In modern times a number of Jewish astronauts have soared into outer space. One of these is Dr. David A. Wolf, whose modern-day chariot of fire is the United States Space Shuttle. "If anything was a religious experience, it was the spacewalk," says the NASA astronaut. "It's kind of a leap of faith-your first time opening the hatch and clipping on and pushing yourself outside on those tethers."

Logging 142 days aloft, Dr. Wolf's space experiences include three shuttle flights as well as a four-month sojourn in the Russian space station Mir. Those months-from September 1997 through January 1998-encompassed Rosh Hashana, Yom Kippur and Hanukka. But the remarkably accomplished scientist, now 44, has made a point of maintaining his Jewish identity and observances proudly while hurtling around Earth.

"We had greetings from space at our Rosh Hashana service," reports his father, Dr. Harry Wolf. His son had recorded a greeting for his parents' congregation, Beth-El Zedeck in Indianapolis. "The congregation just couldn't believe they were being wished a happy New Year from Mir," recalls his mother, Dottie. "It was fantastic!"

Yom Kippur was unlike anything on Earth. "All I had to do was fast for an hour and a half," Dr. Wolf explains, "because sunrise occurs every 90 minutes. I fasted a few sunrises."

While there is no rabbinic consensus about observing Jewish laws in outer space, rabbis have noted that pikuah nefesh, saving a life, overrides observance even of Shabbat. So when vital work on the space station would arise on Shabbat or a holiday, Dr. Wolf's participation could actually be viewed as a mitzva. "We were so busy with the nuts and bolts of staying alive and operating the station," he says, "that I didn't have much time for philosophy."

He did find the time, however, to observe Hanukka. "I had a menora, but I couldn't light the candles," Dr. Wolf says, explaining that open flames would pose extreme hazards in the oxygen-rich atmosphere. So he took advantage of zero gravity to enjoy another tradition: "I probably have the record dreidel spin; it went for about an hour and a half until I lost it. It showed up a few weeks later in an air filter. I figure it went about 25,000 miles."

Dr. wolf also did a little sightseeing while stationed in Mir. "You can observe Israel a couple of times a day," he reflects. "It's a unique part of the globe. It has kind of an ancient appeal, even from space. You can see a border between Israel and Egypt because of the irrigation; Israel looks really dark, which indicates more vegetation." Experiencing zero gravity is not only about twirling dreidels in midair. It's a matter of managing your body and your environment in a whole new way, as attested to by the "Letters Home" from Mir that Dr. Wolf posted on the Internet for his anxious family and friends. "My mother would be proud of me," he boasted in one such letter. "I spent most of today organizing and cleaning the bathroom. I've also been put in charge of the local lost-and-found; up here things don't necessarily stay where you put them," he continues. "If you don't nail it down up here-we use Velcro-there is literally no telling where something will float."

Despite all the hard work, Dr. Wolf found time to enjoy the unique aspects of weightlessness. He eventually mastered complex tasks such as dressing, drinking and keeping track of his belongings. He admits that although he would love to go to the moon one day, "I really like true zero gravity and on the moon there's gravity, although it's mild."

Describing her son, Dottie Wolf cites a résumé of accomplishments that reads like an all-star team of Jewish sons. "He was a bar mitzva and read from the Torah," she recalls. "He can still speak Hebrew. He speaks Russian. He's an electrical engineer and a medical doctor and a pilot and an avid sportsman. Becoming an astronaut enabled him to use a lot of his talents." Dr. Wolf received his medical degree from Indiana University. A warm and articulate speaker, he was interviewed for the Discovery Channel's Inside the Space Station, which aired in December 2000.

Dr. Wolf's medical background and interest in weightlessness have led to his involvement in cell-growth experiments in space. "The whole purpose of the space program is to improve life on Earth, and that's what an orbiting international laboratory is designed for," he explains, referring to the future applications of the International Space Station now being constructed. "My favorite application is tissue culture, where we're able to grow three-dimensional tissues because they're not restricted to a surface by gravity. It enables us to grow human cancers in three dimensions, for example, where they are genetically better able to represent cancer in the body. We've also grown nerve tissue and cartilage."

An outgrowth of Dr. Wolf's experiments has been the development and patenting, with NASA colleagues, of the Rotating Bioreactor Cell Culture Apparatus. This innovative technology simulates zero gravity, which allows scientists to grow cells and tissues in a "weightless" environment in earthbound laboratories. The invention has been licensed to VivoRx, a Santa Monica-based pharmaceutical firm working on methodologies to grow pancreatic tissue for diabetics. These artificially constructed tissues produce insulin in a diabetic's body so effectively they reduce or eliminate the need to take successive dosages of insulin. According to reports from the Lyndon B. Johnson Space Center, the company has "performed initial clinical trials in which human diabetes patients were treated with implants of encapsulated pancreatic cells." The company also plans to grow other tissues for commercial and medical applications. Weightlessness apparently can cause serious health problems after lengthy space flight. Dr. Wolf himself suffered physical consequences from his four-month stint.

"I had a 14-percent loss of some bones' mineral content," he reports. "It took a year to regain my bone mass [and] a fair amount of working out and exercise."

Some astronauts who have endured longer space missions have never regained the loss, which poses a challenge to scientists to connect this phenomenon to people with osteoporosis who likewise don't regain bone mass.

"The psychological effects were at least as hard as the [physical ones]," Dr. Wolf readily reflects. "Being away from the country [for so long], I found it very difficult getting organized again...to keep a house in condition and cars, insurance, licenses, bank cards. It takes a couple of years to recover."

"My girlfriend was definitely critical in my getting through this," acknowledges Dr. Wolf, referring to Tammy Kruse, a nurse, originally from Indianapolis, who lives with him in Houston. "We talked a lot from space and she was a real moral support. When I came back she was a miracle in getting me readapted and finally settled."

Would he consider another long-term mission, perhaps even to Mars? "It will be anywhere from a two- to three-year mission, and I'd have to think long and hard, but I'd probably end up begging to go," he admits, though he says, "I'd miss Tammy a lot, and my family."

Dr. Wolf recently returned to Svosdny Gorodok (Star City), the Russian equivalent of the Johnson Space Center, where he had trained for over a year for the Mir mission. Enthusiastic about the project, he explains, "this is the first time we've conducted training in Russia, using the American spacesuits with Russian personnel maintaining, assembling and testing them. It's been a large effort for us to install American life-support systems for the spacesuits and train the Russians. It's a real example of technology cooperation; it shows how far we've come. Now we're going to build one great spaceship, this International Space Station, and we're doing it with Russian partners."

The international nature of the program opens involvement for other countries, including Israel. "We have two men of the Israel Air Force training at Johnson for future shuttle flights," Dr. Wolf reports. Colonel Ilan Ramon, 45, from Kfar Hittim in northern Israel, is training for a U.S. Space Shuttle mission that involves "a multispectral camera for recording desert aerosol measure." Lieutenant Colonel Itzhak Mayo, 44, from Tel Aviv, will serve as Ramon's backup. (Desert aerosol refers to dust particles typically arising in the Sahara that get swept up into great clouds and blow westward, changing fine rain particles into torrential downpours not conducive to agriculture.)

Dr. Wolf has made significant contributions to space science, which will have an impact on health on Earth. A member of the board of directors of the National Inventors Hall of Fame, he has received over 11 patents and over 20 Space Act Awards. He was responsible for the development of the American Flight Echocardiograph for investigating cardiovascular physiology in microgravity and chief engineer for design of the space station medical facility.

As one who works at the cutting edge of exploration, he is currently assigned to the Extravehicular Activity (Spacewalk) Group focusing on assembly techniques for the International Space Station.

"When I try to think about what I'd like to do next," Dr. Wolf concludes, "I realize I'm doing exactly what I want to be doing."