NASA's budget alone is still larger than any other country's entire space budget. (Steve Helber/AP Photo)

Ever since NASA retired its last space shuttle in 2011, American space travel has taken a back seat to news of growing Chinese space ambitions, Indian Mars missionsIranian space chimps, and Russian space geckos. But make no mistake, the United States is still the global powerhouse in space spending.

Last year, the United States spent roughly $40 billion on its space program, which is more than every other country combined, according to a new study (pdf) by the Organization for Economic Cooperation and Development (OECD). For comparison, China's space budget, which is the second largest in the world, was just under $11 billion in 2013; Russia's the third largest, was roughly $8.6 billion; and India's, the fourth largest, was about $4.3 billion.

Here's a list of the top 37:

America's space budget isn't quite as exceptional when adjusted for population, but it's still number one. On a per capita basis, the United States spent roughly twice that of any other country last year.

Space spending is also slightly down in the United States, by the OECD's estimate.

National space budgets can be fairly difficult to track, because they often include a wide range of activities, spanning not only research and development, but also a number of civilian and defense programs that aren't necessarily housed under agencies that are explicitly dedicated to space exploration.

In the case of the United States, the budget largely reflects activities carried out by NASA, which cost roughly $18 billion in 2013. The bulk of that was spent on science, space operations (largely the international space station, which other countries contribute to as well), exploration, and cross-agency support, including those for commercial firms like Elon Musk's SpaceX.

But the U.S. space budget also includes activities that fall under the Department of Defense, the Department of Energy, the Department of Transportation (Office of Commercial Space Transportation), the Department of Commerce’s National Oceanic and Atmospheric Administration (NOAA) and the Department of the Interior’s Geological Survey (USGS), to name a few.