ASA needs parts no one makes anymore.

So to keep the shuttles flying, the space agency has begun trolling the Internet — including Yahoo and eBay — to find replacement parts for electronic gear that would strike a home computer user as primitive.

Officials say the agency recently bought a load of outdated medical equipment so it could scavenge Intel 8086 chips — a variant of which powered I.B.M.'s first personal computer, in 1981.

When the first shuttle roared into space that year, the 8086 played a critical role, at the heart of diagnostic equipment that made sure the shuttle's twin booster rockets were safe for blastoff.

Today, more than two decades later, booster testing still uses 8086 chips, which are increasingly scarce. NASA eventually plans to create a $20 million automated checking system, with all new hardware and software. In the meantime, it is finding and hoarding 8086's so that a failed one does not ground the nation's fleet of aging spaceships.

The same is true of other obsolescent parts, dozens of them.

"It's like a scavenger hunt," said Jeff Carr, a spokesman for the United Space Alliance, the Houston company that runs the shuttle fleet. "It takes some degree of heroics."

Troves of old parts that NASA uncovers and buys, officials said, are used not in the shuttles themselves but in flotillas of servicing and support gear. Such equipment is found, and often repaired, at major shuttle contractors around the nation, as well as at the Kennedy Space Center in Florida, where the shuttles blast into orbit.

That old computer in your basement? NASA is not interested. The agency and its contractors do not buy equipment from individuals but instead use Web searches as a way of finding stockpiles of old parts. They then buy them in bulk for repairing old machinery and building inventories of spare parts.

Recent acquisitions include outdated computer chips, circuit boards and eight-inch floppy-disk drives. "One missing piece of hardware can ruin our day," said Mike Renfroe, director of shuttle logistics planning for the United Space Alliance at the Kennedy Space Center.

Recently, Mr. Renfroe said, his team swept the Internet to find an obsolete circuit board used in testing the shuttle's master timing unit, which keeps the spaceships' computers in sync. None could be found. A promising lead turned false. Finally, a board was found. It cost $500.

"That's very inexpensive," Mr. Renfroe said. "To hire a design engineer for even one week would cost more than that."

NASA's growing reliance on antiquated parts is in some ways a measure of how far its star has fallen. In the early 1960's, the agency played a leading role in founding the chip industry. Its mass purchase of the world's first integrated circuits set the fledgling commercial enterprise on the road to success and profitability.

In turn, the expensive chips let NASA achieve feats of miniaturization that put advanced satellites into orbit and men on the moon. Thousands went into the lunar lander, making its guidance computer "smaller, lighter, faster, more power-efficient and more reliable than any other computer in existence," as T. R. Reid wrote in "The Chip" (Simon & Schuster, 1984).

Today, NASA is increasingly a victim of its own success. Civilian electronic markets now move so fast, and the shuttles are so old, that NASA and its contractors must scramble to find substitutes.

In the past, NASA procurement experts would go through old catalogs and call around to networks of suppliers to try to find parts. Today, the hunt has become easier with Internet search engines and sites like eBay, which auctions nearly everything. A few clicks of a space-agency mouse can now reveal a low-tech cache.

Mr. Carr of the United Space Alliance said that when the government bought complex systems like jet fighters, the contracts often had provisions that call for routine upgrades and improvements as a way to limit obsolescence. But the shuttles, with a design lifetime of a decade, never had that kind of built-in refurbishment plan.

The winged spaceships are to fly until 2012. But NASA is researching whether their retirement date can be pushed back to 2020.

For parts hunters, it could be a long haul. The shuttles, Mr. Renfroe of the United Space Alliance noted in an awed tone, "could go for 40 or 50 years."