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Why didn't Herzer get his hand fixed in East of the Sun, West of the Moon? I get the whole bit early on in the book about not wanting to abuse his relationship with Megan and get something not available to the other soldiers but IMHO once he got assigned to the tanker mission that argument should have gone out the airlock. Although it's not actually discussed in the book designing a spacesuit that would allow him to actually use his prosthetic would have been extremely difficult (if not impossible) and a super-critical, no-margin mission that is taking place in space is not really somewhere that you want anyone who isn't absolutely 100% unless you have no other choice (i.e. the techs aren't as good physically as would be ideal but given the time constraints you take what you can get). Given that Herzer is probably the best person to command the mission itself regenerating his hand to bring him up to 100% would seem like a very sensible option.