How to set a law allowing space explorers to collect keepsakes
I'm in the early stages of thinking up a space science fiction story about a particular group of scientists and young explorers on mission to investigate some points of interest in the galaxy. Their mission is to visit some interesting phenomena (unexplained astrophysical phenomena, possible signals from an alien civilization, ruins of a fallen civilization that they know to be there, candidates for expansion, etc) that have been observed and perform some hands-on research on what's going on. Part of their job would be bringing some stuff to the laboratory on board for study and sometimes carry them back to headquarters on the return journey.
One small detail I've been thinking about is that some of the crew might want to keep for themselves some keepsakes and trinkets to remind them of their journey: stuff like a mineral naturally carved into an ornate shape found on an asteroid, a sample of a newly-discovered element, a trinket from a civilization they encountered, a piece of useful technology from a derelict space station and so on. But although allowing some degree of personal collection can be a good way to strengthen the emotional intimacy of the crew to their mission and might even directly aid in the mission sometimes, we can't have the crew just pocketing (or worse, hauling) stuff on their missions, especially if the items are very valuable or the method of obtaining them is unacceptable.
Now, space is big and weird. Nobody knows what the explorers are going to find, it's going to be impossible to try and write a full list of what's allowed and what's not, let alone draft a totally loophole-free law. So I'm not looking for a complete answer, rather to gather some points on what considerations should be taken by both the headquarters and the crew when deciding whether an item can be taken as a personal belonging. For example, one consideration would be whether the item is a unique thing or something that's either available in plenty where they found it or easy to reproduce now that they know how it's made, and in the latter case it usually wouldn't hurt to let the crew take a small amount unless the nature of the item makes it difficult to allow it to be personally taken (and potentially sold or released). And then, how is "a small amount" determined?
Some context and considerations: 1. The nature of this expedition is scientific, not expansionist (that's handled by another branch of expedition teams). Discovering valuable resources is not even an expectation but simply something that might happen and need guidelines. And the expedition is organized by either a government or an institution or something, definitely not a corporation, plus there are very serious moral standards not just for this mission but in the society as a whole. 159
All this means profit isn't the goal, they just want to learn. 2. Communication between the explorers and the headquarters is quick and reasonably prompt, but there are numerous expedition teams. With so much going on, the explorers are expected to make their own decisions as much as possible. Note, by the way, that value assessment is going to be a difficult task to carry out immediately even when brought to the attention of the headquarters. 3. There are automated protocols to periodically report what happened during the expedition in great detail, and that includes diagnostic scans on the ship, so it's practically impossible to sneak any significant cargo on board and keep it hidden. There's extensive screening including personality tests when selecting candidates so that there's reasonable expectation that the selected explorers won't do it with or without those scans anyway. They'd still need these rules though: the reasonable expectation could still be betrayed, no one knows what values could be found in the far reaches of the galaxy, and even if nothing goes wrong about their morality, having guidelines can still help the crew avoid some lapses of judgment. 4. They aren't going to say that everything found during the expedition is the property of the headquarters and ask the crew to officially purchase whatever they want to keep for themselves.
Looking forward to discussions on space exploration laws. 500