South Korea's manned space program has effectively been shut down, after the resignation of its first -- and only -- astronaut.

The Korea-based Yonhap news agency reported the country's space agency, the Korea Aerospace Research Institute, has accepted a resignation letter submitted by female astronaut Yi So-yeon, 36, who became the first Korean in space when she traveled to the International Space Station in 2008, according to the Australian Broadcasting Corporation.

Yi was actually the second choice for the government-run Korean Astronaut Program, after Russia asked that the original candidate, Ko San, be replaced.

Ko was rejected after the Russian Federal Space Agency accused him of violating security protocol for maintaining secret information twice while studying at the Yuri Gagarin Cosmonaut Training Center -- for which Ko later apologized.

A bio-systems engineer, Yi conducted 18 scientific experiments during her historic mission, but in an interview with the ABC in 2012 said she doubted she'd ever get back to space again because her government lacked a "stable and long-term human space flight program."

Yi had been on a leave of absence from the space program since 2012, while studying in the United States.

She cited personal reasons for her decision to step down from her post.

In fact, in a June interview with Korean newspaper Dong-A Ilbo, Yi said she was worried about her career prospects.

"I feel bad that I'm the one always blamed for the failure of the space business -- even though there are problems with government policy toward the space business," she said in the newspaper interview.

Now, the South Korean government, which paid nearly $27 million in U.S. dollars for Yi's time aboard the ISS, is facing accusations that the entire mission was little more than an expensive publicity stunt.

Otherwise, KARI is being accused of picking the wrong person for the job and wasting taxpayer money, while Yi herself has been called a quitter by some in the media.