Solar Orbiter: PHI passes hardware tests

The instrument behaves in space exactly as planned - and has already set a record.

April 23, 2020

An important milestone has been reached in the commissioning of the instrument PHI (Polarimetric and Helioseismic Imager) on board ESA's Solar Orbiter spacecraft: comprehensive tests have shown that the instrument's hardware is working perfectly. Over the past few days and weeks, scientists and engineers from the Max Planck Institute for Solar System Research (MPS) have successfully commissioned all of the telescope’s operating modes.

The Solar Orbiter spacecraft ist currently on its way towards the Sun.

PHI consists of two telescopes that image the Sun and also study the its magnetic properties. At the closest approach to the Sun, the High Resolution Telescope can image structures with a size of 200 kilometres on the solar surface. In contrast, the Full Disc Telescope keeps the entire solar disc in view.

"Both telescopes work exactly as we designed them to - and give an idea of what PHI will be capable of during the further course of the mission," PHI Instrument Scientist Dr. Achim Gandorfer from MPS sums up. The instrument already holds a record: it is the telescope that has peered at the solar surface from the smallest distance from the Sun, namely from about 0.8 astronomical units (equivalent to almost 120 million kilometres). In the course of the mission, Solar Orbiter will fly within 0.28 astronomical units of the Sun.

However, the commissioning of PHI has not yet been fully completed. "An important building block for later scientific investigations is the data processing in the instrument itself", explains Dr. Johann Hirzberger, PHI Operations Scientist at MPS. Solar Orbiter offers a comparatively low data transmission rate due to the large distance to the Earth. However, since imaging instruments like PHI generate large amounts of data during scientific operations, the telescope processes and reduces the data onboard. From mid-May onwards, MPS scientists and engineers will test whether this feat works as planned.

The Solar Orbiter space probe was launched into space on 10 February this year and is currently on its way to its designated trajectory around the Sun. Solar Orbiter is an ESA mission with strong involvement from NASA. The aim of the mission is to make unprecedented close-up observations of the Sun from high latitudes, to provide the first images of the Sun's unexplored polar regions, and to study the connection between the Sun and Earth. PHI was developed and built under the leadership of MPS. The institute is also involved in the instruments EUI, Metis, and SPICE.

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