Enhanced ISS Maintenance and Servicing Through SPDM Ground Control

Paper number

IAC-09.B3.3.4

Author

Mr. Mustafa Mirza, Canada

Coauthor

Mr. Aaron Kratt, Canada

Coauthor

Mr. Richard Rembala, MDA, Canada

Coauthor

Mr. Kyle Lee, MDA Space Missions, Canada

Year

2009

Abstract

The Mobile Servicing System (MSS) is critical to the assembly and operation of the International Space Station (ISS).  It consists of the Space Station Remote Manipulator System (SSRMS) also known as Canadarm2, the Mobile Base System (MBS), and the Special Purpose Dexterous Manipulator (SPDM) called Dextre, all of which are currently on-orbit.  Dextre was designed to perform ISS maintenance and servicing tasks with command and control performed by on-orbit crew, using the Robotics Workstation (RWS).

Through the first decade of Station operations, it has become apparent that there is a greater premium on on-orbit crew time than envisaged during the original ISS design.  To reduce the amount of crew pre-flight training, on-orbit skill retention training, and on-orbit crew time demand related to MSS robotics tasks, a successful initiative to perform some SSRMS operations from operators directly from NASA Johnson Space Center was undertaken.  This prompted the question of whether Dextre’s operations to replace Orbital Replaceable Units (ORUs) on the ISS could be performed by ground operators.

In 2008, a potential maintenance task was identified for Dextre that involves swapping two Remote Power Controller Modules (RPCMs) on the ISS.  Not only did the ISS program office mandate that the task of swapping the two failed RPCMs was to be performed by Dextre, but was to be performed entirely via Ground Control.  This lead to a thorough review of the new operations concept and hazard assessments.  Software control algorithm enhancements were identified to maximize existing control features on Dextre such as Force Moment Accommodation (FMA), add additional safe-guards to ensure the operation could be safely performed within the stringent manned space flight safety requirements, and to allow for more efficient commanding.

To validate the operations concept and the software control algorithm changes, a demonstration of the RPCM swap was undertaken utilizing the SPDM Ground Testbed, a kinematically and dynamically representative manipulator of Dextre, along with representative models of the RPCM ORU, berthing site and the robotics tool required for this operation.  The demonstration facilitated definition of the hardware characteristics, such as the RPCM insertion envelope, and operational techniques to address nominal and contingency scenarios.

This paper will summarize this new dexterous robotic operations concept, the results of successful ground verification, and highlight some of the enabling technologies.  The experience and techniques developed for the RPCM Swap are applicable to any Dextre compatible ORU and position Dextre to take on an even broader ISS maintenance and servicing role via Ground Control.

Abstract document

IAC-09.B3.3.4.pdf

Manuscript document

IAC-09.B3.3.4.pdf (🔒 authorized access only).

To get the manuscript, please contact IAF Secretariat.