Studying the impact of solar wind on Earth’s magnetic field

Researchers from the University of Leicester have provided a vital element for a novel mission to examine the effect of the solar wind on Earth’s magnetic field.

Space scientists from the University of Leicester’s Space Research Centre have finalised the structural and thermal model for the UK’s latest X-ray telescope, the Soft X-ray Imager (SXI), destined for space aboard the SMILE (Solar wind Magnetosphere Ionosphere Link Explorer) probe when it launches at the end of 2024.

The model, which has now been transported to Airbus in Spain for incorporation and assessment within the prototype satellite system, is not the flight model, but will facilitate engineers’ understanding of the ultimate necessities for the final design.

Specialists will subject the prototype to the considerable vibrations, shocks, and G-forces suffered during the launch of the spacecraft, on top of the severe temperatures it must function at in space below -150oC.

Soft X-ray Imager instrument

Dr Steven Sembay, Principal Investigator (PI) for the SXI instrument, based at the University of Leicester, commented: “The STM testing is always a slightly nervous time, especially when you see videos of how much the instrument is shaken during testing!

“It is the first time you go from conceptual design in computer models to a real object in metal. I shouldn’t have worried. It is a testament to the skill of our engineering and manufacturing team that what is a complex piece of kit works as predicted.”

The SXI group is being headed by the University of Leicester in cooperation with UCL Mullard Space Science Laboratory (UCL MSSL) and the Open University, as well as European partners.

UCL MSSL is running the construction of the electronics that operate the SXI detectors and retrieve the signals that generate X-ray images of the space around the Earth.

The UK Space Agency has confirmed a total of £10.5m in funding for UK leadership roles on SMILE, such as the SXI instrument. The compact X-ray telescope is the only European instrument planned for the mission.


SMILE is the first collaborative venture between the European Space Agency (ESA) and the Chinese Academy of Sciences (CAS) from conceptual design to operations, and will study the continuous stream of charged particles emitted by our Sun.

Professor Graziella Branduardi-Raymont of UCL MSSL, European Co-Principal Investigator for the mission, explained: “One of the most interesting aspects of SMILE SXI is the fact that we are using technology so far applied for looking outwards to X-ray sources in the far Universe to study how our own Earth responds to the impact of the Sun’s activity.”

The Earth’s magnetic field

The extremely variable stream of high energy particles, known as the solar wind, affects the Earth’s magnetic field. At periods of high intensity, this stream can be a threat to space-based instrumentation or even, in exceptional cases, ground-based electrical systems.

Luckily, the Earth’s magnetic field acts as a safeguard, but this shrinks and enlarges as it reacts to variations in the highly dynamic solar wind.

SXI will incessantly examine the location of the boundary between the region of space controlled by the Earth’s magnetic field and the solar wind. Its images will, in concurrence with the other instruments on SMILE, assist scientists in refining models of how this Sun-Earth connection reacts to the most infamous example of ‘space weather’.

Dr Caroline Harper, Head of Space Science at the UK Space Agency, concluded: “Space weather – such as the solar wind – has the potential to disrupt satellites we rely on every day for services such as global communications or managing power grids.

“This mission is a prime example of how, by working with our international partners, the UK is doing innovative science in space, while underpinning the broader economy by supporting the development of real-world applications, such as space weather modelling. It is fantastic to see the first full model of the SXI instrument being delivered, and we look forward to the completion of the engineering model and eventually the flight instrument over the next two years.”

SXI weighs approximately 36kg and needed to be compact and relatively low mass to meet the mission level conditions of the spacecraft. To accomplish this, the telescope utilises a very lightweight optical system to focus X-rays; a ‘lobster-eye’ lens that mimics the mechanism within the eye of a crustacean.

The University of Leicester’s Space Research Centre is a world leader in the development of X-ray instruments for space and SMILE’s SXI is the third instrument to use similar optics to be built at Leicester following the Mercury Imaging X-ray Spectrometer (MIXS) instrument on ESA’s BepiColombo, which has recently successfully completed its first fly-by of destination planet Mercury, and the soon-to-be-launched MXT instrument on the French-Chinese SVOM mission.

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