Short Waves of Activity in the Satellite Universe

The music pop-up channels are produced with the permission and cooperation of the artists, and "we work with the artist and their management about how long they feel they want the channel to be up," Greenstein says.

Neither Sirius nor XM will release numbers showing the audience size for the microchannels, but XM's Logan says that the more successful short-term formats match and even exceed the audience for some of the company's most popular regular channels.

Some of XM's most successful microstations have been built around holidays, such as a three-day Saint Patrick's Day celebration of Irish music called XM Green, a Labor Day blowout of songs about cars and driving called Car-B-Q, and a Halloween channel called Igor that blended scary sound effects with songs such as "Monster Mash" and spoken-word ghost stories. XM last year added a Radio Hanukkah channel that had only the most limited of audiences -- and a painfully limited playlist -- but certainly won points for novelty.

XM just finished a month-long Michael Jackson channel called Thriller and this week started Strait Country, an all-George Strait service that will run through May.

Sirius ran its Strait Up channel back in 2006, and of course the rival services each claim to be the inventor of short-term formats. Sirius started out with intensive music channels and has branched into a Bing Crosby Christmas Radio channel and one that played only the radio dramas written by Oscar-winning movie team of Joel and Ethan Coen.

XM got into microchannels three years ago, when a hurricane took out power in southwestern Florida and Logan called the radio station he formerly worked at, only to find that the station was off the air, muted by the power outage.

"It hit me that we have two transmitters in space," Logan says, so the company launched Red Cross Radio, which both then and in the aftermath of the Katrina disaster in Louisiana and Mississippi enabled volunteers on the ground to communicate with one another and plot logistics even when power and cellphones were out.

But the short-term format idea really has its roots in old-fashioned terrestrial radio, in the AM Top 40 stations of the 1950s and '60s that regularly created themed weekends featuring extra helpings of girl bands, Motown or a single artist.

The satellite services say that adapting that model helps keep subscribers feeling that they are paying for something exciting and unpredictable. But microchannels are also a new way to package entertainment and information for a society that consumes popular culture in short but intense bursts -- from espresso shots to text messages to viral videos, and now to radio formats that delve deeply into a single artist and vanish before some of us even knew they existed.