Forty years ago today, two Americans were on the moon, getting ready to blast off from home.

Apollo 15 is another of the lesser-known moon missions, although it did introduce the very cool moon buggy.

In the past we've presented five off facts about the moon landing, Alan Shepard's flight and Apollo 14; let's see what Apollo 15 has to offer.

5. The most casual moonwalkers ever Before Apollo 15, crews that reached the moon could not wait to get out onto the surface. Apollo 11 was supposed to have a sustained rest and sleep period once the Eagle landed, but they figured there was no way they were going to sleep anyway so what was the point?

Not Apollo 15. David Scott and Jim Irwin put the Falcon down during Houston's afternoon rush hour and decided to call it a night. They both probably were five-year-olds who first ate a healthy breakfast before looking for Christmas gifts, too.

4. The moon buggy didn't go very far By far the most intriguing thing about Apollo 15 was the moon buggy. Tucked inside Falcon, it was lowered out via a system of pulleys and ropes and then sort of snapped itself together in a proto-Transformers way.

It greatly aided exploration, but not by driving vast distances. The astronauts were allowed to take it only far enough that they could reasonably walk back to the LM if the buggy died. It never got farther than about three miles from the Falcon. Of course, it allowed the astronauts to explore many more spots within that radius.

The lunar land speed record on it, by the way, was set by Apollo 17's Gene Cernan. Even though astronauts were told not to exceed 8 mph, Cernan gunned that ride to 11.2 mph, a record that will likely stand for some time.

Also, the rover camera allowed, for the first time, a view from the distance of the LM lifting off.

As the astronauts snoozed on the moon, Mission Control detected a small but sustained oxygen leak. It wasn't enough of an emergency at the moment to wake the pair up, but when they did get up everyone tried to figure out what caused it. Someone had left a valve open on the Urine Transfer Device.

Leading to this thrilling dialogue, all done on the "non-public" communications system:

Mission Control --- Could you describe the Urine Transfer Device for me? Did the urine go into a holding tank in the vehicle?

Irwin -- I don't think the urine was ever dumped overboard and certainly not drained onto the Moon.

Mission Control -- So it went into a holding tank of some sort? In the descent stage, I would imagine.

Irwin -- Yeah. And it had a metal cap, as I recall, with a rubber ring around it. That was the capping device. We'll read on here, but I think Dave had used it during the night, and I might have, too. But I think Dave was the last one to use it and he just left it in the open position. That's where the oxygen leak occurred -- through that valve. It's surprising that it leaked, even though it was capped...Maybe that cap wasn't that secure. 2. A teachable moment Scott and NASA prepared an easy-to-follow experiment with a great "wow" factor. Galileo had said that in a vacuum, all objects fall at the same speed.

Scott took out a hammer and (appropriately) a falcon feather and said he would drop them. "Hopefully, they'll hit the ground at about the same time"

They did.

"How about that?" Scott laughed.

Apollo 15 was considered a great success in all aspects but one: public relations. And NASA does not like to look bad in public relations.

Scott, Irwin and Al Worden took along about 400 stamps with them, with plans lined up to sell them on the open market. They said they wanted to set up trust funds for their kids.

Astronauts had done such things before, but this was a little more blatant, and NASA reacted swiftly. None of the astronauts was fired, but none ever flew again.

Worden, pitching a new autobiography, says he has no idea where the stamps are now: "Lord only knows. Some of them sold, some of them are still in a safety deposit box. They're probably all over the world by now."

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