(CNN) -- Although there were no signs of missing aviation adventurer Steve Fossett Tuesday evening, an official leading the rescue said she remained optimistic.
Aviation record-holder Steve Fossett is missing and a search is under way.
Maj. Cynthia S. Ryan of the Civil Air Patrol said Fossett, who has been missing for a day, once walked 30 miles to get help after making a forced landing.
But Ryan noted the challenge rescuers are facing as they comb the high desert region, which is covered with sagebrush and hides deep ravines.
Rescuers are focusing on 600 square miles. "It's a very large haystack," she said. "And an airplane is a very small needle. No doubt about that."
The Civil Air Patrol has 10 aircraft that will be searching until dusk for Fossett, who has been missing since Monday afternoon, she said. The search will resume Wednesday at 7 a.m. (10 a.m. ET).
Fossett, 63, was in a single-engine plane when he took off at 9 a.m. (noon ET) in good flying conditions from hotel magnate Barron Hilton's Flying M Ranch, Ryan said.
He had planned to return to the ranch, which is about 30 miles south of Yerington, Nevada, at noon (3 p.m. ET). The search for him began about six hours later, Ryan said.
Fossett did not file a flight plan, which is not required on flights using visual navigation.
Fossett is the first person to solo around the world in a balloon, and has broken numerous other flight records.
When he left, he had four to five hours of fuel for flight, said Ryan.
"Steve took off toward the south and was going to fly southbound, looking around for some dry lake beds for some plans he had for the future," Ryan said.
Those plans, she said, involved testing a vehicle in an attempt to set a world land speed record.
Ryan said authorities are analyzing information from radar intelligence to try to track Fossett.
Helicopters and planes from Naval Air Station Fallon, in Fallon, Nevada, the Nevada Air National Guard and the California Highway Patrol are helping in the search. Watch CNN's Miles O'Brien, who is a pilot, describe the search »
Fossett was flying in a single-engine, Citabria Super Decathlon -- a plane capable of aerobatics -- with tail number N240R, according to CAP. Fossett, though, had no parachute, which is required for aerobatics. See where Fossett took off »
There has been no sound detected from the plane's emergency locator radio beacon, which goes off if there is a hard impact.
The aircraft, with serial number 635-80, was manufactured by Bellanca, and is registered to the Flying M Hunting Club Inc. in Yerington.
"Steve is a tough old boot. I suspect he is waiting by his plane right now for someone to pick him up," predicted Sir Richard Branson, president of Virgin Atlantic, in a written statement. "The ranch he took off from covers a huge area, and Steve has had far tougher challenges to overcome in the past. Based on his track record, I feel confident we'll get some good news soon."
Virgin Atlantic sponsored the GlobalFlyer, which Fossett flew in 2005 during the first nonstop, solo flight around the world without refueling.
A year later, he used GlobalFlyer again to break the world's flight distance record, traveling more than 26,000 miles in 76 hours, 45 minutes from Kennedy Space Center in Cape Canaveral, Florida, to Bournemouth, on the coast of southern England.
He made an emergency landing during that flight after electricity on the aircraft failed over Shannon, Ireland. His goal had been to land at Kent International Airport in Manston, England.
In 2006, Fossett piloted the plane to its new home, the Smithsonian National Air and Space Museum's Steven F. Udvar-Hazy Center in Chantilly, Virginia.
In 2002, he achieved the first solo balloon flight around the world, traveling 20,626 miles in 14 days.
He's credited with 115 world records or world firsts, and holds official world records in five sports, according to his Web site.
CNN.com interviewed Fossett last year after he published a book about his life's passion for breaking world records, titled "Chasing the Wind."
Asked which of his record-breaking feats was his personal favorite, he said, "The first solo around-the-world balloon flight. We had to really upgrade the technical capability of balloons and the flight was much more difficult than I'd ever imagined it would be. I tried six times over the course of six years before succeeding."
"I think I'm a risk averse person, which might sound very strange because of the sports I'm involved in," Fossett said, in response to a question about whether anything scares him. "What I do is try and reduce the risk. I don't do any of this for the thrills. I'm doing them for the personal achievement."
Asked how long he'll keep going, Fossett answered, "I imagine that when I'm 80 years old and sitting in a wheelchair that I might do something like take a remote control airplane and try and fly it around the world. I plan to be setting and breaking records indefinitely."
The aviator was in Sparks, Nevada, northeast of Reno, in August, preparing a jet racer to break the land speed record at Bonneville Flats in northwest Utah.
Fossett was born in Jackson, Tennessee, but grew up in California, where he attended Stanford University, graduating with a degree in economics in 1966.
Two years later, he earned an MBA at Washington University in St. Louis and became a successful commodities broker, eventually launching the Chicago-based securities company Lakota Trading in 1980.
He married Peggy Viehland in 1968. The couple have no children.
His interest in adventure started early. As a Boy Scout, he grew up climbing the mountains of California. "When I was 12 years old I climbed my first mountain, and I just kept going, taking on more diverse and grander projects," he told CNN in the 2006 interview.
Fossett fueled his drive for adventure with the money he made from Lakota Trading. E-mail to a friend
All About Steve Fossett