STS-75 Day 4 Highlights
Back to STS-75 Flight Day 03 Highlights:
- On Sunday, February 25, 1996, 6 a.m. CST, STS-75 Payload Status Report # 05
reports: (2/15:42 MET)
- "At this point, all of the instruments are working fine and
returning data," concluded Theory and Modeling in Support of Tether
(TMST) Principal Investigator Dr. Adam Drobot in a live interview with
WSFA-TV in Montgomery, Alabama. "I think everybody is quite excited
that things are going very well." Last night, data collection for the
STS-75 mission continued to take advantage of the additional science
opportunities afforded by the extra day of predeployment operations as
the crew performed science activities in preparation for this
afternoon's deployment of the Tethered Satellite System (TSS- 1R).
- These activities included observations of electrically charged, or
"ionized," gas in Columbia's environment and its interactions with
electron beams and orbiter water dumps. This will enhance the control
and monitoring of the electrical charge on the Shuttle as it moves
through the ionosphere. During tethered satellite deployment, the
tether's ability to form a complete circuit and generate electrical
power will be dependent on the path electrons take while traveling in
the vicinity of the orbiter's immediate environment and the satellite.
According to TSS-1R Mission Scientist Dr. Nobie Stone, the science
teams have already gathered "very interesting data" from these
- One of the investigations involved using the Shuttle Electrodynamic
Tether Effects (SETS) experiment's Fast-Pulse Electron Guns to fire a
series of electron beams along the Earth's magnetic field lines. It
also used the Shuttle Potential and Return Electron Experiment (SPREE)
to detect returning electrons which were reflected back into the
payload bay. This reflection results from a variety of processes,
including scattering by neutral particles and magnetic reflection.
- Another investigation of Columbia's surroundings made use of the
orbiter's Flash Evaporator System (FES). To accomplish this
experiment, the crew participated in activating and deactivating the
orbiter's water release systems and manually operating the Shuttle's
attitude control system jets. This provided a controlled means of
studying the distribution of neutral and charged particles in the
vicinity of the payload bay during Shuttle water dumps.
- Meanwhile, science teams at the Marshall Space Flight Center used
the SETS experiment's instruments to give measurements which related
to the ionized gas as it interacted with the water cloud. The water
molecules in this cloud exchanged electrical charges with the
surrounding ionized oxygen and formed a ring shape which could be
easily distinguished from the ionized gas background around Columbia.
This gave scientists and crew members an idea of how the Shuttle's
environment might react to water dumps released while the tethered
satellite is deployed.
- For a third investigation of the orbiter's ionospheric surroundings,
the SETS and SPREE experiments teamed up with the Tether Optical
Phenomena (TOP), Research on Orbital Plasma Electrodynamics (ROPE) and
Research on Electrodynamic Tether Effects (RETE) experiments to study
the electron beams fired from the SETS experiment's electron gun.
Previous measurements indicated that a thin electron beam emitted from
the orbiter quickly expands in width to form a cylinder. The
effectiveness of these electron emissions from the orbiter depends on
various factors, including the beam's direction, the local
ionosphere's density, and the orbiter's electrical potential compared
with that of the ionosphere.
- While Mission Specialist Claude Nicollier used the TOP camera to
watch the electron beams, the tethered satellite-mounted ROPE and RETE
experiments used their plasma diagnostic instruments to observe the
beams during both sunlight and darkness to obtain data.
- The RETE investigation also participated in an electromagnetic
environment calibration with the SETS instruments. This calibration
observes low-frequency waves not produced by the tethered satellite.
Sources of these waves include interaction of the orbiter with the
ionosphere, ground-based transmitters, atmospheric lightning, orbiter
electrical machinery and electron gun firings. Essentially, this
experiment calibrates the "background noise" that can be picked up by
tethered satellite instruments.
- The RETE experiment, led by Dr. Marino Dobrowolny of the Italian
Space Agency, will provide information about the electrical potential
of the ionized gas, or "plasma," sheath that will surround the
tethered satellite during its deployed operations. The ROPE
investigation, led by Dr. Nobie Stone of the Marshall Space Flight
Center, is designed to study the behavior of charged and neutral
particles around the tethered satellite under a variety of conditions.
Last night, these investigations helped scientists to determine how
quickly electrons will be returned to the ionosphere to complete the
tether system's electrical circuit and allow the tethered satellite
system to generate electricity.
- During the night, the crew also reconfigured the laptop computer to
enable it to communicate with both cores of the smartflex data relay
in Columbia's cargo bay. During the next twelve hours, actual
deployment operations for the tethered satellite will begin at 2:45
p.m., CST as the crew releases the satellite so it can be reeled out.
- On Sunday, February 25, 1996, 8:00 a.m. CST, STS-75 MCC Status Report # 06
- Columbia's crew will begin the deploy sequence of the Tethered
Satellite System about 2:45 this afternoon after a one-day delay to
allow flight controllers and the astronauts additional time to
properly check out the various science instruments and equipment that
will be used throughout the two-day operation.
- The delay also gave flight controllers time to refine any
troubleshooting procedures that might be used in the event the Smart
Flex computer relay system develops problems during the deploy
operations. The system has been operating trouble-free for more than
24 hours since being systematically checked out early Saturday
- Prior to initiating the deploy sequence, the boom supporting the
Tethered Satellite will be raised out of the payload bay to a height
of about 39 feet. The satellite will be released from its docking
ring capture latches at the top of the boom and will slowly and
deliberately be deployed to a distance of slightly more than 12 mile
(20 kilometers) over a five and a half hour period. The satellite
will remain 'on station' for science operations for about 22
- Retrieval of TSS would follow with the satellite being reeled back in
during another five and half hour period, stopping for additional
science data gathering at a distance of about one mile from the
Shuttle. This second 'on station' operation is scheduled to
last for nine hours before the final retrieval and docking of the
satellite. The entire TSS operation is scheduled to last about 48
- Communications and commanding of the satellite during deploy and
retrieve is done by a radio link to the Space Shuttle by ground
commands from NASA's Marshall Space Flight Center in Huntsville,
which has overall program management for the TSS project.
- With Columbia's systems in excellent shape, activities today are
focused on the deploy of the Tethered Satellite. Columbia continues
to circle the Earth every 90 minutes at an altitude of 184 miles.
- On Sunday, February 25, 1996, 6:00 p.m. CST, STS-75 MCC Status Report # 07
- Three and a half years after an errant bolt halted its deployment, the
Italian Tethered Satellite successfully began its journey from the
Shuttle Columbia for two days of scientific studies.
- Suspended at the end of a slim tether, the satellite's thrusters
nudged TSS away from a docking ring atop a 40-foot boom towering over
Columbia's cargo bay at 2:45 PM Central time. The satellite slowly
moved away from Columbia into the darkness of space as the astronauts
reported little oscillation in the long tether. An hour later, the TSS
had passed the distance of maximum deployment achieved on its previous
flight, 843 feet, during the STS-46 mission in the summer of 1992.
- Astronauts and ground controllers overcame previous difficulties
with data handling equipment and portable computers which had caused a
one-day delay in the deployment. Operating on a normal timeline
today, the crew checked out the satellite and its associated systems
before extending the TSS boom above the bay like a giant tower. After
making sure that Columbia and the TSS could communicate over radio
links, a power umbilical to the satellite was released, placing the
satellite on internal battery power. Columbia's maneuvering jets
were temporarily disabled during the TSS deployment, to avoid any
disturbances to the tether during the satellite's initial flyaway.
- TSS is expected to reach its farthest distance from Columbia,
almost 13 miles, by late this evening for more than 24 hours of
scientific studies on electromagnetic phenomena and the use of tethers
for satellite management. The satellite will begin its slow creep back
to Columbia Monday night in advance of its final retrieval and docking
back on its boom at about 12:43 PM Central time Tuesday afternoon.
- Columbia is functioning perfectly in support of TSS operations as it
orbits the Earth every 90 minutes at an altitude of about 180 statute
- On Sunday, February 25, 1996, 6 p.m. CST, STS-75 Payload Status Report # 06
reports: (03/03:42 MET)
- Today marked a major milestone as the STS-75 crew aboard the Space
Shuttle Columbia began deploying the joint NASA/Italian Space Agency
Tethered Satellite System (TSS) on schedule at 2:45 p.m. CST. The
world watched as the satellite smoothly and gently lifted from its
cradle atop the latticework boom that previously had been extended
some 40 feet (11.3 meters) out of Columbia's cargo bay. The crew
continues carefully unreeling the satellite on its slender tether.
Mission Specialist Jeffrey Hoffman reported that "the satellite is
rock solid," an observation confirmed by downlinked telemetry being
viewed by the TSS ground crew.
- After Mission Manager Robert McBrayer of the Marshall Space Flight
Center affirmed that his team was ready, the crew began actual
deployment, known as "flyaway," by activating small tether-aligned
thrusters mounted on the satellite. It will take about 5.5 hours for
the 12.8-mile (20.7-kilometer) tether to fully extend above the
Shuttle. Although not yet fully deployed, voltage is already being
created across the copper-cored tether, and current is flowing
through the tethered system.
- Shortly before flyaway, Mission Scientist Dr. Nobie Stone, also of
the Marshall Center, made a final readiness check among the 12
science teams at Spacelab Mission Operations Control. He then gave
the go-ahead to initiate the master timeline. This timeline is a
computer-controlled sequencing of science instrument activities. One
unique feature of this mission is the TSS investigations effectively
work together as a single experiment to learn more about Earth's
charged particle environment and how tethered satellites might be
used to generate power in space.
- At full deployment, more than 22 hours of science data collection
will begin. During this mission phase, known as "On Station 1,"
researchers will gather the real-world information needed to verify
theories and computer-based models for many physical processes active
in the Earth's near-space environment and for a number of proposed
future uses of tethers in space. Ideas range from producing
alternate forms of spacecraft power, to unraveling the mysteries of
Earth's upper atmosphere by deploying instruments downward into
regions that have not been fully explored.
- The TSS Deployer Core Equipment (DCORE) Principal Investigator Dr.
Carlo Bonifazi, of the Italian Space Agency, reported that the DCORE
successfully completed the first performance run at about a 3.8 mile
(6 kilometer) tether length, generating a current of 195 milliamps, a
level 97 times greater than the level obtained during the TSS-1
- DCORE consists of control electronics and two electron accelerators,
known as electron guns. These will be used to reemit the electrical
charge that collects on the satellite as the TSS moves through
Earth's electromagnetic field and flows down the tether to the
neutral environment in the cargo bay. These electron guns, and those
provided by the Shuttle Electrodynamic Tether System, then will eject
these electrons back into the ionosphere, effectively continuing the
circuit required for current to flow.
- Activities between science teams and crew members were carefully
coordinated as final deployment preparations were completed.
Predeployment science activities earlier in the day included
gathering more baseline data, effectively "testing the waters" around
the Shuttle and in its cargo bay prior to initiation of more complex
conditions that accompany deployed operations.
- Pressure readings and profiles of the electron and ion density in the
vicinity of the Shuttle and in its cargo bay were made by orbiter-
mounted Shuttle Potential and Return Electron Experiment instruments
and satellite-mounted Research on Orbital Plasma Electrodynamics
instruments. At the time these measurements were made the Research
on Orbital Plasma Electrodynamics experiment was still located in the
Columbia's cargo bay. These measurements give scientists and
engineers a better understanding of how the shuttle-tether-satellite
system works during full deployment operations.
- During the next 12 hours, full-up science activities are expected to
- On Sunday, February 25, 1996, 9:30 p.m. CST, STS-75 MCC Status Report # 08
- The tether on the Italian Tethered Satellite broke about 7:30 p.m. CST
Sunday as the satellite was nearing the full extent of its deployment
from the Shuttle. The satellite, which was nearing the end of its
planned 12.8 mile distance, immediately began accelerating away from
Columbia at a rapid rate as a result of normal orbital forces. TSS is
separating from Columbia at a rate of 420 miles each 90 minute orbit.
- The tether apparently snapped near the top of the 39-foot TSS boom
in Columbia's cargo bay. Neither the astronauts nor the Space
Shuttle were ever in any danger.
- Following the break, Mission Control asked the astronauts to record
television of the boom and broken tether for post-flight analysis.
- Flight controllers now will be determining when and how to secure
the TSS support equipment, including the deployment boom, before
moving on with other mission objectives. Scientists and engineers
managed to gather about five hours of data on the performance of the
satellite and tether dynamics before the break.
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