This is a short story of only about seven pages, set before The Martian by Andy Weir. It can be found for free here: https://blog.whsmith.co.uk/andy-weir-the-short-story-prequel-to-the-martian/
The story is written in the form of three entries from Mark Watney’s diary. The first entry was written after he found out he was selected to go to Mars. The second entry tells about one of the training scenarios he and his team had to endure. The third entry was written the night before the launch.
I haven’t yet read The Martian, but that’s next up on my list. There wasn’t much meat to this story, but it served to introduce me to Mark, who I assume will be a main character. I also gained some insight into the team dynamics and learned a little bit about the plans for their mission to Mars. Mark seems like he’ll be a fun and enthusiastic character to read about.
As a standalone story this would seem pretty pointless I think, but I enjoyed it since I knew it was just the beginning of a larger story. It made me eager to dive into the actual book.