Additionally, daily passes are also released online on the half hour starting at 9:30am. The link listed https://nmaahc.si.edu/visit/passes takes you directly to the page where you can access the sameday online passes link
You have to pay to get in I went on a bus trip from Baltimore then you don't have to worry about parking and the the tickets have a time for you to enter
Entry is free, you do need a pass contact museum.
Admission is free. Passes may be required. Walk-up to the museum without a pass on weekdays after 1pm. Timed entry passes are required every Saturday and Sunday and for groups of 10 or more. The website below has the tickets but in general the same day tickets come out at 6:30 am and are sold out by 7:00. When I got mine there appeared to be a timeout for periods of time that was pretty confusing. If a time window says unavailable they might become available again any minute. If it says sold out then the tickets are out for the day. https://nmaahc.si.edu/
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