OBSS Sensor Protect for Soyuz Flyaround and WLEIDS Status Reviewed

by Chris Gebhardt

NASA is gearing up for what will be a jammed packed STS-133, along with the possibility of a Soyuz fly-around during Discovery’s docked mission still under consideration. To this end, NASA has created a plan to protect Discovery OBSS (Orbiter Boom Sensor System) sensor packages during the proposed maneuver. The vehicle’s Wing Leading Edge Impact Detection System (WLEIDS) and associated procedures have also been thoroughly reviewed.

OBSS Sensor Protect for Soyuz Flyaround:While things seem to be moving in a positive direction based on comments from Friday’s post-Agency FRR (Flight Readiness Review) in terms of a proposed plan to undock the Soyuz TMA-01 spacecraft during Discovery’s docked mission for the purpose of a fly-around maneuver, NASA is taking steps to ensure that all possible scenarios from this event are planned for prior to next week’s liftoff of the 133/ULF-5 mission.

Specifically, the Russian Federal Space Agency (RSA) is still evaluating the proposed maneuver, which would be used to gather photographic information on the health of various ISS external features (such as portions of the Integrated Truss Structure).

Of course, the fly-around would also provide a once-in-a-lifetime opportunity to photograph the International Space Station (ISS) with all five of its partner’s visiting vehicles docked at the same time. Simulation footage of the potential views from the Soyuz during the maneuver can be seen in a stunning multi-view CGI video acquired by L2 (further article will follow).

The pending retirement of the Space Shuttle later this year and the fact that the HTV-2 will have already been deorbited by the time Endeavour launches in mid-April on STS-134 means that this will be the only time in history to photo the ISS in this unique configuration.

Nonetheless, this exclusive opportunity comes with several challenges (both from the RSA and NASA side) that must be addressed prior to the maneuver, which would likely be inserted into the STS-133 mission timeline on a newly-planned FD-9 (Flight Day 9) with NASA taking the option to extend Discovery’s mission by one day to accommodate the Soyuz fly-around.

For the maneuver itself, special consideration will be taken toward protecting the sensor packages located on the end of the Discovery’s OBSS. The boom, which is critical toward detecting damage to the orbiter’s WLE (Wing Leading Edge) and nose cap RCC (Reinforced Carbon-Carbon) panels, will be required in the post-undock timeframe for the customary late-inspection.

As such, an OBSS protect document, available for download on L2, shows that Discovery’s crew – in the event the Soyuz fly-around is approved – would position the OBSS “underneath” the orbiter’s left-hand wing.

As indicated by the presentation, this would place the OBSS sensors 70-inches from Discovery’s underbelly TPS (Thermal Protection System) tiles. In all, the LCS, IDS, LDRI (Laser Dynamic Range Imager), and ITVC sensors will be “pointed straight at the belly tiles.”

Discovery’s crew will have to perform two OCAS maneuvers and one SINGLE maneuver to get the OBSS into this position. Likewise, a SINGLE maneuver and two OCAS maneuvers will be required after the fly-around to get the OBSS into the proper undock configuration.

In all, it is estimated that it will take 20mins for Discovery’s crew to position the OBSS into the proper fly-around maneuver position; twenty (20) minutes will also be required to move the OBSS into the undock position. This will subsequently require 40 minutes of crew time.

For the purposes of docked loads considerations, this maneuver will be classified as “docked viewing position, not scanning.”

STS-133 Wing Leading Edge Impact Detection System (WLEIDS) Overview:

In preparation for the upcoming second launch campaign of Discovery/STS-133, NASA has implemented a full review of the vehicle’s critical WLEIDS, a system that allows NASA engineers to assess ascent stresses on critical areas of the vehicle’s TPS (and determine if any debris impacts occurred during liftoff) as well as monitor the health of the vehicle’s TPS during on-orbit periods.

Personnel and System Overview:

According to the STS-133 Wing Leading Edge Impact Detection System Overview presentation, available for download on L2, the overall primary duties of the Ground Team (assessment team) will be to perform data assessment and reporting. 

The Ground Team itself will be broken-down into three divisions: ES/Structural Engineering (or WLE MER), EV/Government Furnished Equipment (WIS GFE), and DO5/Assembly & Checkout Officer (ACO) Flight Controllers.

The WLE MER team will be further broken-down into two categories: Post-Ascent and On-orbit MMOD (Micro-Meteoroid Orbiting Debris) monitoring. Specific post-ascent duties will include providing impact summary for TPS assessment and supporting WLE (Wing Leading Edge) survey inspections and focused inspections.

For the On-orbit MMOD monitoring portion of the flight, the Ground Team will be tasked with providing standalone results for any WLEIDS triggers and supporting late-inspection activities.

STS-133 Specific – Including ET Stringer Issue – Articles: http://www.nasaspaceflight.com/tag/sts-133/

For the WIS GFE division, system management and evaluation will be their primary task during the mission, with a focus on commanding, data processing, battery life estimation, and temperatures of the system.

The DO5/ACO Flight Controllers will be tasked with keeping abreast of and developing crew procedures, overall system cognizance, Ku-Band coverage capability at critical times, leading anomaly resolution, and reporting on system and operation status to the flight crew.

However, none of this will be possible without the numerous hardware elements installed on Discovery (and her sisters Atlantis and Endeavour).

In all, 132 accelerometers (66 per wing) and 40 temperature sensors (20 per wing) have been mounted behind the first 20 RCC panels on the wing spars of Discovery.

In turn, 44 sensor units (22 per wing) are located in Discovery’s Delta wings. Each Sensor Unit, which is designed to gather and process data from accelerometers and temperature sensors, has three (3) accelerometers and one temperature sensor attached it.

Each Sensor Unit contains internal temperature and battery voltage measurements, and the units are grouped together into clusters known as “sensor farms.”

In each wing, eight Sensor Units (units 1-8) are located on each wing glove “sensor farm” mounting plate. Units 9-22 (14 total units) are located on the wing cavity “sensor farm” mounting plate.

In turn, these Sensor Units will communicate via Radio Frequency with the Wing Relay Units, of which there are 2 units per wing and one per “sensor farm.”

The wing glove “sensor farms” will communicate with their respective Wing Relay Unit on Channel A; the wing cavity “sensor farms” will communicate with their respective Wing Relay Unit on Channel B.

The Wing Relay Units are in turn connected via hardline to the Cabin Relay Units located in middeck cabin locker MA9G.

The Cabin Relay Units (2 + 1 spare) will then communicate the data received by the Wing Relay Units to the Laptop Receiver Unit via RF. The two Laptop Receiver Units will then transmit the data to the primary A31p Laptop which runs the WLES (Wing Leading Edge Sensor) software and stores the data from the Sensor Units.

In all, there are two A31p laptops, one primary and one backup. Only the primary laptop will communicate with the WLES system.

All sensor and relay units have independent battery units; thus, the entire system is not subject to the same power source and can maintain operational status even if one sensor or relay unit’s battery source is depleted prematurely during the mission.

Pre-launch/Post-launch System Overview:

Use of the WLEIDS for STS-133/ULF5 will begin on Monday (L-4 – Launch minus 4 days) when KSC personnel will program the sensor units with event files. In all, four launch opportunities will be programmed into the system with emphasis on Ascent Data Collection and Assessment.

Final verification of battery charges for the system will be taken at this time and the system secured in a deactivated mode.

On launch day, the system will remain in the deactivated mode until SSME (Space Shuttle Main Engine) ignition at T-6.6 seconds. At this time, Discovery’s computers will trigger the activation of the WLEIDS. At this time, all 44 units will begin collecting 16-bit data at 20,000 samples her second. This will continue through MECO (Main Engine Cutoff).

Then, at MET (Mission Elapsed Time) 10-mins, the sensor units will create ascent summary data files before transitioning to on-orbit power-saving mode (“idle” mode).

Four hours after launch, Discovery’s flight crew will set up the LAN (Local Area Network)/OCA (Orbiter Communications Adaptor) system and verify nominal WLES operation.

MCC (Mission Control) will then, at some point later in FD-1, command the primary A31p laptop to download all WLEIDS information from the Sensor Units at a rate of 0.4 KB/s. It will take about 1minute to transfer a single ascent summary file and 1.5 hours to transfer ascent summary data.

After this, the raw data will be downlinked to the ground and assessed. This will be accomplished through the Ku-Band antenna at a rate of 250 KB/s or 500 KB/s depending on the Ku-Band channel utilized.

Should the option be taken to downlink the data via the DTV channel, the downlink rate will be 40 Mbps.

Following the review of this data, the Mission Evaluation Room (MER) will determine if any additional data should be downlinked.

WLES On-orbit Ops and Crew Procedures:

Following ascent, the WLEIDS sensor units will transition to “idle” mode to preserve battery power. From this point (MET 10mins) through their scheduled deactivation on FD-11, the sensor units will be used to monitor Discovery for MMOD impacts during both free-flight and docked periods.

This monitoring will be accomplished by placing the sensor units into 2 or 3 monitoring groups per wing. This will enable MCC to rotate through the monitoring groups so that one group is in use for no more than 21hrs at a time.

This will allow for maximization of battery life on the system and, in turn, ensure MMOD monitoring during the highest MMOD risk periods.

A temperature of at least -40-degrees F will be maintained inside each wing structure during the on-orbit operational period of the WLEIDS to ensure proper functionality of the system.

In terms of crew procedures/interaction with the WLES during the flight, there will be three categories of interaction: nominal, off-nominal, and reconfiguration.

For nominal ops, the crew will perform activation and checkout of the system on FD-1, perform rendezvous tools checkout prep prior to docking and undocking, and perform deactivation of the system on FD-11 in preparation for entry and landing.

Off-nominal activities could include Laptop Receiver Unit R&R (Removal and Replacement), Cabin Relay Unit R&R, and Laptop Receiver Unit troubleshooting.

For reconfiguration activities, the crew could have to prepare for laptop transfer to a different location within Discovery. The crew has elected not to perform prep & post docking & undocking reconfig.

For crew actions toward the WLEIDS, both Mike Barrett and Alvin Drew are trained for these operations. All WLES procedures are contained within the Orbit Ops Book, and nominal crew WLEIDS activities will take ~40 minutes of crew time.

(Numerous articles will follow. L2 members refer to STS-133 live coverage sections for internal coverage, presentations, images and and updates from engineers and managers – which will ramp up into full Flight Day coverage during the mission. Images used, via L2 and acquired PRCB presentations).

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