Swiss instruments to measure solar activity

The Hessi satellite should provide answers to some of the sun's mysteries.

Swiss scientists from the Paul Scherrer Institute (PSI) in canton Aargau have built a series of new instruments to survey the Sun. The devices are part of an American satellite due to be launched from Florida this week.

This content was published on June 11, 2001 - 17:07

The High Energy Solar Spectroscopic Imager (HESSI) satellite is to measure peak solar activity, which happens every 11 years. Scientists hope to find the reasons of some well-known phenomena.

"We want to observe solar flares", says Alex Zehnder, head of the astrophysics laboratory at PSI. "These events produce energy equivalent to millions of atomic bombs."

This solar activity produces high atmospheric disturbances, which lead to distortions of radio waves. The explosions are also behind the famed Northern Lights.

The high-resolution instruments produced by the PSI should help answer some of the questions that are puzzling researchers.

The most important Swiss device is a kind of telescope, which "sees" X-rays and gamma rays. The telescope is small because of a lack of space on board. Among its tiny parts are a grid-like filter, used to view X-ray activity. The distance between the grid elements is less than a third of the width of a human hair.

Two other elements onboard HESSI are an electronic eye, which determines the centre of the sun 120 times a second, and a camera which films the star field.

These two instruments allow the satellite to position itself relative to known stars. "We need to know at all times exactly what we are looking at", said Zehnder.

The equipment underwent extensive tests to see if it was up to withstanding a punishing stay in space where temperatures can vary between -30 degrees Celsius and +50.

Vibrations at lift-off are also another problem faced by the designers. "We tested the systems at 10 times the Earth's gravitational force, and nothing seemed to suffer from it", said Zehnder.

The scientists won't have to wait long after the launch to discover if all their work was worth it. The satellite will start transmitting 10 minutes after lift-off, and the systems will be switched on after nine hours.

If all goes well, the first pictures of the sun should be relayed back to Earth a week later.

The HESSI project has cost the American space administration, NASA, $73 million (SFr131 million). The satellite is to be launched by a Pegasus rocket, which is carried aloft by a jet aircraft.

swissinfo with agencies

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