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The S-6 solar array stuck by stiction that threatened station power · Space Exploration Stories

• 0:03
  Speaker 1: A free-tailed bat clung to the side of Discovery's external
• 0:07
  Speaker 1: tank on the morning of March 15, 2009. Photographs taken
• 0:11
  Speaker 1: at the pad showed it gripping the foam insulation. Wings
• 0:15
  Speaker 1: folded tight against its body. A wildlife specialist examined those
• 0:19
  Speaker 1: photographs later and concluded the animal almost certainly had a
• 0:23
  Speaker 1: broken wing. It could not fly away. At 7.43 in
• 0:27
  Speaker 1: the evening, roughly 19 million newtons of thrust ignited beneath it.
• 0:32
  Speaker 1: Launch Director Michael Leinbach would later call it the most
• 0:36
  Speaker 1: visually beautiful launch he had ever seen. What was riding
• 0:39
  Speaker 1: inside that tank was the last piece of a puzzle
• 0:43
  Speaker 1: eight years in the making. The S-6 truss segment, the
• 0:46
  Speaker 1: fourth and final starboard section of the International Space Station's
• 0:50
  Speaker 1: integrated truss structure, had been packed in storage since before
• 0:54
  Speaker 1: the Columbia accident. Before two shuttle losses reshaped everything, NASA
• 0:59
  Speaker 1: knew about risk. Now it sat in Discovery's payload bay
• 1:03
  Speaker 1: its solar arrays folded and compressed for nearly a decade,
• 1:07
  Speaker 1: waiting to unfurl in a place where there is no
• 1:09
  Speaker 1: forgiving second chance, the question nobody could answer with certainty.
• 1:14
  Speaker 1: Would hardware that old still open? The International Space Station
• 1:18
  Speaker 1: runs on electricity, every life support system, every science rack,
• 1:24
  Speaker 1: every gyroscope that keeps the structure pointed correctly draws from
• 1:28
  Speaker 1: a power grid, orbiting 400 kilometers above the Earth. By
• 1:32
  Speaker 1: early 2009, that grid was running at roughly half its
• 1:36
  Speaker 1: designed capacity. Three of four starboard truss segments were installed.
• 1:41
  Speaker 1: The fourth slot, S6, had been waiting empty since the
• 1:44
  Speaker 1: station's earliest assembly flights. When S6 was finally bolted into place,
• 1:50
  Speaker 1: it would bring total station power to 120 kilowatts, 30
• 1:54
  Speaker 1: kilowatts of that available purely for science. That number had
• 1:58
  Speaker 1: been the destination for years. The S-6 Truss itself had
• 2:02
  Speaker 1: been manufactured and certified years before it could fly. When
• 2:06
  Speaker 1: the Columbia accident grounded the shuttle fleet in 2003, S-6
• 2:10
  Speaker 1: went into storage at Kennedy Space Center. It stayed there
• 2:14
  Speaker 1: through the return-to-flight period, through the resumption of assembly missions,
• 2:18
  Speaker 1: through the slow, methodical process of rebuilding the program's confidence.
• 2:23
  Speaker 1: Eight years passed. The Truss's solar arrays— Enormous accordion-folded panels,
• 2:29
  Speaker 1: each one roughly the size of a standard solar array wing,
• 2:32
  Speaker 1: sat compressed inside their blanket boxes the entire time. Engineers
• 2:37
  Speaker 1: had a name for what that compression could do to
• 2:39
  Speaker 1: the mechanism. They called it stiction, sticky friction. When metal
• 2:44
  Speaker 1: and fabric are held tightly folded for years without movement,
• 2:48
  Speaker 1: the materials can bond slightly at their contact surfaces. Not
• 2:52
  Speaker 1: enough to weld them together, but potentially enough to resist
• 2:55
  Speaker 1: unfolding when commanded. The longer the storage, the higher the risk.
• 3:00
  Speaker 1: And Array 3B had been in its box the longest
• 3:03
  Speaker 1: of all. The team knew this going in. Stiction was
• 3:06
  Speaker 1: a documented risk, noted in the mission planning. It was
• 3:09
  Speaker 1: not a surprise. What nobody could model precisely was the threshold.
• 3:15
  Speaker 1: At exactly what point does Stiction become an obstruction rather
• 3:19
  Speaker 1: than merely resistance? There was a second problem that almost
• 3:22
  Speaker 1: prevented the mission from launching at all. On the previous
• 3:25
  Speaker 1: shuttle flight, STS-126, which had landed in November 2008, engineers
• 3:32
  Speaker 1: discovered a broken hydrogen flow control valve. This was not
• 3:37
  Speaker 1: a minor finding. Hydrogen flowing through the wrong path at
• 3:40
  Speaker 1: the wrong pressure during launch could compromise the main propulsion system.
• 3:45
  Speaker 1: The valve failure on STS-126 triggered an immediate review of
• 3:50
  Speaker 1: all three orbiters in the fleet. Discovery, Atlantis, and Endeavour
• 3:56
  Speaker 1: were each inspected. Suspect valves, identified by flight hour count
• 4:01
  Speaker 1: rather than visible damage, were pulled and replaced with lower
• 4:05
  Speaker 1: flight time units. That process took time. STS-119 had already
• 4:11
  Speaker 1: been scheduled. The delay pushed the launch window into March. Then,
• 4:16
  Speaker 1: on March 11, 2009, the crew was already at Kennedy
• 4:20
  Speaker 1: Space Center when the countdown was halted. A liquid hydrogen
• 4:23
  Speaker 1: vent line leak had appeared at the ground umbilical carrier plate.
• 4:28
  Speaker 1: The interface between the pad's ground support equipment and the
• 4:31
  Speaker 1: external tank, the launch was scrubbed. Engineers worked through the problem.
• 4:36
  Speaker 1: The leak was contained enough for the attempt four days later.
• 4:40
  Speaker 1: Though the root cause, a misalignment at the carrier plate,
• 4:44
  Speaker 1: would not be fully understood until after the mission returned.
• 4:47
  Speaker 1: Commander Lee Archibald and his crew of seven had now
• 4:51
  Speaker 1: waited through valve concerns, a fleet-wide inspection, a cross-country schedule compression,
• 4:57
  Speaker 1: and a launch day scrub. They launched on March 15th
• 5:00
  Speaker 1: at 19.43 Eastern Time, with a station running at half
• 5:04
  Speaker 1: power and a truss full of eight-year-old hardware waiting in
• 5:08
  Speaker 1: the payload bay. The Bat, by then, was already gone.
• 5:12
  Speaker 1: Discovery docked with the International Space Station on March 17th
• 5:17
  Speaker 1: at 21.20 UTC. When the hatches opened at 23.09, the
• 5:22
  Speaker 1: crew moved between two worlds. one that had been running
• 5:26
  Speaker 1: on half its intended power for years, and one that
• 5:29
  Speaker 1: carried the hardware meant to fix that. The hardware was
• 5:32
  Speaker 1: in the payload bay. Four blanket boxes. Inside each one,
• 5:37
  Speaker 1: folded accordion style, were sections of solar array fabric that
• 5:42
  Speaker 1: had been compressed since 2001. Eight years of sitting still,
• 5:47
  Speaker 1: the arrays were made to unfurl in the vacuum of space,
• 5:51
  Speaker 1: but fabric... and metal under constant compression for that long
• 5:54
  Speaker 1: develops a resistance called stiction, sticky, friction, the tendency of
• 6:00
  Speaker 1: material to resist moving from the position it has held
• 6:03
  Speaker 1: for too long. Engineers at Kennedy knew this was coming.
• 6:07
  Speaker 1: They had planned for it. What they could not calculate
• 6:10
  Speaker 1: precisely was how much resistance eight years would produce. The
• 6:14
  Speaker 1: S6 truss segment itself, the fourth and final starboard section
• 6:18
  Speaker 1: of the station's integrated truss structure, was installed on March
• 6:22
  Speaker 1: 18th using a dual-arm robotic handoff. The shuttle arm handed
• 6:26
  Speaker 1: it to the station arm because the clearance restrictions around
• 6:30
  Speaker 1: the docking geometry made a direct installation impossible. It took
• 6:34
  Speaker 1: careful coordination between two robotic systems working across a structure
• 6:39
  Speaker 1: the size of a football field. By the time S6
• 6:42
  Speaker 1: was bolted into position, the physical question had shifted from
• 6:45
  Speaker 1: whether the truss could be attached to whether what was
• 6:47
  Speaker 1: inside it would ever open. EVA-1 launched that answer into motion.
• 6:53
  Speaker 1: On March 19th, Steve Swanson and Richard Arnold spent six
• 6:57
  Speaker 1: hours and seven minutes outside. They bolted S6 in place,
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  Speaker 1: connected cables, removed the launch locks that had held the
• 7:05
  Speaker 1: arrays secured during ascent, and deployed the blanket boxes, pulling
• 7:09
  Speaker 1: the compressed accordion sections out of storage and exposing them
• 7:13
  Speaker 1: to space for the first time in nearly a decade.
• 7:16
  Speaker 1: The blanket boxes opened without incident. The arrays were now
• 7:20
  Speaker 1: free to be commanded open, but commanding them open and
• 7:24
  Speaker 1: having them actually open were two different things. The original
• 7:29
  Speaker 1: plan had array deployment scheduled for flight day 8. Ground
• 7:33
  Speaker 1: managers moved it to flight day 6 because an additional
• 7:36
  Speaker 1: EVA could not be slotted later in the mission timeline
• 7:39
  Speaker 1: given suit and prep constraints. The reason was simple arithmetic.
• 7:44
  Speaker 1: If an array stuck and refused to deploy fully, An
• 7:47
  Speaker 1: additional EVA would be required to manually assist it. EVAs
• 7:51
  Speaker 1: take preparation time, suit checks, airlock cycling, crew positioning. The
• 7:57
  Speaker 1: mission timeline had no slack for an unplanned spacewalk unless
• 8:01
  Speaker 1: that spacewalk was attempted early enough to fit inside the
• 8:05
  Speaker 1: remaining schedule. Moving deployment earlier was not optimism. It was
• 8:10
  Speaker 1: insurance purchased with time. Array 1B began its commanded deployment
• 8:15
  Speaker 1: at 15.06 UTC on March 20th. Astronaut Phillips monitored the
• 8:20
  Speaker 1: deployment from inside the station. The array started to move,
• 8:24
  Speaker 1: slat by slat, the accordion sections unfolding outward from the mast.
• 8:29
  Speaker 1: Then it stopped, halfway deployed. 45 meters of solar fabric
• 8:35
  Speaker 1: hanging open on one side, the rest still compressed. The
• 8:39
  Speaker 1: decision made in the next few minutes was one of
• 8:42
  Speaker 1: the quieter acts of engineering on the mission. Phillips held
• 8:45
  Speaker 1: the array in place and waited. No motor reversals, no
• 8:49
  Speaker 1: additional commands, no attempt to force the remaining sections. The
• 8:53
  Speaker 1: array was rotated to face the sun directly and left
• 8:56
  Speaker 1: there for 45 minutes. The logic, sunlight would warm the
• 9:00
  Speaker 1: metal and fabric, reducing the stiction that had built up
• 9:03
  Speaker 1: across eight years of compression. There was no procedure that
• 9:06
  Speaker 1: guaranteed this would work. The temperature differential between sunlit and
• 9:11
  Speaker 1: shadowed hardware in orbit can exceed 200 degrees Celsius, and
• 9:15
  Speaker 1: the thermal expansion that produces could either loosen the stiction
• 9:18
  Speaker 1: or stress already aged material in unpredictable ways. Forty-five minutes passed.
• 9:24
  Speaker 1: The deployment command was sent again. Array 1B finished its
• 9:28
  Speaker 1: extension without resistance. One down, the harder one still waited.
• 9:33
  Speaker 1: Array 3B had been in storage the longest of the four.
• 9:37
  Speaker 1: It was the one engineers had flagged as the highest
• 9:40
  Speaker 1: diction risk. Its deployment began at 1635, UTC on March 20th,
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  Speaker 1: 89 minutes after 1B finished. The same pause procedure was
• 9:51
  Speaker 1: built into the plan from the start this time. Deploy
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  Speaker 1: to the halfway point, stop, rotate to sun, wait. The
• 9:59
  Speaker 1: array moves to its pause point it stopped the station
• 10:03
  Speaker 1: turned toward the sun then when the deployment command came
• 10:07
  Speaker 1: something different happened stiction was observed the array did not
• 10:12
  Speaker 1: move cleanly the motor was working the mast was extending
• 10:17
  Speaker 1: but the slats The individual accordion sections that needed to
• 10:20
  Speaker 1: flatten out as the array unfurled were resisting. The team
• 10:25
  Speaker 1: watched the deployment data. There was no manual override available.
• 10:29
  Speaker 1: No astronaut could reach that section of the truss from
• 10:31
  Speaker 1: any EVA position. The array would open on its own,
• 10:35
  Speaker 1: or it would not open at all. The slats held.
• 10:38
  Speaker 1: Then they shifted. Then, one after another, they flattened. At
• 10:43
  Speaker 1: 17 UTC on March 20th, 2009, Array 3B reached full extension.
• 10:50
  Speaker 1: The station's power budget changed in that moment from a
• 10:52
  Speaker 1: system running at half capacity to one producing 120 kilowatts total,
• 10:57
  Speaker 1: 30 of them available for science. The fourth and final
• 11:00
  Speaker 1: starboard solar array had been waiting eight years for that minute.
• 11:04
  Speaker 1: What no one outside the mission documentation would notice for
• 11:07
  Speaker 1: some time was that Discovery had flown the entire deployment
• 11:12
  Speaker 1: sequence with one additional detail attached to its underside. A
• 11:16
  Speaker 1: single thermal protection tile had been deliberately raised a quarter
• 11:19
  Speaker 1: of an inch, 6.4 millimeters above the surrounding surface. Not
• 11:24
  Speaker 1: a defect, not damage. A deliberate experimental installation designed to
• 11:30
  Speaker 1: trigger a boundary layer transition during re-entry and generate data
• 11:34
  Speaker 1: about the aerothermal conditions that had destroyed Columbia six years earlier.
• 11:38
  Speaker 1: The shuttle carrying eight-year-old hardware into orbit was simultaneously serving
• 11:43
  Speaker 1: as a laboratory for understanding how shuttles die The crew
• 11:47
  Speaker 1: did not need to know it was there. The data
• 11:50
  Speaker 1: would write itself into the tile's surface on the way home.
• 11:54
  Speaker 1: Discovery undocked from the station on March 25th, 2009 at
• 11:59
  Speaker 1: 1953 Udo TC. The arrays were fully extended behind her
• 12:04
  Speaker 1: as she pulled away four wings of photovoltaic panels catching
• 12:08
  Speaker 1: light over the Pacific, generating power for a crew she
• 12:11
  Speaker 1: was no longer carrying. The three EVAs had logged 19
• 12:15
  Speaker 1: hours and 4 minutes of total spacewalk time. Swanson, Arnold,
• 12:20
  Speaker 1: and Acaba had bolted the S6 truss into position, connected
• 12:24
  Speaker 1: its cables, removed the launch locks, photographed a radiator panel,
• 12:28
  Speaker 1: reconfigured the Zenith 1 connector, and relocated a cargo cart.
• 12:32
  Speaker 1: They had also encountered a stuck pin on a piece
• 12:35
  Speaker 1: of hardware called the UCC CAS, the Unpressurized Cargo Carrier
• 12:40
  Speaker 1: Attachment System. The pin would not fully deploy. Every standard
• 12:45
  Speaker 1: technique failed. Mission controllers documented the problem, secured the hardware
• 12:50
  Speaker 1: in its current position, and closed the EVA without resolution.
• 12:55
  Speaker 1: Some problems do not yield to the tools on hand.
• 12:58
  Speaker 1: That pin would remain stuck for months. It was not
• 13:01
  Speaker 1: released until the next flight, STS-127, when engineers had time
• 13:06
  Speaker 1: to design a custom-made tool built specifically for that geometry.
• 13:11
  Speaker 1: The solution required knowing exactly what had failed and fabricating
• 13:15
  Speaker 1: something that had never existed before. The station waited. The
• 13:19
  Speaker 1: tool was made. The pin released. The hydrogen vent leak
• 13:23
  Speaker 1: that had scrubbed the March 11th launch attempt received its
• 13:27
  Speaker 1: own post-flight investigation. Engineers traced it to a misalignment in
• 13:31
  Speaker 1: the ground umbilical carrier plate, a fitting on the launch
• 13:35
  Speaker 1: pad itself, not on the orbiter. The leak had never
• 13:38
  Speaker 1: threatened discovery in flight. It had threatened the timeline, the window,
• 13:43
  Speaker 1: the margin. Once identified, the misalignment was corrected before STS-127 flew.
• 13:51
  Speaker 1: Two problems from STS-119 were thus resolved by the mission
• 13:57
  Speaker 1: that followed it. That is how the shuttle program worked
• 13:59
  Speaker 1: at its best, each flight generating the specific knowledge the
• 14:03
  Speaker 1: next flight needed. There is one more piece of data
• 14:06
  Speaker 1: from STS-119's return that belongs here. the deliberately raised tile.
• 14:12
  Speaker 1: The one set a quarter inch above the surrounding surface
• 14:15
  Speaker 1: to trigger a boundary layer transition during re-entry, performed exactly
• 14:19
  Speaker 1: as designed. At Mach 15, the airflow over Discovery's underside
• 14:24
  Speaker 1: tripped from laminar to turbulent at the location of the
• 14:27
  Speaker 1: raised tile that temperature data recorded. The aerothermal profile was captured.
• 14:33
  Speaker 1: The experiment was successful enough that engineers repeated it on STS-128,
• 14:39
  Speaker 1: with the tile raised further to 0.35 inches, where it
• 14:44
  Speaker 1: tripped the boundary layer at Mach 18. Discovery had flown
• 14:48
  Speaker 1: home as a laboratory for understanding how shuttles survive the
• 14:52
  Speaker 1: violence of re-entry. The data from that quiet quarter-inch of
• 14:55
  Speaker 1: raised ceramic went into the engineering record, where it remains
• 14:59
  Speaker 1: alongside the mission itself. Discovery touched down at Kennedy Space
• 15:03
  Speaker 1: Center on March 28, 2009, at 15.13.18, It was the
• 15:10
  Speaker 1: shuttle's 36th flight. It was the 156th crewed NASA space flight.
• 15:17
  Speaker 1: It was the 100th crewed mission since Challenger. Those are
• 15:21
  Speaker 1: the numbers in the record. They do not fully account
• 15:23
  Speaker 1: for what the flight had done. The station's total power
• 15:26
  Speaker 1: output now stood at 120 kilowatts, of which 30 kilowatts
• 15:30
  Speaker 1: were available for science. The final wing of the integrated
• 15:34
  Speaker 1: truss structure was in place. The assembly of the International
• 15:38
  Speaker 1: Space Station The structure that had been growing in orbit
• 15:41
  Speaker 1: for over a decade was functionally complete in its primary
• 15:45
  Speaker 1: power architecture. There is a detail from the morning of
• 15:48
  Speaker 1: March 15th, 2009, that the mission documentation preserves. A free-tailed
• 15:54
  Speaker 1: bat had attached itself to the external tank and was
• 15:57
  Speaker 1: still there when the main engines ignited. A specialist later
• 16:01
  Speaker 1: concluded it likely had a broken wing and could not
• 16:04
  Speaker 1: fly away. Launch Director Michael Leimbach, watching from the firing room,
• 16:09
  Speaker 1: described the STS-119 launch as the most visually beautiful he
• 16:14
  Speaker 1: had ever seen. He had witnessed a great many launches.
• 16:18
  Speaker 1: The bat left no record beyond the photographs. That image
• 16:22
  Speaker 1: sits at the beginning of this story, and it belongs
• 16:24
  Speaker 1: at the end of it too, though it means something
• 16:26
  Speaker 1: different now. At the start, the bat was a strange detail,
• 16:30
  Speaker 1: a small creature holding on, while 19 million newtons prepared
• 16:34
  Speaker 1: to ignite beneath it. It read, as fragility, as something
• 16:39
  Speaker 1: that should not have been there. By the end of
• 16:41
  Speaker 1: the mission, the image shifts. Seven people had traveled to
• 16:45
  Speaker 1: orbit carrying hardware that had been sitting in storage for
• 16:48
  Speaker 1: eight years. They had installed the final power segment of
• 16:51
  Speaker 1: a station that took over a decade to assemble. They
• 16:54
  Speaker 1: had paused an array deployment to let sunlight warm eight-year-old metal.
• 16:58
  Speaker 1: They had watched slats that seemed stuck release, one after another,
• 17:02
  Speaker 1: until the panels reached full extension. They had flown home
• 17:06
  Speaker 1: with a tiled, deliberately raised to collect data that might
• 17:10
  Speaker 1: save future crews. And somewhere in the documentation of all
• 17:13
  Speaker 1: of that, a bat with a broken wing held on
• 17:16
  Speaker 1: through the admission sequence and was not found again. A
• 17:20
  Speaker 1: bat with a broken wing held on through the admission
• 17:22
  Speaker 1: sequence and was not found again. Not everything that witnesses
• 17:27
  Speaker 1: a launch survives it. Not everything that clings to the
• 17:30
  Speaker 1: work makes it to the other side. The arrays that
• 17:33
  Speaker 1: waited eight years in blanket boxes did survive They unfolded.
• 17:38
  Speaker 1: They are still there, generating power above the atmosphere, catching
• 17:43
  Speaker 1: light over a station that was completed by people who
• 17:45
  Speaker 1: solved the problems the schedule did not leave room for.
• 17:48
  Speaker 1: The bat held on. The arrays opened. The arrays are
• 17:52
  Speaker 1: still there, generating power above the atmosphere, catching light over
• 17:56
  Speaker 1: a station, completed by people who solved the problems the
• 18:00
  Speaker 1: schedule did not leave room for. While no record of
• 18:02
  Speaker 1: the bat's survival was documented, The slats that seemed stuck
• 18:06
  Speaker 1: released one after another until the panels reached full extension
• 18:10
  Speaker 1: above a world that never saw them fold. This show
• 18:14
  Speaker 1: is made by Obo Media.