In 2016 NASA is sending a silicon microchip with the InSight lander and it will contain all the names of everyone who signs up for a "boarding pass" on the project's website. The InSight lander was designed to drill deep into the surface of Mars to study the planet's interior for the first time. It'll take a number of instruments with it to accomplish that, including a seismometer to monitor Martian earthquakes.
If you signed up to fly your name aboard the Orion spacecraft for its test flight last year, you'll just have to log in to earn "frequent flier points." If you didn't, just go sign up and you… the process is easy.