Signing Up for a Mission to Mars, and Planning to Never Return Thousands of candidates are trying out for Mars One's mission of a lifetime.

 -- Kellie Gerardi is training for the mission of her life, one from which she might never return.

Gerardi is one of thousands of applicants vying for a trip to Mars, courtesy of an audacious new company called Mars One.

Only 100 potential astronauts will be finalists, but there’s a pretty massive catch: It’s a one-way ticket.

Despite the no-return clause, Mars One said 200,000 people from around the world, including Gerardi, have applied to leave everything on Earth behind.

“I know for a fact that no matter what, in my lifetime, I’m going to space,” said Gerardi, who is newly engaged.

The 26-year-old Florida native trained for the mission in the rocky plains of remote Utah, where she spent three weeks at the Mars Society’s Desert Research Station to learn what it takes for humans to survive on Mars, from moving and breathing in a space suit, to eating bizarre cuisines like zebra tarantulas, because bugs would be a food source on Mars.

The commercial space industry has boomed in recent years, with companies like Space-X and Virgin Galactic building their own rockets and spaceships in an effort to make outer space available to everyone who wants to go.

And it’s not just for sport. Some scientists believe settling other planets is the best hope for human survival.

And when it comes to colonizing Mars, Bas Landorp, the 37-year-old CEO of Mars One, and his team of space experts claim they can do what NASA, so far, has not.

“Accept the new reality,” Landorp said. “Literally everybody on the globe will be watching, just like when Neil Armstrong and Buzz Aldrin landed on the moon.”

“We’re hiring the established aerospace companies from all over the world to design the systems, to build them, to test them, but no new inventions are needed to implement our program,” he added.

But while Landorp said the technology exists to get people to Mars, his company does not have the technology to bring people back to Earth, so the plan is to form a permanent colony with new crews arriving each year.

Of course there are extreme hurdles to overcome. Mars is about 200 million miles away from Earth, which translates to at least seven months of space travel to get there -- and no one has ever been there before.

But for people like Kellie Gerardi, the unknowns are not scary, just part of the dream.

“I think either you get it or you don't,” she said. “I would equate it almost to seeing Mt. Everest for the first time. Here is this hostile challenging environment, and either you feel a yearning to climb it or you don't. And if you don't, I don't know if--that I could ever explain that to you.”

Gerardi is planning her wedding, but says getting married won’t stop her from leaving Earth and her fiancee is supportive of her decision.

“Everyone makes the joke to us, ‘til Mars do us part,’” she said. “I'm getting married next year. I couldn't be more excited. I couldn't be more in love. Do I still see myself going to space in the future? Yes… I would go, and that's a hard reality.”

Another Mars One hopeful is Sue Ann Pien, a 35-year-old tech worker from Los Angeles. She said finding out she was a potential candidate “changed the entire trajectory” of her life, and she started a sort of Earth bucket list.

“I just took off and I went and I experience amazing things around the world that I wanted to do,” Pien said. “I was going up volcanoes in Bali and scuba diving.”

Like Geraldi, Pien believes Mars is her destiny. Her family is mostly supportive of her choice, Pien said, but her girlfriend Cynthia struggles with her desire to leave Earth.

“She's not going to lie about the fact that she doesn't like it--that there's something that might take me away from her,” Pien said.

Mars One hopes to launch their potential astronauts in the next 10 years, but there is a lot of skepticism that this mission will even launch, much less succeed. Famed astrophysicist and author Dr. Michio Kaku is among the skeptics.

“This has the atmosphere of a circus, where you have amateurs simply raising their hand, volunteering to be the first person on Mars,” Kaku said. “They have set impossibly unrealistic deadlines, and the amount of money that you have to have to go to Mars is incredible, perhaps 50 to several hundred billion dollars.”

“And given the fact that this will be untested technology, I would assume that the failure rate would be about 90 to 95 percent for a mission of this magnitude,” Kaku continued. “In other words, it’s a tragedy waiting to happen.”

A recent MIT study hypothesized that Mars One astronauts would suffocate within months of touching down on the red planet.

Mars One says the MIT study is flawed, and that the company won't risk human lives until they are confident in their technology, but still, “there is no safe mission to Mars," Landorp said. "It’s impossible to eliminate all the risks."

These risks aren't enough to deter these Mars mission dreamers from hoping they are among the 100 finalists chosen.

But the doubts aren't enough to deter these Mars mission dreamers from hoping they make the cut to be among the 100 finalists chosen.

So who makes it and who doesn’t? Tune in to “Nightline” tonight at 12:35 a.m. ET to watch the full story and find out what happens.