STS-135: Atlantis completes TCDT – External Tank death camera ready
With her team ably dealing with the usual pad flow hiccups, Atlantis is heading towards her July 8 launch date with no major issues, with the Terminal Countdown Demonstration Test (TCDT) completed on Thursday. While inspections continue on the numerous stringers on Atlantis’ External Tank (ET-138), work on the camera modification – designed to film the tank’s destructive re-entry – has been completed.
STS-135 Pad Flow Latest:
The TCDT – otherwise known as S0017 operations – is a full scale dress rehearsal for the big day, allowing the STS-135 crew to conduct Emergency Egress Training, along with suiting up and ingressing Atlantis for a simulated countdown. The operations began at 7:30am local time on Wednesday, ending with a simulated countdown to T-0, marked at 11am local on Thursday.
Atlantis’ engineers also met with the crew at the TCDT L-1 meeting on Wednesday, briefing the astronauts on the health of their orbiter. The meeting discussed the brake fire from Endeavour’s landing on STS-134 – of which there are no real concerns – through to ongoing work with the Main Fuel Valve (MFV) replacement on SSME-3 (Space Shuttle Main Engine).
The engineering teams also presented Commander Chris Ferguson and his crew with a large cardboard key to the orbiter with all the systems engineers signatures on it.
Meanwhile, teams are continuing to secure Atlantis’ payload, known as S0600 Vertical Payload Operations. This included work on the Orbiter Boom Sensor System (OBSS), which was observed to have an issue with a camera on Sensor Package 1.
“The Remotely Operated Electrical Umbilical (ROEU) mate/functional checkout and the Pico-Sat Solar Cell (PSSC) installation were completed,” noted the NASA Test Director (NTD) report (L2). OBSS Sensor Pack 1 and 2 update: During testing of OBSS Sensors, problem with camera on SP1. I Iris will open and close manually but will not respond in auto.
“Potential removal of SP1 and return to Flight Crew Lab to verify whether the Test controller box or the Camera that is discrepant. There is a spare camera on site if it is required.
“There was a galled nut plate discovered during the installation of the RMS Sideview Camera (RSC), and it has been repaired. As a result, the RMS side view camera and thermistor testing have been rescheduled to Friday.”
Technicians are also carrying out methodical inspections of ET-138’s flanges, scanning the Thermal Protection System (TPS) foam for signs of cracks in the underlying stringers. The checks are being carried out after last week’s Tanking Test, so as to ensure the radius block modifications have provided the expected protection against the problems suffered by sister tank ET-137.
“Supported the successful tanking test. Electrical, propulsion and thermal were all nominal performance. There is no evidence of any off-nominal structural performance at this time,” noted ET management on the Shuttle Standup/Integration Report (L2). “The Failure Investigation Team (FIT) inspection did not show any anomalies.”
So far, NDE (Non Destructive Evaluation) inspections – carried out via the use of X-Rays and Backscatter equipment – have found no issues with the LO2 flange, which is the main area of interest. Scans are now taking place on the lower LH2 flange on the Intertank, which are expected to wrap up by the end of the week.
“ET NDE operations: NDE X-rays are in work and will continue through the week. The NDE on the LO2 flange was completed,” added the NTD report. “The equipment and ET access platforms were re-positioned and NDE on the LH2 flange is in work. No problems have been detected on the x-rays that have been analyzed to date.”
While the Tanking Test found a problem with the MFV on SSME-3 (see left), with work continuing on installing a replacement valve, another smaller problem was found with an indicator on LO2 17 inch disconnect valve.
“Had a small valve problem during the tanking test on PD #1, which is the LO2 17” disconnect. It has two position indicators for the “Open” state. The “B” indicator did not come on. It was working last week. It was cycled a couple of times, but still did not work,” noted the Orbiter Project Office (OPO) on the Standup report.
“The team will troubleshoot the problem to try to recover the indication. If they cannot, LCC (Launch Commit Criteria) is one of two, so it would still be “GO” for launch.”
This issue, charged as IPR-45 (Interim Problem Report), now has a root cause, found by engineers out at Pad 39A during their investigations into the problem, while preparations are being made for the retests on SSME-3’s MFV (IPR-49).
“IPR 0045 PD1 LO2 17” disconnect open B indicator update: Troubleshooting revealed faulty wiring. R&R of the connector and associated wires in work,” added the NTD. “IPR 0049 SSME MFV R&R update: Replacement MFV installation was completed. The wire harness connector and associated wires were R&R and reconnected to the valve. The retest is scheduled for next Wednesday.
“MFV retest is currently scheduled for this weekend and will include SSME 3 FRT and He Signature test.”
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ET Camera Mod:
As previously reported by this site, managers have approved a modification to the External Tank camera which is mounted inside the tank’s liquid oxygen (LOX) feedline fairing. The modification will allow for continuing footage of the tank, after separation from the orbiter, through to re-entry.
The modification involved the rewiring of the camera’s battery pack – specific to the G-Switch timer activation – allowing it to film from lift off, through ascent to MECO, but then allowed to continue operating through until the ET breaks up – depending on how long the camera survives as the tank re-enters.
This modification work has since been carried out at the pad during the continuing NDE inspections of ET-138’s stringers, with retests conducted on Thursday.
“PRCB request to assess feasibility of leaving LO2 feedline camera on and recording the downlink TV signal for as long as possible until ET entry and/or breakup,” outlined a Program Requirements Control Board (PRCB) presentation on the modification’s approval. “Receiving facilities must be able to receive and record analog FM TV signal.
“Two parts to the problem: Coordinate with countries regarding transmitting in airspace. Disable ET FL Camera timer that would otherwise turn the camera off at L+15 mins. Identify and secure receiving stations along ET flight path.”
Due to the lack of TDRS ability as an “overhead option” – given they are not configured to receive analog FM TV – a Special Temporary Agreement (STA) was submitted to National Telecommunications and Information Administration (NTIA) for 30 days beginning July 8 for European airspace transmission, with an agreement reached with DoDand Germans.
Work had also begun to re-activate Diego Garcia (REEF) ground station, while Navy ship-based assets are still being investigated. Aircraft options, such as the P3 Orion, were classed as unavailable.
With the aforementioned work in place, and the camera transmitting through until the tank’s destruction, the opportunity to gain first-of-its-kind imagery of a tank’s death plunge is now on the cards. However, it is questionable as to the quality of the footage.
“It is presumed that after EI (Entry Interface) a plasma sheath will envelope the tank and either prevent or make very difficult any subsequent TV signal transmission and reception,” noted the PRCB presentation. “A basic assumption has been made that any meaningful TV reception apparatus must be positioned upstream of EI.
“We have not yet been able to analytically confirm if a plasma blackout condition will present a TV reception problem prior to breakup.”
Another problem will be the tank’s tumble, given there is no attitude control for the tank during entry.
“Shortly after Orbiter sep, the tank is regularly observed displaying a slow 3-axis random tumble. The unstable attitude is presumed to continue until EI and breakup,” the presentation continued.
“Any TV reception will most likely be unpredictable and intermittent. It is unknown if the tank assumes a more stable aero attitude during entry. A fusion tool analysis has been requested using STS-134 crew handheld HD video to quantify tank tumble rates.”
From an engineering standpoint, the actual modification work on the ET camera was relatively simple, requiring only a single wire to be clipped in the electronics box to disable the timing circuit.
“Description of Change: Crit. 3 ET camera system electronics box modified to allow operational run time beyond currently designed run-time (15 minutes after g-switch activation),” noted STS-135’s ET-138 SSP FRR Presentation (all FRR presentations available on L2).
“Change requested by SSP to provide extended video of tank during re-entry / break-up. Change requires deactivating timer circuit by removing g-switch signal to logic board (g-switch wire clipped, insulated and taped). Camera operation now limited by battery life (~90 minutes).”
The approval for the modification came after the work was successfully demonstrated on a spare box at the Michoud Assembly Facility (MAF) in New Orleans.
“Rationale for Acceptance: Modification demonstrated on spare unit at MAF. G-switch verified operational prior to modification. Electronic box output verified beyond 15 minutes run time (>40 minutes before manually shut down),” added the FRR presentation.
“Electronics box lid to be re-installed per engineering requirements. RTV sealant applied to mating surface. New fasteners / loctite. Camera system open-loop functional test planned to re-verify system operation. Battery re-charged prior to launch.”
The FRR presentation also listed the expected problems with the footage, adding that technicians will attempt to record the video feed, as opposed to feeding it live to NASA TV, etc.
“Performance Expectations. Camera lens / visibility may be obscured due to TPS erosion during highheating re-entry environments. Real-time video coverage limited by ground tracking station availability. Majority of data expected to be recorded and not live feed.”
However, the PRCB presentation did add that the video of the footage will be made available, likely prior to an edit, similar to other videos recorded on orbit, prior to transmission on NASA TV.
In summary, the FRR approved the change – pending no dissent at the Agency FRR next week – with hope a good level of unique footage will be captured via the modified camera system.
“Camera System Modification Provides Robust Option to Provide Video. Coverage of ET During Re-entry,” summarized the ET-138 FRR presentation. “Modification Demonstrated on Spare Unit. Change will be Implemented via Field Engineering Change.”
(Images: Via L2 PRCB and FRR presentations. Further articles on STS-135′s status will be provided as information arrives, driven by L2′s fast expanding STS-135 Special Section which is already into the FRR content and live flow coverage, plus more. As with all recent missions, L2 is providing full exclusive level flow and mission coverage, available no where else on the internet. To join L2, click here: https://www.nasaspaceflight.com/l2/)