RESULTS
Testing in the risk-tolerant environment of the ISS has allowed SPHERES researchers to push the
limits of their algorithms. The initial test sessions showed the hardware operated correctly and
the software programs uploaded successfully to the satellites. The SPHERES team identified and
corrected many of the operational and programmatic difficulties encountered by lengthening
session frequency, using real-time audio and video, and allowing the crew to run tests
sequentially. All data collected has been used to continually improve formation flight and
docking procedures, creating many space firsts such as the first free-flyer to operate aboard the
ISS, the first to demonstrate docking to a tumbling target in a microgravity environment, and
docking using on-line path-planning. The final integrated tests of the autonomous docking
algorithms culminated with the successful demonstration of docking to fixed and tumbling
targets, with and without obstacles or failures. Various flight maneuvers (such as 2-stage
reconfiguration, scatter, and imaging) were successfully performed with 2 and 3 satellite
formations. In addition, several algorithms for collision avoidance and formations starting from
random positions have been developed, tested, and validated on the ISS. Several tests included
robotic experiments where the satellites were controlled by astronauts on the ISS. Results
showed that including assisting elements, like autonomous collision avoidance, enhanced the
operator’s performance by allowing the operator to concentrate on the assigned task rather
than worry about collision avoidance.
PUBLICATION(S)
Tweddle BE, Setterfield TP, Saenz-Otero A, Miller DW, Leonard JJ. Experimental evaluation of
on-board, visual mapping of an object spinning in micro-gravity aboard the International Space
Station. 2014 IEEE/RSJ International Conference on Intelligent Robots and Systems, Chicago, IL;
September 14-18, 2014:2333-2340. doi: 10.1109/IROS.2014.6942878.
Chamitoff GE, Saenz-Otero A, Katz JG,
Ulrich S. Admissible Subspace TRajectory
Optimizer (ASTRO) for autonomous robot
operations on the space station. AIAA
Guidance, Navigation and Control
Conference, National Harbor, Maryland;
January 13-17, 2014;AIAA 2014-1290:17.
doi: 10.2514/6.2014-1290.
Ramirez-Riberos JL, Slotine JE. Contraction
theory approach to generalized
decentralized cyclic algorithms for global
formation acquisition and control. 51st IEEE
Conference on Decision and Control, Maui,
HI; December 10 -13, 2012:6223-1546. doi:
10.1109/CDC.2012.6426902.
ISS020E018324 - NASA astronaut Michael Barratt
(left) and Japan Aerospace Exploration Agency (JAXA)
astronaut Koichi Wakata, both Expedition 20 flight
engineers, perform a check of the Synchronized
Position Hold, Engage, Reorient, Experimental
Satellites (SPHERES) Beacon / Beacon Tester in the
Destiny laboratory of the International Space Station.