STS-75 Day 3 Highlights
to STS-75 Flight Day 02 Highlights:
On Saturday, February 24, 1996, 8 a.m. CST, STS-75
MCC Status Report # 04 reports:
Troubleshooting a balky experiment data relay box was the focus of work
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 operations.
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 cargo bay.
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
On Saturday, February 24, 1996, 6 a.m. CST, STS-75
Payload Status Report # 03 reports: (1/15:42 MET)
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
to replace the faulty connection with a spare cable.
After complete reactivation of the Core, SETS
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
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
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.
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.
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 reports:
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 operations.
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. CST Sunday.
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
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 science operations.
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 satellite deployment.
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
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 angles.
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.
science team members viewed live video images and sent voice commands to
vary the filters and exposure setting for better viewing. The heart of
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
The crew also resumed calibration of on-board instruments and electron
accelerators, including one test of the Shuttle Electrodynamic Tether System
instruments, mounted in the cargo bay, will make measurements of tether
voltage and current, as well as background magnetic fields and plasma characteristics.
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.
to STS-75 Flight Day 4 Highlights: