The Dish is Alive and Tracking
Across the street from the Alpine Gate and up a cow-studded hill, the Dish is one of SLAC's nearest scientific neighbors. The landmark 150-foot-wide reflector antenna still sends and receives radio waves to probe the Milky Way while it checks on satellites and spacecraft.
Entering the control room tucked beneath the metal lattice bowl is like stepping back in time to the early days of SLAC. Both facilities were built in the early 1960s, and the Dish still uses an antique klystron to generate the UHF-frequency waves that it transmits.
"We can move the receiver toward the center of the galaxy in a minute," said Ivan Linscott of the Radio Science Group at Stanford.
Linscott, who studies hydrogen clouds, twists two black knobs to tilt the Dish and rotate it on a circular track, aiming it toward the center of the Milky Way Galaxy some 10,000 light years away. Radio frequency energy pours into the Dish, passes through a spectrum analyzer, and shows up as an EKG-like signal on a display, with a peak at 1420 Mega Hertz—the rest frequency of hydrogen gas.
"A lot of energy shown on this display is relic radiation from the Big Bang," he said.
The Dish also has assignments closer to home. When the Mars Odyssey rovers were on the way to the Martian surface in 2003, the Dish tested their UHF-communication system. The test also revealed echoes from the planet's surface and possibly its sub-surface. Since then, Stanford graduate student Hrefna Gunnarsdóttir and a small collaboration have been studying the radio images, with the hope of discovering buried ice. Dish data are also part of an effort to pick good landing sites for the soon-to-be-launched Phoenix lander, which will dig for ice.
SRI International in Menlo Park manages the Dish, and uses it for monitoring and calibrating global positioning system (GPS) satellites. SRI also operates the nearby baby dish, only 60 feet across, for tracking small satellites and spacecraft. SRI and the Radio Science Group revitalized the once-rusting Dish in the 1990s and developed a technology crucial for filtering out the ever-increasing electromagnetic noise of cell phones, aircraft radar and broadcast television.
—Heather Rock Woods, February 13, 2007
Above image: The Dish. (Image courtesy of Brad Plummer.)