​The exact conditions are still being decided around the shuttle but the generally idea is "free as in beer" for "free as in freedom". You can have a look over Google's documentation about licenses for open source projects at https://opensource.google/docs/thirdparty/licenses/#types​ for some idea of what is going to be suitable. If you don't have a strong preference, just use Google's default license choice of Apache 2.0 -- From https://opensource.google/docs/thirdparty/licenses/#hardware​

The Apache license is our preferred license not only for source code but also for hardware."​

Stay well away from the licenses listed under https://opensource.google/docs/thirdparty/licenses/#banned​