STS-135: Initial Ascent Reviews point to superb launch performance by Atlantis

Following a typically eventful shuttle launch countdown, the Mission Evaluation Room (MER) teams have confirmed Atlantis enjoyed a flawless launch on Friday, as her crew prepare to head into Flight Day 2′s tasks relating to the inspections of the Thermal Protection System (TPS). Atlantis is currently in pursuit of the International Space Station (ISS) for docking on Sunday.

STS-135 Countdown:

Going into the Mission Management Team (MMT) Tanking and Weather Brief, most people expected the team to be a GO to tank, as much as the expected T-0 weather held little optimism of improving. This proved to be a great call by the teams.

With the tanking initiated at 0201 EDT on Friday, LO2 and LH2 reached the point of stable replenish without issue, while the Final Inspection Team (FIT) observed no areas of concern on the stack.

Hope that a gap in the weather would be available started to look realistic, as conveyed by Weather Officer Kathy Winters during the numerous weather briefings in both Florida and at the Johnson Space Center (JSC).

Atlantis also played her part, behaving well on Pad 39A during the countdown, with only one minor diva moment in the form of unexpected closure of a valve on her Left OMS tank. This proved to be her last pre-launch Interim Problem Report (IPR).

“IPR 135V-0064 taken to document an unexpected Left OMS tank A helium isolation valve changing state,” noted the NASA Test Director (NTD) report during the countdown (L2). “Initial investigation indicates this is an explained condition related to a TCS sequence running at that time.”

Engineers in the Firing Room later explained that the OMS problem came up during the normal regulator lock up operations and may not have been flagged for quite some time after it happened. It was thoroughly investigated, with results showing it was ‘offset’ by about -3 psig, which caused it to be just slightly over the maximum pressure, causing the TCS to react.

No fault of Atlantis, a LOX fuel pump then required swapping over to its redundant partner, a task completed in just 21 minutes, resulting in no ill effects during the pump’s role of stable replenish for External Tank ET-138.

Engineers explained that the LOX GSE (Ground Support Equipment) pump was switched because the bearing temperature in pump 126 was getting colder, down to about -20 degrees. This indicated a seal problem, with LOX leaking into the bearing.

Although the pump could have continued operations, the short period of time required to make the switch led to the decision it would be advisable to be using pump 127 later in the count. After the pump switch was completed, the bearing temperature started to return to normal in pump 126, allowing it to be considered as a backup to 127, thus returning redundancy.

With the weather surprisingly being just good enough for launch – based on some additional acceptance on the forecasted conditions in the Shuttle Landing Facility (SLF), had a Return To Landing Site (RTLS) abort been required – the countdown clock dramatically stopped at T-31 seconds, just prior to the Autosequence Start.

This was based on a lack of an indication that the GOX Vent Arm had properly retracted and latched, something engineers were aware could happen, but were still surprised it showed during an actual launch countdown.

Engineers from the Firing Room noted the teams were prepared for the problem and verified the arm was retracted and latched with a closed circuit camera, per criteria. Thanks to this camera, known as the OTV CICE camera, teams were able to verify the GOX position and returned to a launch stance.

It was later fully confirmed the arm was latched, but oddly neither of the limit switches – used to indicate this showed it as being latched – were showing the right indications – which has never occurred before in the history of the program.

Atlantis’ Launch:

Rising majestically one final time, Atlantis spread her wings and powered uphill with what is understood to have been one million people in attendance.

“The STS-135 mission was launched at 189/15:29:03.996 GMT on July 8, 2011, on the thirty-third Space Shuttle Program (SSP) mission of the Atlantis vehicle and the thirty-seventh mission to the ISS,” noted one of several opening Mission Evaluation Team (MER) reports (L2), which noted a nominal ascent by Atlantis, bar a couple of minor instrumentation hiccups.

“The Backup Flight System (BFS) quantities in the left Reaction Control System (RCS) fuel and oxidizer tanks were erratic during ascent. This signature has been seen on previous missions. The measurement returned to a nominal condition and did not impact ascent operations,” added the MER report.

A second report also noted the Flash Evaporator System (FES) – used to cool the orbiter’s systems prior to the opening of the Payload Bay Doors (PLBDs) – which then expose the vehicle’s radiators – also recovered from a minor issue.

“A 17F pre evap cooling was observed before the FES activation,” noted the expansive SSP MER Consolidated Ascent Report (L2) of which this article contains only highlighted snippets. “Some FES outlet temp oscillation was also observed, but it was eventually stabilized, and the FES provides nominal cooling performance.”

The audible issue heard over the loop during ascent was also only instrumentation, related to the natural strain – or ‘stretch’ on the pressurized crew cabin on the vehicle via the aerodynamic stresses of ascent.

“All Life Support Systems are nominal. Cabin Leak check was successfully completed prior to liftoff. We got a BFS (Backup Flight Software) Alarm, when the BU BFS dp/dpt went to -0.14 psi/min (limit -0.12 psi/min) during cabin stretch. Cabin Dp/dt was nominal at -0.06 psi/min. No issues are being worked at this time,” added the Consolidated Ascent Report.

All major systems used for powered flight, such as the Solid Rocket Boosters (SRBs), Main Propulsion System (MPS) and Space Shuttle Main Engines (SSMEs) performed perfectly, as has been the case for the vast majority of missions over the proud history of the Shuttle Program.

“The Main Propulsion System (MPS) performed nominally during loading and ascent operations. All Fill and Drain Valves performed nominally. The ECO (Engine Cut Off) sensors performed as expected; all checkouts and voltages were within limits with no anomalies noted,” added the MER reports.

“The GH2 and GOX pressurization system performed as expected and the GH2 FCVs (Flow Control Valves) cycled 8, 13, & 9 cycles, respectively. Post MECO dump and vacuum inert were nominal.

“The Reusable Solid Rocket Booster (RSRB) separation was visible. A nominal Orbital Maneuvering System (OMS) assist maneuver was performed following RSRB separation. Ignition occurred at 189/15:31:17 GMT [00/00:02:13 Mission Elapsed Time (MET)], and the maneuver was 96.3 sec in duration,” noted the MER reports.

However, the emotional notes from NASA managers at the post-launch media briefing, that the launch seemed to be in slow motion due to the historic nature of the final lift off, may have been ironically accurate, albeit unintentionally.

“Peak to peak lateral acceleration at liftoff was about 0.12 g which is less then the value of 0.19 g’s that could indicate a stud hang-up at liftoff. Final evaluation of hold down bolt performance depends on strain gauge analysis, and launch pad and booster skirt inspection but there is no early indication of any issues,” noted the consolidated ascent report.

“SRB performance is indicated to be nominal as shown by a value of +0.082 seconds for TDEL-ADJUST which is within the dead band for Adaptive Guidance and Throttling of +/-0.21 seconds. The first stage throttle bucket was the nominal bucket of 104/104/72/104 percent.”

Making orbit for her final time, Atlantis enjoyed a nominal Main Engine Cut Off (MECO), soon followed by the separation of ET-138, which is expected to have had its death plunge back into the atmosphere recorded via the special camera modification. Video from that event is currently being collated for editing and playback.

“Main Engine Cutoff (MECO) occurred at 189/15:37:28 GMT (00/00:08:24 MET). The External Tank (ET) separated from the Orbiter at 189/15:37:49 GMT (00/00:08:45 MET). A nominal OMS-2 maneuver was performed at 189/16:06:49.1 GMT (00/00:37:45 MET). The maneuver was 64.8 sec in duration,” added the MER report.

“The payload bay doors were opened at 189/17:03:20 GMT (00/01:34:16 MET). The Ku-Band antenna was deployed and the self-test was completed with satisfactory results.”

Flight Day 2:

With the Remote Manipulator System (RMS) checked out on orbit during Flight Day 1, the crew went to sleep ahead of a busy day of inspections on Atlantis’ Reinforced Carbon Carbon (RCC) Wing Leading Edges (WLE) and other elements of her TPS.

STS-135 Specific Articles: http://www.nasaspaceflight.com/tag/sts-135/

While the main inspections will come via Flight Day 3′s Rendezvous Pitch Maneuver (RPM), Damage Assessment Team (DAT) engineers have already gone to work on ascent footage imagery, handheld post separation ET photography, soon to be combined with the array of data which will be gained by the Orbiter Boom Sensor System (OBSS) during Saturday’s operations.

Another article will follow on Saturday.

(Images: Via Larry Sullivan of MaxQ Entertainment/NASASpaceflight.com (with thanks to Alan Walters), L2 content and NASA.gov. Further articles on STS-135 will be produced during and after her mission, driven by L2′s fast expanding STS-135 Special Section which is following the mission at MMT/MER level, surrounded by a wealth of FRR/PRCB/MER/MMT and SSP documentation/pressentations, videos, images and more.

(As with all recent missions, L2 is providing full exclusive level mission coverage, available no where else on the internet. To join L2, click here: http://www.nasaspaceflight.com/l2/)

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