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Astronaut Edwin Aldrin's son, Andrew, signs an OK from the top of his treehouse. Apollo 11 video here.

Here's who was on the rocket that day: Astronauts Neil Armstrong, left, Michael Collins, center, and Edwin A. Aldrin, are pictured in this 1969 Apollo II crew portrait. Apollo 11 video here.

This photo shows Apollo 11 crew members, led by Neil Armstrong, heading for the van that will take them to the rocket for the launch to the moon. Apollo 11 video here.

The Saturn V makes history. The launch is marked in the annals of time by a period that included two other key events: Sen. Edward Kennedy's crash at Chappaquiddick (July 18) and Woodstock (Aug. 15). Apollo 11 video here.

The 3,817 ton ship rises from the earth. Who gave the order for ignition? Jack King, the "voice of Apollo." Apollo 11 video here.

Apollo 11 launches into orbit. Apollo 11 video here.

Astronaut Edwin Aldrin's son, Andrew, with some neighborhood friends. Left to right: Mark Frantz (10), Charley Merrifield (11) and Andrew. Apollo 11 video here.

When NASA astronauts were suiting up to go to space in the 1960s, they had to make a big decision before they explored the world above us: How large of a man are you?

Getting it wrong could damage the mission.

MOON RACE: Why do moon landing conspiracies live on?

According to a former NASA life support system expert who helped construct space diapers, otherwise known as Maximum Absorbency Garment systems, each astronaut in the Gemini and Apollo programs had to wear a condom-type sheath with a hole at the end for urination inside their suits.

In an interview on the Science Channel's Moon Machines documentary series about early space travel, engineer Donald Rethke, known in space history circles as "Dr. Flush", describes how these condoms came in specific sizes to accommodate each astronaut's anatomical size.

Astronauts had to estimate their size correctly. If they claimed to be bigger than they were, the sheath would be loose and liquid leakage could damage the suits and lead to bigger problems for mission astronauts.

The condom initially came in only three sizes: small, medium, and large. Of course every astronaut fancied himself a large, and why not? He was riding on the top of a powerfulpotentially dangerous rocket, exploring parts of the outer world that men had not yet touched. No one wants to called "small" when they are planting an American flag on lunar soil.

In the Moon Machines interview, Rethke said that the sizes were changed to large, gigantic, and humongous to better cope with the astronaut's sense of humor.

LOST MOON: Apollo 13's harrowing week in space

The need for space diapers arose on May 5, 1961, when Freedom 7 astronaut Alan Shepard had to ask permission to wet his space suit on the launch pad. NASA scientists didn't think the need for bladder evac would be an issue in what was to be a 15-minute excursion. The incident made for a pretty humorous scene in 1983's space epic The Right Stuff.

Shepard was inside the Freedom capsule much longer than anticipated, nearly four hours, before finally being shot into near-Earth orbit.

These days, the MAG systems are only needed for missions outside space vehicles, as restroom facilities are a major part of space station outposts.

Craig Hlavaty is a reporter for Chron.com and HoustonChronicle.com. 

Craig Hlavaty is a freelance writer for chron.com and the Houston Chronicle.