The University of Hawaii at Manoa says it plans a new call for applicants once an investigation is completed following the cancellation of its Space Exploration Analog and Simulation (HI-SEAS) Mission VI last week after a crew member voluntarily withdrew from their participation in the study.

“Regrettably, it is not possible to perform a mission with a crew of three,” the university said in a statement. “Further, an investigation is ongoing into an incident which occurred on February 19, 2018, temporarily suspending the mission. After a full safety inspection of the habitat has been performed, a new call for applicants will be released to compose a new crew for another mission based on a review by the institutional review board.”

UH is not naming the crew member that voluntarily withdrew.

Now in its sixth year, HI-SEAS began Feb. 15 with what it called “the most international crew in the history of the research project,” according to an earlier press release issued by the university. It was the first time a crew from four different countries of origin was selected. The mission was suspended five days after it began because of a medical incident that sent one of the crew members to Hilo Medical Center.

At that time, the four crew members — two men and two women — announced were: Sukjin Han, an assistant professor in economics at University of Texas at Austin; Calum Hervieu, an astrophysicist and systems engineer from rural Scotland; Lisa Stojanovski, a professional science communicator who manages the Australian chapter of the Space Generation Advisory Council; and Michaela Musilova, an astrobiologist with a research focus on life in extreme environments.

The crew were expected to participate in an eight-month mission at Mauna Loa, with isolated, Mars-like conditions designed to be similar to those of a planetary surface exploration mission, where they were to perform exploration tasks such as geological fieldwork and life systems management.