You can just show up and stand in line to get in
If you happen to be staying at a hotel, the concierge can typically take care of that for you. They did this for us.
www.nmaahc.si.edu While it is correct that you can go and wait in line at 1p, your chances of getting in are slim if you are trying during peak season. You can go to website every morning at 6a to attempt to get same day tickets. Military personal can get in without standing in line or having a same day pass. Hope this helps. Oh and make sure you have plenty of time cause to tour the museum as it should be by starting on 3rd level is normally a 45 min to an hour wait time during peak season.
No tickets needed. Just go and get in line. No food or beverages allowed, just water.
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