Solar Orbiter

[Artist's impression of Solar Orbiter]

Artist's impression of Solar Orbiter (Image credit: ESA/ATG Medialab)


Solar Orbiter (SolO) is an ESA space probe that is part of the Cosmic Vision program. The science payload consists of ten instruments built by different consortia in Europe. NASA also participates in the project, among others by taking charge of the launch (see also the Solar Orbiter blog). SolO has been launched on February 9, 2020 at 11:03 p.m. local time (February 10, 2020 at 5:03 CET) from launch Complex 41 at Cape Canaveral Air Force Station in Florida on an Atlas V 411 rocket.


[Lift-off of Solar Orbiter]

Lift-off of Solar Orbiter on top of an Atlas V rocket (Image credit: United Launch Alliance).
[Click image to watch a video of the launch.]


After launch, the spacecraft will travel for an extended period before the Nominal Mission Phase can start in November 2021. SolO's mission is to explore the Sun - our nearest star - with unprecedented resolution at wavelength ranges that cover visible, radio, extreme ultraviolet, and X-rays. SolO will boldly perform in-situ measurements that no other probe has done before.

SolO's trajectory will take the spacecraft in the vicinity of the Sun. During closest approach SolO will only be about 60 solar radii (42 millions km, or 0.28 astronomical units; an astronomical unit corresponds to the distance between Earth and Sun) away from the Sun's surface. There the spacecraft will experience about 13 times the radiation flux that it would experience from Earth's orbit. In order to protect the spacecraft and its instruments, it carries a sophisticated heat shield (sandwich structure of high-temperature multi-layer insulation foil coated with "Solar Black") that can withstand the high temperatures.

SolO will be in a resonant orbit around the Sun with Venus. With each gravity assist manoeuvre at Venus that SolO will perform every third orbit around the Sun, its inclination will increase slightly. At the end of the Extended Mission Phase (in 2030), SolO will have reached an inclination of about 30° with respect to the solar equator.

SolO will permit high-latitude and close-up studies of the Sun. At nearest approach, SolO's velocity will come close to the angular velocity of the Sun, allowing for extended observations of a given region on the Sun.



SolO is equipped with a set of in-situ and a set of remote sensing instruments.
The in-situ instruments are designed to measure and observe the environmental conditions in the immediate vicinity of the spacecraft, whereas the remote sensing instruments will observe the Sun's surface and atmosphere in great detail.


[Solar Orbiter Payload]
Accommodation of Solar Orbiter's remote sensing and in-situ instruments (image courtesy of ESA)


Shortly after the launch, an extended period of tests known as Near Earth Commissioning Phase (NECP) has started. It ended on June 15, 2020, when the commissioning of all 10 instruments on board SolO was declared successful.

The Leibniz-Institut für Astrophysik Potsdam (AIP) significantly contributed to the development of the remote sensing instrument STIX. Furthermore, the AIP was involved in the development of the in-situ instruments EPD/HET&EPT.


Spectrometer/Telescope for Imaging X-rays (STIX)

STIX is a state of the art imaging X-ray telescope, which was built by a consortium led by the University of Applied Sciences and Arts Northwestern Switzerland (FHNW). It provides imaging spectroscopy with highest ever spatial resolution and sensitivity of solar thermal and non-thermal X-ray emission. The AIP contributed by building and delivering the imager, which is a pivotal part of the instrument.


[Flight model of STIX Imager and Detector Electronics Box]

Flight model of STIX imager (front) and detector electronics box (rear) (image credit: Hakan Önel, AIP)


[Details of STIX instrument]

The different parts of the STIX instrument (Image credit: STIX consortium)


The two main parts (i.e., the imager and the detector electronics box) of STIX are mounted independently on the spacecraft. The imager consists of 32 pairs of X-ray opaque tungsten grids mounted in front of 32 solid-state Cadmium Telluride X-ray pixelated detectors which are located in the detector electronics box and make up the spectrometer.

STIX covers the energy range between 4 keV and 150 keV with an energy dependent resolution of 1 keV to 15 keV. Its finest angular resolution and temporal resolution are 7 arcsec and 0.1 second, respectively.
By observing hard X-ray bremsstrahlung emissions from solar flares, STIX will provide diagnostics of the hottest flare plasma while quantifying the location, spectrum, and energy content of flare-accelerated nonthermal electrons. Thus, STIX will provide the high-energy link between remote and in-situ observations.

In 2017, STIX and the other instruments have been integrated into Solar Orbiter in the Airbus spacecraft assembly hall in Stevenage, UK.

[Instruments integration]

Some of the instruments integrated on the side panel of the spacecraft (Image credit: Airbus)


Energetic Particle Detector (EPD)

The AIP also contributed to the Electron Proton Telescope (EPT), which is part of the EPD suite of instruments.

[The Energetic Particle Detector instrument]

The Energetic Particle Detector instrument (EPD) (Image credit: EPD consortium)


AIP Team working on Solar Orbiter (in alphabetical order):

- apl. Prof. Dr. Gottfried Mann (since 2008)
- Dr. Hakan Önel (2008-2019, since 2020 in consulting capacity)
- Dr. Jürgen Rendtel (since 2008)
- Dr. Frederic Schuller (since 2019)
- Dr. Alexander Warmuth (since 2008)

AIP's hardware contributions are supported by AIP's Technical Section.

[AIP Team working on STIX]

Some members of the AIP team who have been working on STIX (Image credit: AIP)


Further references:

- ESA: Solar Orbiter - Mission
- STIX: Project Website
- Twitter: Solar Orbiter