At 3:58 a.m. this morning, the twang of homemade country music came clanging into the cockpit of America's first space shuttle, and it went like this: "We can't say she's sleek or lean, but I'll tell you right now she's a mean machine. The Columbia. Not the kind you smoke. This here's a bird.Gets high on herself."

And from outer space came a down-home response. "Awwllright," drawled astronaut Robert L. Crippen.

So began the first full day in space for Crippen and his commander, John W. Young, in the Columbia, a craft that is not only performing better than expected but includes creature comforts not enjoyed by other American astronauts. One is the first commode ever in space.

The food also is a major improvement. Young and Crippen are enjoying hot entrees and chilled drinks from a menu that includes beef with barbeque sauce, broccoli au gratin, Italian vegetables and peach ambrosia.

Much of the food is dehydrated, similar to what backpackers carry into the earth-bound wilderness. Some of it is irradiated, which means it has been exposed to ionizing radiation to improve preservation.

Young and Crippen are preparing their food -- 3,000 calories a day -- with the help of a warming tray, and they eat with normal utensils. But on future shuttle flights, astronauts will have a galley, complete with oven and work space.

Water is plentiful aboard the Columbia. In addition to some water loaded on board at the beginning of the flight, the orbiter produces more through condensation than the crew can use during flight, and a chilling system makes it possible to have cold drinks any time. Although there is no shower, the astronauts can clean up at a personal hygiene "station" near the galley.

America's first shuttle astronauts spent the night sleeping in their seats, which were adapted from jet planes. In the future, astronauts will sleep in zippered bags strapped on the mid-deck just below the flight deck where Young and Crippen are piloting the Columbia. The zippers are necessary to keep the astronauts from floating around the gravity-free craft while asleep.

The major advance in creature comfort is a specially designed commode, built by General Electric. Through a series of mechanical operations, waste matter is pulverized, dehydrated and stored in the commode, rather than bagged as in past trips. The toilet has curtains that allow privacy for the astronauts, and advancement made necessary because future crews will be composed of both men and women.

This is a work trip for Young and Crippen, with little time programmed for relaxation. They rise early, as they did today, and spend less than a hour getting ready for the day's activities.

Breakfast today was at 5:45 a.m., with beef jerky, applesauce, granola, rolls, and orange-grapefruit drink on the menu.

Before 7 a.m., the two were at work on the many tests, primarily maneuvers this first space shuttle must perform. "They're trying to get every bit of engineering information they can," a NASA official said.

Although they have little time to themselves, Young and Crippen have a more comfortable and spacious working environment than the astronauts in the Apollo series who flew to the moon. The space inside the cabin is about seven times as large as Apollo's.

"With 2,300 to 2,400 cubic feet, there's a good deal of room," said Frank Samonski, support division. Still, after looking inside a mockup of the Columbia, one NASA official remarked, "It's smaller than I thought."

Young and Crippen worked 16-hour days in space, with some free time just before going to sleep. They have come to expect some surprising wake-up music from Mission Control and vice versa. Today, after the country music serenade, the two astronauts sent back to earth a rendition of "Waltzing Matilda."