So what do you do if you're the astronauts of the space shuttle Atlantis, and they give you the day off?
Wednesday, the tenth day of the flight, they were supposed to rest. But not really.
The truth is, you still work in space, even when you're not supposed to. The Atlantis astronauts still had to configure power systems, keep an eye on the controls, and exercise (not optional, since the heart and legs quickly weaken in weightlessness).
"Most of the days off end up being catch-up for things they fell behind on in the timeline," said Dan Barry, a former astronaut who flew three shuttle missions.
They did a staged ship-to-ship call with the three men on board the International Space Station, flying thousands of miles away in a different orbit. "Spaceflight is great, isn't it?" said Atlantis' commander, Scott Altman, during the conversation.
They also spent an hour talking to reporters in a very-long-distance news conference. And -- just another day in space -- they took a call from President Obama.
"I think you're just providing a wonderful example of the commitment to exploration that represents America and, you know, the space program generally," said the President.
But when they can get real time off, everything changes.
"On my first flight I was glued to the window," said Dr. Barry. "The colors of the Earth, you'll never see in a picture. The blues, the textures, the white of the clouds, the sheer blackness of space -- a camera can't capture that."
Barry's second flight was to the International Space Station, which is far more spacious than the shuttle cabin.
"On the shuttle you can float," he said. "On the space station, you can fly.
"You've been in the simulator, so the place is very familiar to you. So you're not in a new place, you have magic powers."
NASA realized, as long ago as the 1970s, that tired astronauts are inefficient astronauts. One three-man crew on Skylab, America's first space station in 1973, got so annoyed with mission control's unceasing requests for more experiments that they went on strike for a day, sleeping in, taking pictures out the window, and only answering the most urgent calls from Houston.
Ever since, down time has been built into flight plans.
The Atlantis crew has been shooting "crew choice video" -- home movies of themselves in the cabin. In one sequence, transmitted last night, the camera drifts lazily toward the shuttle's airlock -- and astronaut Drew Feustel floats into view, upside down from the camera's point of view.
Down Time, Up There
"What ya doin'?" asks astronaut John Grunsfeld from behind the camera.
"Hanging around," says Feustel.
"What are you, a bat?" says Grunsfeld.
"No, just a spacewalker," says Feustel.
No Rest for the Weary
The crew did take some time to relax and look out the window. Their day was busy, just less structured than others, when astronauts talk about eating meals on the run.
"This is an unbelievably beautiful planet we live on," said spacewalker John Grunsfeld.
But the astronauts had more immediate issues to deal with. At one point they passed over Florida, which has been getting heavy rain for several days. The weather forecast for Friday, the shuttle's scheduled landing day, is not much better, and it's still unlikely to be clear on Saturday.
As a result, mission control has told the astronauts to turn off unnecessary lights and computers to save electricity. If landing is delayed, as has happened on many missions before, the crew will have more down time up there than they expected.
It is actually easier to keep the astronauts in space for a few extra days than to land at Edwards Air Force Base in California -- where the weather is fine, but it costs $1.8 million to ship the shuttle back to Florida for its next launch.
"I never imagined that the flight would go as, uh, interestingly as it has," said commander Altman.
The astronauts may not mind. Dan Barry, who left NASA in 2005, tells of turning on music and dancing, weightless, with crewmates.
"You can actually play Quidditch in space," he said. "No brooms, but I brought a ball, and we chased it, and bounced off each other as it sailed past us."
Astronauts keep such adventures going -- until mission control notices the whole space vehicle moving because of the acrobatics inside.
"You do these magical things," said Barry. "And you do this with incredible joy."