ADR:

All orbital debris is a threat to active spacecraft, most of which is tracked via ground stations, allowing spacecraft such as the International Space Station (ISS) to undertake Debris Avoidance Maneuvers (DAM) if there’s a threat of a conjunction.

Such an event of a threat is not uncommon, though most of the time the debris is eventually cleared of entering the “red box” once the tracking calculations have ensured the object will avoid the ISS by a margin of safety.

Examples of when a late “red” conjunction has been spotted include the March, 2009 event, when a small piece of debris called a “yo weight” – which was originally part of a Delta PAM-D stage used to launch GPS 37 in 1993 – caused controllers on the ground to prepare the crew for a potential – though unlikely – evacuation of the orbital outpost. The debris passed without any impact.

Small pieces of debris, such as MMOD (Micrometeoroid Orbital Debris) also impact the Station and the Space Shuttle orbiters, with small impacts regularly seen on the orbiter’s flight deck windows late in missions, whilst a few impacts have been found on the orbiter’s radiators once they return to their Orbiter Processing Facilities (OPF) for post flight processing.

Endeavour after STS-118, and Atlantis after STS-115, provide such examples, with bullet-like holes was found on their radiators.

Forensic examinations on Atlantis’ damage found a small piece of circuit board – originating from an “exploded Upper Stage” – in what was classed as the second largest orbital debris strike on an orbiter in the history of the program.

Thankfully, the MMOD just missed one of Atlantis’ Freon-22 coolant loops, unlike Columbia’s STS-109, when a small piece of debris was lodged stuck in her coolant loop 2 and restricted the flow of Freon-22 in that loop. The amount of Freon-22 in the coolant loop was slightly below the flight rule red-limit, but after exhaustive analysis by the engineers on the ground, they decided to press on with the mission.

However, ADR is being tasked with the removal of far larger pieces of debris, and from a higher altitude than that which the ISS and orbiters transit in.

The associated presentation (available on L2) is aimed with a focus on the potential utilization of their skills and experience, as the ADR project builds the foundation of planning the technology and development of a system which is capable of removing the “massive objects” from orbit, with the potential to remove small objects via splinter versions of ADR.

“Leverage the unique capability of the Orbital Debris Program Office (ODPO), Engineering, and Mission Operations to lead the early technology development and operations planning of ADR,” opens the presentation. “Provide new opportunities for Shuttle/Constellation workforce.

“Position JSC to lead a major space activity in the future (routine removal of ~5 massive objects every year, likely with international cooperation).”

EDIT: Although JSC is referenced, it has since been noted that ADR is simply an ongoing internal study conducted by the NASA Orbital Debris Program Office and it does not represent the official position of JSC. nor NASA.

At five objects per year, ADR wouldn’t be short of targets, with over 270 spent upper stages from the Russian SL vehicle alone, all running around in an orbit of between 600 and 1000 km.

“An active debris removal of about five objects per year. These are objects with the highest risk in the environment. Most of the targets are spent Russian SL upper stages (~270),” listed the presentation. “Masses: 1.4 to 8.3 tons. Dimensions: 2 to 4 m in diameter, 6 to 12 m in length. Altitudes: ~600 to ~1000 km regions. Inclinations: ~7 well-defined bands.”

Noting that “to preserve the near-Earth space for future generations, ADR must be considered,” the presentation adds that even if there no new launches were conducted from now onwards – and taking into account some vehicles use a “25 year decay rule”, where expended stages are designed to eventually deorbit – the situation eventually worsens due to what is known as collision fragments.

“Collision fragments replace other decaying debris through the next 50 years, keeping the total population approximately constant. Beyond 2055, the rate of decaying debris decreases, leading to a net increase in the overall satellite population due to collisions,” the presentation noted.

“Major breakups may continue to occur (e.g., Fengyun-1C ASAT test, Briz-M explosion). Postmission disposal (such as the 25-year decay rule) will help, but will be insufficient to prevent the debris self-generating phenomenon from happening.”

The threat of orbital debris – especially from a collision fragment standpoint – has been known for some time, such as via the 2005 “Assessment of the Current LEO Environment” study, which was cited in the ADR presentation.

“A major study (using NASA’s LEGEND model) on the debris environment was conducted in 2005. The current debris population in the LEO region has reached the point where the environment is unstable and collisions will become the most dominant debris-generating mechanism in the future.

“Only remediation of the near-Earth environment the removal of existing large objects from orbit can prevent future problems for research in and commercialization of space.”

The mass of debris in orbit was also recently updated in October, 2010, which estimated that as much as 5,900 tons of debris exists, with 2,500 tons residing in Low Earth Orbit (LEO).

As to the design of a spacecraft capable of sweeping up the large pieces of debris, no real details are forthcoming at this stage of the project.

However, some basic ground rules – and questions to be worked on – are noted, such as the need for the system “repeatability” – thus avoiding the need to launch the spacecraft for the removal of each piece of debris.

“Operations/Technology Challenges: Launch Single-object removal per launch is not feasible from cost perspective. Propulsion: Solid, liquid, others (plasma, tether, etc.)? Precision Tracking: Ground or space-based? Stabilization (of the tumbling targets): Physical or non-physical? Rendezvous: Autonomous and non-cooperative? Capture: Physical (where, how) or non-physical (how)? Deorbit: When, where?

“Other requirements: Affordable cost. Repeatability of the removal system (in space).”

The next steps are also listed, NASA centric for the utilization of engineers from their skills and capability standpoint.

“Determine level of MOD support for this activity. Suggest modest support from within MOD CS/Contractor workforce over the next few months. Identify additional funding opportunities to develop an ADR implementation plan/CONOPS. JSC IR&D. Center Management through JSC Executive Council.

“Identify areas where JSC (1) can lead/support, (2), should lead/support, and (3) is in a unique position to lead/support future ADR activities.”

With NASA’s future still somewhat in limbo, as political efforts are made to stabilize the appropriations of funding outlined in the passed Senate bill – which refined President Obama’s FY2011 budget proposal – the project is likely to remain at the study level for some time.

However, the National Space Policy of the United States of America (28 June 2010) – as referenced in the ADR presentation – does provide some ammunition for taking the project forward.

“Preserving the Space Environment and the Responsible Use of Space: Preserve the Space Environment. For the purposes of minimizing debris and preserving the space environment for the responsible, peaceful, and safe use of all users, the United States shall:

“Pursue research and development of technologies and techniques, through the Administrator of the National Aeronautics and Space Administration (NASA) and the Secretary of Defense, to mitigate and remove on-orbit debris, reduce hazards, and increase understanding of the current and future debris environment.”

(Images – All via the ADR presentation (L2), with the MMOD strike image via L2).

No related posts.

Fourth EVA Potential:

The three scheduled EVAs have been successfully carried out by STS-131 spacewalkers Rick Mastracchio and Clay Anderson, as they completed tasks associated with the changeout of Ammonia Tank Assembly (ATA).

“The third EVA started at 103/06:14 GMT [07/19:12 Mission Elapsed Time (MET)] and was completed at 103/12:38 GMT (08/02:17 MET) for an EVA duration of 6 hr and 24 min,” reviewed the latest Mission Evaluation Room (MER) report (L2).

“Tasks accomplished during the EVA included hooking up the fluids lines to the Ammonia Tank Assembly (ATA), installing the old ATA on the Lightweight Mission Purpose Equipment Support Structure Carrier (LMC) in the Payload Bay (PLB), retrieving the Airlock MMOD shield and preparing the Z1 Space-to-Ground antenna.

“The activities that were not completed during the EVA were the installation of the Lightweight Adapter Plate Assembly (LWAPA) on the LMC, the troubleshooting of the P1 Radiator Grapple Fixture Beam and one get-ahead task.”

During EVA-3, controllers noted a problem with the associated NTA, via a stuck Gas Pressure Regulating Valve (GPRV). Troubleshooting is continuing, although the possibility of adding an additional docked day to STS-131 was discussed.

The purpose of adding an extra docked day related to the consideration of a fourth EVA – which was to be decided at the Integrated Mission Management Team (IMMT) meeting on Thursday, but finalized late on Wednesday - which would have been conducted on Flight Day 13. A Flight Day 12 option had already been ruled out.

During an extra EVA, Mastracchio and Anderson would have worked on replacing the NTA with a spare – one of two spare units – on ESP-1 and 2 (External Stowage Platform), which is attached to the S3 zenith outboard PAS (Payload Attachment System).

The NTA task can’t be deferred to STS-132, due to a full schedule of EVA tasks for Atlantis’ mission, although numerous challenges would have existed with a late inclusion on STS-131. Another option – now likely to be taken – would be to add the NTA task to a Stage EVA, to be conducted by ISS crewmembers.

UPDATE: Fourth EVA removed as a possibility for STS-131.

UPDATE 2: Problems between the Common Berthing Module (CBM) and MPLM delayed the uninstallation of Leonardo. Troubleshooting continued for several hours, prior to a successful resolution related to the Control Panel Assembly. A review will follow in the next article.

Discovery Status:

The veteran orbiter is continuing to perform admirably whilst docked to the International Space Station (ISS), as her crew completed transfers from the attached MPLM Leonardo. Final tasks will focus on transfers to and from Discovery’s middeck.

“The fourth Contingency Water Container (CWC) was filled at 103/09:44 GMT (07/23:22 MET) with 89.6 lbm of water,” added MER status. “With four CWCs and eight CWC-Iodines (CWCIs) filled, a total of 685.6 lbm of water have been transferred to the on the International Space Station (ISS).”

Discovery’s systems are all in great shape, aiding any potential decision on adding a second additional docked day in support of MPLM troubleshooting.

“All Life Support Subsystems are working nominally. Life Support console is working no issues. N2 Repress Currently in progress. Total GN2 = 254.6 lbm. Total Water = 520.4 lbm. Total Waste Water = 57.2 percent (97.7 lbm). System Status: Subsystem performance is nominal,” added MER status.

“The PRSD (Power Reactant Storage and Distributation) O2/H2 manifold 1 isolation valves were cycled closed for crew sleep at 102:17:28 GMT and reopened at 103:02:24 GMT. There have been 142 sustaining heater cycles on fuel cell 2. One sustaining heater cycle has been observed on fuel cell 1 during this flight.”

Following the review of minor communication issues during EVA-1, only one item of interest was noted during video reviews of EVA-3, relating to observed debris liberating from the Payload Bay.

“MER Funny (minor issue): Object observed floating from Orbiter Aft Payload Bay area during EVA 3,” a report to the Mission Management Team (MMT) noted.

Video of the liberation (L2) – which appears to show what is likely to be a piece of insulation departing from aft of Discovery’s cargo bay – although this is not being classed as an item of concern.

Given the location, it may have liberated from the old ATA, which had just been installed on to the Lightweight Mission Purpose Equipment Support Structure Carrier (LMC).

The Payload Bay will welcome back the MPLM on Flight Day 11, ahead of docked Late Inspections – currently scheduled for Flight Day 12.

“The OBSS (Orbiter Boom Sensor System) remains grappled by the SRMS (Shuttle Remote Manipulator System), and is at the MPLM viewing position. OBSS personnel completed review the Docked Late Inspection procedures, and sent review comments to (management),” added the MER.

“Also completed review of the zoomed out ITVC (camera) views for use in assisting the crew with pointing the LDRI (Laser Dynamic Range Imager) during the Docked Late Inspection, and sent the views to (management). Set up the video capture directories on the SES Capture PC, and verified that the ODRC SRMS joint encoder biases look correct.”

Also reviewed and cleared was the first MMOD strike of the mission, observed via photography taken of Window 1 on the flight deck. One or two visible MMOD strikes are common, especially during the latter stages of missions.

“MER-11: Window 1 MMOD impact (less than 1mm, is well below threshold for concern),” added a MER report to the MMT.

Preset rules for the allowable size of a MMOD impact on an orbiter window note that forward and middle windows have no issues associated with diameters of less than 1.2mm. Side and overhead windows are ok if the diameter is less than 0.49mm.

Managers also discussed the potential of Discovery aiding the Shuttle/Station stack in a DAM, as a debris conjunction was tracked during Wednesday night.

“EOM Plans for OA (Orbit Adjust) and DAM: Possible debris conjunction early in crew day on FD11. Solar activity making it difficult to track object. If a debris avoidance maneuver is required, it will occur sometime during FD10,” noted the MER. “OA Burn will be performed post hot fire. This will be a retrograde maneuver of 21 fps.”

Although there has been no confirmation a DAM was called for at time of publishing, Discovery continues to have no issues with her thrusters – should such a situation arise.

“OMS (Orbital Maneuvering System) and RCS (Reaction Control System) data has been reviewed through 103/14:30 GMT. No new anomalies were noted. Vernier thruster pulse data has been reviewed through 103/14:30 GMT. No anomalies were noted. 25 of 38 primary thrusters have been fired. No new Primary thrusters were fired since previous report.”

No related posts.

With the unique nature of Atlantis’ STS-125 mission in prime focus for NASA managers, of particular interest – mainly the increase of orbital debris concentration at the mission’s altitude – is the region of Low Earth Orbit Atlantis will fly in for the majority of her mission.

Originally analyzed last September ahead of the original STS-125 launch date, the all-powerful Program Requirements Control Board (PRCB) has re-evaluated the threat posed to Atlantis and her seven member crew by MMOD.

The new results, which take into account recent satellite breakups and a variety of other components, show that the overall risk of a Loss Of Crew and Vehicle (LOCV) scenario due to MMOD impact(s) to the Thermal Protect System (TPS) is 1 in 185 – the exact same ratio as the original assessment back in September.

NASA analysts were able to reach this particular ratio by making use of the known probability of detecting and repairing critical TPS damage while on orbit, the “IDC of RCC panels 8-11,” the flight’s mission duration and the Orbit Adjust maneuver post-HST release, and the STS-400 rescue mission.

However, as defined by NASA guidelines, the Space Shuttle Program cannot accept a LOCV ratio in excess of 1 in 200. Since the STS-125 LOCV ratio is 1 in 185, the final decision on whether or not this ratio is acceptable will be discussed during the SOMD FRR on April 30 – at which it is anticipated that this LOCV risk will be accepted for STS-125.

On the other hand, the MMOD LOCV ratio for the STS-400 rescue flight is 1 in 294 – with late-inspection of the Wing Leading Edge (WLE) panels and Nose Cap on FD-5 and a short mission duration of seven days driving the calculations.

If the STS-400 crew does not perform any TPS inspection, the LOCV ratio rises to 1 in 217.

The PRCB presentation goes on to note that the LOCV ratios for STS-125 and STS-400 have an error factor of 1.35 based on MMOD distribution, velocity, and density uncertainties.

Additional MMOD Risk Mitigations Since October:

For the original October 2008 launch date of STS-125, NASA determined the overall MMOD risk to be 1 in 185.

In formulating this ratio, NASA determined that the now standard late-inspection of the Orbiter’s TPS would reduce the MMOD threat by 37 percent and that altering Atlantis’ orbit after the TPS late-inspection so the perigee would be 160NM would further reduce the MMOD threat by 6 percent.

Furthermore, the mission was “designed (timeline, attitudes, TPS Inspections, etc.) to minimize critical TPS exposure to MMOD while staying within the HST systems operational constraints,” notes the expansive PRCB presentation available for download on L2.

Additional elements taken into consideration were: protecting the HST’s aft shroud and Orbital Replacement Units from direct sunlight during the mission’s EVAs, maintaining a “Payload Bay to Earth” orientation as much as possible, and minimizing EVA and Orbiter MMOD exposure.

All of these assessments and mission design elements remain unchanged for the now-planned May 12 launch. However, as the presentation notes, the MMOD environment has changed since October.

“Recent satellite breakup events have increased the background Orbital Debris flux by 36 percent.”

These breakups include the Chinese ASAT/Fengyun 1C, the Kosmos 2421, and the Kosmos 2251/Iridium 33 satellite collision – all of which respectively account for 27 percent, 1 percent, and 71 percent of the total orbital debris flux increase.

These satellite breakups themselves resulted in an increase of the MMOD LOCV risk to 1 in 157 for Atlantis.

However, given the lengthy delay to STS-125, mission planners were able to investigate and baseline several new MMOD mitigation tactics.

The first change to the mission’s timeline relates to the FD-9 activities.

Instead of performing the late-inspection of Atlantis’ WLE panels and Nose Cap on FD-9 and then adjusting Atlantis’ orbit on FD-10, both activities will now be performed on FD-9.

“Moving the Orbit Adjust maneuver to FD-9 reduces the MMOD risk by an additional 3 percent,” notes the presentation.

Moreover, IDC imagery of the Atlantis’ RCC panels 8-11 will further reduce the MMOD risk by 14 percent as the lower surfaces of RCC panels 8-11 have the tightest failure criteria.

“First four passes of the starboard and port Wing Leading Edge LDRI scans will be scheduled during daylight to support parallel IDC imagery ops,” notes the PRCB presentation. “Dedicated Port IDC Scan added for critical areas not available during parallel ops.”

With these mitigations, as well as a few others which are not mentioned in the presentation, the overall MMOD LOCV risk for a May launch of STS-125 is the same as it was for October: 1 in 185.

Additional Mitigation Studies:

In addition to the already baselined MMOD mitigation tools, mission managers are continuing to assess other mitigation options.

The first alternative mentioned in the PRCB presentation is the option of delaying the TPS late-inspection by 15 hours, thereby pushing the activity into FD-10. This would result in an approximate risk reduction of 3 percent to 1 in 190.

Nevertheless, the effect this delay would have on imagery review and repair operations has not been assessed.

This, however, is the last risk reduction option that would not involve shortening the mission. The three remaining options all involve the deletion of mission content or crew off duty time.

These options include eliminating one EVA day (which would reduce risk by ~6 percent to 1 in 196), eliminating two EVA days (which would reduce risk by ~12 percent to 1 in 208), and eliminating the crew off duty day post-HST release (which would reduce risk to 1 in 201).

Whether or not any of these options are added to the mission’s timeline, work to prepare the STS-125 mission for flight is in full swing, with the STS-125 mission’s payload scheduled to be delivered to Pad-A later this week and STS-400 rescue vehicle scheduled to take her place atop Launch Pad 39-B Friday morning.

See also: Endeavour: MMOD hit to radiator
See also: Atlantis: MMOD hit originated from another vehicle
See also: MMOD hit on Endeavour window

L2 members: Documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.

Related posts:

1. Atlantis to rollback to VAB on October 20 – Hubble troubleshooting latest As NASA and the SSP (Space Shuttle Program) refine their...
2. STS-125 launch target moves to February 17 – crucial week for Hubble STS-125 has been given a new “work-to” launch date of...
3. Hubble control system failure – STS-125 launch date delayed A major failure of the “Side A” control system on...

Impacts from MMOD are a usual – if not undesirable – event during missions, with several recent flights suffering from impacts to the orbiter’s windows on the flight deck.

MMOD is the third biggest threat to losing a vehicle during a mission – second only to launch and re-entry. Mitigation of MMOD strikes – such as when docked to the International Space Station (ISS) – and the tracking of space debris, provides some protection for the orbiters, though small strikes are commonplace.

Several strikes on the orbiter’s windows have been observed throughout the shuttle program – the last on STS-123 – and at least two MMOD strikes have also been suffered on the radiator panels since Return To Flight.

One such strike was later found to be a small slice of circuit board from an expended stage of another launch vehicle, which managed to punch a reasonably large hole through one of Atlantis’ radiators, thankfully missing a Freon-21 coolant plumbing in the panel, which would have caused an emergency to be called, and the immediate order to land.

It was previously believed that a similar event occurred on STS-109 in Columbia’s Freon Coolant Loop (FCL1), which restricted the flow of Freon-21 in that loop. However, in a correction from the first publication of this article, the FCL1 orifice was blocked via an internal piece of debris, rather than MMOD.

More recently, a MMOD strike was found on Endeavour during the STS-118 mission, again missing a Freon-21 coolant loop.

Impacts on the windows are more commonplace – or at least are observed shortly after they impact due to their visibility – with the latest strike spotted by the STS-126 crew, who sent photographs down to the ground for evaluation.

In another sign of how NASA extensivily works a problem, the Mission Management Team (MMT) immediately discussed the strike at their morning meeting.

“MMOD Window 6 Impact – crew reported 0.5” diameter to the PLT right window to the thermal pane, 1/32” depth,” noted the Mission Evaluation Room (MER) “Funny” report.

“Based on analysis the window should have no issues for peak heating M=8.0, but could form cracks but remain intact during peak loading M=0.7. Pilot visibility should not be hindered by this location if it cracks.”

“No concern for orbit thermal cycles. Dynamic loading on the pane takes into account for the window frame thermal response. Adding a day for the mission does not effect this window,” noted one manager at the MMT, according to MMT minutes on L2.

“If you had a problem that you were concerned about what could you do? Different entry designs have different heat loads,” asked MMT chair Leroy Cain.

“The thermal pane can handle defects like this in peak heating, but the concern would be pressure down low,” responded Steve Stich from the Orbiter Project, “but not much you could do different for the pressure. Can’t say if it will crack or not.”

Clarifying the impact is not risking safety, Mr Cain asked for confirmation that the hole would not be risking a LOV/C (Loss Of Vehicle/Crew) during re-entry, which one manager responded that it would have to be a hole through more than just the thermal plane of the window where “we might have to not come home,” which referenced calling LON (Launch On Need) rescue with Discovery.

In response to Mr Cain asking about flight history with similar and greater strikes to the windows, the response was noted that similar size has not been an issue, though there was uncertainty in crew measurement, but that on previous missions they have not seen flaw growth for this size of frame.

“We run the conservative analysis that comes out with negative margin, then run mission specific with a pressure profile that shows no effect, low density cracking, high density cracking or window blows out at ~M=1.0 which still wouldn’t be an issue,” added JSC Engineer’s Steve Altemus. “Not a concern for orbit or entry for a defect of this size.”

Other orbiter engineering groups and the Crew Office added comments ranging from “there was some sensitivity in the analysis when we talked this at STS-123 case and maybe run this case and see what we have,” to “trying to give heads up and no issue with this defect from orbiter perspective for emergency D/O (Deorbit),” which is typical for an engineering discussion.

In the end Mr Cain concluded that “I am okay with the heads up and not all the analysis/charts are presented. Wanted to make sure no one had concern for this window impact. We will wait for final answer.”

The initial removal of the impact from a re-entry standpoint will be finalized later this week, with a meeting of the Orbiter Project Office (OPO) on Wednesday, before their findings are sent to the MMT.

“Will talk it again at OPO on Wednesday and could bring back more details to MMT, but don’t think story will change,” added an Orbiter manager. “Will not be catastrophic and any failure would occur late.”

Backing up the opening thought process on the window damage has been an associated presentation – acquired by L2 – that also shows the damage should be ok to re-enter with, even if the window does crack during re-entry.

“STS-126 crew reported a micrometeoroid orbit debris (MMOD) impact on thermal window 6,” opened the presentation. “Estimated diameter of defect is 0.5” (Measurements on orbit are not accurate through three pane system).

“Evaluation of STS-126 Window 6 Damage: Damage diameter is estimated @ 0.5 inch. Damage depth is unknown, but it is estimated based on the crew estimated diameter. Research collected over the life of the program and from ISS, resulted in the development of a “rule of thumb” for estimating MMOD depth

“10:1 is on the conservative end of the scale and was chosen to estimate the depth of MMOD based on a reported diameter. Estimated depth is used in a fracture mechanics assessment for margin generation. It is not absolute, but provides an appropriately conservative estimate of glass strength when combined with typical fracture mechanics methods applied to glass.

“Applying the 10:1 dia/depth ratio, the estimated damage depth is 0.050”. Using the descent certification load case (time consistent loads), side window #6 descent capability is 0.0029” (Mach 0.8, ∆p = 3.18, negative margin with FS = 1.4).”

As with all evaluation presentations, the worst case scenario is shown. For the case of an orbiter window, even far worse damage can be sustained by the three panel window system, and even then the window would not blow out.

“Window Failure Mode: A ding in the glass will fail by propagating cracks outward from the ding. Low pressure/stress loads that cause propagation result in a less dense cracking system,” added the presentation. “High pressure/stress loads result in dense cracking systems.

“From experience (proof testing of a window in a frame), the failed pieces will not be released from the window frame, even with a dense cracking system (high stress/pressure) failure. Proof test failure occurred at approximately 7-8 psi (delta pressure).

“Glass stayed intact under this load (restrained by the frame). Glass resisted engineers’ attempts to “push it out” of the frame. Highest burst load expected during descent is 3.18 psi. Load is not sufficient to push the glass pieces out of the frame.”

Other bases were covered, such as via “trajectory consistent load cases”, which also backed up the forward plan to give acceptance rationale to re-enter without any concern over the window failing.

“Acceptance Rationale: The highest potential for window failure will occur at peak descent loads Mach 0.70 (past peak heating; in excess of Mach 8.0). Delta pressure across the pane is 2.04 psid,” added the presentation. “At this low pressure, flaw propagation may manifest itself in the form of cracks radiating out from the defect site.

“Based on previous testing, if a crack should occur, it is highly likely the windowpane will remain intact and retained, and peripheral view across the window will not be detrimentally affected.

“Accepted Risk, MMOD criteria: no hole through the pane. Recommendation: Nominal Entry.”

While all issues gain such wide-ranging discussion, this particular MMOD strike has proven to be one of only a few issues with Endeavour as she heads towards undocking on Friday.

With no TPS (Thermal Protection System) issues, and only a couple of minor engineering notes being listed by MER, Shuttle manager John Shannon noted his pride with the engineering team that processed Endeavour at the Kennedy Space Center (KSC), a team tasked with five launches in 2009.

“The Cape has put together an unbelievable vehicle. We are able to concentrate on the mission and supporting the ISS team. Entire organization is really pulling together, and you can see over the next year we will have a string of really good flights,” noted Mr Shannon on the latest Shuttle Standup/Integration report.

“We just have to keep it going, keep vigilant like we always have been. Keep doing that good work.”

L2 members: All documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.

Related posts:

1. Endeavour and her SCA piggyback ride arrive in Louisiana, via JSC flyover The Shuttle Carrier Aircraft (SCA) and Endeavour departed from Edwards...
2. STS-126: Super smooth Endeavour easing through the countdown to L-1 A loose washer on a ground support carrier plate is...
3. Dual flow ballet for Endeavour and Atlantis – De-stack debate Preliminary milestone schedules have been created for the complex dual...

Flight Day 11 focused on the fourth and final spacewalk of the mission, which involved the final tasks on the starboard SARJ (Solar Alpha Rotary Joint) – such as work on the final Trundle Bearing Assembly (TBA) that was outstanding from EVA-3, and the clean/lube tasks on the final 30 degrees of the Race Ring.

The spacewalkers – Steve Bowen and Shane Kimbrough – utilized most of the EVA on the port SARJ, as a pre-emptive action of cleaning and lubing, although this SARJ has not suffered the same vibration issues as seen on the starboard side.

Several other tasks were included in the EVA, such as the installation of a GPS antenna on Kibo, along with the P3 truss thermal cover removal and installation of camera system on the truss.

The MMT decided to extend the mission by a day in order to support STS-126′s crew efforts in finding a solution to problems that have been encountered with the hardware that is vital for the six person crew next year.

According to the Flight Day 11 MMT Minutes – available in L2′s expansive coverage of STS-126 – the extension by one day, resulting in a Sunday landing on a nominal EOM (End Of Mission), was always in their back pocket.

“Always planned for extension day and we told folks to plan for it,” noted MMT chair Leroy Cain. “No issues Orbiter is working that would have any issues with staying up another day.

“No concerns with extra day, ISS sleep shift and Progress docking, comfortable with the off duty time that was scheduled,” added Crew Office Brett Jett.

During the MMT, Mr Cain asked for any issues with the extension to aid his final decision. The only reference of note came with regards to the ISS crew’s workload, with the next Russian Progress soon to launch to the Station.

“Some concern for the violation of GGRC (progress launching during docked ops loop hole) hoping to get ISS crew half day off to help ease this concern,” noted Space and Life Sciences (S&LS). “Good from sleep shift and when progress docks at Nadir after crew wake up.”

“ISS supports the half day off and the team should be working towards that,” answered ISS program manager Kirk Shireman.

This led to Mr Cain decision that they would “officially extend a Day and defer the Entry briefing until Friday.”

The problem with the WRS is specific to the Urine Processing Assembly, which shuts down after just a few hours of run time.

Monday’s plan has been to hard mount to structure to see if can isolate the vibration that is understood to be causing the centrifuge to undergo thermal variations – resulting in a shutdown – then refill and restart processing. This has now been completed.

If – in the worst case scenario – the assembly needs to be returned, the MMT noted they are looking at MPLM stowage if required to bring it home.

“Having issues with the distillation assembly of the urine processor. On Spacehab flight a unit flew with no issues hard mounted for four days,” added Mr Shireman at the MMT on Monday. “Working towards success and learn what we can. Appreciate you staying the extra day.

“For REGEN, got a wet indication on a sensor and looking at the nuisance messages. INH wet indication since have other ways to know water on the fan. TOCA had some air bubble issues and we changed some software to clear this up.

“Readiness review for Sunday’s Progress docking. Some open work but ready for docking (6:23 am CST, Sunday).”

The only other new issue that has been discussed relates to a Micrometeoroid Orbital Debris (MMOD) strike to Endeavour’s window 6, reported as 0.5” in diameter to the PLT right window to the thermal pane (estimate 1/32” depth).

Based on analysis the window should have no issues for peak heating M=8.0, but could form cracks but remain intact during peak loading M=0.7. Pilot visibility should not be hindered by this location if it cracks. The MMT concluded that the damage is ok, at present, to re-enter with as-is.

Numerous images, presentations and notes have been acquired by L2, with a round up forthcoming in the next article to be published on site.

L2 members: All documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.

Related posts:

1. STS-126: EVA-1 opens major effort to repair SARJ on Station Spacewalkers Heidemarie Stefanyshyn-Piper (EV1), and Stephen Bowen (EV2) have completed...