STS-75 Day 3 Highlights
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- On Saturday, February 24, 1996, 8 a.m. CST, STS-75 MCC Status Report # 04
- Troubleshooting a balky experiment data relay box was the focus of
work aboard Columbia throughout Friday night and into this morning as
the astronauts and flight controllers attempted to track down the
problem and preserve their options for deploying the tethered
satellite at 2:37 this afternoon.
- Early this morning, in a methodical step-by-step process, the crew and
flight control team slowly activated several experiments individually
at first and then together trying to isolate the problem. At about 2
a.m., all experiments were activated and data was being transferred
through the relay box to a laptop computer on the flight deck of the
orbiter and data was transmitted successfully to the ground. The
computer relay is continuing to perform well and is not evidencing any
of the communications problems previously observed. Mission Managers
are meeting this morning to review the system's status and make a
determination on whether to deploy TSS on time or to delay 24 hours.
- Called a Smart Flexible Multiplexer Demultiplexer, or "Smart Flex"
for short, the relay box reset itself several times and even
switched to an alternate system on occasion when it perceived it was
being overloaded by the checkout work associated with ensuring the
experiments were ready to support Tethered Satellite System
- The relay box is used as a way station for obtaining and distributing
data collected from four science experiments designed to take
measurements during the deployment, on- station, and retrieval
operations of the satellite. The "Smartflex" must be operating
for a deploy of the tethered satellite since it provides data and
commands to the satellite-related experiments and equipment in the
- Once deployed, the tethered satellite will slowly fly away from
Columbia, eventually reaching a distance of 12 miles (20 kilometers).
Communications and commanding of the satellite itself during deploy
and retrieve is done by a radio link to the Space Shuttle by ground
commands from NASA's Marshall Spaceflight Center in Huntsville,
which has overall program management for the TSS project.
- The tethered satellite will slowly be deployed to a 12 mile distance
over a five and a half hour period. The satellite will remain "on
station" for science operations for about 24 hours. The retrieval
process would follow with the satellite being reeled back in during
another five and half hour period.
- On Saturday, February 24, 1996, 6 a.m. CST, STS-75 Payload Status Report # 03
reports: (1/15:42 MET)
- After TSS-1R Payload Commander Franklin Chang-Diaz finished
replacing a defective cable connecting the Data Display and Control
System (DDCS) laptop computers and the smart flexible
multiplexer/demultiplexer (smartflex) computer in Columbia's cargo
bay, Mission Specialist Claude Nicollier reactivated the Tethered
Satellite Deployer Core Equipment, the Shuttle Potential and Return
Electron Experiment (SPREE) and the Shuttle Electrodynamic Tether
System (SETS). Science teams at the Marshall Space Flight Center in
Huntsville then readied all three experiments for performing
preliminary measurements. Currently, the satellite-carried
experiments are all operating well in preparation for Saturday's
afternoon deployment of the Tethered Satellite System (TSS- 1R).
- Earlier in the day, the smartflex computer, which sends crew
commands to the tethered satellite and collects science data,
experienced some timing errors, causing it to automatically switch to
its backup system. The DDCS laptop computer in Columbia's cabin that
displays TSS data had also been operating sluggishly. Ground
controllers and engineers at Marshall did intensive troubleshooting
with computers on the ground to simulate and diagnose the problem.
After determining that a defective cable had caused overloads in both
computers, they then requested Chang-Diaz to replace the faulty
connection with a spare cable.
- After complete reactivation of the Core, SETS and SPREE experiments,
the smartflex computer relay again experienced errors and
automatically switched over from its backup system, in which it had
been operating since the earlier timing errors, back to its primary
system. The crew then worked to reconfigure the laptop computer to
restore communications and command ability to the experiments.
Chang-Diaz again disconnected the laptop cable and successfully
rebooted the computer.
- While reestablishing the link between the laptop and the smartflex,
Chang-Diaz reported that the smartflex, which acts like a data
switching box and checks the status of each experiment, again entered
a "warm start" or reset mode because it found that the SPREE
experiment had been deactivated. Then, he again rebooted the laptop
after Nicollier had reactivated SPREE.
- After a fourth crash of the smartflex computer, Chang-Diaz then
allowed it to operate with the three experiments turned off and only
the data acquisition and control assembly (DACA) computer activated.
Ground controllers then monitored the smartflex relay box as
Chang-Diaz activated and deactivated the Core, SPREE and SETS
experiments one at a time. After encountering no problems with any of
these experiments, he reactivated the laptop DDSC computer and
observed how it operated in conjunction with the smartflex while the
three experiments were inactive. The smartflex, laptop and the three
experiments were then successfully operated together and continue to
function normally in preparation for the tethered satellite deployment
later this afternoon.
- The SETS investigation, by Brian Gilchrist of the University of
Michigan, is designed to study the ability of the tethered satellite
to collect electrons by determining the current and voltage of the
tethered system and measuring the resistance to current flow in the
tether itself. The Italian Space Agency's Deployer Core Equipment,
developed by Dr. Carlo Bonifazi, will demonstrate the capability of a
tether system to produce electrical energy and allow studies to be
made of the tether's interaction with the ionosphere. It does this by
controlling the current flowing through the tether between the
satellite and the orbiter, and by making a number of basic electrical
and physical measurements of the Tethered Satellite System. Finally,
the SPREE experiment, conducted by David Hardy of the Department of
the Air Force, will measure the charged particle quantities around
Columbia before and during active tethered satellite operations.
- Meanwhile, Nicollier took video of Earth's horizon using the Tether
Optical Phenomena (TOP) equipment. This experiment, conducted by
Stephen Mende of Lockheed Martin, involves the use of a camera system
with image intensifiers and special filters and will provide visual
data that will allow scientists to answer a variety of questions
concerning tether motions and optical effects generated during the
Tethered Satellite's deployment. In particular, this experiment will
examine the high voltage sheath of electrically charged, or "ionized"
gas that will surround the satellite as it flies through Earth's
- One means to control the current developed by the Tethered Satellite
System involves the use of electron accelerators which return
electrons to the ionized gas, or plasma, surrounding the orbiter. The
interaction between these electron beams and the plasma is not well
understood. By using the TOP images to make measurements of the
visible light radiated by the plasma, this process, and how it affects
the spacecraft, can be better understood.
- During the next twelve hours, experiment operations will be
performed as mission managers and ground controllers meet to discuss
their schedule for deploying the tethered satellite.
- On Saturday, February 24, 1996, 10:30 a.m. CST, STS-75 MCC Status Report # 05
- STS-75 mission managers Saturday morning decided to delay deployment
of the Tethered Satellite by 24 hours to give flight controllers time
to gain additional confidence in the operations of a data relay that
provides satellite system information during deploy and science
- The Smart Flex data relay box has been stable since early this
morning, but mission managers wanted additional time to understand its
previously observed behavior. The relay box had experienced several
unexpected "restarts". It has been performing without incident,
however, since early this morning.
- The 24-hour delay also gives flight controllers the opportunity to
enhance any contingency procedures that might be used in the event the
Smart Flex develops problems during the deploy operations.
- Late this afternoon, the astronauts will begin a standard
one-day-before-deploy timeline, allowing them to catch up on some
activation steps which were omitted during the compressed timeline
which would have been required if TSS were deployed as originally
scheduled this afternoon.
- On Saturday, February 24, 1996, 6 p.m. CST, STS-75 Payload Status Report # 04
reports: (02/03:42 MET)
- With the decision to delay deployment of the joint NASA/Italian
Space Agency Tethered Satellite System (TSS) by one day, researchers
located at Spacelab Mission Operations Control are working around the
clock, analyzing initial data and ensuring that their instruments are
ready for full-up science operations. The initiation of satellite
deployment, known as "flyaway," now is scheduled for around 2:45 p.m.
- TSS principal investigators and their science teams view this
adjustment of the mission timeline as an opportunity to accomplish all
their major science objectives. Specifically, Mission Scientist Nobie
Stone, of the Marshall Space Flight Center (MSFC), pointed out that
important baseline data collection would have been sacrificed by the
rush to complete instrument activation and checkout if the satellite
deployment had not been postponed by 24 hours.
- Dr. Stone emphasized that gathering baseline measurements before
deployment is "like learning to walk before you run." Part of this
data set reveals how the sensitive TSS scientific instruments react to
periodic thruster firings to maneuver the Shuttle and the satellite.
Today's science activities included mapping Earth's charged particle
upper atmosphere, which varies dramatically as Columbia orbits through
periods of daylight and darkness every 45 minutes. Scientists will
use these and other predeployment background readings when they
analyze data collected during the more than 30 hours of planned TSS
- One example of baseline data is the Joint Science Display produced
earlier today by combining measurements gathered by several TSS
instruments. This graphical profile of the intensity of charged
particles around the Shuttle is giving scientists an indication of how
instruments may respond when the tethered satellite collects such
particles when deployed. This display showed intense electron and ion
collection in the Shuttle's flight direction, or "ram," versus the
trailing side, known as the "wake" direction.
- Another example of baseline data is a "space weather map" produced
today by the Theory and Modeling Support of Tether (TMST) Sundial
investigation. The map provides a global view of the plasma density
and temperature in the ionosphere at the altitude of the STS-75 orbit
(160 nautical miles). This map is produced from a combination of
theoretical ionospheric models and measurements obtained from 30
ground-based stations around the world.
- Mission Manager Robert McBrayer, also of MSFC, said the deployment
delay "makes sense," especially since the satellite will be operating
on battery power once the umbilical that attaches it to the Shuttle's
power system is removed shortly before flyaway. He emphasized the
satellite and its deployer, as well as the TSS experiments, have been
activated and are operating properly. McBrayer noted that ground-
based flight controllers are using the extra time to better understand
problems that arose and to develop enhanced contingency plans for
- Essentially turning back the clock 24 hours, the crew spent the day
stepping through normal science and satellite predeployment activities
that were interrupted yesterday while they performed troubleshooting
for three on-board computers. As part of a dress rehearsal for
satellite deployment, the crew maneuvered Columbia to the altitude for
satellite flyaway. They also worked through a number of steps
designed to simulate the same orbital conditions and environment for
actual deployment the satellite, including lighting and lighting
- During some nighttime orbital passes, crew members worked with the
Tether Optical Phenomena Experiment (TOP), which gave a stunning view
of atmospheric air glow and auroras over the South Pole as viewed from
the flight deck's overhead window. This is the window through which
the crew later will watch the deployed satellite. TOP science team
members viewed live video images and sent voice commands to vary the
filters and exposure setting for better viewing. The heart of the TOP
instrument is a hand-held low-light video camera with special filters
whose primary purpose on TSS is to observe luminescence produced by
electron beams and the interaction of the electrically charged
satellite with the local charged-particle and neutral atmosphere. The
TOP has many advantages over similar photographic recordings made on
previous flights because it allows real-time observations of the
images seen by the orbiter crew.
- The crew also resumed calibration of on-board instruments and
electron accelerators, including one test of the Shuttle
Electrodynamic Tether System (SETS). SETS instruments, mounted in the
cargo bay, will make measurements of tether voltage and current, as
well as background magnetic fields and plasma characteristics. SETS
also provides one electron accelerator, known as an electron gun,
designed to propel charged particles back into the ionosphere after
they travel from the satellite, down the conducting tether, and
collect in the cargo bay. The ejection of electrons is one step in
completing the circuit required for current to flow.
- During the next 12 hours, science data will continue to be
collected while the crew continues predeployment activities.
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