Results on the STS-127 stack – called for after a number of lightning strikes were registered at the pad on Friday night – had cleared Endeavour to proceed with another launch attempt on Sunday. However, poor weather near the Shuttle Landing Facility (SLF) caused another scrub, prior to coming out of the T-9 minute hold. STS-127 will make another launch attempt on Monday.
STS-127 Launch Attempt 4 Scrub:
Endeavour’s External Tank (ET-131) had been filled with LH2 and LOX, with an aim to launch at 19:13:55 local time. However, thunderstorms started to threaten the 20 mile radius of the SLF, with no sign of clearing in time for launch. As a result, the launch was scrubbed.
Endeavour has opportunities to launch on Monday and Tuesday, prior to standing down for the Russian Progress launch to the International Space Station (ISS).
Good news was at least noted during tanking, with no leaks detected on the Ground Umbilical Carrier Plate (GUCP) – as the fuel loading went into topping operations. This adds confidence the issue has been resolved via interim troubleshooting.
For all 18 NASASpaceflight.com articles on the GUCP, click here: http://www.nasaspaceflight.com/tag/gucp/
One problem that was being worked earlier in the count led to ISS managers meeting for over an hour at 2pm Central, where they discussed a sensor issue on the US side of the orbital outpost, observed during Progress 33’s rendezvous test.
Managers decided Endeavour could proceed to launch, even if this issue could not be resolved in a timely fashion. Further evaluations to take place this evening, as was planned even if Endeavour had launched.
The only problem near the end of the count was the RED weather observed near the 20 mile radius of the SLF. The landing site is required in the event of a Return To Launch Site (RTLS) abort. Ultimately, this constraint failed to clear in time for launch, leading to the scrub.
Earlier, a loose tyvek cover and an area of slush/ice were also been observed on the vehicle – and had both been cleared as a concern for launch. However, the Mission Management Team decided it would be prudent to replace the cover – as announced by NASA shortly after the crew had egressed the vehicle.
Located on the F1D Reaction Control System (RSC) thruster, the cover is designed to liberate shortly after launch, but not before – as it provides weather protection for the thruster’s nozzle/outlet.
The replacement work was to take four hours – which can fit into the normal 24 hour scrub turnaround, at least it was claimed at the time.
However, given this process required the Rotating Service Structure (RSS) to be moved back to mate – which would have required several RSS engineers to be called into work, thus placing timeline and resource pressure on the scrub turnaround – managers reversed the decision at around 10:30pm local time.
Endeavour will make a fifth – overall – launch attempt on Monday, tracking a launch time of 18:51 local. The MMT will meet at 8:45am local, ahead of tanking.
The STS-127/2J/A mission package includes the Japanese Experiment Module – Exposed Facility (JEM-EF) and the Japanese Experiment Logistics Module – Exposed Section (ELM-ES) as well as the Integrated Cargo Carrier – Vertical Light Deployable (ICC-VLD).
Endeavour has been waiting to launch for exactly one month since the opening opportunity on June 12.
STS-127 Launch Attempt 3 Scrub:
Saturday’s attempt was scrubbed during the Mission Management Team (MMT) meeting that had convened to give a go/no go for tanking.
Given the large amount of data that had to be worked through on the overnight lightning strikes, the latter proved to be the best course of action available to MMT chair Mike Moses.
Sources claimed the initial decision by the MMT was to scrub the launch, but still press ahead with the tanking of ET-131, thus providing an opportunity to build further confidence in the GUCP – which has undergone a series of troubleshooting efforts since causing the opening two scrubs.
However, the decision to place the vehicle into a 24 hour turnaround stance specifically to gain data via the electrical systems put pay to that opportunity.
“If you were here at the Cape, we had a pretty nice electrical storm. We took eleven strikes within the 0.3 miles of the pad,” noted Mr Moses after the scrub.
“If a strike comes into the 0.3 miles radius, it kicks off a formal review of the strike to determine if the strike was big enough to declare a lightning event, then we go from there.
“Of the 11 strikes, seven hit the Catenary Wire System (Lightning mast, Water Tower, wires) – the CWLIS (Catenary Wire Lightning Instrumentation System) was triggered 7 times, so we know we took 7 hits.”
Engineers have been checking electrical paths on the Space Shuttle Main Engines (SSMEs), External Tank, Solid Rocket Boosters (SRBs) and the orbiter herself.
The Lightning Protection System:
Four main systems are used to monitor, register and observe lightning strikes at the pad, namely: CWLIS (Catenary Wire Lightning Instrumentation System), LIVIS (Lightning Induced Voltage Instrumentation System). CGLSS (Cloud to Ground Lightning Surveillance System) and the OTV (Operational Television) cameras.
Observed/registered strikes at the pad result in the generation of a “Quick Look Lightning Notification Report” for any valid indication of a lightning event as seen by LIVIS or CWLIS.
Interestingly, elements of the overall lightning protection system were modified ahead of STS-117’s launch. These improvements provided an expansive overview of the systems to the Program Requirements Control Board (PRCB) in 2007.
“LIVIS Background: Designed 25 years ago as an advisory tool. Limits were originally determined through modeling and analysis. Analysis based on an anticipated transient value produced as a result of a 100KA lightning strike to the ET,” noted one of seven presentations related to the system (available on L2).
“Voltage measurements are referenced between SSV (Space Shuttle Vehicle) sense points and MLP (Mobile Launch Platform) ground, subject to ground plane changes.
“Modification: Coils placed downstream of ground points. Reconfigure existing LIVIS channels to directly monitor Orbiter Main and Preflight Buses. Physical connections made in the ITCU (Impedance Transient Control Unit). MLP 1 testing took place 5/3/07.”
“CGLSS – Cloud to Ground Lightning Surveillance System: CGLSS is the lightning detection system designed to record cloud-to-ground lightning strikes near the Pads. Utilizes an integrated magnetic detection/time-of-arrival technology.
“CGLSS reports are posted at the beginning of each hour and captures all lightning strokes (1st return stroke only) that have during the previous 60 minutes that have occurred within 5NM of Pad. Four Dimensional Lightning Surveillance System (4DLSS) being certified that will capture all return strokes.
“Evaluating the National Lightning Detection Network (NLDN) and its effectiveness at detecting and locating lightning strikes. Cape Weather provides an automated Pad Overview Plot showing position of lightning strike(s), within 0.45 NM, in relation to the Pad.
The system that gained numerous mentions from Mr Moses was the CWLIS, which is a system that provides adequate lightning detection on the lightning mast and catenary wire.
This system was verified acceptable by the Lightning Assessment Team (2006), and was not in need of modification.
“Two current sensing coils, one on each end of the catenary wire connected to high-speed digitizers. CWLIS utilizes identical high-speed digitizers as LIVIS,” noted the overview.”
Visible indications of lightning strikes are captured on numerous cameras placed in view of all areas of the pad. Ahead of STS-117, the number of cameras increased by six, as per improvements to the overall system.
“Six (6) additional OTV cameras are to be re-positioned to monitor for lightning strikes at Pad: Camera 35 and 44 monitor Fuel Storage Area. Camera 40 monitor Oxidizer – Hypergolic Storage Area. Camera 58 monitor LH2 storage. Camera 36 and 38 monitor LO2 Storage.”
The pre-set plan for a lightning strike at the pad is also noted in the system overview, which was put into action on Saturday.
“Decision Point: IF a lightning event was confirmed via LIVIS, CWLIS, CGLSS or OTV, THEN perform lightning strike work steps/data gathering and analysis, per S0018.100 Operation 20. OTV/CGLSS will be used to determine whether a lightning strike has actually occurred within the Pad perimeter,” added one presentation.
“If unable to verify that the lightning strike was outside of the Pad perimeter, and CWLIS or LIVIS indicates that a lightning event has occurred, then the conservative approach is to be taken, and the data collection and analysis process performed.
“If able to confirm that lightning strike occurred outside of the Pad perimeter and there are no CWLIS and LIVIS indications of a lightning event, then the data collection and analysis process is not required.”
The modifications allowed for that process – from the point a lightning strike is confirmed, to the point shuttle managers are able to work out their forward plan – to be improved.
“This will enable the engineering community to make well informed critical recommendations to senior management,” one PRCB presentation outlined.
“These recommendations, will in turn enable senior management to make critical decisions affecting flight status following a lightning attachment either to the SSV, or to the ground within a distance from the SSV equivalent to the average pad perimeter radius.”
Refer to live update pages – linked above – for up to the second live coverage.
L2 members: Documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.