As a Brit who consigns big ticket artifacts to US auctions every now and again I can tell you that they require proof of import into the US so that the artifact(s) can be legally sold. This is in part due to the fact that if the lot goes unsold it needs to be returned to the origin country and the correct paperwork needs to accompany it. This is true whether you decide to ship them or bring them in yourself so either way they need to be declared.So if you were to carry the artifact(s) yourself and not declare the item at customs, A. you won't be able to sell them at auction for the reasons mentioned above, and B. you're also looking at some possible legal consequences.
It doesn't take much to be refused entry into the US and send you on a flight home. They can also ban you from entering the country again for X years if they think your reasons for entry are untoward (not declaring two big suspicious suitcases full of spacesuit hardware would most likely fall under that category).
But with that said I would also speak to the auction you're considering consigning too - they will probably have more information and may be able to accommodate your situation.
I hope this helps. Also feel free to reach out if you need any more help.