China) and their current heavy-lift capabilities, compared to the upcoming commercially developed Falcon Heavy from SpaceX. As you can see at a glance, the SpaceX craft has capabilities that far exceed those of anyone else.

But note that the Falcon Heavy is still in development, while the others are all real and actually flying; and further, note that most of these spacefaring powers have larger craft in development. Yet even those don’t approach the Falcon Heavy’s capabilities (except for the United States’ Space Launch System, which has versions proposed to be even larger than the Falcon Heavy but these are not remotely to the development stage and may never be).

The system that takes people up to the International Space Station is very small. Currently they use a Soyuz-FG rocket, with a Low Earth Orbit payload of only 7100 kilograms — that’s a bit more than half that of the smallest rocket shown on this chart. This raises a really obvious question: Since we have all these rockets flying with more than enough capability, why the heck do we have to hitch a ride on Soyuz???

Two basic reasons: cost, and human rating. Rockets have to be human rated to be considered safe enough to fly people. Nobody really cares if we blow up a load of ham sandwiches and toilet paper for the space station, but we care a lot if we blow up people. (The Soyuz-FG has a 100% success rate so far; Russia’s older Soyuz-U rocket, used for cargo runs, has failed about 3% of the 745 times it’s been launched.)

Russia’s big Proton M shown on the chart is not human rated either; it’s used mainly for gigantic spy satellites (as far as we know). Spy satellites are, in general, much larger physically than most people know; some are the size of a bus. They are the main reason why these non-human rated heavy lift rockets exist.

Human rating is one of those issues where there is perhaps more bureaucracy than there needs to be. There are two schools of thought: Make things as safe as possible, or make things as safe as we can reasonably afford to. Page through this document: Human Rated Delta IV Heavy Study: Constellation Architecture Impacts to get an idea. Realistically, the Delta IV heavy is not likely to ever be human rated (in my reasonably-informed estimation).

To one degree or another, these other operational heavy lift systems listed on the chart are not likely to be human rated any time soon either. The exception is that big one at the top: SpaceX designed the Falcon Heavy to be human rated from the very start. Founder Elon Musk has little interest in doing things halfway or in getting bogged down in bureaucracy. The Falcon Heavy has twice the capacity of a Delta IV Heavy, yet costs only a third as much to build and launch. And it qualifies to be human rated.

The Falcon Heavy’s smaller sibling, the Falcon 9, already has two resupply launches scheduled for the International Space Station in 2012, and two more in 2013. The Falcon heavy is scheduled for a demo flight sometime toward the end of 2012, which is slated to meet all of the qualifications for human rating.

So why can’t the US launch its own guys into space? If you want a single answer, it’s because governments’ resources are split. They need to buy big heavy-lift rockets for spy satellites on the cheap, and they need to create highly engineered human rated rockets. These are two different applications, and it’s simply too difficult to do both.