| MULTIMEDIA |
|
|
Formation flying is a critical element in NASA's search for Earthlike planets. The ultimate goal is to develop the technology needed to fly multiple spacecraft in such perfect harmony that they become a single instrument -- bigger and better than could be launched ready-made from Earth.
Terrestrial Planet Finder, NASA's first space-based mission to directly observe planets outside our own solar system, will rely on formation flying for one of its two observatories. Five separate spacecraft will work together to function as a single huge telescope. They will create an instrument powerful enough to distinguish the faint light of small Earthlike planets from the much brighter light of the stars they orbit.
"Formation flying provides an alternative approach to flying large structures in space," said Dr. Fred Hadaegh, a senior research scientist and manager of the Distributed Spacecraft Technology Program, the JPL research and technology development group charged with creating this technology for future NASA missions. "Instead of one large instrument, the idea is to arrange several smaller spacecraft and bring them together to work as one. Each piece of the system is brought together virtually, as opposed to integrated physically."
Flying multiple spacecraft in formation rather than one big instrument offers many advantages, Hadaegh said. "It is actually easier to control two telescopes in space well enough to achieve the level of accuracy of a single instrument than it is to design and control a single large structure." In addition, multiple spacecraft may be able to do jobs that a single spacecraft can't perform. Additional spacecraft could be added to change, augment, or update an existing formation.
The challenge is to develop both the software and the hardware to allow separate, unconnected spacecraft to function as if they were a single, solid structure. "The key is coordination and control," Hadaegh said. Each spacecraft will have to be in constant communication with all the others, aware of its position in relation to all the others, and capable of making adjustments. While some commands will come from humans on Earth, the multiple spacecraft will have to make many decisions autonomously, relying on very sophisticated computer software.
With more than two dozen engineers and scientists, JPL has one of the largest teams of formation flying experts in the world. Testing some of the new technology being developed for Terrestrial Planet Finder has already begun at JPL's new Formation Flying Technology Laboratory. The lab houses three different testbeds that let researchers see how well their software and hardware perform under conditions that simulate those in space.
For Terrestrial Planet Finder, five spacecraft, flying in formation about 1 kilometer apart, will function as an optical interferometer. Four of the spacecraft will have telescopes, while the fifth will act as a combiner . Optical interferometry combines observations from multiple telescopes of the same target to achieve the results of a much larger telescope. The further apart the individual telescopes are, the greater will be the resolution.
The components of Terrestrial Planet Finder's interferometer will be connected virtually rather than physically. Flying together in formation will allow them to create something greater than the sum of their parts.
