BOSTON — Astronaut Jeffrey Hoffman admits "it was a bummer for the crew" when the space shuttle Columbia lost the Italian/American tether satellite last February. But he says the experiment's scientific results have "made us feel a whole lot better."
The findings of the board that investigated the satellite loss now confirm Dr. Hoffman's view that, while the experiment involved a disappointing operational failure, it was a scientific success. Presenting the board's report at a Washington press conference Tuesday, chairman Kenneth Szalai noted that the tether broke for reasons unrelated to the basic design of the experiment. In fact, the data show that the concept of generating electricity by dragging an electrically conducting tether through Earth's magnetic field "looks like a doable and practical approach," Mr. Szalai said.
The tether satellite program, a joint project of the Italian Space Agency and the US National Aeronautics and Space Administration (NASA), is exploring the concept for generating electric power and propelling satellites.
Just as an electrical conductor moving through a magnetic field generates electricity in a power plant, so should a conductor moving through Earth's magnetic field generate electricity in near-earth space. When that conductor is tethered to a spacecraft, it can become an auxiliary power source. Also, by using spacecraft electric power to drive current through the tether, it can act like an electric motor that, reacting against Earth's magnetic field, can boost a satellite in its orbit.
But after Hoffman had reeled out 12.2 miles of the 12.9 mile tether on Feb. 22, electrical sparking tore the tether apart.
The investigation found microscopic nicks in the tether's copper wire and microscopic metal bits and other "dirt" both inside and outside the tether. With the tether operating at thousands of volts, any one of these could have punctured the insulation and led to the electrical sparking and tether burnout. No one realized how vulnerable the insulation was to such contamination. The board's recommendations include maintaining "clean-room" standards in future tether manufacture.
Meanwhile, the scientific results have surprised and delighted the team. They show tether electricity generation to be two to three times more efficient than expected and confirm that the tether could be used for propulsion as well as for generating electricity.
Although team members didn't get all the data they wanted, they did get a very informative and clean data set and have funding for a year to study it. Hoffman and others say they are eager to try again.
So far NASA has announced no plans for a tether reflight.