During Autumn 2017 the Code Club I was running took part in Astro Pi 2017/18, as discussed in my blog post: https://geektechstuff.com/2018/01/31/astro-pi-mission-zero-day-2018/ .
The great news is that the Astro Pi 2018/19 challenges are now live! If you want to take part please make sure to visit the official website: https://astro-pi.org
Mission Zero is for young people under the age of 14 years old. It involves using an online version of the Pi Sense Hat to detect the environmental variables on board the International Space Station (ISS), and then displaying them with a message. As long as the criteria is met the code is later sent to the ISS to be run.
Mission Space Zero is for young people under the age of 19 years old. It involves designing an experiment to run onboard the ISS using the Raspberry Pi, and then analysing the results of the experiment after it has run on board the ISS.
Personally I think both are great missions and my only wish would be for an adult mission to be available as I would love to create an experiment/program for the ISS 🙂