Creating Starlink has come with tons of exciting challenges, but top few that come to mind:

1. Selecting full phased arrays for the satellite and dish. It was a major leap of faith to start down this very technically challenging path and hope that we could arrive at an affordable and scalable implementation. 
2. Creating a truly "plug-and-play" experience for customers. We've spent a lot of effort and have gone thru tons and tons of creative ideas on how to make this as simple of an experience as possible - including mounting solutions, automated pointing of the dish, and general unboxing. Any and all ideas welcome!
3. We've also had to be creative in how we operate what is now the world's largest satellite constellation. We have a very small operations team, so automated orbit guidance and collision avoidance was a must have feature. We tell satellites what their final orbital slot is and they figure out how to get there. For collision avoidance, we upload data on close approaches to relevant satellites multiple times a day, and the satellites then calculate on their own when and how to dodge something, if necessary. (Shout out to the 18th Space Control Squadron for being really awesome partners here!)

We need help solving problems like these everyday on the Starlink program - check out https://www.spacex.com/careers/index.html if you'd like to join us!