The story is enjoyable, but like most such tales is amounts to building a string of deadly obstacles for the protagonist and then giving him just enough to survive each one. (FWIW the least realistic step was the ship turning around to get him, because spaceships typically don't carry any extra fuel. But in general there were too many resources lying around for him to use, especially the unattended lift vehicle. The plutonium core and the potatoes were a nice touch, though.)

Even hard science fiction takes liberties since it pushes the boundaries of science or engineering. It explores the plausible, rather than what has been accomplished. If it didn't do so, it would not differ all that much from regular fiction (i.e. the story may be made up, but it is anchored in everyday reality).

As for the ASCII table, I wouldn't be surprised if it is one of the most commonly reproduced data tables in print and I would be surprised if it wasn't the mostly commonly reproduced table digitally. Virtually every *ix system will have a copy of it. The documentation for most development tools will probably have it. All you need is someone technically inclined in your life, which you will almost certainly have on a mission to Mars, and you will likely have a copy of an ASCII table (whether anyone knows it is there or not).