BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: August 3, 2005
Astronauts Stephen Robinson and Soichi Noguchi, floating in the shuttle Discovery's airlock, switched their spacesuits to internal power at 4:48 a.m. to officially begin the third spacewalk of the first post-Columbia mission. A few moments later, they floated into the shuttle Discovery's cargo bay.
This is the 61st spacewalk devoted to station assembly and maintenance and the third for Robinson and Noguchi, who logged 14 hours and four minutes of spacewalk time in two previous excursions. The cumulative total for the previous 60 spacewalks is 362 hours and 19 minutes by 53 astronauts and cosmonauts.
The primary goals of today's planned seven-hour excursion are to attach a massive external tool box to the space station's Quest airlock module; to mount an experiment package on the top of the station's solar array truss; and to remove two "gap fillers" sticking up between heat shield tiles on Discovery's belly.
The impromptu repair job was added to today's spacewalk because of uncertainty over what sort of damage might result if the gap fillers were left in place for re-entry. The concern was that the gap fillers, sticking up into the hypersonic wind flow across the belly of the shuttle, could trigger an early onset of turbulence that would result in higher downstream heating.
To remove the gap fillers, Robinson will ride the space station's robot arm, operated by astronaut Wendy Lawrence, down below the right side of the shuttle and under its belly. Parked a foot or so away, he will attempt to pluck the gap fillers out with his gloved hand. If that doesn't work, he will use forceps to apply additional force, up to about 10 pounds. If that doesn't work, he will use a hacksaw blade to cut the fillers off at the surface of the tiles.
Here is a timeline of today's activities based on the actual start time of the EVA. Soichi's call sign is EV-1 while Robinson is EV-2 (times subject to change):
EDT........HH...MM...EVENT 04:48 AM...00...00...Airlock egress 05:18 AM...00...30...EV-1/EV-2: External stowage platform (ESP-2) installation 06:03 AM...01...15...EV-1: MISSE 5 experiment group installation 06:03 AM...01...15...EV-2: Grapple fixgture removal 06:18 AM...01...30...SSRMS: ESP-2 ungrapple 06:23 AM...01...35...Station robot arm (SSRMS) walkoff to mobile transporter 06:48 AM...02...00...Shuttle robot arm (SRMS): TPS sample box scan 07:03 AM...02...15...EV-1: Radiator rotary joint coupler removal 07:03 AM...02...15...EV-2: Gap filler too prep 08:03 AM...03...15...EV-1: Attach foot restraint to SSRMS 08:03 AM...03...15...EV-2: Attach tethers, ingress SSRMS 08:18 AM...03...30...EV-1: Close TPS sample box; monitor EV-2 08:18 AM...03...30...EV-2: gap filler removal 08:28 AM...03...40...SSRMS moves EV-2 to work site 1 09:08 AM...04...20...SSRMS moves EV-2 to work site 2 10:18 AM...05...30...IV egress for shuttle EVA 11:03 AM...06...15...EV-1/EV-2: Payload bay cleanup and tool stow 11:48 AM...07...00...Airlock repressurization
The repair job has generated widespread attention, in part because no astronaut has ever attempted to work on the belly of the space shuttle and because any slipups by Robinson or Lawrence could result in damage to the tiles needed to protect Discovery from the heat of re-entry. But engineers say the worry is misplaced and that the work is straight-forward.
"I have every confidence the EVA is going to go well to remove the gap fillers as well as do the other tasks," said mission management team chairman Wayne Hale. "We've given ourselves three different ways to deal with the gap filler. Yes, we have the capability to perform another EVA. If something happens, either we didn't get the gap fillers where we wanted or something else needs to be worked on, then we will attack that and go deal with it. But right now, I am very confident we'll take care of the gap fillers."
Lead flight director Paul Hill said once the gap fillers are removed, engineers will have no concerns about heat damage during Discovery's return to Earth Monday.
"Once we pull the gap fillers, there's no concern in the TPS (thermal protection system) community about the bottom of the vehicle during deorbit," Hill said. "These particular gap fillers are there not for entry heating, but to protect from buffeting on the way up hill because of the turbulent flow between the external tank and the bottom of the orbiter. So once we pull them out, no issue.
"Now, if for some reason we damage the area while we're pulling them out, they're going to want some pictures and bring down some data to show them what the area around the work site looks like. We're not expecting there to be any damage. If for some reason we have to cut the gap fillers flush, then there is a greater likelihood of scuffing up or scratching the outside RCG coating on the tiles."
It is that presumed sensitivity to damage that initially made flight controllers nervous about attempting any sort of repair.
"The reaction across the community is that we'd be nuts for trying to put a crew member that close to glass-covered tiles where if we drop a tool or a boot comes out of a foot restraint, we could kick the tile and damage it worse. So there is that generic sense already. We don't want to get close to TPS and risk damaging it and making a bad problem worse."
But after an exhaustive analysis, the team was convinced the risk of damage due to the repair was less than the risk of possibly significant heat damage during re-entry.
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