Minutes for March 27, 2001 EVA AIT

Because the presentation was provided at the previous EVA AIT, AIT members had reviewed the clearance envelope violations prior to the EVA AIT and all participants agreed the violations are acceptable. There was a brief resurrection of the discussion on the non-captive fasteners involved, however everyone agreed that the risk is to the ISSP, and they had already agreed to the risk.

Decision: The EVA AIT concurred with the waiver/SSCN

3. EMU extended contact re-certification test results XA/Brian Johnson, ILC/Scott Cupples, Maria Garza, ES/Jay Leggett, B-Hou/Ryne Baker, HSMS/Vicki Margiott, LMES/Grant Bue, John Iovine

Ms. Garza presented an overview of the air-bearing floor evaluation conducted January 17 and 18 to determine the contact loads required for EMU extended contact thermal analysis. Ms. Garza reported that the test subject was placed on his side in a sleigh and asked to impart a load on structure with a knee, elbow and forearm. The subject was asked to first impart a load that was the highest load possible without knowing that you were experiencing contact (i.e. just prior to the subject feeling contact with the suit). This was designated a “nominal” contact pressure. The subject was then asked to impart the highest load possible that could be sustained for approximately 3 minutes. The subject could definitely tell that he was making contact at this pressure because he could feel the suit against him. This was designated the “maximum” contact pressure. In order to conserve time in the air-bearing floor itself, the evaluations first took place in a 1-g environment so the test subject could calibrate the loads he would sustain in the air-bearing floor. The crew office did not supply the test subject, however they did participate in the test.

The evaluations determined that the knee provided the highest contact loads. The pressure range for the nominal pressure was from .01 to .9psi. The pressure range for the maximum pressure was from .08 to 3.17psi. Ms. Garza reported that the test subject did not attempt to provide the highest contact pressure for any crewmember for any task since that is highly crewmember specific. EVA AIT members agreed that since the maximum pressure was the highest pressure that could be sustained for three minutes, and it is noticeable to the crewmember, the test adequately enveloped the extended contact pressure for normal ISS operations.

The EVA AIT also discussed the maximum contact pressure for short periods of time, and whether the analysis results will cover shorter duration, higher contact pressures. ILC indicated that the MLI would be fully compressed at 10psi, and higher pressures would not affect the thermal capabilities of the EMU. Therefore the 10psi contact pressure analysis will suffice for all tasks that require contact. Because there is no vendor data for a contact pressure of 3psi, HSMS will concentrate on the 1psi and 10psi contact pressures for thermal analysis. If there is a large discrepancy, the EVA AIT will consider requesting an interpolation of the data to 3psi.

LMES/John Iovine then presented information on whether you can determine an incident sun angle at which an MMOD shield will exceed the touch temperature limit. Mr. Iovine explained that because it depends on how long the shield is exposed to the sun at a specific angle (which is dependent on orbital beta angle), the touch temperature couldn’t be completely divorced from beta angle. Mr. Iovine, using the 240ºF maximum allowable temperature, was able to correlate the solar vector angle with the beta angle to provide a graph that can be used by the console team to determine whether and when given shields will exceed the allowable temperature range. The chart plots the sun beta angle against the solar vector angle. The result indicates the sun angle at which any shield will exceed the touch temperature limit for a given orbital beta angle. For example at beta angle of 30º, the sun angle has to be within 12º of normal to exceed the temperature limit. At beta 75º, the temperature will be exceeded when the sun angle is within 55º of normal. Operations agreed to evaluate the data provided and determine if this will be sufficient for real time support. Mr. Iovine noted that the application of the data applies to MMOD shield cylindrical sections only, and excludes worksite surfaces that are susceptible to solar entrapment.

Ms. Garza and Ms. Margiott then addressed the EMU thermal analysis status. Since the last report, they have gained additional information on the EMU scrim maximum allowable temperature. Rather than 240ºF temperature that they had hoped for, the allowable scrim temperature is 215ºF. This temperature will bring the EMU extended contact down to about this temperature. ISS thermal reported that most of ISS will exceed this lower temperature limit, and it will be often. The operations community agreed to begin looking at the EVA operations that require extended contact to get an idea on how extensive the problem is. ILC/HSMS agreed to look into any possibilities for opening the envelope back up. In addition, LMES and HSMS agreed to look at providing an acceptable heat transfer rate for the EMU, similar to what is allowed for the existing touch temperature requirement based on the glove capabilities. Those present thought that this would help considerably, since the MMOD shields have a low thermal mass, and most of ISS was able to meet the touch temperature requirement because the hardware had a low heat transfer rate. The EVA AIT agreed to wait until the final analysis numbers are in before developing a formal recovery plan. The EVA AIT agreed to discuss the analysis results at the EMU Panel on April 4, prior to the EVA CCB on April 6.

(Note: at the 4/4 EMU Panel, HSMS and ILC reported that they were still working on determining whether the allowable scrim temperature can be raised and updating the EMU thermal model so the analysis was not yet complete. However both parties felt that they will gain significant relief from the 215ºF temperature, most likely getting back to at least 240ºF. The topic was deferred from the 4/6 EVA CCB until the analysis is complete. The results will be addressed at the 4/10 EVA AIT.)

The EVA AIT also briefly discussed whether protected NZGL connectors would exceed the extended contact limit. ISS thermal reported that the operating limit for the connectors is 282ºF. The way that the thermal analysis was performed, as long as a connector stayed below 282ºF it was passed and reported that it didn’t require thermal protection (aluminized tape or thermal booties). The tape and booties were certified to protect the worst connector to within the 282ºF limit. So the only conclusion about any of the NZGL connectors, whether with thermal protection or not, is that they will be below 282ºF.

Conclusions: The EVA AIT concluded the following:

Air-bearing floor testing results accurately characterize the extended contact pressures expected for ISS operations. Contact pressures of 1psi, 3psi and 10psi are the ones of most concern for analysis of EMU thermal capabilities. Further conclusions on the impact to operations and analysis plans are deferred until the final EMU extended contact thermal analysis is complete.

Action Item Closure: AI-582 was CLOSED

Action 593: Evaluate the sun angle from normal vs. sun beta angle plot to determine if this data is sufficient for determining whether worksites will exceed EMU extended contact temperature limits.

Actionee: DX32/Bob Adams

Due Date: April 24, 2001

Method for Closure: Report to EVA AIT

No other formal actions were assigned. The issue status will be evaluated once the thermal analysis is complete and an allowable extended contact temperature is established.

4. SSAS Contingency Bolt Task Assessment Status PG1/Larry Price, Berta DeLeon

The EVA AIT briefly reviewed the SSAS contingency bolt assessment status. Ms. Patrick reported that ES/Hung Nguyen indicated prior to the EVA AIT that the bolt torque data/accuracy has not yet been assessed, and he did not know when it would be. Mr. Nguyen reported that the team has been concentrating on resolving the issues associated with the primary, automated attach system. Ms. Patrick reported that she informed Mr. Nguyen that the EVA AIT is happy to work to the ES schedule for this issue, however this data was integral to providing a final EVA concurrence on the contingency tasks. Mr. Nguyen agreed to provide the data as soon as time permits.

EVA AIT members then discussed the S0 graphics and worksite analysis provided by Ms. DeLeon. The EVA AIT confirmed the data provided were the type of data required for evaluating the contingency bolt EVA tasks. The EVA AIT requested that Ms. DeLeon continue for the remaining segments. Ms. DeLeon reported that the remaining data should be available by the next EVA AIT. The EVA AIT will review the remaining data at the 4/10 EVA AIT and confirm it is complete. EVA AIT members will review the data as time permits, until ES develops a schedule to address the contingency bolt tasks.

Action 594: Provide worksite analysis/graphical support for SSAS contingency bolts for remaining segments (all other than S0)

Actionee: PG1/Berta DeLeon, Larry Price

Due Date: April 10, 2001

Method for Closure: Provide WSA, report to EVA AIT

5. EVA tool interference with MTS struts (ref. S0 FCA PG1/Eric Fukushima, Larry

Action Item #RFI-S0FCA2-356) Price, ES/John Zipay, DX32/Michelle Hollinger

Mr. Fukushima summarized the clearance issues presented at the 3/13 EVA AIT, and the actions associated with those issues. Mr. Fukushima reported that he was scheduled to present to the Launch Package Team during the week of April 2. Mr. Fukushima also presented preliminary information on the torque tolerance requirements, supplied by PG1 Structures representatives. The torque tolerances reported were very narrow, in the 3-5% range. The EVA AIT noted that those tolerance ranges couldn’t be met by any of the EVA tools available. ES/John Zipay requested that the EVA AIT entertain no further discussion of torque tolerance at this time. Mr. Zipay requested time to work the torque tolerance requirement with PG1 and report back to the EVA AIT. Ms. Patrick re-iterated the EVA tool capability and tolerance ranges reported at the 3/13 EVA AIT and requested that Mr. Zipay keep those in mind when developing the torque tolerance requirements. Mr. Zipay agreed to develop a reasonable torque tolerance requirement by late April

The EVA AIT then addressed the operations plans to assess use of the torque wrench and PGT/RAD/TM tool combinations. DX32/Michelle Hollinger reported that NBL runs are scheduled for May and the tool evaluation will be included at that time. Ms. Hollinger will develop the detailed plans for evaluation (which tools at which sites) when closer to the run. The EVA AIT briefly discussed some of the considerations for the evaluation, including minimizing the risk of having real time tool interferences by ensuring that the tools with the most clearance will work at all locations, and minimizing the number of different tools required to work on all the MTS struts. Ms. Hollinger will take all these considerations into account in defining the evaluation procedures.

The EVA AIT then discussed the history of the worksite analysis and why it did not flag this tool interference. PG1/Jon Bonuan reported that early worksite analysis was complete 6/95, after NBL testing that the TM operations were inconclusive, but prior to the changes to the TM and PGT. The WSA at that time indicated the clearance was close but that there was clearance. When the TM and PGT PIRNs were submitted, 11/95 and 6/96 respectively, the changes were seen as minor, and individually did not indicate a potential interference. Later NBL testing (10/98) provided acceptable ratings, however NBL tools were not necessarily volumetric at that time. Later WSA did not address the tool clearance question because of the acceptable NBL ratings. Mr. Price and Mr. Bonuan agreed to develop a list of other tasks, based on WSA that use the TM and look at potential interferences.

OC/Ben Sellari, S0 launch package manager was present for the EVA AIT discussion and agreed with the EVA actions assigned and schedule for completion.

Action Item Closure: AI-587, 588, 589 were Closed

Action 595: Determine the recommended torque and torque tolerance required for MTS strut bolts

Actionee: ES/John Zipay

Due Date: April 24, 2001

Method for Closure: Report to EVA AIT

Action 596: Evaluate new tool configurations suggested for MTS strut bolts to overcome the PGT/TM clearance issue. Evaluate structure based WIF operations for use of torque wrench.

Actionee: DX32/Michelle Hollinger

Due Date: May 29, 2001

Method for Closure: Present results to EVA AIT

Action 597: Develop list of worksites that use the TM to evaluate whether there is an interference concern similar to the MTS strut bolts.

Actionee: PG1/Larry Price, Jon Bonuan

Due Date: April 10, 2001


Method for Closure: Provide list to EVA AIT

6. MISSE keep out zone evaluation OZ/Bob Miley, CB/Joe Tanner

Mr. Miley presented a request for approval of a MISSE keep-out zone for EVA. This was a follow-up to a November 28 EVA AIT discussion where Mr. Miley reported that the MISSE configuration on an ISS handrail does not meet the EVA inadvertent contact/kick-load requirement. Mr. Miley provided details on how and where the configuration does not meet the requirement. The crew office has had a limited opportunity to evaluate the proposed MISSE locations over the past several months and explained their position on whether the MISSE locations are acceptable.

Mr. Miley reported that the MISSE PECs must first sustain inadvertent contact to move the pointer ball to its hard stop before there is a concern. Once at the hard stop, if MISSE sustains additional inadvertent contact, damage will result. Where the damage occurs is dependent on the location of the contact. If the contact occurs further along the PEC, the weak link is at the airlock secondary structure and the result is an “ultimate load”. No one present could say definitively what an “ultimate load” meant to the airlock secondary structure. However it was thought that the handrail would no longer be safe to use, but the pressure shell would not be damaged. If the contact occurs closer to the stem/handrail, the weak link is at the PEC stem and the result is most likely a bent stem. Depending on the load and placement, the stem could break and the PEC would become free. The EVA AIT noted that without a better definition of the failure modes, we couldn’t determine how much risk the program is incurring with accepting the MISSE manifest plan.

CB/Joe Tanner reported that even though the MISSE PECs are located off primary and secondary translation paths, the airlock is a high traffic area and there is no guarantee that the PECs won’t be kicked.

The EVA AIT questioned whether there was any way to make the stem the weak link in all cases to ensure that no damage is done to the airlock. MISSE representatives indicated that based on their assessments there is no easy way to accomplish that. Weakening the stem would make it very difficult to meet normal on-orbit loads and the PEC would not be able to stay in position. It would also be a cost and schedule hit to change the PEC design at this time.

Conclusion: The EVA AIT concluded that the risk to the program was not an EVA risk to buy. The EVA AIT recommendation was that the airlock not be put at risk for a payload, however the EVA AIT acknowledged that the risk is probably very low. The EVA AIT deferred a final assessment of the risk until the failure modes are more definitively characterized.

7. EVA standard ICD status follow-up discussion LMES/Mark Messinger, All

The ICD PIRNs status was updated as follows:

– 72A: Non-concurrences were received during the review and negotiations are in work.

– 73: Revision A would be ready for submittal by the end of the week

– 74A: All concurred on revision A. Ms. Patrick signed for the EVA AIT and sent to the ICDWG

– 79: No progress on the PIRN. Ms. Patrick requested that LMES propose a revision to include a statement that the torque wrench accuracy can be improved at some torques under some orbital thermal conditions and that each case must be addressed individually. B-CP requested that data be included in the ICD that documents the torque wrench’s capabilities and the conditions under which it can meet the better accuracy. A meeting will be scheduled with EC to review the options and determine the best approach for the ICD.
80: Revision A was submitted on March 26.

Mr. Messinger also provided a schedule with ECDs for many of the PIRNs required to document the remainder of tools in development. Mr. Messinger will continue to report progress monthly

8. Upcoming Events/Future Agenda Review XA/Nancy Patrick, All

Ms. Patrick reviewed the preliminary EVA AIT agenda for April 10, 2001. Presenters were requested to confirm agenda topics by COB Thursday, April 5.