Former astronaut Mike Massimino was rejected thrice by NASA before he achieved his childhood dream and received a selection letter from the American space agency for his dream job in 1996. After years of astronaut training, Massimino flew into space and completed two space missions, first in 2002 and second in 2009.

“The most important thing is to never give up. As long as you keep trying, there is always a chance,” Massimino told CNBC Make It.

Astronaut Michael J. Massimino was born in New York in 1962, according to NASA. He graduated from Columbia in 1984 and received his Masters of Science in Mechanical Engineering (also M.S. in Technology and Policy) from Massachusetts Institute of Technology (MIT) in 1988.

When Massimino was pursuing his Ph.D. at MIT, he applied to the NASA astronaut program and was able to make it into the top 10 percent of the applicants. Unfortunately, he was rejected by NASA for having bad eyesight.

Massimino underwent an eye procedure after some time and then applied again to astronaut program next year. By that time, he had also completed his Ph.D. from MIT. But, the end result was not different, and NASA had rejected him again. According to Massimino, he made the mistake of listing references (in his application) that were not very much familiar with him, and these references provided recommendations that failed to impress NASA.

“I picked people I thought were important instead of people who knew me. That was a mistake,” Massimino said.

#OTD in 1970 #Apollo13 lifted off for the 3rd piloted moon mission with Jim Lovell, Jack Swigert and Fred Haise aboard. Here I am with my good friend Jim Lovell and his son Jeff pic.twitter.com/uld17bJIh5 — Mike Massimino (@Astro_Mike) April 11, 2018

After his second rejection, Massimino was disappointed a bit, but he was still optimistic and decided to apply for the third time. This time, he reached the final round of the astronaut selection process, but at the end, he was rejected for having imperfect eyesight.

“I was crushed. It’d been 10 years. Ten years of my life I’d been working toward this goal. I didn’t know whether to feel angry or sad or frustrated or what,” Massimino revealed.

He was quite disheartened. Luckily, he contacted the program selection committee that told him that there was still a chance for him provided he corrects his eyesight.

By this time, Massimino had completed his Ph. D. and was teaching at the Georgia Institute of Technology and Rice University. He went through vision-improvement training for several months before applying to astronaut program for the fourth time in 1995. This time, he reached the final round, passed the eye exam, and received a selection letter from NASA in May 1996.

After years of astronaut training, he flew into space and completed two missions (STS-109 in 2002 and STS-125 in 2009) that were aimed to service the Hubble telescope. On May 12, 2009, Massimino became the first person ever to tweet from orbit. According to NASA, Massimino spent more than 571 hours in space and performed four spacewalks during his two space trips.

From orbit: Launch was awesome!! I am feeling great, working hard, & enjoying the magnificent views, the adventure of a lifetime has begun! — Mike Massimino (@Astro_Mike) May 12, 2009

Massimino lives in New York City. According to Mikemassimino.com, he is serving as an advisor at the Intrepid Sea, Air, and Space Museum and is also a Professor of Mechanical Engineering at Columbia University. He has appeared on several television programs, documentaries, talk shows, and the hit CBS comedy The Big Bang Theory. This former astronaut has also authored the book Spaceman: An Astronaut’s Unlikely Journey to Unlock the Secrets of the Universe, which is a New York Times bestseller.

“It’s important to have dreams. Sometimes they come true like it did with my astronaut opportunities and sometimes you get disappointment,” Massimino says.