ABOUT 10 YEARS AGO a long-forgotten genre of popular instrumental music—full of gimmicky stereo effects and heavy on theremins, synthesizers, and similar otherworldly sounds —was dug up from the oblivion it had long inhabited and revived for today’s reflexively ironic youth under the name Space-Age Bachelor Pad Music. The sobriquet itself has become such a cliché that it now qualifies as a retro ’90s reference, but even without the added layer of camp, it reeks of antiquity, from the quaint bachelor to the expired slang of pad to the most archaic term of all, space age , which might best be symbolized graphically with a Davy Crocket cap.

Inevitably, as the days when the space program seemed important enough to define an entire era continue to recede, artifacts of the space age have started popping up where all old trends enjoy an afterlife, on eBay. But that’s not the only place you can pick up an astronaut-signed Mercury instrument-panel diagram or a pen that flew in Skylab, for as baby boomers pay off their mortgages and the original astronauts reach retirement age, space collectibles have become a thriving business. Another factor in the growth of the market is the fall of the Soviet Union, which has made all sorts of Soviet space artifacts available to those with hard currency. Christie’s, Superior Galleries, Sotheby’s, and Swann all have held auctions of space memorabilia, and dozens of Web sites have popped up to serve collectors.

As is true with most collectibles, the buyers are a mix of hobbyists and investors. For the latter group, space artifacts seem to bear out the old saying about the advantage of investing in land: “They aren’t making any more of it.” Since they aren’t landing on the moon any more, either, Apollo memorabilia is unlikely to lose its scarcity. On the other hand, as the market grows, astronauts and others associated with the space program are ransacking their attics and closets for anything that has ever been in orbit. A nametag that belonged to the late astronaut James Irwin, for example, with “certification from NASA identifying the gray stains as lunar in origin,” recently sold for $310,000. Also available are astronautused spoons and toothbrushes as well as post-mission commemorative watches and cigarette lighters.

Not every item needs a certificate to distinguish it from garage-sale leftovers. A complete and intact Soyuz re-entry vehicle can be yours for $1.5 million—a bit pricey, perhaps, but the grandchildren will love playing in it. Swann is currently offering a Playboy centerfold that went to the moon with Apollo 17 , lovingly preserved and signed by that mission’s astronauts. It was listed in a recent catalogue at an estimated $40,000. Autographed letters and crew photographs can be surprisingly valuable, especially if one of the astronauts is dead or publicity-shy, though collectors must be ever vigilant against the menace of the autopen. A separate category includes traditional collectibles, such as first-day covers, flags, medallions, and the like, that have flown in space on various missions.

Other astro-bilia ranges from working documents (mission rules, navigational charts, data-card books) to whimsical items like a Snoopy astronaut doll signed by the late astronaut Eugene Cernan. An interesting subgenre consists of beautiful and detailed models made by contractors of the space vehicles they were building. Also available are newly manufactured models much more sophisticated than the ones you assembled as a child, including a set of handcrafted and painstakingly researched miniatures of astronauts and Apollo hardware from Code 3 Collectibles that has the official imprimatur of the National Air and Space Museum.

Full and partial space suits can be bought as well, along with parachutes, gloves, tools, instruments, and uniform patches. No one has yet thought to cut a space suit into pieces and glue them into trading cards, as is done with baseball players’ uniforms, or of selling vials of water that astronauts swam in, as was done with the Beatles. But it’s probably just a matter of time.

Can space tchotchkes be relied upon to skyrocket in value? Knowing the answer to that question requires an ability to predict the course of the public’s fickle tastes, and if you can do that, there are much better ways to make money than buying signed posters and space-flown parts lists. As a reminder of the wonder of space exploration, however, such memorabilia will never lose its value. Back in the space age, visionaries predicted that extraterrestrial trips would one day become as unremarkable as flying on an airplane. It didn’t happen, and as recent events have shown, space flight remains anything but routine. That’s why the sense of awe that we attach to any object that has been in orbit is still the most potent reminder of what several generations of space engineers and scientists have achieved.