Same day free museum passes are available online at the museum website at 6:30 am. Monday through Friday. The other same passes are available at 1 pm Monday through Friday. You can line up at about 12 pm - 12:30 pm. You can also ask the museum staff wearing red vests if they have extra passes. Also ask people who are in line to enter the museum for extra passes. If you have a military id you do not need a pass, just show your id any day for entrance for yourself and a guest.
If you're coming in a weekday, you should be able to get an ticket day-of.
Tickets are free but you do have to go to their website the morning of to get them.
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