Technology SIXS ASIC: Shedding light on the history of the Solar System

A SIXS-P ASIC mounted on the electronics

The only way for us to properly understand the formation of our solar system is to study the makeup of the planets and other bodies orbiting the Sun, and the only way we can achieve this is to send probes to study them up close.

Launched in October 2018, the joint ESA/JAXA mission, BepiColombo, with its two probes (MPO and MMO), was sent on a seven-year journey through the solar system. It will make no less than nine planetary flybys on route to its ultimate destination, the solar system’s innermost planet, Mercury.

BepiColombo will be only the second mission ever to orbit the planet Mercury, and packed with modern scientific instruments, it will also be the most complex so far.

The measurements made by the BepiColombo suite of instruments will help answer many perplexing questions about the planet, such as why it has a magnetic field and what forms the mysterious 'hollows' seen on its surface.

One of the instruments on this historic mission is the Solar Intensity X-ray and Particle Spectrometer or SIXS as it’s known, onboard the Mercury Planetary Orbiter (MPO).

SIXS measures the direct solar X-rays, energetic protons, and electrons that bombard, and interact with, the surface of Mercury. These interactions make the surface glow with X-rays, so by monitoring the incident and emitted radiation, the abundance of some chemical elements and scattering properties of the outermost surface layer of the planet can be established. To achieve this SIXS is used in partnership with the Mercury Imaging X-ray Spectrometer (MIXS).

SIXS has already proved a success, collecting new data throughout the seven-year cruise phase of the mission and enabling scientists to investigate the solar X-ray corona and solar energetic particles (SEP). It will also provide the first-ever opportunity for measurements of the propagation of SEPs, their interactions with the interplanetary magnetic field, and space weather phenomena in multiple locations throughout the inner solar system and far away from the Earth.

To help achieve these milestones, the SIXS particle sensor (SIXS-P) incorporates an ASIC developed by microelectronics engineers based in Technology's ASIC Design Group.

These engineers worked with the SIXS instrument team from Finland to identify the ASIC requirements and figure out how the ASIC would work as part of the detector system.

Following an initial prototyping phase, a flight-ASIC was manufactured, functionally tested, and subjected to a series of tests intended to qualify the ASIC as flight worthy, i.e. able to survive the launch and mission environments.

The ASIC has 8 channels that readout the charge deposited by particles in the detectors. These channels contain low-noise low-power amplifiers, filtering, peak-hold, and comparator circuits.

An on-chip 12-bit Analog-to-Digital Converter (ADC) translates the analogue signals from the channels to a digital format that can be processed by the FPGA used in the instrument Data Acquisition (DAQ) electronics.

Space is a hostile environment with extremes of temperature and radiation that affects the performance of electronics. For this reason, the engineers designed the ASIC using special techniques derived from their experience in high-energy particle physics experiments to improve the tolerance of the CMOS process to radiation effects.

BepiColombo has now completed its last Mercury flyby and will approach the planet at a slow enough relative speed to enter orbit in December 2025, when the real fun will start with two to three years of close-up observation of the planet closest to our sun.

Mark Prydderch, Technology's ASIC Design Team Group Leader, said:

"We developed the ASIC for BepiColombo over a four-year period. This development, while ultimately successful, was challenging at times – involving rigorous tests to ensure that the packaged ASICs were prepared for the stresses of rocket launch and many years space travel to reach Mercury orbit.

"Our work on the SIXS-P Instrument demonstrated that integrated electronics such as ASICs, can replace the discrete, off the shelf component designs traditionally used for these sort of projects - empowering future space instrument developers to consider new operating methods and features to enhance performance in ways that would otherwise be difficult to achieve.

"We were very happy in early 2025 to see the spacecraft’s final flight past Mercury in preparation for entering Mercury orbit next year to begin the main science operations. It’s exciting to think that after a journey of 8 years and encounters with Earth (once), Venus (twice), and Mercury (six) along the way, the SIXS ASIC will be our first ASIC to undergo interplanetary space travel!"