STS-75 Day 5 Highlights

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On Monday, February 26, 1996, 1 a.m. CST, STS-75 Payload Status Report # 07 reports: (3/10:42 MET)

The tether on the Italian Tethered Satellite System (TSS-1R) separated at about 7:30 p.m. CST Sunday as the satellite was nearing the full extent of its deployment from the Shuttle. Just prior to last evening's unexpected separation of the tether attaching the satellite to Columbia's cargo bay, science activities aboard the STS-75 Tethered Satellite System reflight (TSS-1R) mission had been proceeding very smoothly, resulting in collection of about five hours of extensive and exciting scientific data on the performance of the satellite and tether dynamics and electrodynamics before the break.

Tethered Satellite System science teams were able to take good advantage of this period of deployed operations to collect data on a variety of phenomena including the generation of electrical current as the extended structure of satellite, tether and Shuttle circled the Earth at approximately five miles per second.

Soon after satellite release at 2:45 p.m. Sunday, the science investigators began stepping through their plans for conducting integrated science operations during the satellite-unreeling phase of the TSS-1R mission. Primary objectives for this phase included characterizing relatively low-voltage operations of the tether system, with controlled electric current flows through the tether and associated electron gun firings from apparatuses mounted in the Shuttle cargo bay.

Tether voltages of as high as 3,500 volts were developed across the tether, and current levels of approximately 480 milliamps, or nearly half an amp were achieved, giving the science teams an indication of results surpassing expectations.

During deployment, science teams for the Deployer Core Equipment (DCORE), led by Dr. Carlo Bonifazi of the Italian Space Agency, operated their electron generators successfully completed initial performance-evaluation runs, generating a 480 milliamp current along the tether. That level was nearly 200 times greater than that obtained during the TSS-1 (STS- 46) mission, which was limited to a much lower voltage (60 volts) by the shorter tether length. The Core team members reported that their equipment was performing better than predicted by analytical models.

It was pointed out that at the time of the break, the electrical system had been in a passive mode with no current flow in the tether for over four minutes. The tether apparently separated 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.

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 orbit forces. TSS is separating from the Shuttle at a rate of 420 miles each 90 minute orbit. Following the separation, Mission Control asked the astronauts to record television of the boom and the broken tether for post-flight analysis.

The several hours of deployed operations were summarized by Mission Specialist Jeff Hoffman aboard Columbia, who noted "We did get a lot of good data during the deploy." 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

On Monday, February 26, 1996, 10:00 a.m. CST, STS-75 MCC Status Report # 09 reports:

Columbia's astronauts are preparing to retract the Tethered Satellite boom structure today after the Italian science probe suddenly seperated from the Shuttle last night following a break in the tether. The boom tower, upon which TSS was anchored prior to its deployment Sunday afternoon, will be slowly lowered back into its berthing platform once the remaining tether inside the boom is reeled in.

After its connecting cable seperated from Columbia last night, the Tethered Satellite is trailing the Shuttle at a distance of more than 3,000 nautical miles this morning.

The satellite is in an orbit about 30 miles above Columbia and the distance between the two spacecraft continues to increase at a rate of about 280 nautical miles with every orbit of the Earth. At the time the tether broke, it was extended 12.2 miles from Columbia, just short of its planned 12.8 mile fully-deployed length.

About 32 feet of tether remains on the reel assembly inside the TSS support boom in Columbia's payload bay. Once the tether is fully retracted, the 39-foot boom will be restowed to its launch configuration. On Columbia, the astronauts this morning saved TSS onboard computer data for post-flight analysis.

Once the tether is retracted and the boom is restowed, the crew members will turn their attention to the science activities involving the U. S. Microgravity Payload. The USMP experiments will study various aspects of materials science investigation.

On Monday, February 26, 1996, 5 p.m. CST, STS-75 MCC Status Report # 10 reports:

Astronauts aboard Space Shuttle Columbia today reeled back the remaining length of tether and stowed the mast for the Tethered Satellite System following last night's loss of the satellite. The crew and flight control teams spent much of the day putting TSS equipment in a safely stowed condition and preparing for experiment operations with the U.S. Microgravity Payload.

The Italian Satellite unexpectedly separated from Columbia about 7:30 p.m. CST Sunday as the tether broke within the mast. No immediate explanation for the incident was apparent and the crew and Mission Control concentrated last night and today on gathering any data that might be useful in discovering the cause. NASA today named a board chairman for the investigative body looking into the incident. Members to the board are expected to be named within a few days.

Following separation from Columbia Sunday, the satellite moved rapidly away from the Shuttle into its higher orbit. The satellite is in an orbit about 30 miles above Columbia and the distance between the two spacecraft continues to increase at a rate of about 280 nautical miles with every orbit of the Earth. At the time the tether broke, it was extended 12.2 miles from Columbia, just short of its planned 12.8 mile fully-deployed length.

The crew members will now turn their attention to the science activities involving the U. S. Microgravity Payload. The USMP experiments will study various aspects of materials science investigation. The astronauts held a crew news conference today at 2:03 p.m. Central time to discuss the loss of the Tethered Satellite and other aspects of their flight.

On Monday, February 26, 1996, 6 p.m. CST, STS-75 Payload Status Report # 08 reports: (4/3:42 MET)

After successfully reeling in the remaining tether and stowing the deployer boom, the STS-75 crew aboard the Shuttle Columbia resumed the normal mission timeline. They turned their attention to completing post-satellite-retrieval science and starting full-up operations for the third United States Microgravity Payload (USMP- 3). During USMP-3, the crew will conduct combustion science experiments in the middeck glovebox, while crystals for high- technology electronics and industrial metals research grow in materials processing furnaces in the cargo bay. Also, researchers located at Spacelab Mission Operations Control will explore a substance as it simultaneously exists in two states of matter, liquid and gas, to shed light on how materials can be manipulated on Earth by looking at how they act in microgravity.

As part of TSS post-satellite-retrieval investigations, the Shuttle Potential and Return Electron Experiment (SPREE) and Shuttle Electrodynamic Tether System (SETS) continued making measurements of the plasma environment in the Shuttle's cargo bay. The crew maneuvered Columbia into position for both instruments to gather more information about the composition of the upper atmosphere in the Shuttle's wake, similar to that of a boat moving through water. In addition to supersonic wakes produced by the orbiter, the payload bay often houses structures that form their own wake, adding to the complexity of the environment surrounding the system. Since wake profiles are difficult to accurately predict, especially at the edges, SETS mapping will enhance future missions.

Relecting over the activities of the past 24 hours, Mission Manager Robert McBrayer confirmed that a good deal of data is "in the bank" and reported that ground crews are gathering evidence to determine what happened to cause the tether to break. He added that "everyone is happy over what we got, and disappointed over what we didn't get."

Describing more than five hours of data collected during the deployment phase, Tethered Satellite System Mission Scientist Dr. Nobie Stone reported that "things in the data really pop out at you, that are unexpected and unexplained. We are anxious to see what these are and what they entail." Data showed that current levels in the unreeling tether were higher than predicted by the models and that electrons detected at the satellite, when current flowed in the tether, were much more energetic than expected.

Although obviously disappointed with the loss of the tethered satellite, scientists got an exciting glimpse of the data they had hoped to collect at full deployment. The Tethered Satellite System Science Investigator Working Group at Spacelab Mission Operations Control is looking at options for reactivating the satellite as it flies over the Johnson Space Center on Tuesday to gain additional insight into Earth's charged atmosphere. Plans are tentative at this time.

Dr. Carlo Bonifazi, of the Italian Space Agency, summed up mission accomplishments by saying that "when you do research, it's not the amount of data you collect that's important, but the information that you can extract from the data. If we discover two weeks from now that we got the information we were looking for to understand the basic behavior of the system, we could move forward." Payload Specialist Dr. Umberto Guidoni also observed that for the first time, "we demonstrated that tether dynamic applications work and we can generate electricity using tethers."

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