Bonifazi's experiment was mounted in the payload bay on the MPESS structure and its task was to control the flow of electrical current in the tether using two electron guns. Before the break, its first performance run had successfully generated a current of 480 milliamps from the electrical charge that had collected on the satellite's surface: this was 200 times greater than the levels obtained during the first TSS mission in the summer of 1992. Other experiments in Columbia's payload bay continued to operate in support of the satellite and tether until as late as 6 March.
''We did get a lot of good data during the deploy,'' Hoffman told reporters in a space-to-ground news conference. Currents measured during the deployment procedure were at least three times greater than predicted in analytical models.
Voltages as high as 3,500 volts were developed across the tether, achieving current levels of 480 milliamps. It was also possible for researchers to study the interaction of gas from the satellite's thrusters with Earth's ionosphere. A first-ever direct observation of an ionised shockwave around the satellite itself - impossible to study or model in the laboratory - was also made.
Moreover, as the satellite and its trailing 19 km of tether sped through the ionosphere, it was possible to continue investigations despite the fact that it was no longer physically connected to Columbia. On the evening of 26 February, TSS-1R Mission Manager Robert McBrayer told journalists that a good deal of data was ''in the bank'', regardless of the mishap, adding that ''everyone is happy over what we got and disappointed over what we didn't get''. Nobie Stone agreed, saying that ''things in the data really pop out at you, that are unexpected or unexplained''.
''If you don't ever get your nose bloodied, you're not in the game,'' said Lead Flight Director Chuck Shaw, paraphrasing Theodore Roosevelt's famous comment. Meanwhile, Capcom Dave Wolf told the disappointed astronauts that it was too early to speculate on the cause of the breakage. ''We are really in the data-gathering mode,'' he told them. ''The teams are assembling for a thorough review and we will all have a lot to do with that when you get back.'' In fact, an investigative board convened that same day, under Kenneth Szalai, the director of NASA's Dryden Flight Research Center in California.
On 27 February, as the free-flying satellite and tether flew above JSC's Electronic Signal Test Lab in Houston, ground controllers transmitted commands to successfully reactivate three of its onboard experiments: the Research on Orbital Plasma Electrodynamics (ROPE), the Magnetic Field Experiment for TSS Missions (TEMAG) and the Research on Electrodynamic Tether Effects (RETE). With a possible two extra days of data-gathering capabilities now re-established before the satellite's batteries were predicted to expire around 1 March, Stone's team scrambled to put together a hasty, last-minute research timetable to squeeze as much as possible from their payload.
The ROPE experiment had been developed by Stone himself and sought to examine the behaviour of charged particles in Earth's ionosphere, as well as those surrounding the satellite and tether, under a variety of conditions. Italian National Research Council physicist Marino Dobrowolny's RETE investigation, meanwhile, measured the electrical potential in the plasma 'sheath' around TSS-1R and identified waves excited by the tether. Meanwhile, the TEMAG study, provided by Franco Mariani of the Second University of Rome, mapped fluctuations in magnetic fields around the satellite.
It was hoped that, even though Columbia and TSS-1R were now physically separated by thousands of kilometres, firing electron beams from guns mounted in the payload bay would still disturb the ionosphere and be detectable by the satellite's instruments. On 28 February, scientists were able to observe a sunlight-induced electrical charge on the satellite's surface as it moved through the daytime and nighttime portions of its orbit. They also succeeded in reactivating and acquiring valuable data from two other satellite-mounted experiments. It was even possible, according to Hoffman, for ground-based observers to see TSS-1R from the southern United States.
Since the tether break, orbital dynamicists had predicted that Columbia would approach to within possible retrieval distance of TSS-1R on 29 February, and such a scenario was briefly considered but ultimately discarded due to insufficient propellant margins on the Shuttle. The retrieval, had it been approved, would have consumed up to six days of the crew's time. In anticipation of its rendezvous with Columbia, the satellite's batteries were placed in a 'low-power' mode from the late evening of 28 February until mid-afternoon on the 29th to keep it alive just long enough.
Right on cue, at 5:15 pm on 1 March, Allen spotted the satellite and its tether, just 75 km away. ''Basically, all we really see are pinpoints of light real close together,'' he said. ''It's beautiful!'' added Chang-Diaz. By this time, however, TSS-1R's batteries were rapidly failing - very weak signals had been detected through the Merritt Island and Bermuda tracking stations earlier that day - and no further signals were received after 1 March. Nevertheless, it had survived much longer than expected, prompting Stone to joke that ''it's like the Energiser bunny - it just kept on going!''
Clearly, a significant amount of electrodynamic data was gathered and Carlo Bonifazi later told reporters, ''When you do research, it's not the amount of data you collect that's important, but the information you can extract from that data. If we discover, two weeks from now, that we got the information we were looking for to understand the basic behaviour of the system, we could move forward.'' Added Umberto Guidoni: ''We demonstrated that tether dynamic applications work and we can generate electricity using tethers.'' Nonetheless, the mood on board Columbia was, for a time, grim.
''Every time I turn around and look through the window and I see this empty bay, it's like a part of myself has left,'' Maurizio Cheli told journalists. For Allen, who had been on board Atlantis for the previous ill-fated TSS mission, during which a bolt had snagged the tether early in its deployment, it was yet another blow. ''Scientists on the ground have lost a lot and we feel for them,'' he said. ''We were looking forward to demonstrating that we could actually retrieve a satellite from 20 km, and we've put an amazing amount of work into it.''
Of course, the main scientific breakthrough of the mission was, as Nobie Stone said, the discovery of tether currents three times higher than theoretically predicted. It was speculated that this might indicate some degree of ionisation around the satellite, even when its cold-gas thrusters were not switched on. In fact, when the thrusters were activated, the current climbed even higher, to 580 milliamps. Overall, Stone told journalists on 8 March, the day before Columbia came home, that TSS-1R demonstrated that its electrical current-collection and power-generation capabilities were several times higher than predicted.
The EDO pallet and now-empty TSS-1R deployer are visible in Columbia's payload bay during the STS-75 mission.
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