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Floating Robots Set Stage for Cosmic Choreography
Under a velvet black dome studded with sparkling stars, a lone figure glides gracefully, tilting and whirling across a shining floor. Instead of music, however, there's the slight hiss of compressed air.
A formation robot on display
Image right: The formation flight robot travels on a paper-thin cushion of air supplied by a ring of pressurized tanks in its base. Click here for video. Image credit: NASA.

Standing about waist high and weighing a chunky 318 kilograms (700 pounds), the rotund robot looks more like something from "Star Wars" than "Shall We Dance?" Yet, as it floats on a paper-thin cushion of air, it is testing the initial moves in a complex choreography that researchers eventually plan to execute in space as part of the search for Earthlike planets.

The blue robot is a ground-based predecessor to NASA's Terrestrial Planet Finder, a revolutionary space telescope that will combine the light from multiple satellites to simulate one enormous telescope. When the mission launches, sometime before 2020, five robotic spacecraft will fly in formation to create an instrument powerful enough to capture the faint light from small planets orbiting stars outside our solar system. These are the kind of planets that scientists think have the most potential for harboring life.

To prepare for that future debut in space, the robot is rehearsing on Earth in JPL's Formation Flying Technology Laboratory, inside a cavernous, two-story chamber. Thirty-four lights embedded in the domed ceiling mimic stars, at least three of which are always visible to the robot's star-tracking camera.

An elevated floor, 30 feet in diameter and covered in a polyester film provides a glass-smooth surface above which the robot hovers. On-board air cushions allow it to glide with minimal friction, much as its eventual successors will float in space. Another air cushion separates the robot's base from its top, a disc-shaped platform that houses its brains and navigation system. Though bristling with microprocessors, sensors, gyroscopes and thrusters, the top is perfectly balanced. The robot receives commands through a wireless connection from a mini flight-control center in an adjoining room.

The robot and its special environment are part of what engineers the formation control testbed, one of three formation flight testbeds developed for the Terrestrial Planet Finder mission. Here, the new system created to enable multiple spacecraft to control their positions precisely enough to fly in formation gets its first test in a realistic setting. (More about the formation flight testbeds)

For the moment, the blue robot is performing solo, but next spring when its golden-hued twin arrives, the dance will become a pas de deux. By the end of 2006, a third robot will complete the testbed trio. As the number grows, so will the challenge to keep them all in harmony. The new technology will have to be mastered on the ground first before it flies in space.

Manager Dan Coulter and Flight Control Testbed Lead Asif Ahmed look at the robot frame Image left: Terrestrial Planet Finder Project Manager Dan Coulter (left) and Flight Control Testbed Lead Asif Ahmed look at the robot frame prior to the installation of its onboard electronics. Click here for larger image. Image credit: NASA.

"We have a lot of work to do," said JPL engineer Asif Ahmed, formation control testbed lead. "We've never before needed the degree of control required for multiple spacecraft. They will have to be able to talk to each other constantly. Each spacecraft will have to know where all the others are and be able to coordinate all its activities. They'll also have to depend on on-board smarts because they can't depend on humans on Earth to tell them what to do."

The testbed lets Ahmed and his colleagues observe and fine-tune some of the complex maneuvers that the future spacecraft will have to execute. "First, they have to be deployed in a way that they don't crash into each other," Ahmed said. "Then, like five people in a dark room, they'll start by talking to each other before they move around." One of the robotic spacecraft will take the lead and plan a path for each to take that will create the desired formation while avoiding any collisions.

Once they're in formation, the spacecraft have to control their positions so precisely that, though unconnected, they achieve virtual rigidity and function as a single instrument. Their positions relative to each other won't vary more than a few centimeters and their aim towards their target by only a fraction of degree. They'll maintain this same level of precision as they make observations on the fly, reorienting in space to view a target from different angles.

"We simulate all these maneuvers on the computer first," Ahmed said, "then we move to the testbed." When the testbed's three robots have their synchronized performance down pat, the show will be ready to go on the road - and into space.

Terrestrial Planet Finder is managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., for NASA's Science Mission Directorate, Washington, D.C. It is part of NASA's Origins program, a series of missions and studies designed to answer the questions: Where did we come from? Are we alone?

Information about NASA's hunt for extrasolar planets is available at http://planetquest.jpl.nasa.gov.

Written by Rosmary Sullivant/PlanetQuest