In May, Endeavour docked at the international space station; this photo came from a Soyuz craft, which will continue to serve the station. (NASA/NASA)

After Atlantis returns to Earth this month, NASA’s space shuttles will no longer take Americans into space, but that doesn’t mean the end of an American presence in orbit.

The international space station, expected to operate through 2020, will house at least one American astronaut at all times.

“We’re certainly going to continue using the station to advance our mission of space exploration,” said Mark Uhran, NASA’s assistant associate administrator for the space station program.

While the station — a joint venture of the United States, Russia, Europe, Japan and Canada — is not yet complete 13 years after its first components were launched into orbit, assembly of the U.S. portion was finished during the final few shuttle missions.

That portion includes facilities for NASA’s continued research on human physiology and space technology. It also includes a new national laboratory that will be overseen by a nonprofit entity to be selected by the end of September.

The lab will house projects by companies, universities and government agencies. The National Institutes of Health, for example, will conduct research on immune cell function, the Defense Department will study solar cells for satellites and biotech company Astrogenetix will investigate vaccines. Many groups have already been conducting research on the station, but, Uhran says, “all of this is ramping up now that assembly is coming to a close.”

In that respect, the end of the shuttle program marks a welcome milestone for the station’s scientific goals. There is, however, concern that the loss of the shuttle will weaken the station’s supply chain.

“There’s going to be a crunch on what’s going up and what’s brought back down,” said Scott Pace, the director of George Washington University’s Space Policy Institute. NASA will have to work with fewer flights and less cargo space in the coming years.

According to Uhran, future cargo flights will carry on average only two to three metric tons, compared with the 10 to 20 tons of the shuttle. Agreements have been made with the European Space Agency and Japanese Aerospace Exploration Agency to use their cargo vehicles, and NASA has a contract with Russia for cargo and crew transport. In addition, the agency has committed $500 million to two private companies, SpaceX and Orbital Sciences, which should be providing cargo services within six to 18 months.

“We’ve planned for all kinds of contingenicies, and we expect that all our research needs should be met quite readily,” said Julie Robinson, NASA’s program scientist for the space station. A massive $2 billion spectrometer for detecting cosmic rays was delivered to the station in May.

Uhran said there should be no change in the number of American astronauts on the station or to their usual stays of six months.

“Many people don’t realize that we’ve been using the Russian Soyuz for several years and that the shuttle was only bringing assembly crews, who would come and go,” Uhran said.

NASA and its international partners plan to evaluate the station’s scientific benefits, costs and future in the latter half of this decade. A recent survey of equipment showed that the station is viable until at least 2028, according to Uhran.

“It’s certainly been a diplomatic success and an engineering success,” Pace said of the space station. “Now we’ll find out if it’s a scientific success.”