Picosatellite Docking with MEMS Ciliary Arrays
Smart Attachments for Spacecraft (1999-2002)
Joel Reiter, M. Terry, Karl F. Böhringer, R. Bruce Darling
David Meller, Mark Campbell (Aeronautics & Astronautics)
John W. Suh, Greg T. A. Kovacs (Stanford)
Miniaturized spacecraft offer exciting new possibilities for low-cost
future space applications, such as large antenna arrays for communications,
Earth and space science, defense and intelligence, and free-flying cameras
that supervise the repair or construction of space facilities. However,
they also pose significant challenges: their energy supply, communications
and data storage capabilities, and memory for mission control software
will be very limited. Thus, phases of free flight may be interrupted regularly
by docking phases for recharging, data exchange, or reprogramming. A reliable
docking system is essential for efficient operation. Key requirements
for the docking mechanism include:
- minimal size, weight, and hardware requirements,
- reliable electrical connections for recharging and refueling, and
- low cost.
Our goal is to achieve reliable docking for small satellites without
the need for large mechanical structures such as catchers or chamfers.
We propose a robust, lightweight, precise, and low-cost docking system
for miniature spacecraft. In this project, we conduct a thorough analysis
of the system requirements and build a proof-of-concept system that demonstrates
the feasibility of our concept.
Our design takes advantage of recent advances in microelectromechanical
systems (MEMS) which allow batch fabrication of thousands of devices in
a single fabrication run on a silicon wafer. The system is based on microactuator
arrays that have been developed in our group over the past six years,
and that have already gone through several iterations of design improvements
and thorough testing. The MEMS actuators create an "active surface" that
is densely covered with hundreds or thousands of microscopic "cilia,"
each of them only a quarter millimeter in size. Operated together, these
actuators are capable of precise positioning tasks with micrometer resolution.
They have already been used in successful demonstrations of precision
positioning under optical and scanning electron microscopes (air or vacuum
as ambient medium).
The MEMS docking device will achieve the fine positioning after the miniature
spacecraft have made contact with the docking site. For the device to
be useful, it must be integrated into a complete system that can achieve
the coarse positioning during the free-flight phase of the docking approach.
Navigation and control strategies for this phase must be sufficient to
bring the spacecraft into contact with positioning errors of less than
a few inches. This goal of this project is an end-to-end docking system
that fulfills these requirements.
|Figure 1: Free-flying miniature
satellites (~1 kg) for inspection and repair of a space facility.
Highly specialized micro-satellites are used to deliver supplies,
perform robotic assembly, and collect or transmit video images. Requires
frequent docking with other spacecraft to up/download data, reprogram,
recharge batteries, refuel, deliver cargo, execute inspection / repair
/ construction missions.
|Figure 2:Docking system for miniature
spacecraft (conceptual design). A MEMS actuator array aligns the approaching
micro satellite with the docking area. Magnets or clamps generate
the required normal forcc.
|Figure 3: Airtable experimental
setup to simulate microsatellite docking. An 8" × 6" perforated
aluminum plate with 3 adjustable support screws provides levitation
support for an aluminum puck (‘picosat'). Microcilia chips are mounted
on a vertical copper plate with heat sink.
This work was listed among the "Top
100 Science Stories of 2002" in Discover magazine.
- M. Terry, Joel Reiter, Karl F. Böhringer, John W. Suh, Gregory
T. A. Kovacs, "A Docking System for Microsatellites Based on MEMS Actuator
Arrays." IOP Journal of Smart Materials and Structures 10(6):1176-1184,
December 2001. Paper.
- David M. Meller, Joel Reiter, M. Terry, Karl F. Böhringer, Mark
Campbell, "A Docking System for Microsatellites Based on MEMS Actuator
Arrays." 42nd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics,
and Materials Conference & Exhibition, no. 2001-1504, Seattle, WA,
April 16-19, 2001. Paper.
- Joel Reiter, M. Terry, Karl F. Böhringer, John W. Suh, Gregory
T. A. Kovacs, "Thermo-bimorph Microcilia Arrays for Small Spacecraft
Docking." ASME International Mechanical Engineering Congress and
Exposition (IMECE), Micro-electro-mechanical Systems (MEMS), vol.
2, pp. 57-63, Orlando, FL, November 5-10, 2000. Paper.
A complete list of our publications
(many of them available online) can be found here.
- DARPA/AFRL contract F29601-98-D-0210 - USRA subcontract 9500-20
- NSF CAREER award ECS-9875367
© Karl F. Böhringer, Department of Electrical Engineering, Box
352500, Seattle, WA 98195-2500, USA