I really liked Timerover51's original idea of interpreting various worlds from H. Beam Piper's novels for Traveller, and hoped to see more of that. Attempting to practice what I preach, how about Uller and Niflheim?
Piper's book "Uller Uprising" includes an essay by John D. Clark with physical details on the star systems of both Uller and Niflheim, including especially the chemistries of the two named planets.
Niflheim could be dropped in anywhere as a world with an Insidious atmosphere which is nevertheless the site of efforts to mine valuable minerals. This world has an atmosphere of fluorine and various fluoride gasses, which defeats all efforts at completely closing it out of exploratory/mining vessels. The book has one chapter describing the efforts of a group of Terrans (plus one Ulleran observer) to mine deeply-buried metals using nuclear explosives to bring all the good stuff up to the surface - extreme strip-mining, but nobody likes the place enough to protest (the name of this planet is used as a swear word in other novels by Piper).
Uller could be used just as it is in the novel, with substitution of the Third Imperium or alternate interstellar government in place of the Terran Federation. The physically interesting thing about Uller is that its lifeforms are based on silicon rather than carbon. More interesting, however, is the native sapient species invented by Piper, and the relationship of different cultures within that species to the humans of the Chartered Uller Company, which has exclusive rights to explore and exploit the planet. The novel tells the story of an uprising by most of the native Ulleran population against the humans and some Ullerans who remain allied with them; a great adventure setting, whether you choose the time period before, during, or after the uprising. Another option would be to use Uller as a setting
long after the uprising, when the world is developed and the Ullerans are part of interstellar civilization, although this would require a lot more work and speculation.
The
e-book "Uller Uprising" by H. Beam Piper, including the essay by John D. Clark, is available in full on Project Gutenberg.
BONUS: While googling for the Gutenberg link, I found
this Enderra blog with notes on the blogger's attempt to map the worlds of H. Beam Piper. Haven't read it yet myself, but first paragraph looks promising.
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