Starting off the year: the rollout, launch campaign, and flight of STS-130/Endeavour:

After spending the holiday season of 2009 inside of the VAB safely mated to her External Tank/Solid Rocket Booster (ET/SRB) stack, the Space Shuttle orbiter Endeavour and the STS-130 vehicle began the slow crawl to Launch Complex 39A at 0413 EST on January 6 – a rollout that garnered attention not only as the first rollout of the year, but also as one of the coldest rollouts undertaken by the Space Shuttle Program.

So cold were the overnight/morning temperatures at the Kennedy Space Center, that the normal, pre-rollout ops at the Kennedy Space Center were spread out over a longer period of time than the started 4hrs from rollout Call to Stations to rollout first motion.

In fact, Call to Stations occurred nearly 11 hours prior to rollout, starting at 1700 EST January 5th. Much of this extra time was dedicated to the activation of special heating and purging equipment to ensure that certain Endeavour systems could be maintained at adequate temperatures for the duration of the rollout since the temperature at the start of rollout was 32 degrees F and dipped as low at 30 degrees F roughly three hours into the rollout.

Once at Pad-A, ground crews completed all pad integration activities and began a planned 32-day flow toward a targeted February 7 launch date. Less than one day into the pad flow came word that Endeavour’s primary payload, the Node-3/Tranquility module had a rather significant engineering issue relating to its exterior ammonia (NH3) cooling hoses.

As noted by ISS Flight Director Robert Dempsey, “While proof testing one of the new flight unit ammonia lines there was another rupture. A tiger team has been formed and dispatched to California to begin looking at options and schedule impacts.”

The lines, which were expected to be delivered to the Kennedy Space Center for launch at the end of January, were undergoing additional ground proof testing following two previous ruptures in December 2009.

NASA immediately began reviewing options which ranged from truncating the STS-130 mission from 3 EVAs (Spacewalks) to 1 EVA and still launching in the February timeframe without a resolution/modification to the ammonia lines, or delaying the mission until later in the year when a resolution would be available – a move that would have placed the following STS-131 mission on Discovery ahead of Endeavour/STS-130 in launch order.

“Due to the history, options could be a full redesign, a tweak, a new vendor – which would mean a slip to the nominal mission timeline. As you might expect, (ISS Program Manager Mike) Suffredini wants us to assess the impact to performing a modified mission where we just install the Node 3 and hook up the LTA (Launch To Activation) cables.

“We will also consider swapping the order of the missions.”

The issue itself arised primarily because of a last-minute change to Node-3′s berthing location on the ISS. This change in berthing location meant that the ammonia coolant lines would have to bend at a near 90-degree angle to properly interface with ISS systems.

Nonetheless, within a few days of the issue’s rise to prominence, NASA had demonstrated an amazing work effort to understand the jumper hose failure issue and design a potential workaround that would allow the nominally planned STS-130 mission to maintain its target launch date of Feb. 7.

According to another ISS Flight Director Robert Dempsey memo from early January, “There are two parallel paths being worked to get us NH3 lines in time for our launch date, or with a slight delay. We are by far not out of the woods yet, but this is promising that we can launch on or near 2/7 and have a full mission.”

These two options pertained to a redesign of the original ammonia lines via a double braid or the welding together of smaller, spare hoses identified at the Kennedy Space Center.

These two options were identified early in the process as being the preferable options since they preserved – at least initially – the ability to launch in the February window. However, NASA refused to allow these two paths to usurp other potential options – demonstrating a firm commitment to finding the best possible solution to the issue and simply letting the launch schedule fall where it would.

STS-130 Specific Articles: http://www.nasaspaceflight.com/tag/sts-130/

By January 18th, both hose options were being pursued, with the welding together of spare hoses at the Kennedy Space Center being the preferred option. Under the mid-January schedule, the newly welded hoses carried an estimated delivery date of February 2 – a delivery date that would allow for a February 7 launch attempt.

Over the next 10 days, work proceeded along those fronts and, as a result of the amazing and inspiring work across the agency from thousands of dedicated engineers and managers, NASA officially and unanimously cleared Endeavour for launch on February 7 at the January 27 SOMD FRR (Space Operations Mission Directorate Flight Readiness Review) – an amazing turnaround from an issue which initially threatened any chance of launching Endeavour on time.

Moreover, the Agency FRR for STS-130 also brought to fruition the year-long investigation into the Flow Control Valve (FCV) poppet cracks discovered after the November 2008 flight Endeavour/STS-126.

The year-long investigation yielded six recommendations to the Space Shuttle Program, the first of which was an official closure to the investigation with “ground flow induced damage as the most likely source of crack initiation.”

The second recommendation advised the continued use of flight rationale based on NDE (Non-Destructive Evaluation) inspections and hardware observations (eddy current, Materials Laboratory review, MPI, and SEM). The third recommendation was to maintain “evaluation of the vast acoustic emission data that has yet to be analyzed.”

The fourth recommendation, specifically targeted for STS-130, advised for the “emphasized attention” to Endeavour’s LV-57 position FCV. “This particular position is the only one of the 1301 family of poppets to exhibit considerable crack growth consecutively (STS-126 failure, and STS-127 zone 3 crack development to .22 inch flaw).”

The final two recommendations pertained to the ground processing side of the FCVs.

Recommendation #5 advocated the implementation of a redesign of the outlet tube housing for the GH2 and GN2 ground testing model in order to remove numerous acoustic frequencies to the noise level and demonstrate the effectiveness of Acoustic Environment sensors.

The final recommendation was to remove or reduce the full stroke shimmed flow balance test, and/or implement effective GH2 and GN2 ground testing controls to “improve repeatability and reduce runtimes.”

However, the final push toward the 24th and penultimate flight of Endeavour would not be as smooth sailing as some would have hoped, with a burst FIREX pipe causing Launch Control Center (LCC) water damage, the announcement of the cancellation of the Constellation Program by President Obama (and the creation of an even more uncertain plan for NASA’s future), and weather all playing key roles in the final days of the STS-130 launch campaign.

On Thursday, January 28th at 2025 EST “the LCC experienced a FIREX pipe burst that flooded multiple floors,” noted the January 29 NTD (NASA Test Director) morning update. The burst pipe resulted in the closure of the Firing Room to be used just days later for Endeavour’s launch.

Thankfully, the damage from the pipe burst was not serious and all wiring and console systems necessary for launch operations were not damaged thanks to thorough weather proofing already in place and a quick response from LCC personnel to cover all equipment to prevent any damage from water dripping onto the console from the floors above.

In the end, the LCC flooding did not impact STS-130 S0007 operations and Endeavour’s 3-day countdown began right on time.

As attention shifted more and more toward launch and the actual mission, Shuttle Flight Director Kwatsi Alibaruho rallied his teams with an Admiral Bill Adama (Battlestar Galactica) style address, stating that “I know many of us have watched with great interest as the President’s 2011 budget proposal was unveiled.

“The President’s plan and direction for the Agency calls for a dramatic restructuring of the Constellation Program, including indefinite suspension of plans for returning humans to the moon, and an expansion of support for development of commercial interests in space and Earth Sciences interests.

“There will be much dialogue between the President and the Congress before a final direction is codified.

“Such redirection can be incredibly challenging; however, it is especially difficult for many since we are at the beginning of what is to be the last year of the Space Shuttle Program. It is at these times that we are reminded that we are agents of the United States Government and servants of the Executive Branch. We are living in difficult times, and such times call for leadership.

“Leadership is not about making everyone happy, although it would be nice if one could. Real leadership is about setting a direction, developing a plan, leveraging resources, and making the difficult trades demanded by the difficult times.

“Please, do NOT be discouraged. This is not the end, by any means. All of this has happened before, and all of this will happen again. This is part of the natural process that is endemic to our special and enduring system of government. This is the nature of the process by which policy is made.

“But we are not policy makers. We are executors and stewards of a unique trust. History will barely remember the underlying fiscal and political factors that drove this policy and the subsequent direction for NASA, but what history will record in bold letters is how we perform.”

With everything in place, the stage was set for a spectacular night time launch of Endeavour. As the countdown proceeded, Endeavour behaved extraordinarily well on the pad (a testament to the hard work of her processing teams), allowing launch personnel more than enough time to analyze a few (very few) minor issues that cropped up during the count.

But in the end, it would come down to the weather. While official forecasts in the days leading up to the February 7 attempt called for an 80 percent chance of acceptable conditions, it would be the slight possibility of low clouds that would eventually force a scrub at the T-9mins and holding mark.

But this call proved slightly more dynamic than other recent weather scrubs, with a fascinating on-net discussion of the weather rules and whether or not the cloud cover hanging over the Kennedy Space Center was acceptable in the event of an RTLS (Return To Launch Site) abort or not.

As discussed in the post-launch press conference of February 8, Mike Moses explained that “Our Flight Rules cover what we need for RTLS in terms of ceiling and visibility. [The cloud ceiling] limit is 5,000ft for RTLS and the Range rules for visibility sit at about 4,000ft depending on thickness of clouds.

“Basically, we’ve always had this slight disconnect about what the Range would be go for and what RTLS landing would be go for. And they’re off by about a 1,000ft. Over the years, we’ve learned to constantly evaluate that if you have a condition that is acceptable for the Range but not RTLS, what does it take to be acceptable [across the board].

“Each of the pilots practice various visibility runs. They learn what they need to have to be comfortable: what would be good [and] what would be bad. Really, you’re looking for a [cloud] deck that allows you to gain the horizon as you’re rolling around the HAC (Heading Alignment Circle) so you understand clearly where you’re at.

“Last night we had that in the fact that there was nothing above that [cloud] deck. So clear skies up to that point (about 3,800ft).

“Then you look at the thickness of [the cloud deck] as you go through it. So you’ve got a good reference point, you know where you’re coming through, you punch through the ceiling really fast so you know you’re on your approach path. And once you get through it’s clear on down [the runway].

“The other big factor is what the wind’s doing from about 10,000ft on down and the work load that that then drives for the pilot. If all he has to do is pay attention to that glides slope as he comes in, that’s a little more acceptable. So we send the STA (Shuttle Training Aircraft) up there to fly that path and characterize that for us. So we send the STA up there with an astronaut to go fly that approach and go see what it really is compared to what our weather data is telling us.

“So what we were talking about yesterday was: could we get comfortable with the fact that, even though we were a little bit lower than our limits, we could still have good [conditions for RTLS]. And we were debating back and forth as to how comfortable we really were there. And we just didn’t get there on that yesterday.”

Despite this on-net discussion, weather was never “go” for launch during the T-9min hold and Launch Director Mike Leinbach made the correct call that even with potential weather waivers (of which none were being discussed) the weather would have been unacceptable from a flight safety standpoint.

Recycling for a 24hr turnaround, teams configured for a second launch attempt for Endeavour on the morning of February 8. This time, it would be the TAL (Trans-oceanic Abort Landing) sites in Europe that would pose an issue in terms of weather.

Thanks to real-time weather reconnaissance, however, one TAL site was declared “go” and at 04:14:08 EST, Endeavour lit up the partly-cloudy and cold night sky of Florida, thundering away from the Kennedy Space Center to begin STS-130 – the first of what would be three Space Shuttle missions in 2010.

In all, Endeavour reached orbit unscathed thanks to a superb job from the External Tank teams in preparing Endeavour’s tank for flight. TPS (Thermal Protection System) inspection data revealed NO (0 – ZERO) underbelly TPS scuffs or damage zones – a first and so far only occurrence in the Space Shuttle Program.

In fact, there were only 3 areas of TPS concern across the entire vehicle, a milestone that creates a highly visible accomplishment of all those across NASA who dedicated themselves to the reduction/elimination of damaging ET foam liberation from the tank during ascent.

The extremely clean nature of Endeavour’s TPS allowed all those involved in the execution of the mission to focus on the mission’s objectives – the delivery and installation of Node-3 and Cupola.

After successfully installing Node-3 and configuring Cupola, the STS-130 crew had the honor of opening up Cupola’s window covers for the first time and taking in the breath-taking 360 degree view of Earth from ~200miles above the planet’s surface.

After 13 days 18 hours 8 minutes and 3 seconds in space, Endeavour Commander George Zamka and Pilot Terry Virts fired Endeavour’s OMS (Orbital Maneuvering System) engines for 2minutes 38seconds, dropping Endeavour to suborbital speed.

Earth’s gravity pulled Endeavour into the atmosphere where friction between Endeavour and her contact with atmosphere created a stream of plasma around and behind the orbiter – an event imaged by crewmembers aboard the International Space Station from the newly installed Cupola.

Endeavour glided to a dark landing at the Kennedy Space Center at 22:22:10 EST on February 22 to cap off the first NASA flight of 2010.

STS-131: The Challenges of Launch Processing and the Rewards of Orbital Success:

With weather playing a significant role in the rollout, pad processing, launch, and landing of Space Shuttle Endeavour/STS-130, weather would again prove troublesome during early launch processing ops for STS-131/Discovery.

Initially targeting launch on March 18, NASA managers pushed back the mission’s targeted launch date due to Dual Docked Ops (DDO) constraints with the departing and arriving Russian Soyuz spacecraft for ISS crew rotation.

While Discovery would have initially been able to meet the March 18 launch date, the decision to delay launch due to DDO constraints proved fruitful when unacceptably cold weather at the Kennedy Space Center prevented workers from rolling Discovery from her OPF (Orbiter Processing Facility) to the VAB for 10 days.

Technicians were forced to delay Discovery’s rollover to the VAB from the OPF due to a requirement that temperatures in the VAB not drop below 45 degrees for more than 12 hours at the time of rollover and in the initial days of mating ops. This rule is in place to protect a Shuttle orbiter’s OMS and RCS (Reaction Control System) systems from potential cold weather damage since those systems cannot be hooked up to heating and purged air for rollover and mate.

STS-131 Specific Articles: http://www.nasaspaceflight.com/tag/sts-131/

The long delay to rollover ops would have eliminated March 18 as a launch opportunity for Discovery/STS-131, thus making the delay to April 5 from a DDO perspective a fortunate coincidence as it restored over 7 days of contingency time to the STS-131 pad flow.

After 8 days in the VAB, Discovery rolled out to launch pad 39A on March 2 at 23:58 EST – one day later than planned due to thunderstorms in the vicinity on March 1/2. Discovery arrived at Pad-A at 0649 EST March 3 and technicians began processing the vehicle for launch.

While processing initially went smoothly for Discovery, a visible RCS hydrazine leak occurred during the multi-day OMS/RCS fueling operations. As noted by the daily NTD reports, “Leak: RCS Helium Iso Valve on the right pod for the fuel system.” This meant that the Iso valve was stuck in the “open” configuration.

During RCS thruster operations, the correct flow of helium is essential for providing the proper flow path of oxidizer from the propellant tanks into the combustion chamber of the thrusters, allowing them to carry out their function of aiding the orbiter’s maneuvering on orbit.

While replacing the valve would have solved the issue, replacement could not have been performed at the launch pad. Instead, Discovery would have had to have been rolled back to the VAB, destacked, returned to the OPF, her right OMS pod removed, and the Right OMS Pod from Endeavour donated to Discovery for STS-131.

Since that would have induced a multi-month delay to the mission, NASA looked for other, less intrusive solutions for the issue.

The two less intrusive options developed were a “blowdown” procedure to blow helium through the system for a period of time and then cycle the helium valves to purge any contaminants that could have been causing the valve in question to remain in the open position.

The second option would be to simply accept the condition “as is” via flight rationale and fly the mission as planned thanks to built-in redundancy and on-orbit flight experience with a stuck open and stuck closed Helium Iso valve.

In the end, even though root cause of the issue could not be identified, flight rationale was accepted and the decision made to fly “as is.”

But this would not be the only technical issue to plague pad workers during the month of March. Shortly after Discovery’s arrival at Pad-A, Pulse Code Modulator Master Unit (PCMMU) 1 on Discovery experienced a “momentary failure” on March 5, kicking off a round of troubleshooting and engineering evaluations.

The PCMMU “routes the orbiter data to the OPS recorders and the communications systems for downlink to the MCC (Mission Control Center),” notes a Data Processing System (DPS) Familiarization Workbook (L2).

According to the STS-131 Space Shuttle Program (SSP) FRR summary (available on L2), “On March 5th, the four GPCs (General Purpose Computers) running in the redundant set all logged an I/O (input/output) error. Reviewed the data and saw that the PCMMU and several OI MDMs (Multiplexer Demultiplexers) had logged data validity errors.”

Following the March 5 failure, a second failure occurred the following day with a third failure occurring on March 9. “The GPCs responded nominally so the focus is now on the instrumentation buses,” notes the 131 SSP FRR summary.

In the end, no anomalies could be identified on PCMMU 1 and the engineering community recommended switching to and launching on PCMMU 2 without the replacement of PCMMU 1 – which operated nominally after the three previous issues on March 5, 6 and 9.

On March 26, the SOMD FRR unanimously approved launch of Discovery for April 5, and the three day countdown began in the early morning hours of April 2 and proceeded without major issue.

On the morning of April 5, 15-minutes before the targeted liftoff, the International Space Station flew almost directly over the Kennedy Space Center and Space Shuttle Discovery/STS-131, bisecting the moon as viewed from the KSC press site.

Fifteen minutes later, at 06:21:22 EDT (49 minutes before sunrise and with a light glow on the horizon), Space Shuttle Discovery lifted off from Pad-A, a light layer of fog creating the presence of a halo-like glow around Discovery as she headed toward space.

With sunlight barely breaking across Earth’s horizon as seen from Discovery’s ET camera, Discovery slipped into orbit after what was arguably the most visibly impressive launch of the Shuttle Program.

Following SRB separation, high altitude sunlight refracted from the water vapor contrail created by Discovery’s three main engines, creating a visible second stage contrail.

Furthermore, the SRB contrail, drifting into the upper atmosphere, formed a shape remarkably similar to that of a dragon. When this contrail caught the pre-sunrise light, it turned an impressive shade of orange and red – a natural tribute to Japanese astronaut Naoko Yamazaki who launched onboard Discovery.

Once in orbit, Discovery’s crew quickly realized that the orbiter’s Ku-Band antenna – the primary communication’s antenna on the vehicle – was experiencing an issue following several failed self-tests. These tests are conducted automatically by the Ku-Band antenna upon activation and deployment on orbit.

Commands to power cycle the two black boxes on the hardware failed to correct the problem. Thus, the Ku-band antenna was inoperative in both the forward and return link configurations, which prevented high bandwidth download and upload between the ground the Discovery.

Nonetheless, all TPS inspections were performed nominally with some information downlinked via the S-Band antenna during passage over the continental US.

The remaining data was downlinked following docking to the ISS when Discovery’s crew could make use of the Station’s Ku-Band antenna for the duration of the docked mission.

Like Endeavour and the previous mission, Discovery’s TPS was found to be in excellent condition with only a Rudder Speed Brake tile partial liberation gaining the bulk of the Debris Assessment Team’s attention.

However, the failure of Discovery’s Ku-Band antenna led NASA to extend the mission and move the customary TPS late-inspection into the docked portion of the flight – a procedure which had been accomplished before on STS-123 in March 2008.

This was done to ensure that all scan imagery could be transmitted to the ground and analyzed in a timely manner prior to reentry.

With the docked late-inspection in place, Discovery undocked from the ISS for a targeted April 19th landing. However, poor weather at the Kennedy Space Center forced a wave-off of the landing to the following day.

After 6.23 million miles, Discovery reentered Earth’s atmosphere over the North American continent on April 20, performing the second – and to date last – descending node reentry over the heartland of America in the post-Columbia era.

After 15days 2hours 47minutes and 11seconds in flight, Discovery came to a stop on Runway 33 at the Kennedy Space Center. With this mission duration, STS-131 became Discovery’s longest flight, beating out STS-120′s mission duration by a mere 23 minutes.

The STS-131 flight of Discovery also marked the final Space Shuttle mission with a seven member crew, the final Space Shuttle mission to carry a rookie astronaut to orbit, and the first time that four women worked together in space (three on Discovery and one on the Space Station), and the first time that two Japanese astronauts worked together in space (one on Discovery and one on the ISS).

The flight was the 18th post-Columbia flight, the 33rd flight of the Space Shuttle to the ISS, the 35th American manned night launch (of which 34 have been by the Space Shuttle and 22 of which have occurred from Pad-A), the 38th and penultimate voyage of Discovery, the 106th post-Challenger flight, and the 162nd American manned spaceflight.

(Part 2 of NASASpaceflight.com’s 3-part 2010 Year in Review series will be published December 31.)
(Images via L2, Larry Sullivan: MaxQ Entertainment, NASA.gov)

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STS-133 Launch Attempt 1 Scrub:

With the flight rationale now in place for the issues suffered by the redundant Main Engine Controller (MEC) on Main Engine 3 (ME-3), the weather was Discovery’s next challenge. Forecasts had placed the acceptable weather as bad as just one percent overnight, with at least 40 percent unacceptable weather conditions for tanking.

MMT Chair Mike Moses hosted the tanking meeting at the Kennedy Space Center (KSC), with the possibility already pre-empted that he could delay 24 hours if the weather showed no signs of giving Discovery a chance to launch later in the day. Options also remained to press ahead with loading the External Tank, prior to calling a scrub throughout the day, including just ahead of coming out of the T-9 minute hold.

For the interim, Discovery remains out in the open, following the retraction of her Rotating Service Structure (RSS) on Wednesday night, bathing in the powerful floodlights for what would be potentially the final time. However, by morning, she was receiving a soaking, as the rain started to pour down around 4am, pre-empting the challenging situation faced by the MMT.

S0007 operations at the pad continued to be on schedule, with only a loose strap requiring the attention of pad crews. Discovery’s Interim Problem Report (IPR) count has risen to 64, although the addtional four problems were all cleared during the morning.

Managers have decided to recyle to T-11 hours at 11:39pm on Thursday evening, with the next MMT meeting set for 5am, where it will be decided whether to tank for the Friday launch attempt or delay further. Friday’s tanking would begin at 5:38am – ahead of a target launch time of 3:03pm Eastern.

Friday’s weather is forecasting 40 percent unacceptable weather – far improved on Thursdays.

Further updates will follow. Refer to this article, the live launch day thread, and the L2 STS-133 Special for full coverage.

STS-133 Specific Articles: http://www.nasaspaceflight.com/tag/sts-133/

Explained Anomalies from Previous Vehicle Flight (STS-131):

Before lifting off on her 39th and final mission, preparations for Discovery’s capstone mission included the drive to close the books on the last few outstanding items from Discovery’s previous flight – STS-131.

In all, the Space Shuttle Program (SSP) identified three (3) unexplained anomalies from the STS-131/19A mission, Discovery’s previous flight (April 5 – 20, 2010). Among these unexplained items are a failure of the MDU MFD1 to successfully port mode to the secondary port, multiple communication errors on Data Bus OI-1, and a pump motor condition sensor voltage anomaly on Fuel Cell 2′s H2 pump motor condition sensor.

MDU MFD1:

According to the FRR (Flight Readiness Review) presentation, “During STS-131 ground processing, MDU (Multifunction Display Unit) MFD1 was unable to communicate with IDP3 on its secondary port.”

While a root cause for the issue could not be identified, engineers suspect a temporary copper path irregularity from the coupler and the MDU as the most likely cause of the failure. In turn, the cause of this irregularity is thought to be “either a partially recessed socket or transient contamination in coupler connector 34P26.”

To combat this problem (prior to STS-131), engineers replaced the suspect 1553 data bus stub cable and processed an MR (Material Review) “due to inability to feed new cable through one clamp.” Spot ties were used to secure cable.

Additionally, the DBC (Data Bus Coupler) mating connection 34P26 was R&Red (Removed and Replaced). The DBC itself, however, was not replaced due to the low likelihood of the coupler itself being the cause of the problem and the extremely invasive nature of a DBC R&R.

Therefore, the root cause of the issue was never determined prior to STS-131. As such, the same rationale that was used to clear the issue for STS-131 (Flight 38) remains in effect for STS-133.

“Flight 38 rationale remains valid, with no increase in risk to safety of flight or mission objectives,” notes the FRR. “Problem only affected MFD1 secondary port bus stub – no other MEDS (Multifunction Electronic Display Subsystem) functionality was affected.”

The MDU MFD1 is a Crit1R3 system, but flexibility and work around options for the loss of MFD1 secondary port during flight are available thanks to the “robust” MEDS system which is “two fault tolerant” throughout flight.

Moreover, the “Program has previously accepted flying with one non-CRT forward station MDU down (ref. LCC DPS01a / BFS-10a).”

In the event of an MDU MFD1 secondary port failure during STS-133/ULF5, there would be no impact to the crew’s “operations, procedures, or situational awareness” since the MFD1 would only switch to the secondary port if the primary port or bus commander failed.

Communications Errors on Data Bus OI-1:

The second unexplained anomaly from Discovery’s 38th flight was in the form communications errors on Data Bus OI-1.

“GPC (General Purpose Computer) logged errors were response to BITE (Built-In Test Equipment) errors annunciated by other LRUs (Line Replaceable Units). Multiple LRUs indicated incoming data errors for 2 simultaneous major frames,” notes the FRR.

At the time of the errors, PCMMU 1 (Pulse Code Modulator Master Unit 1) BITE bit 10 was set and the MDM (Multiplexer-Demultiplexer) OF2, OF3, and OA1 also logged BITE bit 2 errors – including a second occurrence of data invalidity errors on PCMMU 1.

On this second occurrence of the PCMMU 1 data invalidity error there were no GPC I/O (Input/Output) errors or MDM BITE bit failures registered, and no vehicle commanding was occurring at the time.

According to documentation at the time of the first error on March 5, “the four GPCs running in the redundant set all logged an I/O error. Reviewed the data and saw that the PCMMU and several OI MDMs had logged data validity errors.”

Engineers initially believed a data bus of an MIA (Multiplex Interface Adapter) to be the cause of the data invalidity errors, but further investigation and troubleshooting failed to identify root cause.

Nonetheless, three probable causes for the issue were identified: a discrepant MIA (of which there are 8, seven OI MDMs and the PCMMU), a damaged data bus path resulting in a noisy OI data bus, and the internal circuitry of the PCMMU itself.

The decision was then made to launch Discovery on STS-131 in PCMMU 2 instead of PCMMU 1 since the PCMMU is a devise that routes orbiter data to the OPS recorders and the communications systems for downlink to the Mission Control Center. The launch/mission proceeded without further communication and data invalidity errors.

For STS-133 ground processing, further resolution of this issue was attempted. “The 1553 Test Box was installed on OI Data Bus 1 at the data bus coupler near Av Bay 4,” states the FRR. “No anomalies occurred during this monitoring [period], and review of the data revealed no unexpected OI Data Bus 1 failures.”

Likewise, the FRR notes that during testing, PCMMU 1 and OI Data Bus 1 were activated in conjunction with the BFS (Backup Flight Software) GPC 5 (General Purpose Computer 5) in an attempt to gain as much insight into the system as possible in the event that the anomalies reoccurred. They did not.

A recommendation was then put forward and adopted to launch STS-133/ULF5 in PCMMU 2 and fly “as is,” thus mirroring the strategy used for STS-131.

Fuel Cell 2 H2 Pump Motor Condition Sensor Voltage Anomaly:

As described by the STS-133 FRR, “During STS-131 S0007, countdown monitoring after Fuel Cell 2 (FC2) start: the FC2 H2 pump motor condition (PMC) voltage measurement was found to have a gradual rise from 0.62 VDC to 0.98 VDC over approximately 5 minutes without a corresponding change in FC2 current.”

The rise in voltage did not violate the LCC (Launch Commit Criteria) and the Fuel Cells were all cleared for flight. The IRP (In Process Report) was deferred following a Firing Room poll and the inability to identify the cause of the voltage rise.

The most probable cause of the voltage rise was determined to be “Unique AC2 bus loads” registered by FC2′s H2 PMC sensor. However, it was not possible to isolate the anomaly to a single system given the “insufficient Shuttle telemetry of the AC Bus loads.”

During ground processing of OV-103 for STS-133, inverters 4, 5, and 6 were R&Red and troubleshooting of FC2′s PMC revealed that the circuit is “‘hyper sensitive’ to any phase imbalance.”

A phase imbalance can occur due to any load on the associated Bus. As the FRR notes, “This puts the team in the unique situation for launch countdown (of STS-133) of potentially having to troubleshoot a recurrence from the perspective of examining all the associated loads on the Bus.”

(Lead Photograph: Brian Papke, NASASpaceflight.com and MaxQ Entertainment. Others: L2)

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STS-132 Pad Flow Latest:

With excellent timing, engineers cleared the outstanding IPR (Interim Problem Report) relating to the calibration of a sensor, while the only new IPR over the past few days – associated with the Left Reaction Control System (LRCS) – is of no issue for the flow.

“Partial Pressure Oxygen (PPO2) sensor C calibration was completed on Friday. The sensor is functioning nominally,” noted the NASA Test Director (NTD) processing report on L2. NEW IPR 0039: LRCS fuel tank ullage pressure regulator A locked up at 269 psi should be no more than 268 psi. Under engineering review (cleared).”

With the regulator deemed to be in a good condition, engineers completed S0071 operations to pressurize the systems for flight, which was followed by the closure of Atlantis’ Payload Bay Doors (PLBDs) for the final time ahead of launch.

“S0071 Main Propulsion System (MPS), Space Shuttle Main Engine (SSME), Orbital Maneuvering System (OMS) and Reaction Control System (RCS) helium and nitrogen tank pressurization for flight is complete,” added the flow report.

“Payload Bay Doors (PLBD) were reopened yesterday for crew sharp edge inspection and Orbiter/Payload Vertical Closeout, and closed for flight.”

S0007 Launch Countdown preps worked through a nominal flow towards Call To Stations (CTS), 30 minutes prior to the start of the count – which began at 4pm Eastern.

STS-133 Specific Articles: http://www.nasaspaceflight.com/tag/sts-132/

Changes to STS-132 RSRMs:

When Atlantis launches, the STS-132 stack will boast two changes to the RSRMs (Reusable Solid Rocket Motors): a new fluorocarbon O-ring V1288 in nozzle joints 4 and 5 and the incorporation of V1288 O-rings in the Igniter Gaskets.

In terms of the Nozzle Joints, “Incorporated V1288 fluorocarbon O-rings in nozzle joints 4 and 5,” notes the RSRM portion of the SPP (Space Shuttle Program) FRR from April 28 – a presentation available for download on L2.

This replacement of the old V1247 O-ring design with the new V1288 design is part of an ongoing replacement process made necessary by the obsolescence of the old V1247 O-ring design – an obsolescence that mandated a requalification of a V1247 ingredient or the creation of a new O-ring design.

Since a new material (dubbed V1288) as available after its creation to “[improve] resiliency … for field joints,” it was decided that using the V1288 material would simplify the manufacturing process for the supplier while increasing safety at the nozzle joints.

Approval for the new V1288 O-rings for nozzle joints 4 and 5 was certified based on the material properties of the V1288 being equal to or greater than the V1247 as well as the fact the “2x tracking requirement still met for joint no. 5 (dynamic).”

Moreover, the new V1288 O-rings decrease the erosion rate at the nozzle joints.

The V1288 O-rings were flaw tested in field joints on FSM-12 (Flight Support Motor 12) and FSM-13 out in Utah. The V1288s were also successfully tested in nozzle joints 4 and 5 on the Ares DM-1 (Demonstration Motor 1) and FSM-17.

The V1288s have also been successful flown in BSMs, RSRM field joints, RSRM nozzle-to-case joints, and RSRM nozzle joint #1 on previous Shuttle flights.

As such, the new O-rings in nozzle joints 4 and 5 are safe to fly on STS-132 and subsequent flights.

The second change to debut on STS-132′s RSRMs is the incorporation of the V1288 O-rings in the Igniter Gaskets.

“Replaced V1944 (V1247 with paraffin release agent) fluorocarbon seal material with V1288 fluorocarbon seal material in Inner, Outer, and Safe & Arm (S&A) gaskets,” notes the SSP FRR RSRM presentation.

Furthermore, the adhesive in the gaskets was changed for the STS-132 RSRMs from Chemlok 5150/607 to Chemlok 8116.

The reason behind this change also comes from the obsolescence of a V1944 (V1247) ingredient that required a requalification or a new material (Chemlok 8116) “specifically designed for peroxide cure elastomers.”

The new material (Chemlok 8116) and integration of the V1288 O-rings were verified for flight based on the fact that the metal retainer design, material, and fabrication processes were not changed from the previous design.

Furthermore, the physical dimensions of the gasket sealing elements were not changed and the material properties of the V1288 material “[met] specification requirements for V1944″ and have been shown to be better than or equivalent to the V1944 O-rings.

Tests on the compression-set of the new design support all stack-life and age-life requirements. Moreover, numerous bounding dynamic pressure tests indicate that the sealing capability of the V1288 O-ring gaskets is “better than V1944 gaskets with the 1.4x tracking requirement still met.”

Retainer-bond-seal system tests also indicate greater than or equal to performance from V1288s and “static tests and 70-lb char motors show improved erosion rates for V1288s.”

The safety and operation of the new design for V1288 S&A and inner gaskets were demonstrated on LAT 85-A and 85-B.

The S&A gaskets were further verified during the static test firings of TEM-13 (Technical Engineering Motor 13), FSM-15, Ares DM-1, and FSM-17 without issue.

As such, STS-132 and subsequent flights are safe to fly with the new igniter gaskets seal design.

STS-131 SRB IFA Review and Forward Action/STS-132 SRB Nonconformance Review:

Following the highly successful STS-131 mission by orbiter Discovery last month, the standard IFA review of the entire vehicle revealed only one issue with the SRBs on that flight.

“In-Flight Anomaly (IFA) STS-131-B-001 RH Data Acquisition System (DAS) Failed to Record Full Flight Accelerometer Data,” notes the SRB presentation to the SSP FRR at the end of April.

According to the SSP FRR presentation, the DAS (serial number 2000003) did not record full flight accelerometer data.

During a post-flight data review, it was discovered that the full flight data was not recorded due to “insufficient time left in memory,” notes the SRB presentation.

In all, the DAS recorded 540-seconds of accelerometer data – with 446-seconds of the data coming from pre-flight testing. After this ground testing was complete, the DAS was not reinitialized, leaving only 94-seconds of memory remaining for in-flight recording.

Despite the failure to record all the accelerometer data, there was no concern for the crew or the mission because of the loss of full data, nor is there an increased concern for the STS-132 crew or mission as the loss of accelerometer data is a Criticality 3 concern.

Nonetheless, to ensure that this problem does not reoccur, a new Preflight Test Procedure Reset will be required if a DAS unit is powered up before the final g-switch activation. Furthermore, “Track power on time for g-switch activation to ensure sufficient memory available for flight” will also be performed notes the presentation.

In addition to this potential change for STS-132′s SRBs, there were (at the time of the SSP FRR on April 28) 3 open problem reports, or nonconformances, with the STS-132 SRBs.

These nonconformances – all of which will be managed or accepted as is with paperwork before launch – include a discrepancy in the Bolt catcher Thermal Protection System width dimensions, a DAS unit access plate Changeout, and an unapproved electrolyte and neutralizer performance in an Auxiliary Power Unit (APU) part.

In all, the STS-132 stack’s SRBs and RSRMs have been cleared for flight on Friday with Atlantis on the 34th Space Shuttle mission dedicated to construction and outfitting of the International Space Station.

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STS-131 Post Flight:

Discovery returned from the International Space Station (ISS) after delivering tons of cargo via the MPLM (Multi-Purpose Logistics Module) Leonardo and installing a new Ammonia Tank Assembly (ATA). The veteran orbiter also returned an array of down mass from the Station – including science experiments – along with an old ATA.

Despite some minor challenges during two of the mission’s three EVAs (spacewalks), the mission was highly successful, earning the praise of shuttle management.

“Mr (LeRoy) Cain (Chair of the Mission Management Team) thanked the team. STS-131 was a good mission and had outstanding support every day at the MMT and throughout the mission through the teams that support,” noted the latest Shuttle Standup/Integration report (L2).

“This mission was a little tough because of the hours of the crew’s day, but you could not tell in terms of support received from the team. Great job. Had a beautiful landing on Monday.”

“It was a tremendous flight,” added SSP manager John Shannon. “The Operations and Engineering teams are working together very well. They worked around the loss of the Ku-Band antenna to figure out clever ways to get the required data down. The process is working so smoothly to assess the health of the vehicle.

“We also help out the ISS with assessment on doing additional EVAs and getting the ATA squared away. So proud of the team and how everyone is doing, finishing up in a tremendous manner.”

Discovery was given a preliminary inspection whilst sitting on the runway at the Shuttle Landing Facility (SLF), with reports showing nothing more than minor dings and cosmetic damage to her Thermal Protection System (TPS).

One area of interest related to Discovery’s numerous ceramic inserts – one of the main Flight Readiness Review (FRR) and Special PRCB (Program Requirements Control Board) topics ahead of launch.

While the Payload Bay Door hinge line inserts are currently being evaluated inside Discovery’s OPF-3 (Orbiter Processing Facility), the runway report notes a problem may still exist on the window inserts’ ‘plugs’ – one of the initial trigger for pre-flight checks, following an incident with a protrusion, which was observed during Endeavour’s STS-130 mission.

“From inspections on the runway, no inserts were missing or protruding. They did find two plugs, one each on Windows #5 and #6, that each protruded just a little. There was also one plug on Window #6 totally missing,” added Mr Shannon. “Have on-orbit photos showing that the plug was there. It may end up on the IFA (In Flight Anomaly) list.”

After being towed off the SLF, integrated roll-in operations begin inside OPF-3, as Discovery was put through a preset list of safing procedures.

“APU (Auxiliary Power Unit) plug installations are complete. Potable water sampling was completed,” noted the NASA Test Director processing report (L2). “Flight Crew Systems de-stow is complete less fire extinguisher removal and ET umbilical camera removal. Orbiter mid-body access doors were removed and Power Reactant Supply and Distribution (PRSD) scupper installations have been installed.

“PRSD (Power Reactant Storage and Distributation) Pneumatic Operated Disconnects (PODs) mates and leak checks are complete. SSME (Space Shuttle Main Engine) bearing drying purges complete. PRSD LH2 off load complete. LO2 of load in work.

“Orbital Maneuvering System (OMS) and aft `Reaction Control System (RCS) access panel removal and Quick Disconnect (QD) flight cap removed. OMS/RCS static air sample access panel removal scheduled for today. Air samples began Friday  Main Propulsion System (MPS) and SSME Pressure regulator checkout and SSME pneumatic system validation tests are complete.

Discovery’s Payload Bay Doors received their strongbacks – which aid the opening of the doors, as they can only open under their own power in micro G – on Friday, allowing engineers to opening the doors and begin operations to remove the old ATA and the MPLM – set to begin on Sunday.

STS-133 Flow:

With numerous turnaround tasks being carried out over the weekend, Discovery is now processing towards what is currently scheduled to be her last flight.

“Weekend work: Payload canister arrival, Flow Control Valve (FCV) removal, payload electrical demates, payload removal, engine/body flap carrier panel removals,” added the NTD report on Friday. “TPS post flight inspection, Orbiter power up Saturday second shift for hydraulics operations to position SSMEs, aero-surfaces and lower the nose landing gear.”

Engineers have also begun opening work on the Ku Band uplink/downlink failure that occurred during STS-131. This on orbit issue has been charged as IPR (Interim Problem Report – 5) against the STS-133 flow.

The payload for the STS-133 mission will be the ELC-4 (ExPRESS Logistics Carrier 4) and the Permanent Multi-purpose Module (PMM) – which sees Leonardo once again riding with Discovery, only this time remaining on the Station, as a modified storage area.

Booster buildup for STS-133 continues to take place in the RPSF (Rotation Processing and Surge Facility), while Discovery’s External Tank is on track to arrive at KSC in a timely manner.

“ET-138 In Final Assembly, proceeding nominally,” noted the Michoud Assembly Facility (MAF). “No threat to schedule, no risk to schedule.”

Turnaround of the MPLM into the PMM remains the tightest element on the schedule to make the current STS-133 launch date of September 16. As such, should STS-134 swap places with STS-133 in the running order, Discovery would become the LON vehicle for STS-132.

The gap between the two flights remains under discussion, and potentially could result in STS-132 slipping to the right to close the gap – based on the CSCS (Crew Shuttle Contingency Support) timeline of supporting the STS-132 crew on the ISS until the next shuttle arrives to pick them up.

The manifest question is a result of the heavily delayed delivery of the AMS-02 (Alpha Magnetic Spectrometer-02) payload to the Kennedy Space Center (KSC), due to a changes to its troublesome cooling system – resulting in the launch slipping to at least November.

Switching the running order between STS-134 and STS-133 is no easy task and remains under discussion, following a manifest meeting on Friday at the Johnson Space Center. A full article on the situation will be published later.

Even if STS-133 remains as the final flight on the current schedule, the addition of STS-135 – currently the Launch On Need (LON) shuttle for STS-133 – may yet receive approval.

“As far as the rest of the year is concerned, things are starting to become clearer. (Do) not have any information on STS-135 yet. So, we will continue to work it as we go along,” added Mr Shannon. “A lot will depend on how we come out of this year from a budget standpoint.”

For the interim, the bulk of concentration is being placed on the next mission, STS-132. One of the major milestones will occur next week, when managers conduct the SSP FRR. Several articles will lead up to the two-day review.

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STS-131 Status:

The first landing opportunity related to KSC, which would have called for a deorbit burn at 6:28am Eastern, resulting in a descending node entry over North America and the US’ eastern States, for a landing at 7:34am.

With that opening opportunity waved off, and the next landing possibility in California refused, the second KSC landing opportunity was the  focus, as weather began to improve. A GO was given for the deorbit burn, as Discovery began her journey home, ending in a perfect touchdown on the Shuttle Landing Facility (SLF).

Discovery had enough onboard cryos and consumables to wave off all five attempts, in the unlikely event weather on both coasts proved to be unacceptable.

“The crew performed a Group C power down to conserve cryogenic consumables in an attempt gain another day of margin. An additional day will allow more flexibility for landing opportunities over the next few days,” noted Mission Evaluation Room (MER) status on L2.

“A waste water dump was initiated at 108/12:17 GMT (13/01:56 MET) and completed at 108/12:25 GMT (13/02:04 MET). Approximately 26 lbm was dumped. A condensate dump was initiated at 108/12:37 GMT (13/02:16 MET) and completed at 108/12:49 GMT (13/02:28 MET).”

Via the Group C powerdowns, several items will be powered back on during the deorbit prep list. MER managers outlined that all systems were healthy prior to power down, as Discovery continues to perform exceptionally well during her long mission.

“GPS performance has been nominal throughout most of this period. At 108/09:56:20, after FCS (Flight Control Surface) checkout, MDM FF2 was powered down as part of the modified group C power down, and GPS data became invalid and could not be analyzed from that point forward.

“The receiver status bit (V74X8500E) from OF2 is still valid and shows that the receiver is still on and tracking satellites. MDM FF2 is planned to be powered back on as part of de-orbit preps. There are no issues being tracked by the GPS team.

“All DPS (Data Processing System) systems performing nominally. All passive thermal control systems are performing nominally and all monitored temperatures are remaining within acceptable limits. The PPCO2 level was at 1.80 mmHg during LiOH change out at GMT 109/04:50.”

STS-131 Specific Articles: http://www.nasaspaceflight.com/tag/sts-131/

Dryden Landing:

Entry Flight Direct Brian Lunney noted that he would only take the Californian landing option should KSC weather also look bad on EOM+2 (End Of Mission Plus Two Days – Wednesday), as every effort is made to return Discovery to her home port – especially considering the strain on turnaround of both the orbiter and MPLM Leonardo for STS-133. In the end, the preference of KSC found acceptable weather for her return.

However, had should weather in Florida failed to improve to acceptable levels, the ever-ready Dryden team would have been ready to host the veteran orbiter for up to a week of processing and preparation for her cross-country journey on top of the Shuttle Carrier Aircraft, as they did for her previous landing at the conclusion of STS-128.

“We’re on standby 24/7 from launch until landing. Every morning, the Landing Support Office has a telecon. We have all the [CONUS] sites [on the telecon], so we have KSC, WSSH, and us,” noted George Grimshaw, Chief of the Shuttle and Flight Ops Support Office at Dryden, via an exclusive interview with NASASpaceflight.com’s Philip Sloss.

“So they provide us mission status, they give us our weather forecast for the next two to three days, and then they typically give us the PLS (Primary Landing Site) assignment.

“Typically, by the day that you’re having the meeting, you already know who PLS is, unless there’s been a change – [in which case] they’ll typically sent out an email saying ‘the weather has changed, so we’re changing the PLS site.’  Typically, it stays the same, and then during that telecon they’ll give you [who is] PLS for tomorrow and they’ll typically throw in the next couple of days just for planning purposes.  If you looked at it, we’re PLS about 80 percent of the time.

“Two hours before landing, they [the Air Force] turn the airfield over to us. At that point, all of the aircraft operations on base come to a halt. When we give them the word that it looks like we might get called up, if they have any airplanes up flying, whether they are Air Force, NASA, other tenants here on the base, they call all those people back in and they get them on the ground here or at another airfield, and then two hours before landing they turn it over to us.”

Had Discovery headed to California, she would have landed on the temporary concrete runway – either 22 or 04 – as would have been the case for STS-130. The main concrete runway, Runway 04R/22L (the “outside” runway), is undergoing another period of maintenance

“With two [concrete] runways – and of course now the main runway is closed – if we have two runways available, then they can open up the other runway up for limited operations,” added Mr Grimshaw, who went on to explain their landing day schedule.

“Typically what happens is, the navaids and landing guys come in five hours before landing. They have to be out there (on the runway) and have all their stuff set up and ready to go  We have a T-38 and one of the STA airplanes comes in, they’re flying approaches and checking out the weather – and so they like to fly those systems and that way they can make sure the word gets back to the crew (about) what they’re experiencing and how things are looking.

“The rest of the convoy will typically come in about four hours ahead of time. The (convoy) vehicles are pre-staged for the most part. They can come in, they can start them up, they can do any systems checkouts that they need to do…and be ready to roll to when it’s time to roll. Basically, they like to have them in place and staged for the landing within an hour before the landing.

“Typically, they’ll start the burn as the convoy commander is doing his briefing at the fire station, and then the guys drive out (to the runway).  And that’s another impact to the base – that hour before landing, there’s no movement on the airfield. If you’re not on base, you’re not coming on the base.”

Had Mr Lunney made a decision to send Discovery for a short vacation in California, communication would have played a major role for the Dryden team, from deorbit to landing.

“That’s one the roles that I play in our mission control room here. I’m the communications link between the flight director and the convoy commander during de-orbit burn through landing and even post-landing,” added Mr Grimshaw.

“We have the air-to-ground links established, so when the convoy commander is talking to the vehicle commander – the Shuttle commander – they’re doing that over air-to-ground. And they typically pipe that information from Dryden back to JSC and I think to KSC.

“In the control room, I have the flight director net, I have all the nets, everything, but the convoy commander doesn’t have that. He has the air-to-ground (and) he has all the convoy nets – he has the command net, we call them the purge and cooling nets. The convoy commander operates on (the) command net, USA ops – who is the USA equivalent of the convoy commander – operates on purge, and then the cooling net is just a backup net.”

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STS-131 Landing:

Unacceptable weather conditions put pay to both KSC opportunities, which would have seen Discovery take in what is currently scheduled to be the last descending node entry – pending manifest slips or additional flights past the summer months – which will take passes over numerous American towns and cities for the first time since Columbia.

For the second of the two landing opportunites, flight controllers left the wave off decision to the latest possible moment, as conditions initially improved, before low cloud and fog passed over the Shuttle Landing Facility (SLF).

EOM+1 (End Of Mission Plus One Day) will include landing opportunties at the Dryden Flight Research Facility (DFRC) at the Edwards Air Force Base (EAFB), along with several KSC options – which will once again take in an overhead return over a large part of the United States.

Interestingly, if Discovery is forced to land at Dryden – and thus spend around a week in California for ferry operations - this will delay the turnaround of STS-131′s MPLM Leonardo, which is scheduled to be modified into a PMM for STS-133 – already under the constraint of a tight schedule.

STS-133 is currently scheduled to be the last flight, although major delays are expected for the preceding STS-134 – due to its AMS-2 payload problems during ongoing testing – resulting in a major manifest meeting this week. Ultimately, managers always prefer to land the orbiters at KSC to avoid additional processing turnaround issues.

STS-131 Specific Articles: http://www.nasaspaceflight.com/tag/sts-131/

Discovery DLI Review:

Discovery undocked from the International Space Station on Sunday, following a Docked Late Inspection (DLI) on the orbiter’s Reinforced Carbon Carbon (RCC) and critical Thermal Protection System (TPS).

Thanks to the fine efforts of the Damage Assessment Team (DAT), Level I, Level II and the peer review of all the imagery taken via the Orbiter Boom Sensor System (OBSS) – and downlinked via ISS Ku-Band assets due to the unavailability of Discovery’s own Ku system – was completed in an extremely prompt manner, clearing the orbiter for entry.

“LESS/RCC team cleared all late inspection regions of interest,” noted the DAT presentation (L2) on what was an increase number of ROIs (Regions Of Interest) – higher than the four previous flights, potentially due to the difference between nominal and docked Late Inspection techniques.

However, none of the ROIs were of any concern, which baseline imagery showing no change to the most obvious areas of “damage” – all of which are cosmetic and minor.

“Level 1 review by PRT completed at 7:30 pm (4-16) evening. Level 2 completed at 6:30 am (≈23 hrs from start of data review). Final PRT Review completed at 9:15 am (4-17),” added the presentation. “No ROI exhibited any damage characteristics. From all of the late inspection LDRI imagery. LESS PRT is GO for entry.”

STS-131 High Level Undocking Review:

Discovery then enjoyed a nominal undocking, completing a one and a half lap flyaround of the ISS, prior to separation burns that increased the distance between the two spacecraft.

“Orbiter performed the maneuver to the undocking attitude using VRCS (Vernier Reaction Control System) control. It was nominal,” noted an expansive Mission Evaluation Room (MER) report (L2). “After physical separation, the Orbiter DAP (Digital Auto Pilot) commanded 4 +pitch firings to stop the pitch rate from the spring pushoff. Single -X translation and +X translation pulses were commanded by the crew during this period.

“There was no issue with these firings. They are allowed within the procedures and are covered by the separation database used for pre-flight analysis.

“Orbit IGN&C performance was nominal on FD13. The Orbiter took attitude control with DAP A12/AUTO/VRCS at GMT 107/11:33:23 and the maneuver to undock was initiated at GMT 107/11:35:11. The maneuver took approximately 33 minutes and DAP B12 was selected at GMT 107/12:08:20.

“The DAP was moded to FREE at GMT 107/12:19:56 to power up the Primary Reaction Jet Drivers (PRJDs). The DAP was moded back to AUTO at 107/12:21:18. The DAP was moded to FREE at GMT 107/12:49:26 for the undocking. Rate errors at FREE drift were -0.001 deg/s Roll, +0.008 deg/s Pitch, and +0.0008 deg/s Yaw.

“Physical separation occurred at GMT 107/12:52:21. The flyaround began at GMT 107/13:20:32 and was completed at 107/14:13:20.”

The Rendezvous and Proximity Operations Program (RPOP) also reported a nominal undocking via the MER summary report.

“The RPOP team supported STS-131 rendezvous tool checkout procedure and undocking and separation flight phase on FD13 from the Mission Evaluation Room (MER) in Mission Control Center (MCC). The tool checkout was performed soon after hatch closure.”

“Ground monitoring software indicated the Trajectory Control Sensor (TCS) was performing nominally and the crew reported tool checkout was successful. Undocking and separation was performed about two hours after hatch closure. Based on ground data and crew call-downs, RPOP performed as expected. TCS also appeared to perform nominally based on ground data.”

“Flyaround was nominal. It began just outside the CG-CG range of 400 ft. A CG-CG range > 600 ft was reached prior to -RBAR crossing. Loads on US PV arrays were very low, due to the lack of Y firings,” added ISS structures. “Peak loads on any ISS hardware occurred on the Progress PV arrays for the vehicle on the DC1 nadir. The interaction equation results for these arrays were approximately 21 percent of the limit load constraint.”

Flight Day 14 Checkouts:

As scheduled, Discovery’s crew checked out the orbiter’s Flight Control Surfaces (FCS) and Reaction Control Systems (RCS), while completing the Group C powerdown to conserve cyros in her Fuel Cells and cabin stows ahead of entry.

Auxiliary Power Unit 1 (APU 1) was powered up to supply life to the hydraulic systems that will allow Discovery to transition from her spacecraft phase into that more accustomed to an aircraft, the checkouts were nominal.

All of 38 primary thrusters were pulsed, twice, to check they were also in good working order ahead of their use for Discovery’s dive back towards Earth. Again, no problems were reported.

Thanks to a post undocking water dump, Discovery’s life support systems are all in a nominal condition. The orbiter has plenty of water in stock and – unlike STS-129 – has no problems with her Waste Water System, which blocked during the final part of Atlantis’ mission.

“All Life Support Subsystems are working nominally. Life Support console working no issues,” added MER status. “Total GN2 = 232.0 lbm Total Water = 594.5 lbm Total Waste Water = 15.1 percent (28.2 lbm).”

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STS-131 Latest:

Flight Day 13 marked the final middeck transfers between the Station and Discovery, which were 100 percent completed well ahead of the crew’s farewell ceremony.

High praise for the STS-131 crew was provided by ISS commander Oleg Kotov, who thanked the crew for their excellent work during the docked phase of the mission.

“This is the time when we have to say goodbye. Excellent crew. Discovery 19A did excellent job, enjoyed working with them, really sad to let them go, but it’s time,” noted the Russian commander. “Thank you very much for your help and the job you did for us.”

“Wonderful stay for the shuttle Discovery crew. Thanks for the preparation and prepack you did,” noted STS-131 commander Alan ‘Dex’ Poindexter in returning the compliment. “You treated us with the utmost hospitality. Three outstanding EVAs and great robotics. Thanks for the help with transfers.

“We’re sorry to go, we’d all like to stay much longer. With that we’d like to say thanks and see you back home.”

Hatches on the Shuttle and Station side were then closed – prior to depressurization of the Pressurized Mating Adaptor (PMA), as Discovery’s crew started Rendezvous tool checkouts on the orbiter. A one and a half lap flyaround of the Station followed shortly after undocking, providing a stunning survey of the orbital complex.

STS-131 Specific Articles: http://www.nasaspaceflight.com/tag/sts-131/

STORRM DTO:

The crew were requested to take close-out photographs of docking target after hatch closure, as part of a Detailed/Development Test Objective (DTO) known as STORRM (Sensor Test for Orion RelNav Risk Mitigation), which would have provided help for Orion’s docking to the ISS, prior to its demotion to the role of an ISS lifeboat.

However, it will aid future commercial spacecraft that are set to visit the station in future years.

“STORRM DTO #703 Docking Target Installation: Background: Relative Navigation sensors for Orion vehicle require special ‘reflectors’ on the PMA-2 docking target,” explained STS-131 Flight Readiness Review (FRR) documentation on L2.

“DTO #703 (post-undocking re-rendezvous) slated to fly on STS-134/ULF6. STS-131/19A will fly and transfer STORRM DTO docking target reflectors to ISS. ISS crew will install reflectors and STS-131 crew will take close-out photographs of docking target after hatch closure (prior to undock). STS-132/ULF4 team is aware of the docking target changes.

“Sensor Test for Orion Rel-Nav Risk Mitigation (STORRM) DTO. Advanced relative navigation system test similar to DragonEye and TriDAR. Baseline system for Orion.

“STS-131 (Launch – April 5): Install reflective elements IVA. STS-134 (Launch ~ July 29). Primary DTO tasks. Laser system in TCS slot, recorder on sidewall. Data collection during docking, undocking, and re-rendezvous. STS-133 (Launch ~ Sept 16). Remove reflective elements IVA.”

The final simulation run using the GNS simulator at the Johnson Space Center (JSC) was carried out on Friday, which related to data recording session for STORRM’s role on STS-134.

“Starting this Friday, the GNS will no longer be scheduled for training events,” pre-empted an associated memo (L2) about the end of GNS’ operation lifetime. “It will not be dismantled yet since the future of Human Space flight is still very dynamic.”

TriDAR Status: 

An interference on a cable caused issues with the latest test of the TriDAR system, which debuted during the Approach Rendezvous and Docking (AR&D) phase of STS-128, when Discovery helped verify the performance of Neptec’s vision system for unmanned AR&D via a DTO.

“TriDAR System Overview: Guidance sensor for Rendezvous and docking. Bearing and range up to >3km. 6-DOF relative pose, rates from 3D data up to 200m. Uses target geometry, no cooperative targets,” noted a system overview presentation (L2).

“Combines the sensor with embedded tracking software. Sensor includes triangulation and LIDAR 3D imaging in a single optical path. Optimal performance at both short and long range. Thermal imager added for long range bearing. Largely based on OBSS Laser Camera System (LCS).”

While the system worked well on STS-128, the problems during STS-131 were noted in a MMT (Mission Management Team) presentation on the TriDAR’s issues during Flight Day 3.

“Summary of Events: Initial powerup issues with CB labeling. TriDAR procedures show correct SW PWR 3 labeling. CB was closed during TriDAR activation to correct config. Successful TriDAR activation following CB reconfig,” the presentation (L2) outlined.

“TriDAR communications issue: A/G call informed TriDAR that comms status indicator was yellow indicating loss of comms between PGSC and TriDAR unit. Signature indicates RJ45 cable may not have been seated correctly. Cable was reseated and PGSC TriDAR SW was restarted successfully. Aft Main B power telemetry indicated that TriDAR operated normally for approximately 2 hours following restart.

“Following RPM (R-bar Pitch Maneuver), ground telemetry indicated that nominal operations ceased (confirmed by A/G call post dock). Cause undetermined at this point (waiting for TriDAR PGSC log data).”

Despite the cable issue, TriDAR did provide useful data during Flight Day 3′s Rendezvous with the ISS. As part of the investigation, focus was placed on bringing the system back to full operation for undocking and flyaround.

“Focusing on ensuring undock and flyaround activities. Working to streamline troubleshooting procedure,” added the presentation. “Ground telemetry indicates that TriDAR collected required data until RPM. Undock should cover the ranges missed during rendezvous.”

With the root cause confirmed as cable interference, the plan for undock involved obtaining the backup LCS cable and using it in place of the prerouted TriDAR cable, as they are identical.

The crew’s activation and deactivation procedures were modified accordingly, hopefully resulting in a nominal performance of the TriDAR system.

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STS-131 MER Status:

No new MER (Mission Evaluation Room) items or funnies (minor issues) have been added of late, as crewmembers overcame issues with the unberthing of the MPLM from its Common Berthing Mechanism (CBM) on Flight Day 11.

“The mission continues to progress satisfactorily. KSC Landing is currently scheduled for Monday, April 19th at 0853 EDT with a second attempt at 1028 EDT,” noted the NASA Test Director (NTD) status on Friday. “Flight Days 11 & 12 (4/15-4/16) Completed: MPLM egress. Post EVA EMU reconfiguration. MPLM uninstall from ISS and installed in the Orbiter payload bay.”

The problem with unberthing related to the Control Panel Assembly (CPA) on the CBM, with one of the 36 connectors suffering from an electrical issue.

“While activating the CBM for MPLM uninstall, we experienced a communication error between the Int MDM and CPA 4. This was preceded by a Latch 2 failure annunciation,” noted Flight Director Bryan Lunney via a memo acquired by L2. “Attempted to reactivate on CPA 1, but was no joy.

“After (we) unpowered the system, the crew demated and remated all of the connectors. They noted that a set screw on the Port CPA connector had sheared off. They reported the wiring was intact, so they taped up that connection and reported it was not moving (ie. Good tape job).

“Reactivated the system on CPA 3 and is communicating with CPA 3. However there (was) some conflicting data, (worked) through malfunction procedures to resolve the unexpected indications.”

Eventually, engineers were confident the system was in a nominal condition to continue with the unberthing, which was completed late in the Flight Day. The CBM will continue to be checked out ahead of its next role, hosting a Japanese HTV cargo ship in 2011.

“The MPLM grapple and uninstall was successful. The MPLM has been maneuvered to the MPLM Low Hover position and will remain there during crew sleep,” noted GNC notes. “The SSRMS grappling of the MPLM was delayed approx. 6 hours due to ISS Common Birthing Mechanism (CBM) issues and troubleshooting.”

Meanwhile, mystery still surrounds the identity of the object seen departing from the aft of Discovery’s Payload Bay during EVA-3. Likely to be insulation from the returning Ammonia Tank Assembly (ATA), NASA advised the United States Strategic Command (USSTRATCOM) of the incident, in order to potentially track the object.

“At 103/09:35:58 GMT (07/23:14:33 MET), a bright object was observed on video departing from the aft Payload Bay (PLB). The object appeared to be moving quickly with a departure direction of radial up and out-of-plane with possibly a small posi-grade component,” noted the MER manager.

“Identification of the object was not possible. The crew has verified that all Extravehicular Activity (EVA) tools have been accounted for and the United States Strategic Command (USSTRATCOM) was notified in an attempt to track the object. Tracking may not be possible, but USSTRATCOM is expected to provide an answer within a couple days.”

Discovery herself continues to perform extremely well, with all major systems showing no sign of problems ahead of departure from the ISS on Saturday morning.

“All DPS (Data Processing System) systems performing nominally. All passive thermal control systems are currently maintaining temperatures within acceptable temperature limits,” added MER status to the Mission Management Team (MMT).

“All thermal systems are performing nominally and all temperatures are within acceptable limits. Cycling has been observed on the “A” system on the airlock structural zone 1 heater. The heater was enabled to “B” only as part of the checkout of this heater system.”

And despite the troublesome return of the MPLM, the extra docked day has allowed for the transfer tasks to continue on schedule, with just minor middeck returns from the ISS being worked by the crew, along with the return gift of water from the orbiter.

“The first Payload Water Reservoir (PWR) was filled at 104/10:01 GMT [08/23:39 Mission Elapsed Time (MET)] with 20.3 lbm of water. The sixth Contingency Water Container (CWC) was filled at 105/07:55 GMT (09/21:33 MET) with 96.0 lbm of water. A total of 889.5 lbm of water have been transferred to the International Space Station (ISS) in the five CWCs, eight CWC-Iodines (CWC-Is), and one PWR thus far in the mission.”

STS-131 Specific Articles: http://www.nasaspaceflight.com/tag/sts-131/

DLI Complete:

Most impressive was the completion of Docked Late Inspections (DLI) three hours ahead of schedule, especially considering the very late finish to the previous Flight Day.

With procedures uploaded and discussed with the crew in a timely manner, surveys of the starboard and port wings – along with the nose cap – showed no signs of concern with the potential challenges of tight clearances between the booms and Station modules.

DLI was called for after the Ku downlink ability was lost on Discovery, requiring the use of the Station’s Ku assets for downloading the vast amount of imagery of the orbiter’s Thermal Control System (TPS).

“The main activity for FD12 will be the Docked Late Inspection (DLI) survey for the Reinforced Carbon-Carbon (RCC) Leading Edge Surfaces. This survey is normally conducted after undocking,” added the MER. “However, the failure of the Ku-Band antenna earlier in the mission precludes video downlink of survey imagery while undocked, and performing the survey while docked allows the video imagery to be downlinked using ISS assets.

Challenges were noted for the positioning and translation of the Orbiter Boom Sensor System (OBSS) – relating to clearances between the boom’s movements and the Japanese Pressurized Module (JPM) – which required managers to work on procedures.

While a previous DLI had taken place with Endeavour on STS-123, the addition of the JPM to the Station complex required additional thought for the robotics teams on the ground.

Utilizing a plan that was set to debut on the final mission to the ISS – which will end with the OBSS being left on Station – a plan was soon created, and carried out to the letter early on FD12.

“On behalf of the ground control team, we really appreciate all the hard work. Outstanding job,” noted Mission Control in Houston at the conclusion of DLI, with STS-131 pilot Jim Dutton returning the thanks. “Thanks to the team for the early procedures and yesterday’s tag up.”

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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.”

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EVA-3 Preview / EVA-1 Comm Issue Review:

Flight Day 9 (FD-9) marked the third spacewalk of the STS-131/19A mission. The EVA wrapped up Removal and Replacement (R&R) operations of the ATA on the S1 truss of the ISS as well as the performance of several Cat-2 and Cat-3 EVA objectives.

Following issues with a troublesome bolt used to anchor the new ATA to its berthing location on the S1 truss, EVA crewmembers Rick Mastracchio (EV-1) and Clay Anderson (EV-2) picked up two tasks that were deferred from EVA-2 because of time constraints on the previous spacewalk.

These two tasks – fluid line connections to the new ATA and the retrieval of now-unnecessary MMOD (Micro-Meteoroid Orbiting Debris) shields for the Quest Airlock – although there have been notes of a problem with a valve on the new ATA that requires evaluation.

Under standard mission timelines, Rick Mastracchio and Clay Anderson’s spacesuits (or EMUs as they are known within NASA) underwent pre-EVA purges just under two hours prior to the start of EVA-3.

EVA crews tend to work ahead of the planned timeline, as was the case with this spacewalk, which beat the scheduled start time of 3:16a.m., by 45 minutes.

Pre-mission timelines indicate that four (4) tasks scheduled for EVA-3 are classified as Cat-3 objectives, the lowest EVA Category for the STS-131 mission.

As such, the CP13 ETVCG light, SPDM (Special Purpose Dexterous Manipulator) CLPA1 installation, EP1 cover removal, S1 radiator GF beam installation, and/or WIFEX release tasks could be deferred to a stage (ISS crew) EVA or to one of the next two Space Shuttle missions in order to accomplish the fluid line connections to the new ATA and retrieval of the MMOD shield objectives.

Regardless, the primary activities (in order of performance) were the stowage of the AGB, preparation of the LMC (Lightweight Multi-purpose support structure Carrier) for old ATA berthing, installation of the old ATA onto the LMC for return to Earth in Discovery’s Payload Bay, FGB removal and stowage, setup of the SSRMS (Space Station Remote Manipulator System) for LWAPA (Light Weight Adapter Plate Assembly) retrieval, LWAPA retrieval, SSRMS cleanup, and Airlock ingress.

Due to more trouble with a bolt during ATA installation into the LMC, the LWAPA tasks were deleted from the EVA. Instead, get-ahead work was carried out on work for a space-to-ground antenna, which will arrive on STS-132.

The entire EVA lasted approximately 6.5 hours and wrapping  up around 8:38a.m. EDT – with mission controllers calling the due “EVA superheroes” for their work during the three spacewalks.

With the completion of EVA-3, the two EMUs will be de-serviced and prepared for transfer back to orbiter Discovery on FD-10. The Discovery crew will then head to bed at 3:21p.m. EDT.

Meanwhile, ground controllers have reviewed Comm (Communications) issues experienced during the first EVA for the STS-131 mission.

“EVA-1 Intermittent Loss of Left Ear Audio: At the very end of EVA1, EV1 (CM Mastracchio) experienced intermittent audio drop out in left ear when he turned his head,” notes a status update from the Mission Management Team (MMT).

Following the EVA, the CCA was inspected for any moisture and MBED integrity.

The presentation notes that moisture could lead to potential failure modes of the CCA because of “wiring problems in the CCEM crossover cable.”

A backup CCA was used for EVA-2 and will most likely be used for EVA-3 as well.

STS-131 Specific Articles: http://www.nasaspaceflight.com/tag/sts-131/

TPS DAT Cleared for Reentry:

Meanwhile, while Discovery’s Flight Crew worked tirelessly in orbit, the Damage Assessment Team (DAT) completed their task of reviewing all imagery assets associated with Discovery’s Thermal Protection System (TPS).

Following additional thermal and trajectory analyses surrounding three of the four damaged areas on Discovery, the team reached the unanimous conclusion that Discovery’s TPS could be officially cleared for reentry.

The first area of Discovery’s TPS to gain note in the final and comprehensive DAT presentation were three (3) small areas of tile damage clustered together on the vehicle’s Left Hand (LH) OMS Pod.

“OMS Pod Damages 550-001, -002, and -003: Tile substrate is exposed and AFD photos identified damage depths to be shallow,” notes the final DAT analysis – available for download on L2.

Further assessment of the area revealed that all safety margins are maintained in that area of the vehicle despite the cosmetic damage to the OMS pod tiles.

The second region of discussion in the DAT presentation was the Rudder Speed Brake (RSB) trailing edge tile liberation.

As expected, this area has been cleared of any concern due in large part to the fact that this area of the vehicle experiences higher temperatures during ascent than it does during reentry.

“Structure Maximum Temperatures Ascent: Aft closeout structural temperatures exceed the RTV, aluminum and structural adhesive limits,” notes the DAT presentation.

No temperature or structural exceedances were identified underneath the undamaged TPS areas in the region.

Moreover, “Structure Maximum Temperatures Entry: No Structural or TPS temperature exceedances were identified during entry.”

Further aiding the positive results for the RSB’s trailing edge is the fact that the RSB remains in the closed position from the De-orbit Burn (at Mach 25) until the Mach 10 region, creating a “low heating” environment during the plasma stage of reentry.

Additionally, the RSB trailing edge is “a lightly loaded structure that is the end of the cantilever aero surface and is not part of the load path of the RSB main torque box – i.e., it is structurally isolated.”

Therefore, the RSB trailing edge does not take the brunt of the RSB structural loads, only local aero loads.

“Disbond of closeout does not reduce trailing edge panel capability and propagation of disbonding (during reentry) is not credible,” notes the DAT presentation.

Furthermore, the surrounding TPS as well as the intact portion of the partially liberated TPS tile will remain intact during reentry.

The presentation also notes that “Entry RTV bondline temperatures are below certification.” Thus, the partially liberated RSB tile is not a concern for reentry.

Lastly, the final area of Discovery’s TPS to gain mention in the comprehensive DAT report is a protruding AMES gap filler (G/F) on the left hand side of the orbiter’s FRCS (Forward Reaction Control System) – specifically, its potential liberation properties during reentry.

“Window Summary – Window PRT Assessment: Potential for G/F to liberate during entry,” notes the DAT summary.

While Discovery’s reentry attitude precludes the possibility of the G/F impacting windows #1 and #2 (the two windows to the Commander’s left) should the G/F liberate while Discovery is travelling below Mach 2.5, the G/F does hold the potential to impact the windows during a liberation event between Mach 6 and 2.5.

“Thermal panes protect for descent temperatures which subside ~Mach 8. Panes start experiencing burst loads after Mach 4,” notes the DAT presentation.

“Based on previous window impact tests, it is possible the G/F could create damage to the pane exceeding maximum flaw depth allowable for descent.”

While the likelihood of a G/F impact creating a “through hole” is classed as “unlikely,” a shallow angle (~10 deg) low mass (0.0008 lbm) impact at a velocity of ~1,050 ft/sec at or above Mach 4 could cause damage to the outer thermal pane that could propagate during Mach 4 flight burst loads.

“In the event damage occurs at any of the Mach #’s and flaw propagation occurs, it would manifest itself in the form of cracks radiating from the impact site, when subjected to burst loads,” notes the presentation.

In the event that this was to happen, the thermal pane is expected to remain intact and retained in place with a fairly nominal view across the window.

Therefore, the event would be “non-catastrophic” and is thus deemed an “acceptable risk for entry.”

Likewise, should the G/F liberate and strike the LH OMS pod, WLE RCC (Wing Leading Edge Reinforced Carbon-Carbon) panels, or the RSB, “No structural damage (is) predicted.”

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