They are building a big antenna for the Deep Space Network, which provides radio communications for spacecraft exploring the solar system. The network operates clusters of skyward-facing dish antennas at sites in California, Spain and Australia. The antennas catch radioed information from spacecraft as near as Earth orbit and as far as more than twice the distance to Pluto. They also send commands to the spacecraft. JPL administers the network for NASA.

Construction workers erect steel components atop a new concrete chamber near Madrid, Spain, this summer are helping NASA study Mars and comets. Photo: NASA/JPL

The Spanish construction job has an important deadline.

NASA needs this new antenna operating by the time an unprecedented peak in demand for deep-space communications hits in November 2003, said Jeffrey Osman, Deep Space Network antenna and microwave manager at JPL. During the following three months, three rovers and two orbiters from the United States, Europe and Japan will arrive at Mars, two other spacecraft will encounter comets, and a third comet mission will launch. That's on top of the continuing communication needs of many other missions.

The new antenna will span 34 meters (112 feet) in diameter and will use an advanced design called "beam waveguide," which steers the gathered radio signals to a protected, underground electronics room. The design gives more reliable operation than the older antenna design with processing gear up in the dish.

"Construction is on schedule," Osman said. "The concrete pedestal is in place. The steel is going up. The main reflector portion of the dish will be lifted as a single piece later this year."

The pedestal encloses the electronics room and will support more than 500 tons of antenna structure.

Custom-made steel pieces for the antenna's giant dish and other components are being fabricated at the factory in Tarragona, Spain, of the project's prime contractor, Schwartz-Hautmont Construcciones Metalicas, S.A.

This antenna is the biggest piece in about $54 million worth of improvements NASA chose as priorities for increasing the Deep Space Network's capabilities by November 2003.

Pedestal constructed for the new dish. Credit: NASA/JPL

It will become the network's sixth 34-meter, beam-waveguide antenna. Three are at the network's Goldstone station near Barstow, Calif. The stations near Madrid and near Canberra, Australia, each have one already in operation. Each of the three stations also has a 70-meter (230 foot) antenna and several smaller ones.

The stations take turns linking with various spacecraft as Earth's rotation puts the target spacecraft in view of each station in turn.

Putting the new antenna at Madrid gives the biggest possible advantage for handling the upcoming peak in communications needs, including pictures from two advanced rovers from JPL that NASA plans to land on Mars in early 2004. This antenna will add about 70 hours of spacecraft-tracking time per week during the periods when Mars is in view of Madrid. That's a 33 percent increase from the station's capacity with its existing antennas.

A coincidence of solar system geometry will intensify demand on network resources during the crunch period, Osman said: The comet encounters by NASA's Comet Nucleus Tour spacecraft in November 2003 and by NASA's Stardust spacecraft in January 2004 will happen in the same direction from Earth as Mars will be. That will minimize opportunities to have one station track the comet missions while another tracks the Mars missions.

So, the Madrid construction team keeps its work on schedule in order to have the new antenna ready when needed. Week-to-week progress can be watched on the network's Web site, at http://deepspace.jpl.nasa.gov/dsn/antennas/madrid-gallery.html.

This month, workers will be installing a circular steel track above the concrete pedestal. The track will provide the precision surface for wheels the dish will ride on as it turns to find a distant spacecraft with exciting discoveries to report.