Freeflying Solar Observatory

One of Columbia's payloads was an important research satellite with a name even NASA's best acronym-makers could be proud of: 'SPARTAN', or the 'Shuttle-Pointed Autonomous Research Tool for Astronomy'. Weighing 1,350 kg, it was a cube-shaped box loaded with two instruments and a set of adjunct experiments and was supposed to fly freely for two days.

In effect, it was a carrier - a 'tool', as its name implied - for a variety of payloads, only a few of which had anything to do with astronomy. It had been used in January 1996, for example, to carry advanced technology experiments and on another mission in May to demonstrate an inflatable communications antenna. For Kregel's mission, it was designated 'Spartan-201' and would carry a White Light Coronagraph (WLC) and an Ultraviolet Coronal Spectrometer (UCS) to explore the outermost layers of the Sun's atmosphere (its 'corona'). The two instruments had flown before on board Spartan, on no fewer than three occasions.

Developed by the High Altitude Laboratory, the WLC was a specialised telescope that produced artificial 'eclipses' of the Sun to conduct detailed coronal observations. Meanwhile, the UCS, which had been provided by the Smithsonian Astrophysical Observatory of Harvard University, took spectroscopic measurements of the primary light emitted by highly ionised atoms, as part of efforts to determine velocities, temperatures and densities of the coronal plasma. Adjoining the

Firmly held by the RMS, the Spartan-201 satellite awaits deployment.

instruments were three technology experiments that would support their observations. The Technology Experiment Augmenting Spartan (TEXAS) would provide a real-time communications link with the WLC, as well as adjusting its alignment for optimal performance.

Spartan-201's first flight had taken place in April 1993, when it acquired more than 20 hours of data on the solar atmosphere, investigating specifically the north and south polar coronal 'holes', a southeast 'helmet' streamer and a very active region above the Sun's western limb. Eighteen months later it flew again, this time conducting observations and proton-temperature measurements in concert with the joint NASA/ESA Ulysses solar probe, which was passing 'under' our parent star's south pole at the time. Lastly, almost exactly a year later in September 1995, it performed similar work as Ulysses hurtled over the Sun's north pole.

For its fourth trip, Spartan-201 would be investigating the mechanisms responsible for heating the corona and accelerating the anomalous 'solar wind', which originates there. It was also supposed to conduct joint observations with another scientific satellite, the Solar and Heliospheric Observatory (SOHO), which had been launched in December 1995, as part of efforts to expand physicists' understanding of conditions within the corona.

''The corona has three important properties,'' said NASA manager George Withbroe. ''It's very hot, about three million Fahrenheit, it flows away from the Sun at very high speeds - about a million mph - and it's very gusty. Spartan-201 is designed to address three questions: Why is the corona so hot? How does it get accelerated to such high speeds? And why is it so gusty?'' Insights into these mysteries were expected to allow scientists to better comprehend how stars 'seed' neighbouring regions of interstellar space with matter. Moreover, said Withbroe, ''when the [solar] gusts hit the Earth, they cause a variety of effects. One spectacular example are the aurorae. When you get strong gusts, they can occasionally pump up the Van Allen radiation belts and the particles in these belts can affect spacecraft. For example, during a strong gust in April [1997], a communications satellite lost 15% of its power. A third effect of these gusts is when they hit [Earth's] magnetic field, they move it around! When you move a magnetic field and you have long conductors, like pipelines and electrical power lines, you generate currents. Most of the time, these are just a nuisance, but occasionally, when you get a really strong gust, you can damage power transformers in electric power stations. In 1989, in a particularly spectacular event, Hydro-Quebec was knocked out for nine hours, affecting six million people.''

According to pre-flight plans, Spartan-201 would be deployed by Chawla, using the RMS, on the second day of the mission and would be retrieved about 50 hours later. For its ride into orbit, the satellite was affixed to a Mission-Peculiar Equipment Support Structure (MPESS) in Columbia's payload bay. It was an important responsibility for Chawla, who became the first Indian-born woman to fly into space, but as circumstances would transpire, it would turn into her nemesis. Bad luck could not have seemed further away, however, when Columbia lifted off precisely on time at 7:46 pm on 19 November, beginning 1997's final Shuttle mission.

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