Atlantis’ TPS in good shape as she hooks up with Hubble

by Chris Bergin

With the debris strike on Atlantis’ starboard chine Thermal Protection System (TPS) –  now confirmed as a liberation from an Ice Frost Ramp on External Tank (ET-130) – cleared within hours of its observation via the Orbiter Boom Sensor System (OBSS), the orbiter and her STS-125 crew have completed rendezvous operations with the Hubble Space Telescope on Flight Day 3. As of Wednesday, all areas of evaluated TPS – including critical areas such as the OMS Pods – had been deemed to be in an acceptable condition.

ASA and ET Cam Latest:

No additional anomalies of note have been recorded by the Mission Evaluation Room (MER) since Flight Day 2, allowing engineers to concentrate on evaluating the root cause of the Aerosurface Servo Amplifier (ASA) failure during ascent.

At present, the single channel failure of the quadruple tolerant system has no mission impact. However, a second failure would cause the mission to end – with a landing on the next available opportunity. A second ASA failure is highly unlikely.

Regardless, a Tiger Team level investigation is ongoing, with engineers looking at historical data and engineering records on the ASA system. It is normal for such investigations to be called – especially during a relatively issue-free mission – in order to utilize the large engineering community, gathered for mission support, to build a stock of additional data on the hardware, via what is known as “lessons learned”.

The other main issue of note relates to the troublesome ET Umbilical Well camera system, which appears to be a fleet-wide issue. Several efforts to download the images have failed, although 46 images of the separated tank are available to the crew, and will be assessed once Atlantis returns home.

“ET Umbilical Well Camera File Transfer (AR 3949). Camera failed to transfer imagery to ground,” noted last night’s Mission Management Team (MMT) overview presentation, available on L2. “Generated the same error message on-orbit that was observed during repeated pre-flight tests – ‘unable to transfer images from card’.

“Crew reported that there are 46 images on the camera as expected. Images can be obtained from the memory card post-flight. The team will assess available time at the end of FD2 to see if a follow-up attempt to download these images is possible to support the damage assessment process.”

In other news, the Solid Rocket Booster Retrieval Status lists that: “Dive operations were completed successfully yesterday (Tuesday). Both boosters are under tow; Liberty Star and Freedom Star are expected to dock this morning at 0800L and 1100L respectively. Open assessment is scheduled for tomorrow at 0700L.”

Meanwhile, the damage sustained by Pad 39A during Atlantis’ launch will not delay STS-127’s schedule – with Endeavour due to transfer from Pad 39B to 39A after STS-400 LON (Launch On Need) standdown, for her STS-127 mission next month.

“Post-launch pad securing operations, wash-downs, and walk-downs are proceeding as planned,” added processing information on Wednesday. “The team is continuing to evaluate pneumatic lines that were impacted by liberated Fondue Fyre. Initial reports indicate that the pneumatic lines can be replaced in less than a week and should be no issue for turnaround operations.”

Chine Damage Cleared/TPS Latest:

a61The images will likely confirm the current theory that the debris strike on Atlantis originated from one of the ET Ice Frost Ramps (IFRs), although this can be assessed post-mission, after it took just several hours for the DAT (Damage Assessment Team) to clear the line of TPS ‘dings’ caused by T+102 seconds (estimated) event.

UPDATE: On Wednesday afternoon, DAT images confirmed a liberation from location Xt714 on ET-130 – further information will follow via an upcoming article – 16mb DAT “full vehicle” TPS status presentation being uploaded to L2.

The damage was observed during the OBSS inspections on Flight Day 2, although at no point were members of DAT concerned with the initial observations, including it only as a note of interest in their general first look overview.

“DAT Status: Did see some indications of damage on starboard chine (21” long skip down several tiles) in FD2 inspection imagery. No issues noticed for T-0 or lower surface, but data review is in work.

“Upper Canopy Inspections Complete: No damage failing criteria was identified. Starboard T-0 inspection complete: Data review in work. Lower surface scans initiated: No obvious damages identified. Chine damage identified: 106 sec debris event. WLE (Wing Leading Edge) sensor indications.

“There were two indications from the wing leading edge sensors during ascent on the starboard chine that appear to correlate to available imagery for a noted debris event around the 106 second mark. FD2 inspections identified approximately 4 tiles in the area with dings. The tiles in this area are approximately 2.5 inches thick.”


a54The WLE indications came via a post Columbia modification called the WLE IDS (Wing Leading Edge Impact Detection System), a post Columbia modification that allows the orbiters to “feel” any impacts on their critical leading edge TPS via a network of embedded sensors.

The system is so sensitive, ‘ghost triggers’ can be registered throughout a mission via thermal conditions interacting with the orbiter’s hardware.

It was the WLE IDS sensors that likely ‘felt’ the debris impact on the chine area of Atlantis’ starboard WLE, the first of which was timed at T+104.3 seconds, measuring at 2.9 Grms – which is still a low reading, with only readings over 10 Grms usually deemed as the benchmark for an impact of concern.

The second was timed at T+120 seconds, measuring only 1.8 Grms, immediately adding confidence that the impacts were unlikely to be of a major concern.

“All WLE IDS ascent summary data were down linked and downloaded successfully,” noted the WLE IDS presentation to the MMT, available on L2. “Thirteen (13) half second windows of detailed G time histories were downloaded in order to confirm the implication of cases above 1 Grms. There are no reportable indications on the RCC. However, two (2) indications were identified on the starboard chine area.

“Overall, STS-125 background levels are very similar to background levels of previous missions. No data anomalies have been identified. All units triggered on Main Engine Ignition within 0.15 seconds of each other.”

Tyvek Covers:

a39The only other item of interest via ascent imagery related to a couple of late releasing Tyvek Covers – used to protect the Reaction Control Systems (RCS) thrusters from water and debris intrusion during the pad flow. This is also not an unusual issue, and is only noted as late releases have a small amount of potential to become debris hazards at high velocity.

The covers are designed to liberate from the vehicle within seconds of launch, however, during STS-125’s launch, a small piece of cover remained attached to the F4D thruster, before liberating later in ascent. It failed to impact the orbiter.

“Ground imagery reported that when thrusters F3D’s and F4D’s Tyvek rain covers released at 131/18:02:03.9 (00/00:00:07.9 MET) at ~150 ft/sec (~102 mph) and 131/18:02:4.4 (00/00:00:08.4 sec MET) at ~160 ft/sec (~109 mph), respectively, a piece remained attached to each thruster lip,” noted a report on a MER presentation to the MMT.

“The F3D piece separated at 131/18:02:15.2 GMT (00/00:00:19.2 MET) at ~413 ft/sec (~282 mph). The F4D piece separated at 131/18:02:15.8 (00/00:00:19.8 MET at ~428 ft/sec (~292 mph).

“The estimated size of each piece is ~2 grams, which within accepted limits. Imagery indicates that the pieces that released late did not impact the Orbiter.”

Flight Day 3 (FD3) Overview (refer to live updates for up to the second coverage):

a45During what will be an historic day for the space program, Atlantis will mark the final time an orbiter will rendezvous with the Hubble Space Telescope.

The Flight Day will consist of the rendezvous, HST’s Solar Arrays positioned for grapple by Atlantis’ RMS, HST grapple and berth on Flight Support System (FSS), the Shuttle Robotic Arm survey of HST, and an EVA 1 procedure review.

Pre-empting her arrival, the Space Telescope Operations Control Center (STOCC) at Goddard are finalizing their preparations of the Telescope for the start of its re-servicing.

“Ground Commanding: The STOCC performs several steps to prepare HST for rendezvous and berthing with the orbiter,” noted FD2 to FD3 outlines on the Flight Plan Walkthrough (L2).

“Highlights for FD2 through FN2 include dumping of onboard Solid State Recorders (SSR), closure of the aperture door (AD), maneuvering HST to the rendezvous attitude, reconfiguration of the comm. system from High Gain Antenna (HGA) to the Low Gain Antenna (LGA) direct TDRS, reconfig of three gyro operations, load shedding activity, and HGA deactivation retraction (to maximize clearance for HST grapple).

“The STOCC maneuvers HST to a rendezvous attitude designed to maintain HST power and minimize plume loading on the solar arrays (SA’s) at the 1500 foot normal Z braking gate.

“This attitude is determined by the conditions as follows: Sun in the V1-V3 plane and +V1 pointing down the R-bar at an orbit angle of 59 deg before orbital noon.

“The STOCC slews the solar arrays to 90 degrees, to provide clearance with RMS. The orbiter approaches HST using an R-bar approach to minimize prop usage and potential contamination.”

a210The orbital ballet between Atlantis and Hubble will see the orbiter approach HST from below, rising up the R-bar, ahead of capturing Hubble via the Shuttle RMS.

“Before the orbiter is within 200 feet of HST, HST performs a roll maneuver to the capture attitude to align the +V2 grapple fixture on HST with the RMS. The roll mnvr will place the -V3 52 degrees out of plane north as measured on the anti-Sun side of HST.

“The magnitude of the roll mnvr is ~ V1 = Beta – 52 degrees, resulting in a roll that ranges from 0 deg to -104 degrees. Orbiter then performs an inertial approach.

“HST Approach & RMS Capture/Berth Operations: The RMS is used for grappling and berthing the HST in the orbiter payload bay. Grapple is timed for sunset + 5 minutes. RMS HST maneuvering is done with Orbiter in freedrift.”

Hubble will then be secured on the FSS at the aft of the Payload Bay, latched into place for an imagery survey of the telescope, ahead of the of the EVA work that will result in Hubble’s life span being extended well into the next decade.

“HST Configuration at Berth: Orientation: -V3 Forward. Solar Array Position: 90 deg. External Power Activation (Crew & STOCC) – After umbilicals connected at the end of the Berth (Latch & Mate procedure), FSS Power Control Units (PCU’s) , external main power and external essential power are applied.

“Photo/TV05 Survey (-V3) via RMS and P/TV. Battery Charging – one full daylight pass. Solar Array Slew to 0 degrees in preparation for EVA 1 on FD4. Array’s are slewed after completion of battery charging and maneuver to overnight attitude (–ZLV –XVV).”

EVA-1 will begin on Flight Day 4, conducted by John Grunsfeld and Andrew Feustel – the first of five planned spacewalks during STS-125. Preparations have already begun for the opening EVA.

“Airlock Prep was completed followed by checkout of EMUs 3015 & 3017 starting at 13:37 GMT (Tuesday). All suit data was nominal & battery recharge of s/n 2080 & 2070 was completed. EMUs were then swapped out & checkout of EMUs 3008 & 3004 began at 16:39 GMT. All suit data was nominal & battery recharge of s/n 2081 & 2082 was completed,” noted a status report.

“As expected, the BATT V DECAY message was received after FAN start up on the 3 EMUs with new ICBs installed (s/n 2080-2082). The battery team has observed this signature for the new ICBs during initial cycles & determined this to be nominal.

“Cabin has been depressed to 10.4 PSI in preparation for the upcoming EVAs.”

More will follow throughout Flight Day 3.

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

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