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Submitted by Arthur - N1ORC

Report # 15 
Monday, April 15, 2002 - 6:30 p.m. CDT 

The first railcar in space crept down the track of a newly installed
truss structure at the International Space Station today, paving the way
for the future use of the system on which the station’s robotic arm will
be mounted to travel the full length of the complex.
Expedition Four Flight Engineer Carl Walz sent commands from a laptop
computer to the Mobile Transporter to move off of its launch position on
the forward face of the new S-Zero (S0) truss, and at 7:22 a.m., the
flatcar began its slow trek to an initial worksite 17 feet down a rail
which spans the entire 44 feet of the girder.
It took only a half hour to traverse the distance, but sensitive software
in the transporter prevented an automatic latching of the railcar to the
worksite. Ground controllers accomplished the latching through a
methodical series of commands.
Engineers believe that the subtle effects of weightlessness are causing
the railcar to “lift” off its tracks by a microscopic distance, thus
interfering with magnetic sensors that tell the transporter its position
relative to each worksite. The effect is that the sensors are losing
contact with magnetic positioning strips on the truss rail, preventing an
automatic latching of the transporter. Manual commanding of the latching
is working however, and the system is said to be in excellent working
The Mobile Transporter software controls about 20 motors, directing it to
travel from one point to another, latch itself down to the truss, and
plug itself into a power source. The transporter must latch with about
three tons of force to insure a stable platform for the eventual mounting
of the Canadarm2 robotic arm. On the next shuttle assembly flight to the
ISS in June, a platform called the Mobile Base System will be mounted to
the transporter upon which Canadarm 2 will eventually be attached so it
can travel the length of a football field to support future assembly of
station components.
Late today, the transporter traveled to a second worksite where manual
latching commands were again required, then inched back to the first
worksite, where the railcar was manually latched in place for a final
time and parked at 5:40 p.m. Central time to await the arrival of the
Mobile Base System component on the STS-111 mission. In all, the
transporter traveled 72 feet from worksite to worksite at a glacial pace
of about one inch per second.
Engineers believe a minor software modification may restore the
transporter’s ability to automatically latch itself to any worksite. All
other transporter systems functioned perfectly throughout its initial
Atlantis Commander Mike Bloomfield, Pilot Steve Frick, Mission
Specialists Ellen Ochoa, Rex Walheim, Lee Morin, Jerry Ross and Steve
Smith, and Expedition Four Commander Yury Onufrienko and Flight Engineers
Walz and Dan Bursch spent the day monitoring the transporter tests and
continued the transfer of equipment and supplies from Atlantis to the
In addition, about 100 pounds of oxygen and 50 pounds of nitrogen have
been transferred from Atlantis to the tanks on the Quest Airlock to
support future spacewalk activity.
The fourth and final spacewalk of the flight will be conducted on Tuesday
by Ross and Morin beginning around 9:30 a.m. Central time. At the start
of the planned 6 ½ hour excursion, Ross and Morin will pivot a 14-foot
ladder away from the S-Zero truss for attachment to Quest to act as a
pathway for future spacewalkers. They will also install external lights
on the Unity module, test microswitches on the sides of the S-Zero truss
which will be used to confirm the attachment of future truss segments,
troubleshoot a balky bolt on a cable cutting system on the Mobile
Transporter and tie down a portion of insulation on one of four
navigational antennas on the S-Zero.
The ten Shuttle and Station crew members are scheduled to begin an
eight-hour sleep period at 7:44 p.m. Central time and will be awakened
shortly before 4 a.m. Tuesday to prepare for the final spacewalk of the
The JSC newsroom is now closed and will reopen no later than 5 a.m.
Central time Tuesday.
The next STS-110 mission status report will be issued Tuesday morning
after crew wake up, or earlier, if events warrant.  

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