Why are Space Stations so Hard?

Bill Dwyer, NASA-JSCISS Command and Data Handling System Hardware System ManagerEx-Space Station Freedom Data Management System Integration ManagerEx-Space Station Freedom SW Functional Area ManagerEx-Space Station Freedom Mode Team Chairman (Level-II)

8th Military and Aerospace Programmable LogicDevices (MAPLD) International Conference8 Sept. 2005

Development Environment

• Extended development phase – some articles are on-orbit while others that will interface to it are still in an early phase such as PDR or in some cases not started yet

• Makes interface definition very challenging• Requiring extensive on-ground integration testing is a large complex test rig

• Widely distributed development sites – International world site distribution• Directly contradicting “co-location” axiom for project development• Again makes interface definition and testing very difficult

• After the first two or three element launches, a system can be in multiple lifecycle stages at one time

• Sustaining, on-orbit troubleshoot and root cause work and upgrade development• This multiple-lifecycle-at-one-time state does not allow the post-development resource phase out that is the standard model

• International export-import regulations serve to extend time required for testing and some aspects of development

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On-Orbit Operations• Coordinating flight control across International boundaries

• To date, ISS has had a great deal of success in International operations• Substantial planning and agreements required

• On-orbit troubleshooting and repair of failures has not been done to the scale it is being accomplished on ISS

• Earlier Mir experience very valuable• Command and Control computational systems failures during 6A flight timeframe• Turns the crew into multi-skilled “mechanics”

• On-orbit assembly and checkout of major components, including multi-national assembly• Attaching new element such as truss element S1 and P1 to existing configuration• Upgrading to a new integrated command and data handling system with the addition of multiple new computational systems

• On-orbit change-out of hardware, especially external hardware• Example: CMG failure and change-out on recent flight LF-1 (STS-114)

• New, unforeseen requirements/needs that must be implemented on-orbit with minimal if any integration testing on the ground

• External storage platforms such as Z2-truss and External Storage Platform-3

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On-Orbit Operations• Installation of major software systems on-orbit with no operational fidelity sacrifice

• A “design for” requirement that is ops intensive

• Fixing “whoopses” – requirements that were not anticipated but need arises during ops• For example the 6B box “bowing” problem for C&T and C&DH HW

• Relocation of major systems due to operations or safety needs• For example the Acvanced ECLSS in the U.S. Lab

• Emergent behavior of large complex systems – sometimes things behave in an unanticipated manner

• For example restarting large networks after flight 6A command and control computational system failures

• Difficulty in determining operational life of electronic hardware makes logistical planning very difficult

• Some good: the ISS computational systems, multiplexer-demultiplexers (MDMs) have proven to be extremely robust, some operating nearly 8 years with no problems• Some not-so-good: laptop inventory needs complete replacement

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Conclusion1. “The devil is in the details”2. “The devil is in the integration”3. “The devil is in the magnitude of the undertaking”4. “The devil is resource intensive and costs a lot”

Building a large multi-element, multi-national space station is indeed hard and expensive. If we underestimate the magnitudeof the task, it can, will and has given us more than one “negative surprise”.

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