It's not every day NASA's famous Jet Propulsion Laboratory is open to the public, so when it is, the public shows up in droves.
That happened last October for the annual open house. During the two day event, roughly 45,000 space fans descended on the normally sleepy campus in Pasadena.
Lines got so long that some folks were turned away before even setting foot inside JPL's gated grounds.
So this year, JPL is setting up a reservation system to make things more manageable.
The next open house is set for Saturday, June 4 and Sunday, June 5. Reservations will be available on a special events page, starting April 25 at 9 a.m. PDT. It's first come, first served.
Tickets are free but watch out, there will only be 15,000 spots released for each day. That means fewer people will be able to go this year than last.
Guests will sign up to arrive at a specific window of time between 9 am and 1 pm, according to JPL news manager Veronica McGregor.
Families can score up to five tickets total, and you can't transfer or sell them to someone else, so don't bother checking StubHub if the event fills up.
For science geeks, the annual JPL open house is like Willy Wonka opening his chocolate factory. It's a rare chance to see where some of the most important interplanetary science gets its start.
In the past, visitors could tour the clean room where the Curiosity Rover was built and visit JPL's Mission Control Center where scientists and engineers communicate with spacecraft around the solar system. There are also plenty of exhibits, videos and cool gear on display.
If you are lucky, you'll even meet a rover or two!
This year, expect lots of hype around the Juno mission, which JPL launched in 2011 and which will finally reach Jupiter in July. It'll study the gas giant from orbit and give us insights into how the planet formed.
In 2013, the event was cancelled due to the federal budget fiasco referred to as "sequestration." When it returned in 2014, large crowds showed up for the weekend.
Last year, the event was so popular roads around the campus clogged up with cars.
For those who get tickets and plan to go this year, be sure to wear plenty of sunscreen, wear comfortable shoes and make sure you have plenty of space on your phone or camera for all the cool pictures you will take.
This story has been updated.