Progress antenna pushed back barely enough, photographs show

by Chris Bergin

Spacewalkers aboard the International Space Station (ISS) on Thursday succeeded in their task of clearing an antenna blockage by a matter of only two inches, photographs obtained by indicate.

Without their success, the undocking of a robot supply craft, which must occur in early April to clear the way for the arrival of the next permanent station crew, might have led to serious damage to the Russian end of the space station.

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Far from being the straightforward process portrayed in official reports and press accounts, in which cosmonaut Mikhail Tyurin and astronaut Michael Lopez-Alegria cut one strut and then neatly and effortlessly folded the structure back fully away from the handrail it was jammed under, the emergency task was actually accomplished through significant exertion.

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These efforts overcame space-to-Earth confusion concerning which struts were being cut and how each cut segment was winding up jamming further motion of the recalcitrant Kurs antenna complex. This confusion was compounded by Mission Control’s lack of insight into the actual situation in orbit since there were no televised views of the operation and ground experts had to rely entirely on terse verbal descriptions from the crew.


‘According to the EVA folks, [the antenna] it looks to be about 50 percent stowed,’ explained < ?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />NASA Johnson Space Center spokesperson Lynnette Madison in an email. Other unofficial estimates based on the normal full swing of the retractable platform put the amount of retraction at as little as 25 percent.


‘The clearance is about 5 cm.[2 inches],’ she continued. ‘However, even a 1 cm clearance would have been enough.’


‘Also,’ pointed out another NASA official who requested his name not be used, ‘the crew reported that the dish [at the end of the swiveling structure] is free to tilt and/or rotate.’ This meant, he continued, that ‘even if it did hit the handrail it would most likely rotate out of the way and not hang on the handrail.’


The pictures were among several hundred digital images downloaded by the spacewalkers in the 24 hours following their strenuous and successful six-hour exterior work Thursday morning. Live television during the event was limited to US and Canadian cameras mounted on the outside of the American segment of the station, a distant view often blocked by a slowly rotating Russian solar panel.


The actual workstation, at the back end of the Russian Service Module, was not within line-of-sight of any of the cameras. Only the U.S. spacesuits carry the small ‘helmet cams’ that allow an astronaut-eye view of activities and are transmitted continuously through NASA’s sophisticated network of relay satellites. For this spacewalk, Moscow had insisted on the use of Russian spacesuits.


The consequent absence of good ‘situational awareness’ on the part of ground controllers was obvious. During the struggling that ground controllers characterize as a ‘flail’, Tyurin’s heavy breathing was audible over his helmet microphone and he often spoke in gasps and clipped phrases. Mission Control in Moscow kept asking where the crew was positioned and which strut they were planning on cutting, and exactly where – often with repeated exchanges demanding clarification.


The crew also struggled to articulate exactly how each cut was actually creating new jams as released strut segments swung into blocking positions relative to the desired motions of other struts. At one point they cut a strut in a second location and remarked on obtaining ‘a souvenir’, and Mission Control urgently ordered them not to touch the ends of the cut struts. Prior to the spacewalk, experts had said they expected the cut ends to be sharp, and potentially dangerous to the men’s spacesuits.


The success of the operation was also threatened by overheating in Tyurin’s spacesuit.


According to NASA’s internal ‘daily On-Orbit Status report’ – available on L2 – the cooler’s failure was ‘probably due to being turned on in the lock chamber when not yet exposed to vacuum,’ that is, crew error. Premature manual activation of the water flow without a pure vacuum to allow it to sublimate [flash into vapor, carrying excess heat with it] immediately led to an ice build-up that jammed the unit. The suit overheated to the point of serious visor fogging, until the sublimator was turned off and back on again, and the actual box was manually pounded by astronaut Michael Lopez-Alegria to dislodge the interfering ice crust.


Trouble-shooting the suit malfunction, which was initially confusing because Tyurin’s suit had encountered a cooling problem on his previous spacewalk in November that turned out to have had an entirely different cause, was made more difficult because radio telemetry of the spacesuit’s operating parameters was only available during short intervals every hour and a half. The Russian communications system relies on direct links with ground stations inside Russia, and only voice signals can be transmitted during each complete orbit using a relay through the American communications satellite network.


The trouble with Tyurin’s sublimator had one unintended benefit — it kept the still-controversial ‘phantom torque’ low enough that the station’s CMGs easily handled the disturbing force (they never exceed 40 percent ‘saturation’). NASA engineers are convinced this force, which has disturbed the station’s orientation on past spacewalks to the point that thrusters have had to be fired, is due to high-velocity water molecule ejection by the sublimators of the Russian spacesuits. But the Russians vehemently disagree and instead blame malfunctions of the US CMG’s. This spacewalk provided an inadvertent experimental verification of the U.S. version of the phenomenon’s true cause.


During the post-spacewalk inventory and clean-up, the crew also noticed that a television camera bracket used during the spacewalk was missing. It may, according to the internal NASA status report, ‘have drifted overboard’ and become another piece of short-lived ‘space junk’. However, the crew was reportedly still looking for it inside the pressurized module. Along with towels used to wipe off possible fuel leaks during the spacewalk and then deliberately discarded, the bracket would thus have joined a long list of small items regular jettisoned safely during spacewalks.

Meanwhile, NASA has reportedly received no word from their Russian partners on the most important long-range issue surrounding the antenna jam — its root cause, and the steps needed to forestall its recurrence. JSC spokesman Rob Navias has pointed out that since the antenna jam on the Progress docking in September, another Progress has docked at a different station port and the Kurs antenna retraction worked perfectly. Potentially the pictures brought back on this latest spacewalk may help pinpoint the failure — mechanical, electrical, or otherwise — that led to this anomaly in the first place.

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