brand of formation flying will differ from that of aeronautical performers
like the Navy's Blue Angels or the Air Force Thunderbirds (left). In space,
the levels of precision will be much tighter, the motions will be slower,
and the spacecraft will be autonomous rather than human-controlled.
(PLANETQUEST) -- Engines roaring, the Navy's Blue Angels
thrill audiences as they soar overhead in a tight triangle, their signature
Delta formation. For a few moments, the six perfectly spaced jets appear
to be invisibly joined together in a single unit.
NASA's goal is to take the concept of formation flying to an even higher
level. It is developing the technology 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. Formation flying is a critical element
in NASA's search for Earthlike planets.
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."
|Brent Lytle of ACEi, a JPL industry partner, works
on a ground-based robot that will be used to demonstrate technologies for
precise formation flight at JPL.
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, Hadaegh said.
Working together with university and industry partners, they're now preparing
for the 2014 launch of Terrestrial Planet Finder. Testing some of the new
technology being developed for the mission 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 one 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.