Sam wrote "I often get asked about what people can do for a year or two to make a big impact between projects." If the US government isn't the right fit (especially if you're not an American), consider doing a Fellowship with a non-profit which may also have a big impact. MovingWorlds.org is one place to find those opportunities. We (engageSPARK, a not-for-profit business building the "Twilio for non-techies" for NGOs & Governments) also have a Fellowship program: https://www.engagespark.com/about/#join . :)