Title: Crew Maintenance Lessons Learned from ISS and Considerations for Future Manned Missions
1Crew 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
2Presentation 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
3Introduction
- 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
4Learn 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
5ISS 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
6Moon, 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
7ISS 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
8ISS Crew Time Spent on Maintenance
9MTBF 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
10MTBF 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
11MTBF 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)
12Non-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
13Non-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)
14Non-ORU Failures
- SPCU Repair (on-orbit photos)
Problems removing foam
Insulation mostly removed
15Non-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
16Unexpected 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
17Unexpected Failures Require Expansive Complement
of Tools/Materials
- Example Lab Window Box Construction
18Unexpected 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
19Consumables, 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
20Consumables, 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
21Consumables, 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
22Commonality 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
23Commonality 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
24Commonality 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
25Commonality 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
26Operational 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
27Animated 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(No Transcript)
29High-fidelity Ground Mock-up of Vehicle
- Imperative for performing engineering evaluations
and real-time procedure development after
unplanned vehicle anomalies
30Extensive 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
31Conclusion
- 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
32Questions?
33Back-up Slides
34Nomenclature
- 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
35Summary of ISS Crew Maintenance Time Spent
On-Orbit