Dial-a-spacecraft during comet mission.

On Sept. 11, while a spacecraft called the International Cometary Explorer (ICe) is paying the first-ever visit to a comet by a man-made object (see p. 138), the public will be able to listen in by phone to the actual sounds of the probe as they are transmitted to earth. In addition, callers will hear periodically updated reports on the progress of the mission, in which ICE will head through the fail of Comet Giacobini-Zinner.

Arranged by a Redlands, Calif., organization called the Sounds of Space Group, the service will operate from 2 a.m. EDT to midnight on the 11th. (The center of the encounter is expected to occur at about 7 a.m.) Each call will cost 50^ -- plus an international charge for calls originating in the 16 other countries that are also carrying the service -- and will provide a 60-second response, including the live spacecraft sounds and a recorded status bulletin.

The phone number is 1-900-976-COMET. That is one character too many for a 900 number, but AT&T, according to a Sounds of Space official, says the additional character will not affect the dialed number, while it allows the group to include COMET in its listing. (The actual working number thus ends with "COME," or 2663.)

The spacecraft sounds, picked up directly from NASA's Deep Space Tracking Network, will represent all of ICE's telemetry at once, since separating it into data from individual sensors will require additional computer processing. The "live" sounds, therefore, will not provide immediate indications of changes in ICE's environment as it enters the comet's tail -- with one exception. The dust in the tail is not expected to destroy the spacecraft, but if it darkens the craft's solar panels until their reduced current output trips a built-in switch that turns off everything but the receiver, some callers may find themselves listening in on a single stark datum, as ICE's message abrutply ends. If that happens, NASA will try to reactivate the spacecraft using only three of its experiments, in the hope that the smaller current drain will not re-trip the switch.