STS-130: Endeavour beats the weather and returns to KSC
With the weather at both the Kennedy Space Center (KSC) and Edwards Air Force Base (Dryden Flight Research Facility) originally looking less than hopeful for all Sunday landing opportunities, improving conditions in Florida allowed Endeavour and her STS-130 crew can return home. Meanwhile, a third MMOD strike has been cleared, while engineers evaluated a liberation from the orbiter’s payload bay.
STS-130 Landing Status during Sunday:
A total of four landing opportunities were available for Endeavour on Sunday, two at her home port of KSC and two in California.
The weather situation was dynamic, meaning Entry Flight Director Norm Knight left it until late in the deorbit timeline before deciding to take the opening opportunity – against the odds.
For the opening opportunity, Mr Knight made his call around 8:50pm Eastern, 25 minutes prior to TIG (Time Of Ignition) for Endeavour’s twin OMS engines for the 2 minute 38 second burn that led to the orbiter starting her return home. Taking the opening opportunity resulted in a successful landing at the Shuttle Landing Facility (SLF) at 10:20pm Eastern.
A second KSC opportunity existed for Endeavour, which would have resulted in a landing at 11:55pm Eastern, prior to two Edwards opportunities – with the opening Californian option – now not taken – resulting in a landing at 1:25am Eastern, and a second one orbit later.
Edwards is home to the US Air Force’s 412th Test Wing and is currently operated by the 95th Air Base Wing. The base is strategically situated next to Rogers Lake, an endorheic desert salt pan, and is the home to NASA’s Dryden Flight Research Center (DFRC).
Had Endeavour targetted Edwards, she would have to land on the “new” 12,000 x 200 ft runway – which is shorter and narrower, and runs parallel to the main runway (15,000 X 300 ft). The temporary use of the new, smaller runway was previously required for around three flights in 2008 – while the primary runway was under repair.
Though 3,000 feet shorter than the primary runway, an orbiter will still have lots of margins for her rollout. However, as a precaution, engineers – back in 2008 – looked into the design upper limits on the amount of heat reacted in the carbon-carbon brakes, should there be a problem with the brakes during rollout. All were deemed acceptable.
Had unacceptable weather conditions wave-off Endeavour’s return to Monday, KSC, Edwards and White Sands would have been made available.
Monday was classed as “pick-em” day, with Endeavour expected to return home to one of the sites. EOM+2 (End Of Mission plus two days – Tuesday) was only reserved for a technical wave-off, based on requiring additional time to correct a unlikely issue with the orbiter.
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“There will be no more scheduled MMT (Mission Management Team) meetings for the remainder of the mission. Weather is uncertain at KSC and EDW for EOM and EOM+1,” noted the final MMT status update, available via L2 – which also noted the potential to use a “Descending Node” entry option, which would earn an additional landing opportunity at KSC.
“Current forecast is NO-GO at KSC and EDW for EOM and EOM+1, but could get better. Weather good at EOM+2 for all sites. Debating trade-offs between doing a Descending Node Entry to gain another KSC opportunity, vs prop availability and potential contingencies.”
Despite unfavorable weather forecasts all the way through Sunday, Shuttle Training Aircraft (STA) pilot Chris Ferguson noted the situation was “workable” – leading to Mr Knight making the call to take the first landing opportunity – which proved to be correct as Endeavour returned to KSC without an issue.
Although MMOD (Micro-Meteoroid Orbital Debris) strike are not uncommon, Endeavour has now suffered from three impacts – the latest on Window 1.
“MER (Mission Evaluation Room) List Items: MER-10 Window MMOD Impacts – Added Window 1 impact. No concern for entry,” noted EOM status via L2.
As with the impact to the side hatch window, and window 2 on the flight deck, engineers on the ground have cleared all three for entry, as have the DAT (Damage Assessment Team) – who’s team of engineers found no items of concern via the Late Inspection results – once again showing Endeavour has enjoyed an extremely clean mission.
All three damage sites will be evaluated once Endeavour is safely back in her Orbiter Processing Facility (OPF), with the replacement of windows almost routine for a post flight processing flow.
As has been the case throughout the mission, all of Endeavour’s systems are operating within spec – with only a handful of minor “funnies” – a MER classification for a minor problem that hasn’t been advanced to the status of an IFA (In Flight Anomaly).
Fuel Cell 2:
With a large number of funnies not even relating to the orbiter herself, the 11th note on the MER list referred to Fuel Cell 2, which failed a self-test after undocking from the International Space Station (ISS).
“MER-11 FC2 Substack 3 CPM Intermittent Self-Test Fail. Data indicates a healthy fuel cell. All other systems operating nominally,” noted MER information, which was expanded on via MMT documentation (L2).
“Problem Description: During Cell Performance Monitor Self Test at 011/18:30:39 MET(051/03:44:46 GMT) Fuel Cell (FC) 2 substack (SS) 3 Delta volts indication transitioned from a nominal value of ~24 mV to a an OSH value. At the next self test event (~6minutes, 44 seconds later) the substack delta volts measurement returned to a nominal value of ~24mV.
“An associated onboard SM alert message was annunciated at 011/18:30 MET. There were four additional occurrences with the last transition back to nominal data occurring at 011/19:57:39 MET (051/05:11:46). SM limit sensing for this parameter was inhibited onboard to prevent nuisance alarms.”
Per flight rules, controllers asked for a main bus B to C tie, to allow for monitoring of the Fuel Cell. This showed the FC was in good working order, with the issue relating to instrumentation. This configuration will remain the same until just prior to entry.
“Problem Impact/Significance: Problem: Intermittent loss of insight into FC2 SS3 delta volts measurement. Per Flight Rule A9-59 a main bus tie B to C was performed as a back up method to monitor relative FC performance. The bus tie will be broken prior to entry.
“Additionally the Flight Rule mandates a daily Fuel Cell Monitoring System (FCMS) data take. The first daily FCMS data take was performed at 051/04:53 GMT. Data indicates nominal FC performance. Significance: Instrumentation only. No impact to mission duration.
“Redundancy: Bus tie and Daily FCMS data takes. Concern is that if an individual cell were to develop a cross over condition it may not be quickly discernable. This concern is mitigated by the bus tie and daily FCMS data takes. Program experience is that the early stages of crossover are slow to develop. This Fuel Cell S/N 124 started the mission with zero hours on the stack and crossover.”
As noted by the history of Cell Performance Monitoring (CPM) issues, documentation notes this is not uncommon, and has not held any on-orbit impact.
“History / Previous Occurrences: Roughly 20 instances of CPM anomalies over the course of the program. Some of these were related to the self test function and resulted in CPM R&R. In all cases there was no impact to fuel cell life or performance.
“Current Status: CPM is currently outputting nominal readings. Post-Flight Plans: Post Flight Data Review. Possible troubleshooting. If required, the CPM can be changed without FC Removal and Replacement.”
The only other item of interest that was evaluated – and cleared – by engineers on the ground, was the observation of a FOD (Foreign Object Debris) liberation from Endeavour’s payload bay – listed by the MER as “FOD Observation: FOD Out of Payload Bay. No vehicle concerns.”
While it has not yet been determined what the object is, engineers are confident the debris is not from a critical system required for Endeavour’s deorbit, entry and landing.
“Crew Notes: FOD observed moving in formation with the payload bay, not separating from the vehicle at a high rate,” added a specific MMT presentation on the event (available on L2). “Crewmembers noted that the object appeared to be small, having striations and reflective properties.”
It appears the liberation occurred shortly after the crew berthed the OBSS (Orbiter Boom Sensor System) and RMS (Remote Manipulator System) arms after the completion of Late Inspections.
“Timeline: OBSS Boom latched at 10:18 GMT. RMS pre-cradled at 10:54 GMT. First photo taken at 11:13 GMT. Camera Information. A 200mm lens was used with to capture the images. Camera focus distance was at 19.95 meters (65.5 feet).”
The object could be one of several possible items, ranging from a spring, to a piece of hosing used to house wiring in the orbiter’s payload bay.
“Object Measurements: Length: 1.3 inches (+/- .05 inches). Outer Diameter: .27 inches (+/- .05 inches). Potential Identification. Heli-coil or spring. Hollow piece of rubber or plastic tubing. Sheared-off bolt,” added the presentation.
Although the object was photographed near the Rudder Speed Brake (RSB), the item is known not to have originated from that location. Items have been lost from the RSB in recent years, related to tabs that are used primarily for holding the vertical stabilizer in a stable configuration during ascent.
This article will be updated during the landing opportunities.