HOUSTON — NASA welcomed its first new astronaut hires in four years on Aug. 20 — four men and four women heavy on military experience or time spent in remote global locations.

More than 6,000 Americans applied to the 2013 class and weathered a 1-1/2 year selection process. Those selected were welcomed at Johnson Space Center in Houston by NASA Administrator Charles Bolden. They will now begin a two-year course of basic astronaut training.

The agency is likely three years out from extending another call for astronaut applicants, according to Janet Kavandi, NASA’s director of flight crew operations. That call will likely respond to an anticipated attrition rate of five to seven fully trained astronauts per year.

After reaching a peak of 149 personnel a decade ago, NASA’s astronaut corps has shrunk to 47, 11 of them women, in the aftermath of the space shuttle’s retirement two years ago.

NASA once launched 30 to 35 of its astronauts annually. The annual flight rate has slipped to four astronauts, who train for two years or more to spend five to six months on the International Space Station. That number may climb, or slip, as lawmakers struggle to find budgets adequate to kick off commercial crew transport services to the ISS and develop the Space Launch System and Orion Multi-Purpose Crew Vehicle to achieve the asteroid and Mars missions called for by President Obama over the next two decades.

“We want to maintain about 40-50 active personnel in the office,” said Kavandi, whose staff looked back to the Apollo-era closeout of the 1970s to make comparisons. “That range allows you to maintain the manifest, if people get sick or injured. It leaves management with enough choices to put the appropriate people in the appropriate positions.”

The latest astronaut hires are most likely to draw future ISS assignments, and also participate in the test flights of the Boeing, Sierra Nevada and SpaceX commercial crew transportation vehicles as well as the Orion capsule. ISS operations are authorized through 2020. NASA’s commercial crew partners expect to launch by 2017 — if funding is adequate. Orion’s first piloted test flight is planned for 2021, perhaps as part of NASA’s Asteroid Retrieval Mission, which has received an unenthusiastic response from lawmakers.

It all starts next week, with a visit to the mountains of Maine and three days of survival training at the U.S. Navy’s Survival, Evasion, Resistance and Escape (SERE) course. The few who don’t have military flight experience will then head for Pensacola. Fla., to familiarize themselves with operations in NASA’s T-38. The high-performance jet trainer has been a mainstay in astronaut training since the mid-1960s. Then, they will focus on the ISS operating systems.

 The new astronauts are: Josh Cassada and Victor Glover, both U.S. Navy lieutenant commanders and test pilots; Tyler “Nick” Hague, a U.S. Air Force lieutenant colonel and flight test engineer; Christina Hammock, a National Oceanic and Atmospheric Administration scientist; Nicole Aunapu Mann, a U.S. Marine Corps major and test pilot; Anne McClain and Andrew Morgan, both U.S. Army majors, the first a test pilot and the second a flight surgeon; and Jessica Meir, a marine biologist.