Four volunteer scientists have just emerged from a 45-day stay inside NASA's most realistic Mars simulation yet.

The crew remained completely isolated inside the Human Exploration Research Analog (HERA) - a 650-square-foot habitat at NASA's Johnson Space Center in Houston, Texas - until Monday, when the hatch opened and they finally 'returned to Earth.'

While inside, they completed 18 different studies that will help NASA and other space agencies learn how humans respond to the confinement, demanding work-life conditions and remote environments of deep-space missions, according to NASA.

NASA has set a goal to get humans to Mars by the 2030s. With that deadline fast approaching, simulated missions like HERA provide key insights into how astronauts might survive the farthest crewed space mission ever attempted. 

The four person crew - comprised of Erin Anderson, Sergii Iakymov, Sarah Elizabeth McCandless and Brandon Kent - was the third to enter the HERA habitat.

Their mission was unique in that it included the more detailed assignments designed to closely replicate the living and working experience on Mars.

During the month-and-a-half-long simulation, the crew performed a wide range of tasks.

Their assignments included harvesting plants from a hydroponic garden, growing shrimp, deploying a small satellite, conducting a virtual 'walk' across the surface of Mars and flying simulated drones over Martian terrain. 

'These activities are designed to immerse the crew in the task-focused mindset of astronauts,' NASA wrote in a statement.

NASA even simulated the communication delays that real astronauts could one day face on Mars. During a real Mars mission, communications from Earth could take up to 20 minutes to reach astronauts on the red planet, and vice versa. 

All the while, the crew was being monitored by NASA scientists to assess how their day-to-day tasks, routine, and the isolation and confinement of their habitat affected their behavior and performance. 

When they weren't hard at work, the crew read books, played cards, built Legos and listened to music. 

On Monday afternoon, the crew finally emerged from their tiny habitat, marking the end of their mission. 

'Following our safe passage to Mars, and our safe return to Earth, as the crew of Campaign 7, Mission 3, we hereby officially transfer this exploration vessel to the flight analogs operations team,' said Kent upon exiting HERA.

'We hope this vessel continues to serve as a safe home for future HERA crews,' he added. 

NASA also runs another, bigger simulated Mars habitat called the Crew Health and Performance Exploration Analog, or CHAPEA. This 1,700-square-foot is large enough to sustain volunteers for up to a year. 

The first CHAPEA volunteer crew emerged from their habitat in July. 

If you think you have what it takes to spend weeks inside cramped Mars simulation, NASA is actively seeking non-smoking volunteers between the ages of 30 and 55 for the next HERA mission.