If your driver’s license is going to expire some time during your mission, you will need to renew it before you leave the country. Trying to renew your license from abroad is just overwhelmingly difficult and takes a great deal of time and effort. So look at your driver’s license right away and see if you’ll need to renew it before you start your mission.  Telephone ahead and make sure you have all the documents your DMV will require for early renewal.