NASA has sent four volunteer crew members on a simulated journey to Mars within a ground-based habitat to investigate the isolation and confinement of exploration missions.

The 45-day simulated mission to Mars' moon Phobos began on Friday at NASA's Johnson Space Center in Houston.

The volunteer crew, which included Jared Broddrick, Pietro Di Tillio, Dragos Michael Popescu, and Patrick Ridgley, entered a structure known as the Human Exploration Research Analog, or HERA, which NASA described as "designed to serve as an analog for the rigors of real space exploration missions."

The four guys were spotted entering the HERA structure before the door was formally locked and will not be opened until March 14, according to a video sent to NASA's Johnson Space Center Twitter account.

The guys will have up to five minutes of delayed communication with the rest of the world while within the HERA structure, according to the agency. According to NASA, the purpose is to assist in the training of the crew and NASA coordinators in communicating under these conditions while guaranteeing a seamless operation.

"In this HERA campaign, we're learning more about how teams function in an autonomous environment where they have limited contact with Earth," said Brandon Vessey, research operations and integration element scientist for NASA's Human Research Program.

"What we learn will inform how future exploration missions beyond low-Earth orbit are performed. This will help ensure that our astronaut crews can work effectively through challenges unique to long-duration spaceflight, including communication delays," Vessey said.

According to NASA's website, this is the second of four "Campaign 6" missions done by HERA to aid research into "behavioral and team performance of longer duration missions." The campaign's final mission will take place on Sept. 12, 2022.

Individuals must be healthy nonsmokers between the ages of 30 and 55 to be considered for the missions. To be considered for the HERA crew, applicants must submit their resumes to Johnson Space Center's Test Subject Screening department and pass a physical and psychological test.

The goal is to establish the first long-term presence on the Moon, which will help NASA prepare to send the first astronauts to Mars, according to NASA. HRP will conduct 15 studies throughout the missions to collect data that will help NASA land the first woman and first person of color on the Moon, a plan known as "Artemis."