This looks like a good read, thanks for this. I had not heard of a seed factory before.

Yeah, I've tried posting it on HN before but it's never gained any traction. It is a fascinating read and the author is active on reddit[0] and he'll answer any questions you have about the book.

I just reposted it[1], Let's see if it gets some comments this time.

[0] https://www.reddit.com/user/danielravennest [1] https://news.ycombinator.com/item?id=34795006

Making solar cells like this is a nice first step to making self replicating machines. Being able to make solar cells is especially interesting because these are semiconductor devices, so producing control electronics may be possible too.

But really what needs to be solved for self-replicating machines is determining a way to make actuators. On the Moon this is harder due to the difficulty of making bearings and gears. Because of vacuum welding making bearings is much more difficult. While solid lubricants do exist, it's difficult to obtain the materials necessary on the Moon. Traditional machining and polishing processes don't work well in a vacuum either due to vacuum welding and the inability to use lubricant.

If we wish to carry out said processes in a pressurized environment we run into another problem: seals. In order to make good seals we need elastomers, and elastomers require elements such as hydrogen, carbon, and nitrogen which are difficult to obtain on the Moon.

Is the issue with manufacturing bearings in a vacuum or operating them in a vacuum?

If it is the former it seems like the solution is as simple as building a pressurized manufacturing facility.

Both. And again, the issue with a pressurized manufacturing facility is making seals.

Why not make a solid enclosure out of metal and melt a hole in it when you need to move material in and out?