Testing the camera bound for Saturn

Arizona Daily Wildcat This downward-looking panorama of the UA Mall, taken by a camera built for the Cassini spacecraft to Saturn, shows the corner of the Kuiper Space Sciences Building with researchers milling around on top.

The replica was mounted on a bracket that reached out of the missing door of a four-passenger helicopter. Its three lens-like sensors peered downward at skewed angles from the ground to the horizon.

A stack of computers and electronic equipment filled the chopper's back seat, and an engineer sitting next to the pilot controlled the whole mess from his laptop computer.

The flight was the third helicopter test for the Descent Imager/Spectral Radiometer, a highly specialized camera designed and built by scientists at the University of Arizona's Lunar and Planetary Lab as part of the $3.5 billion Saturn-bound Cassini mission.

The camera's twin is now riding aboard the Huygens probe on the Cassini spacecraft. Launched in October, Cassini is due to reach Saturn in 2004, where it will conduct a four-year orbiting mission.

If all goes according to plan, the Huygens probe will parachute to the surface of Saturn's largest moon, Titan, in November 2004. It will send back to Earth images and spectral data as it falls.

"We think the images will be pretty nice," said UA planetary scientist Martin Tomasko, the principal investigator on the Descent Imager team. "With the resolution we have, we should be able to see large surface features, all the way to fist-sized objects."

But before that data comes back, Tomasko said, the imaging team must learn how to make sense of the pictures the camera takes as it falls - swinging, turning and wobbling - to Titan's surface.

Bashar Rizk, a staff scientist for the project, said the team's goal is to use the camera to piece together panoramic mosaics of the landscape below it.

The difficulty of this task can be compared to patching together a panorama of pictures taken by a photographer spinning around while bounding down a hill.

"The helicopter moves all over the place, and each of its moves can be represented by six degrees of freedom," Rizk said. "If you have 24 different pictures you want to piece together, you have to nail down six different variables for each of those pictures. So you are dealing with hundreds of variables that must be resolved."

A large part of Rizk's task is writing computer programs that can help account for the various camera movements.

Tomasko said the team built three cameras - one to send to Titan, one to be used as a flight spare and a third used in field tests.

Those tests, being conducted at the UA and at various Southern Arizona locations, are invaluable to the Cassini/Huygens mission, Tomasko said.

"We really learn a lot when we take the instrument out to work with it," he said. "We continue to refine our technique."

Last summer, the team used the camera to take a set of images from a platform mounted on the southwest corner of the Kuiper Space Sciences Building.

The team then began a series of tests from helicopter flights, first taking a set of data near the Tucson International Airport, then doing a test flight above Patagonia Lake, about 45 miles south of Tucson.

Now the team is building a rotating platform that can be used to further test the camera, Tomasko said.

"By next summer, we hope to add a wobble to the rotation to see if we can continue to decipher the data as it swings in a manner we expect it will when falling from a parachute on Titan," he said.

After that, the scientists' sights are set on Mount Lemmon.

"We want to take the imager to a lookout point on Mount Lemmon and take a panoramic mosaic of images of the Tucson valley as it rotates and wobbles on its framework up there," Tomasko said.