1. The Apollo's Saturn rockets were packed with enough fuel to throw 100-pound shrapnel three miles, and NASA couldn't rule out the possibility that they might explode on takeoff. NASA seated its VIP spectators three and a half miles from the launchpad.
2. The Apollo computers had less processing power than a cellphone.
3. Drinking water was a fuel-cell by-product, but Apollo 11's hydrogen-gas filters didn't work, making every drink bubbly. Urinating and defecating in zero gravity, meanwhile, had not been figured out; the latter was so troublesome that at least one astronaut spent his entire mission on an anti-diarrhea drug to avoid it.
4. When Apollo 11's lunar lander, the Eagle, separated from the orbiter, the cabin wasn't fully depressurized, resulting in a burst of gas equivalent to popping a champagne cork. It threw the module's landing four miles off-target.
5. Pilot Neil Armstrong nearly ran out of fuel landing the Eagle, and many at mission control worried he might crash. Apollo engineer Milton Silveira, however, was relieved: His tests had shown that there was a small chance the exhaust could shoot back into the rocket as it landed and ignite the remaining propellant.