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Crew Maintenance Lessons Learned from ISS and Considerations for Future Manned Missions

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a calculation that estimates the average length of time equipment operates without failing ... from hardware perspective, but spare has been utilizing stowage ... – PowerPoint PPT presentation

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Title: Crew Maintenance Lessons Learned from ISS and Considerations for Future Manned Missions


1
Crew Maintenance Lessons Learned from ISS and
Considerations for Future Manned Missions
  • Christie Bertels
  • Senior Operations Engineer
  • Systems Engineering Support Services (SESS)
  • Munich, Germany
  • Presented to AIAA SpaceOps Conference
  • Rome, Italy
  • June 23, 2006

2
Presentation Overview
  • Introduction
  • Maintenance Lessons Learned from International
    Space Station (ISS)
  • Recommendations for future long-duration missions
  • Operational Tool concepts to support on-orbit
    maintenance for future programs

3
Introduction
  • Human spaceflight is expected to return to the
    Moon and eventually beyond to Mars
  • Mars missions likely 2-3 years in duration
  • This long duration will present unprecedented
    challenges
  • One of these challenges will be crew maintenance
    of the vehicle

4
Learn from Experience
  • Although human spaceflight has been limited to
    LEO for the last few decades, we have spent
    extensive amounts of time in space
  • 114 Space Shuttle missions
  • ISS operations 2772 days on-orbit/2058 days
    crew-inhabited
  • From a long-duration perspective, ISS provides
    useful lessons learned that can be applied to
    future missions to the Moon, Mars and beyond

5
ISS vs. Future Manned Mars Missions
  • International Space Station (ISS)
  • Long duration (15-year lifetime)
  • Re-supply options (Russian Progress/Soyuz, US
    Space Shuttle), but no ground repairs possible
  • Complex repair capabilities (Large tool
    complement, including diagnostics spare parts
    available on-orbit and on ground)
  • Mission to Mars
  • Long duration (2-3 years)
  • Assume re-supply options do not exist
  • Need to maintain as a habitable vehicle, no
    ground repairs possible during journey
  • Must bring all tools, spares, supplies on-board
    for the journey
  • Needs similar maintenance concept as ISS

6
Moon, Mars Beyond
  • To maximize exploration and scientific
    objectives, it will be important to minimize crew
    time and effort spent performing maintenance
  • Vehicle design and robustness will be key, but we
    can also apply ISS operational lessons learned to
    increase efficiency of maintenance operations
  • Focus of this presentation will be on ISS United
    States On-orbit Segment (USOS) Inter-vehicular
    Assembly (IVA) maintenance only

7
ISS Crew Time Spent on Maintenance
  • More time spent on maintenance than expected
  • In the first 5 years of ISS operations crews have
    spent 4000 hours (through October 2005)
  • Combination of preventive and corrective
    maintenance, includes USOS and RS
  • Averages 1.9 hours per work day, 1.8 hours per
    rest day
  • This is higher than vehicle design estimates
  • Impacts time available to perform science
    operations

8
ISS Crew Time Spent on Maintenance
9
MTBF Inaccuracies
  • Mean Time Between Failures (MTBF)
  • a calculation that estimates the average length
    of time equipment operates without failing
  • based on ground testing
  • ISS used MTBFs combined with equipment
    criticality to determine how many spares are
    pre-positioned on-orbit vs. Launch on Need (LON)
  • In general, this has worked well for ISS
  • In a few cases, MTBFs were extremely inaccurate

10
MTBF Inaccuracies
  • Node 1 Multiplexer/De-Multiplexers (MDM)
  • Operational on-orbit since December 1998
  • Estimated MTBF is 18,648 hours (2.1 years)
  • To date, these MDMs have not experienced any
    failures requiring repairs
  • Exceeded MTBF by more than 350
  • Good news from hardware perspective, but spare
    has been utilizing stowage space
  • ISS Lighting
  • Experienced failures significantly more
    frequently than MTBF predictions
  • MTBF for lights 27,910 hours
  • Actual average operational life 16,235 hours
  • 35 chance of failure before 6,000 hours
  • Not enough spares available, reduced lighting for
    crew operations

11
MTBF Inaccuracies
  • Recommendations for future long-duration
    missions
  • MTBF calculations can be extremely useful for
    determining sparing needs when they are accurate
  • For long-duration missions in the future, it will
    be even more challenging with little or no
    re-supply capability
  • Need adequate supply of spares to maintain the
    vehicle while minimizing stowage volume required
  • Need increased hardware reliability and more
    accurate MTBF calculations (e.g. more thorough
    ground testing)

12
Non-ORU Failures
  • ORU Orbital Replacement Unit
  • Must meet requirements to provide easy
    maintainability
  • Adequate accessibility
  • Standardized tool interfaces for easy removal
  • Captive fasteners
  • Standardized labeling for crew identification
  • ISS has experienced failures of equipment not
    designated an ORU
  • Results in much more complex repairs

13
Non-ORU Failures
  • Example Suit Processing Cooling Unit (SPCU)
  • MTBF exceeded lifetime of ISS
  • ORU not easily accessible
  • Tool interfaces not accessible
  • Insulation foam adhered to structure using strong
    adhesive (RTV)

14
Non-ORU Failures
  • SPCU Repair (on-orbit photos)

Problems removing foam
Insulation mostly removed
15
Non-ORU Failures
  • Recommendations for future long-duration
    missions
  • Assume that any piece of equipment could fail
  • If replacement is critical, should apply ORU-type
    design requirements as much as possible
  • Otherwise maintenance tasks become overly complex
    and time-intensive

16
Unexpected Failures Require Expansive Complement
of Tools/Materials
  • Expect the Unexpected
  • Numerous on-orbit failures/anomalies that
    required unplanned workarounds
  • Examples
  • Tolerance issues with bracket installation ?
    filing part down to fit
  • Valve removal not possible due to higher than
    expected torque ? different tool (strap wrench)
    used
  • Small Leak in Lab Window ? Ultrasonic Leak
    Detection Box construction

17
Unexpected Failures Require Expansive Complement
of Tools/Materials
  • Example Lab Window Box Construction

18
Unexpected Failures Require Expansive Complement
of Tools/Materials
  • Recommendations for future long-duration
    missions
  • Vast complement of tools and repair kits required
    to respond to unexpected hardware failures
  • Even more important for when no re-supply is
    possible

19
Consumables, LLI Calibration
  • ISS includes numerous materials/equipment that
    require re-supply
  • In 2003, Space Shuttle Columbia accident grounded
    the fleet, which severely impacted ISS re-supply
  • Had to rely solely on Russian Soyuz Progress
    vehicles, but much smaller up-mass available

20
Consumables, LLI Calibration
  • Consumables duct tape, non-rechargeable
    batteries had to be rationed
  • Limited-Life Items (LLI) crew cabin filters,
    seals, had to operate beyond certified life cycle
  • Calibrated Equipment torque wrenches,
    pressure/temperature probes had to operate beyond
    calibration date
  • Additional crew time required to perform accuracy
    validations before each use

21
Consumables, LLI Calibration
  • Recommendations for future long-duration
    missions
  • Design certify equipment with longer
    operational lifetime, i.e. beyond mission
    duration
  • Minimize life cycle limitations with robust
    hardware or provide redundant equipment
  • Develop on-orbit calibration techniques

22
Commonality Increases Operational Efficiency
  • ISS comprised of multiple pressurized modules
    designed and manufactured by multiple
    international partners
  • Interface Control Documents ensure modules can
    interface at the sub-system level, but many
    differences in crew interfaces

23
Commonality Increases Operational Efficiency
  • Example ORU Fasteners
  • USOS Equipment uses English Unit-sized fasteners,
    RS uses metric
  • European Lab Columbus uses unique star-shaped
    fasteners
  • Resulted in 3 different tool kits for ISS

24
Commonality Increases Operational Efficiency
  • Example Power Supply Equipment
  • RSOS has 28V power system, all others use 120V
  • Resulted in unique power supply, converters and
    power cables for each
  • Portable equipment using different types of
    rechargeable batteries

25
Commonality Increases Operational Efficiency
  • Recommendations for future long-duration
    missions
  • Use common fasteners wherever possible to
    minimize tool complement requirements
  • Require portable battery-powered or plug-in type
    equipment to conform to a common set of batteries
    or power supply to minimize crew time spent on
    battery charging and equipment set-up

26
Operational Tools for Supporting Crew Maintenance
  • For future long duration missions to Mars, will
    be impossible to pre-flight train for every
    possible maintenance scenario
  • Skills-based training vs. Task-based
  • Operational tools will be essential in providing
    data to crew to relieve complexity, minimize crew
    time, and ensure success of maintenance tasks

27
Animated Demonstration of Maintenance Tasks for
On-board Training
  • 3D-CAD models are now used for design and build
    phases of vehicle, so easily transferable to an
    operational tool
  • Can dynamically demonstrate ORU access and crew
    interfaces required for complex tasks before crew
    is expected to perform the activity on the
    vehicle

28
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29
High-fidelity Ground Mock-up of Vehicle
  • Imperative for performing engineering evaluations
    and real-time procedure development after
    unplanned vehicle anomalies

30
Extensive Pre-Flight Imagery
  • Vehicle mock-ups will not be able to precisely
    duplicate the true vehicle configuration (wire
    cable routing, labeling)
  • Pre-flight imagery is essential for ground
    engineers
  • ISS has imagery database, but many operational
    needs not met
  • ISS crew has been asked to take on-orbit imagery
    to increase completeness
  • Highly recommended operations community involved
    in pre-flight imagery requirements

31
Conclusion
  • Regardless of how well vehicle is designed,
    maintenance needs will exist
  • Includes unexpected hardware anomalies
  • Minimizing the crew time spent on maintenance for
    future long-duration mission will require
  • Applying lessons learned from ISS
  • Developing efficient operational tools to support
    crew training, procedures and engineering ground
    support

32
Questions?
33
Back-up Slides
34
Nomenclature
  • ISS International Space Station
  • IVA Intra-vehicular Activity
  • I-level Intermediate-level
  • LEO Low Earth Orbit
  • MDM Multiplexer/De-Multiplexer
  • MTBF Mean Time Between Failures
  • ORU Orbital Replacement Unit
  • RS Russian Segment
  • RTV Room Temperature Vulcanization
  • USOS United States On-orbit Segment

35
Summary of ISS Crew Maintenance Time Spent
On-Orbit
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