Transportation
Reaction/Momentum Wheel
Being a big wheel in spacecraft lingo may be detrimental if you are
trying to stay competitive in the explosive world of small satellite building.
CTA Space Systems, Inc. of McLean, Virginia has been licensed to sell
commercially a reaction/momentum wheel originally developed for NASA's
scientific satellites. The wheel is unique in its small size, extremely
low residual imbalance, and large, highly controllable torque. These are
the same features required by a growing number of small commercial satellites.
In licensing from NASA, CTA was able to virtually eliminate the technical
risk and minimize the financial investment that would normally be required
to introduce a new spacecraft component.
Reaction/momentum wheels are flywheels used to provide attitude control
authority and stability on spacecraft. By adding or removing energy from
the flywheel, torque is applied to a single axis of the spacecraft, causing
it to react by rotating. By maintaining flywheel rotation, called momentum,
a single axis of the spacecraft is stabilized. Several reaction/momentum
wheels can be used to provide full three-axis attitude control and stability.
| Inside CTA Space System's High Torque
Reaction/Momentum Wheel is an innovative flywheel/bearing arrangement that
allows the entire rotating system to be balanced after it is assembled. |
NASA originally identified a need for the wheel in its Small Explorer
(SMEX) program an initiative to develop highly focused and relatively inexpensive
scientific spacecraft. One such spacecraft is the Submillimeter Wave Astronomy
Satellite (SWAS). Keeping the SWAS instrument pointed at celestial objects
to a high degree of precision (arc seconds) requires extremely low jitter
of the spacecraft. SWAS also required a reaction/momentum wheel with a
torque greater than any comparably sized commercially available wheel.
Those requirements prompted Goddard Space Flight Center to design and
build a Small, High Torque Reaction /Momentum Wheel. This wheel is unique
in that it features a large, highly controllable torque in a small package
with low power and an extremely low residual imbalance. To minimize imbalance,
an innovative flywheel/bearing arrangement is used that allows the entire
rotating system to be balanced after it is assembled.
The development has proven so successful, eight more wheels have been
fabricated by NASA for other SMEX space science missions.
A market assessment by Research Triangle Institute (RTI) for Goddard
Space Flight Center was completed, showing that the flywheel technology
had commercial potential. NASA applied for a patent and pursued commercialization
of the technology with RTI assistance.
CTA had prior experience with the technology while under government
contract. Recognizing that the Small, High Torque Reaction/Momentum Wheel
developed by NASA had unique specifications, CTA applied for a patent license,
with an eye toward commercial sales. The license was granted in the fall
of 1996, and CTA Space Systems, Inc. currently uses the technology in its
complete spacecraft fabrication services.
| Eli Ahronovich, Principal Mechanical Engineer
at CTA Space Systems, connects a momentum wheel to a commercial space satellite.
Several reaction/momentum wheels can be used to provide full three-axis
attitude control and stability. |
CTA Space Systems has successfully built over 10 of the reaction/momentum
wheels for commercial, scientific, and military customers. Engineers from
Goddard Space Flight Center are continuing to work with CTA to transfer
and adapt the technology for wider commercial use and application.
As a leading manufacturer of lightweight satellites, CTA Space Systems
must develop spacecraft and integrate payloads in short time frames to
assure standards for affordability. The reaction/momentum wheel technology
is sure to help maintain that thrust.
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