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CBS NEWS STS-123 STATUS REPORT: 20
Posted: 03:30 PM EDT, 3/13/08

By William Harwood
CBS News Space Analyst

Changes and additions:

   SR-18 (03/13/08): Hatches opened; shuttle crew welcomed aboard space station; mission status briefing
   SR-19 (03/13/08): Reisman joins station crew; engineers troubleshoot power glitch
   SR-20 (03/13/08): Canadians work on software patch to power Dextre components; spacewalk to proceed as planned

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03:30 PM, 3/13/08, Update: Canadians work on software patch to power Dextre components; spacewalk to proceed as planned

Astronauts Richard Linnehan and Garrett Reisman will press ahead with a near full-duration spacewalk this evening to prepare a Japanese logistics module for attachment to the space station and to begin assembly of a Canadian robot known as Dextre. Canadian robotics experts, meanwhile, are working on a software patch that might resolve a problem preventing engineers from routing power to the robot's components. Power is not required for this evening's spacewalk, but the problem must be resolved at some point.

Linnehan and Reisman spent the night in the station's Quest airlock module at a reduced 10.2 psi air pressure. The so-called "camp out" procedure is designed to help purge nitrogen from their bloodstreams before spending the day in a low-pressure spacesuit that might otherwise cause the bends.

The astronauts are scheduled to begin their day with a wakeup call at 4:28 p.m. If all goes well, the six-and-a-half-hour spacewalk will begin around 9:23 p.m.

Endeavour docked with the space station late Wednesday and earlier today, the astronauts used the lab's robot arm to move a Spacelab pallet carrying the components of the $209 million special purpose dextrous manipulator, or SPDM, robot - Dextre - to a worksite on the lab's solar power truss.

Once assembled, Dextre will, in effect, serve as high-precision arms and hands that can be wielded by the station's robotic arm to make repairs that might otherwise require a spacewalk. The goal of today's assembly work is to attach hand-like components called orbital replacement unit/tool changeout mechanisms, or OTCMs, to each of Dextre's arms. The 11-foot-long arms themselves will be attached to the robot's central torso during a second spacewalk overnight Saturday.

Dextre cannot support its own weight in Earth's gravity and it has never been fully assembled. Power and data are provided to the Spacelab pallet through the attachment fitting holding it in place on the mobile base that normally moves the station arm along the solar power truss.

But so far, engineers have been unable to power up the robot's components.

"Shortly after the robotics crew installed the Spacelab pallet with Dextre onto the motion base system, our robotics officer in mission control attempted to power up Dextre," said station flight director Ginger Kerrick. "And that was unsuccessful. So we've been spending the majority of the (day) troubleshooting that and assessing the impacts to (the) timeline.

"Luckily, the primary objective of the spacewalk today is to install the JLP, or the Japanese logistics module, onto the zenith port of node 2 (Harmony) and it does not require Dextre to be powered. We have some assembly tasks associated with Dextre as well that also do not require it to be powered. So the plan is to execute today's spacewalk per the nominal timeline."

Without power, however, engineers cannot turn on internal heaters and the spacewalkers will not remove thermal covers around the robot's joints as originally planned.

"Since we're unable to provide keep-alive to Dextre at this time, we'll probably defer those tasks," Kerrick said. "But those only represented about 25 minutes out of the EVA."

She said engineers have attempted a variety of workarounds to get power to the robot's systems, all of them unsuccessful.

"The power that's provided to Dextre can actually go through two separate strings and each of those strings have two separate channels," she said. "So we attempted to provide power with every combination of channel and string that we could think of, and that was unsuccessful. The second thing we tried from the ground was, when you attach the SLP to the port on the mobile base system, there is a connector that is supposed to mate to provide power and data access through there. So from the ground, we remotely commanded that to disconnect and then reconnect just in case the connection did not mate properly. Then we tried to repower Dextre after that, again, unsuccessful.

"With respect to the mechanical things we can try to restore power, there's one more thing we can do, but it requires the help of the EVA crew. And that is to go off and inspect all the connectors and cables that we were anticipating were already connected to determine whether or not that might be a source of the problem. So that is about everything we can do mechanically.

"Now we have talked to our Canadian Space Agency counterparts and there is a possibility that this could be the result of a timing issue with the software," Kerrick said. "When we command power to Dextre, the lab robotics workstation we're working from attempts to communicate with it shortly after that power command is set up. The theory is that the box we're powering on, which is called the power switching unit, the PSU, that we are trying to communicate with it while it is still powering up. So our Canadian Space Agency counterparts are looking into a software patch that would extend the amount of time between the power up and when the workstation tries to communicate with it.

"This is just a theory, but it's one of the things folks are working on. They're hoping to deliver that patch within 24 hours. As soon as that patch is delivered, we'll uplink it and attempt to repower. Now if that isn't successful, we have another leg that we have talked about on the overnight shift, which would be to attempt to grapple the Dextre with the station arm and attempt to power it that way."

LeRoy Cain, chairman of NASA's Mission Management Team, will brief reporters today at 5 p.m. to provide an update on image analysis, the overall health of Endeavour and any other issues of interest. The briefing will be carried on NASA television.

In the meantime, here is an updated timeline of today's activity (in EDT and mission elapsed time; includes revision C of the NASA television schedule):

EDT........DD...HH...MM...EVENT

03/13/08
04:28 PM...02...14...00...Crew wakeup
05:00 PM...02...14...32...Post-MMT briefing
05:08 PM...02...14...40...EVA-1: 14.7 psi repress/hygiene break
05:53 PM...02...15...25...EVA-1: Airlock depress to 10.2 psi
06:18 PM...02...15...50...EVA-1: Campout EVA preps
07:48 PM...02...17...20...EVA-1: Spacesuit purge
08:03 PM...02...17...35...EVA-1: Spacesuit oxygen prebreathe
08:53 PM...02...18...25...EVA-1: Airlock depressurization
09:23 PM...02...18...55...EVA-1: Spacesuits to battery power (official start time)
09:28 PM...02...19...00...EVA-1: Airlock egress
09:48 PM...02...19...20...EVA-1: Payload bay setup
10:08 PM...02...19...40...EVA-1: Japanese module prepped for unberthing
11:23 PM...02...20...55...EVA-1: OTCM 2 install on Dextre

03/14/08
01:23 AM...02...22...55...EVA-1: OTCM 1 install
01:58 AM...02...23...30...Logistics module unberthing
02:38 AM...03...00...10...SODF deploy
02:43 AM...03...00...15...SPDM assembly preps
03:08 AM...03...00...40...EVA-1: Cleanup
03:23 AM...03...00...55...Logistics module installation
03:33 AM...03...01...05...EVA-1: Airlock ingress
03:53 AM...03...01...25...Common berthing mechanism first stage bolts driven
03:53 AM...03...01...25...EVA-1: Airlock repressurization
04:08 AM...03...01...40...Spacesuit servicing
04:13 AM...03...01...45...CBM second stage bolts driven
05:58 AM...03...03...30...Logistics module leak checks
06:00 AM...03...03...32...Mission status briefing on NASA TV
06:03 AM...03...03...35...Shuttle arm ungrapples logistics module
07:58 AM...03...05...30...ISS crew sleep begins
08:28 AM...03...06...00...STS crew sleep begins
09:00 AM...03...06...32...Daily video highlights reel (repeated hourly)
01:30 PM...03...11...02...Flight director update on NASA TV
04:28 PM...03...14...00...Crew wakeup

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Quick-Launch Web Links:

CBS News STS-123 Status Reports:
http://www.cbsnews.com/network/news/space/current.html

CBS News STS-123 Quick-Look Page:
http://www.cbsnews.com/network/news/space/currentglance.html

NASA Shuttle Web: http://spaceflight.nasa.gov/shuttle/index.html
NASA Station Web: http://spaceflight.nasa.gov/station/index.html
Spaceflight Now: http://spaceflightnow.com/index.html

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