NASA’s Jet Propulsion Laboratory in Pasadena is a pretty legendary place. The homebase for things like the Mars rovers, Jupiter orbiters, and other awe-inspiring creations, the facility opens up to the general public for only two days each year (federal budget permitting, which, somewhat remarkably, it is this year) which always fall around May or June.

Today, JPL announced the dates will be June 9 and 10, 2018, and tickets will become available at 9 a.m. on April 7. Tickets are free, but must be reserved online in advance—and they always sell out.

If you’re able to snag tickets, you’ll be treated to a rare chance to see how cutting-edge outer space missions really work. Tour the machine shop where robots and rovers are fabricated, peek inside Mission Control, and even glimpse some prototypes and concepts for next-generation technology.

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