I suggest you read more in actual biographies of Jefferson. He was quite plain that the main purpose of Lewis&Clark was to gather scientific information. The "finding land to occupy" part was the fig leaf that he used to get funding through the Congress.
You made my own point against yourself — his mindset was unconstitutional and Jefferson got the funding by making it look like a minor matter, a matter of understanding the “details” about the land to be occupied.
We haven’t yet seen any “science amendment” to the constitution. Now when one comes, then you have a conservative, constitutional leg to stand on.