His first week back on Earth "was a bummer," but Story Musgrave, MD, has regained the exuberance that marked his five days last month aboard the space shuttle Challenger.

"For 16 years, I've waited for this experience," Dr. Musgrave said. "This is why I got into this business -- to be on the intellectual and physical frontier. This is why I took the job, what I'm supposed to be. I can't say that I expected it, but I wanted a transcendental experience, an existential reaction to the environment. I'm not talking about an illusion, of seeing something that wasn't there. I'm talking about a magical emotional reaction to the environment, to what's there. This is what I've been after all my life, to experience and feel new sensations. You know, I did my first airplane solo about 30 years ago, so I've been in the business of challenging physical frontiers for a long time, whether it's scuba diving or parachuting or skateboarding or walking in space. I wanted something to remind me that I was no longer practicing in the water tank."

At approximately 4:15 p.m. (Eastern time) on April 7, Dr. Musgrave, 48, cracked the hatch leading to Challenger's cargo bay, and, with fellow astronaut Donald Peterson, became the first Americans to walk in space in nine years. Bundled in thick white $2.5-million space suits, the two astronauts stepped out of Challenger's cabin like two children going for a romp in the snow. For three and half hours, the two floated, somersaulted, and tumbled through the vacuum of space -- restrained by tethers -- while successfully testing their ability to serve as space repairmen.

Dr. Musgrave, the first one out, all but swung himself over the side of the spaceship, doing a handstand on the rail, restrained only by his tether. The Earth, 176 miles below him, was spinning brightly. His space suit and backpack, formally known as the extravehicular mobility unit, is a personal creation, largely designed by the physician-astronaut during his days on the ground. At the time, Dr. Musgrave told mission control in Houston, "It's so bright out here. It's a little deeper pool than I'm used to working in" (astronauts practice for space walks by swimming underwater).

"Today," he recalled, "I guess I was hoping for a kind of religious experience out there. I didn't expect anything particular, I was just open-minded about it. Now, this is a funny thing to say, but things went so smoothly that in a sense I was disappointed by what I felt. I never got that transcendental jolt."

"I never experienced a separation phenomenon, either from the spaceship or the Earth. I had no sense of the Earth being down. In fact, I had no down reference at all. My frame of reference was the cargo bay of the orbiter. There I was, 170 miles above Earth floating on a thin tether and I felt perfectly at home. I had no feeling of falling."

"Now, don't get me wrong, I was terribly excited. I found the zero gravity very appealing, being able to glide to wherever I wanted to go with no feeling of up or down. For those three and a half hours, I did the work I had to do and I grabbed for all the sensory input I could grab."

With fellow astronauts Peterson, Paul J. Weitz, the crew commander, and co-pilot Karol J. Bobko, Dr. Musgrave had just met the press for a formal report on the mission. Now, in his first one-on-one interview, he discussed the personal experience. The Challenger crew members still are committed formally to debriefings, and their general media tour is months away, but Dr. Musgrave said simply, "Let's talk."

"You ask me what will I have to say to doctors about this mission. Well, when I meet with medical groups, I'll talk about everything except medicine. Doctors go to conventions and hear about medicine all day long. When they talk to an astronaut, they want to know what did I feel, see, think. What was it like? They want to know what it would be like if they were to walk in space. Well, here's how it felt to me.

"I had absolutely no butterflies about this mission. I had total confidence in myself and the mission. I knew what was going to happen, and it happened. I knew every valve, every switch, and every number on this flight. It was sheer play for me to be able to so completely interact with my environment.

"The entire experience tremendously turned me on. I was on a five-day high. I had to be commanded to go to bed. I was so hyper and there was so much to do and see that I seldom got to bed before 5 a.m. Houston time.

"Technically, the mission was extraordinarily exciting, because we accomplished everything we set out to do -- launching TDRS (tracking and data relay satellite -- the communications station), performing the EVA (extravehicular activity -- the space walk), conducting the medical experiments (electrophoresis to use electrical charges to separate blood components to a purity 400 times greater than can be achieved in the presence of gravity), and bringing the shuttle home in great shape (this was Challenger's maiden flight and it joins Columbia to create a two-shuttle fleet to carry out NASA's Space Transportation System (STS) goals, which include 15 shuttle flights in the next few years). It was also personally fulfilling, because I've been waiting for this for a long time. I've been working on the design of the space suit I wore since 1972, so I guess it's only poetic justice hat I should break it in.

"The entire five days were exciting, but the space walk was the highlight. It sure was a spectacular sight. I was taking in the sunrises and sunsets -- you can't tell them apart from up there. Even such a simple thing as our flash evaporator was making things of beauty. It would throw out little icicles of water, and you would see a tremendous blizzard of sparklets of light of all sizes, shapes, and velocities come tumbling at you.

"Every hour and a half, we made a complete orbit of the Earth, and it was just like getting a crash course in world geography. Seeing entire continents with the naked eye is something special. We saw oil slicks off India, oil tankers in the Persian Gulf, the swirls in the Earth's crust where Iran, Pakistan and India collided years ago and the mountains were thrust upward by the force. We saw the White Nile and the Blue Nile converge in the Sudan, the dust storms in Mexico, the thunderstorms over Africa, the tranquil beauty of the Bahamian Islands. These are all 'gee whiz' things."

When Dr. Musgrave's "airlock egress" or space walk commenced, Weitz described it: "Story seemed like a butterfly coming out of a chrysalis, only he's not as pretty."

Dr. Musgrave said, "I couldn't wait to get out. Space is a career to me, and this was to be only three hours of experience on top of 48 years, but it's like a surgeon who's been training 16 years to operate. Sooner of later, a surgeon has to operate. Sooner or later, I knew I was meant to walk in space."

In describing his extraterrestrial experience, Dr. Musgrave excitedly shiftede into the conversational rhythms of his native Kentucky. He holds five college degrees (bachelor's degrees in math and chemistry, master's degrees in biophysics and computers, plus the MD), but now he excitedly was dropping his "gs."

I was looking at the sunrises and the sunsets -- they never got tiresome -- looking at the Earth spinning, and realizing how fast we were really going. Even at our high altitude, we were going very fast. We were really hauling."

A common medical problem encountered by astronauts is motion sickness, or space adaptation syndrome (SAS). Remarkably, Dr. Musgrave never experienced a moment's discomfort.

"I've done a lot of research into SAS," Dr. Musgrave said, "and I favor the theory that it's due to sensory conflict at the level of cerebral integration. The brain cannot understand the signals it's being sent in a zero-gravity vacuum, and it responds by commanding nausea and vomiting. It's a lot like seasickness.

"For some reason, I immediately oriented to weightlessness. I was totally at home in zero gravity and felt extraordinarily comfortable in a no-down environment. I trained myself not to expect to see a 'down.' I was prepared to tell myself that the floor of the spaceship was down and to keep myself oriented that way, but I found that I didn't need a down. To me, the Earth was neither down nor up. It was just there.

"Some people are different and get confused by all the sensory inputs telling them that down should be here, but, wait a minute, it should also be there, and the two don't match. I had done a lot of work on integrating the vertical and horizontal parts of the spaceship, and I had no need to see or feel an up or a down. Since I had no fixed notion of down, it never bothered me to see things up that should have been down. The usual treatment for SAS is drugs, but based on a subjective data point of one --me-- we may be able to handle it by never having a notion of down.

"The only time I missed gravity was when I got into my sleeping bag. I tied it horizontally to a structure inside the spaceship and I slept horizontally across the shuttle. I slept up front near the commander just to keep him company, since Bo (Bobko) and Don (Peterson) were sleeping at mid-deck. Now, I'm a 'side sleeper,' and I like to change to different positions throughout the night. But since there's no up or down in space, I really couldn't sleep on my side. No matter what position I tried to take, the zero gravity would keep me locked in a neutral position -- neither up, down, or sideways. I couldn't twist and turn and hold a new position. I was tempted to take a strap and lock my knees in a crouched position, just to get some variety, but I never did. You know, the space program inspired all the medical research on sleeping, on what happens to you when you go to bed.

"It's absolutely amazing that man, a creature genetically coded to live in gravity, can survive in zero gravity. When the space program began 25 years ago, there were people who said that man wouldn't be able to breath or swallow in zero gravity. There were a lot of straw men in those days who said that manned space travel would be a disaster, that it was not survivable.

"As you can tell, I'm an optimist, not a pessimist. I had absolute confidence that this mission would go as smoothly as it did. This is my career, and though I'm not scheduled for another flight as yet, I hope I don't have to wait another 16 years. I wan to go up again.

"What did it mean to me? Well, you're talking about five days' experience on top of 48 years. I've kept myself pretty excited all my life, but there's definitely a 'delta' value to those five days in space. It means something to me. I'd talked to all the other astronauts who'd been up and I'd read all the mission reports, but being there is something else. It's the intensity of the experience. It's like being told how to fly an airplane and what it's like and then really doing it. You have to do it to feel it.

"You remember the little things, too. Like sound. Even though there's a vacuum in space, if you tap your fingers together, you can hear that sound because you've set up a harmonic within the space suit and the sound reverberates within the suit. I can still here that sound today.

"But the main impression is visual. It's like seeing the totality of humanity within a single orbit. It's a history lesson, a geography lesson -- a blue ocean here, a brown continent there, clouds and mountains and ships and seas and trees. It's a sight like you've never seen. I hated to come down."

During re-entry into the Earth's atmosphere, Dr. Musgrave stood up in Challenger's cabin, an action usually prohibited by standard operating procedure. The question came up at the press conference, and Weitz said, "Sure, Story did it on the spur of the moment, but we all knew what he was doing and nobody's quarreled with him -- at least until now."

Dr. Musgrave didn't comment at the press conference, but now he explained, "I was conducting my own experiment. The whole flight had been so totally exhilarating and I was on such a high that I decided to stand throughout re-entry. It's my nature to press and push, to go beyond what's expected. I had my Hasselblad camera and I was taking some photos. Also, I wanted to prove that you can stand while going from zero gravity back into gravity. That's important if an astronaut ever has to leave the top deck and go below to throw a switch or circuit breaker. I wanted to show that the cardiovascular system doesn't have any problem going back into gravity and that you don't have to be strapped down.

"My standing was smooth and steady, and it shows how the STS system is maturing. We all had total confidence. Standing up throughout re-entry, instead of being strapped down, was the perfect end to a perfect trip. I was having fun, as always.

"When I came off the shuttle, I was a little wobbly. I had sea legs, but nothing serious. Within 24 hours, I was running. I played racquetball 24 hours before I left Earth and played 24 hours after returning. I played equally well both times.

"The most surprising thing about this whole mission was the lack of surprises. There's an inverse relationship between productivity and surprises, and we had very few surprises."

Dr. Musgrave has to get back to the debriefings. Dressed in a turtleneck sweater and sport coat and carrying an umbrella as if it were a walking stick, he looks more like a suburbanite who has come in out of the rain than an astronaut who has come in from outer space. In photographs, his clean-shaven head often gives the appearance of fierceness, sort of a Kojak of space. In person, though, he appears much gentler, soft-spoken, and a bit of a dreamer. Like all the astronauts, he is the "right stuff," a believer.

"The next thing that will rival our landing on the moon in terms of public impact," he said, "is when people take space to their hearts, when they realize it's the way of the future." There is time for a final question. How does he view the use of space-age technology for war?

"I'm an optimist," he began. "I like to think positive. But man is not simply a social animal. One of my biggest disappointments is the absolute failure of the human being as a social animal. You get back here to Earth and open the newspapers, and every week there's 10 or 12 new wars breaking out around the world.

"When I was in space, I never thought about war. I never had one negative thought. It was an incredibly positive experience, my five days in space. I don't think that one negative thought ever intruded upon the wonder of what I was doing. There was no time or inclination to think of war or problems, disease or death.

"Say, you know, maybe it did happen to me. Maybe I had it. It just took time to bring it home to me. I did have my transcendental experience, after all."