Is it ok to move away from my son? How might it impact him?

I have the unique opportunity to move overseas for a long-term (1-2 years)mission trip in a 3rd world country. It is through an organization I have previously worked with and have visited the country in the past and this would be a life-long dream fulfilled. I placed my first born son for adoption nearly 2 years ago and have an open relationship with his family. He is still so young that he really doesn’t know me and I have a minor role in his life at this point. He would be nearly 3 years old by the time that I would be leaving the U.S. It is heartbreaking to consider the possibility of being so far away from him for so long. Ultimately I don’t know that it would be much different if I were to stay here, where I am a day’s drive from his home as it is. The place I would be going I would have a cell phone and internet access regularly so I would still be able to communicate with them but visits would be out of the question. I guess my question is, what obligation do I have to my birth son to stay physically present in his life? Would it be acceptable for me to leave the country for a year at this early stage in his life? Am I being selfish to even consider it? What are possible ramifications in his life? I don’t know if many of you have had experience with this type of thing but I would love some insight. *I would like to add that while I would be physically very far away, I do plan to return and I do plan to remain a part of my sons life. I have no intention of dropping off the radar. I will stay as involved as possible regardless of where I end up.