STS-75 Day 4 Highlights

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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 investigations.

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 reports:

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 morning.

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 hours.

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 hours.

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 reports:

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 miles.

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 mission.

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 begin.

On Sunday, February 25, 1996, 9:30 p.m. CST, STS-75 MCC Status Report # 08 reports:

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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