It is true that we were cautious in our planning. There were many uncertainties about how well our Lunar module systems and our Pressure suit and backpack would match the engineering predictions in the hostile lunar environment. We were operating in a near perfect vacuum with the temperature well above 200 degrees Fahrenheit with the local gravity only one sixth that of Earth. That combination cannot be duplicated here on Earth, but we tried as best we could to test our equipment for those conditions. For example, because normal air conditioning is inadequate for lunar conditions, we were required to use cold water to cool the interior of our suits. We did not have any data to tell us how long the small water tank in our backpacks would suffice. NASA officials limited our surface working time to 2 and 3/4 hours on that first surface exploration to assure that we would not expire of hyperthermia.