STS-46 (Atlantis / Tethered Satellite)

Background

By the early 1990s, the Space Shuttle program had matured into a platform for ambitious scientific partnerships that no single nation could pursue alone. STS-46, assigned to orbiter *Atlantis*, brought together two such collaborations simultaneously: the European Retrievable Carrier (EURECA), a free-flying science platform developed by the European Space Agency, and the Tethered Satellite System (TSS-1), a joint NASA–Italian Space Agency experiment that aimed to test one of the more unconventional ideas in orbital mechanics — using a long conducting wire to generate electrical power from Earth's magnetic field.

The TSS-1 concept traced its theoretical roots to proposals from the 1970s, most closely associated with Italian scientist Giuseppe Colombo and NASA researcher Mario Grossi. The principle was elegant: a satellite connected to the Shuttle by a conducting tether tens of kilometres long would move through Earth's magnetosphere, and the relative motion between the wire and the field would induce a current, effectively turning the tether into a dynamo. If the experiment succeeded, it could point toward future spacecraft that harvested power without solar panels or fuel cells. The European Space Agency's EURECA platform, meanwhile, carried microgravity research payloads that would operate autonomously in orbit before being retrieved on a later Shuttle mission.

Crew and Preparations

STS-46 assembled a multinational crew of seven that reflected both the international character of its payloads and the broadening reach of human spaceflight. Commander Loren Shriver and Pilot Andrew Allen led the flight deck, supported by Mission Specialists Jeffrey Hoffman, Franklin Chang-Díaz, and Marsha Ivins. Two payload specialists rounded out the crew: Claude Nicollier of Switzerland, flying for the European Space Agency, and Franco Malerba, representing the Italian Space Agency. Malerba's presence was particularly significant — he would become the first Italian citizen to reach space.

Preparations for the tether experiment were technically demanding. The TSS-1 satellite would be deployed upward from the Shuttle's payload bay using a specially designed boom and reel mechanism mounted in the cargo bay. Controllers planned to pay out the tether gradually, allowing the system to stabilize dynamically as the satellite climbed to a target distance of roughly 20 kilometres. At that separation, theory predicted a measurable electromotive force and a modest but meaningful electrical current through the tether.

The Flight

*Atlantis* lifted off from Kennedy Space Center on 31 July 1992. The moment of launch carried immediate historical weight: Franco Malerba became the first Italian to fly in space, a milestone celebrated both by the crew and by observers in Italy following the mission closely.

The crew first turned their attention to EURECA. The platform was successfully berthed and released from the payload bay, departing *Atlantis* to begin its independent science mission. EURECA carried experiments in materials science, life sciences, and fundamental physics, and its deployment went smoothly, freeing the crew to concentrate on the tether demonstration that was the mission's most technically novel element.

At approximately 25 hours into the flight, controllers began the TSS-1 deployment sequence. The satellite rose slowly above the payload bay, and the reel mechanism began feeding out the conducting tether. Initial progress was encouraging, with the system appearing to behave as predicted during the earliest phase of deployment. Then, at approximately 256 metres of tether extended — a small fraction of the planned 20 kilometres — the mechanism jammed. The reel halted, and repeated attempts to free the obstruction and resume deployment were unsuccessful. The crew and ground teams worked systematically through the problem, but the tether could not be advanced further. After exhausting the available options, mission controllers accepted that the full-length deployment would not be achieved on this flight, and the satellite was retrieved back into the payload bay.

Post-flight analysis identified a protruding bolt in the reel mechanism as the likely cause of the jam. It was a small hardware deficiency with large consequences: the scientific objectives that depended on the full tether length — particularly the electrical power generation measurements — could not be meaningfully assessed at 256 metres. The TSS-1 experiment, for all its conceptual elegance, had been stopped nearly 98 percent short of its goal.

The remainder of the mission proceeded without major incident. *Atlantis* performed its deorbit burn at approximately 190 hours and 35 minutes after launch, with the orbiter touching down at Kennedy Space Center roughly 40 minutes later, closing a mission of just under eight days.

Legacy

STS-46 occupies a distinctive position in Shuttle history as a mission defined as much by what it attempted as by what it achieved. EURECA's release was a success that paid scientific dividends when the platform was retrieved by STS-57 the following year. But it was the tether experiment that left the more lasting imprint on the program's story.

Rather than abandoning the concept, NASA and the Italian Space Agency treated STS-46 as a critical engineering lesson. The tether mechanism was redesigned, and the experiment flew again as TSS-1R on STS-75 in 1996. That reflight came far closer to success — the tether was deployed to nearly its full planned length — but was ended dramatically when the tether broke due to electrical arcing, severing the satellite and sending it drifting into a higher orbit. The two missions together demonstrated both the genuine physical promise of electrodynamic tether technology and the significant engineering challenges that stood between the concept and practical application.

Franco Malerba's flight on STS-46 opened the path for subsequent Italian astronauts through the ESA corps, and the mission reinforced the model of deep international collaboration — crew, payloads, and hardware from multiple nations operating as a single integrated effort — that would define the architecture of the International Space Station era. The TSS program, incomplete across both of its attempts, nonetheless generated data and understanding that informed tether research for years afterward, keeping alive a vision of spacecraft that draw their power directly from the environment through which they move.