Solar-C

Science Overview

Solar-C is the next Japanese solar physics mission to be developed with significant contributions from the US, Europe and Japan. The mission carries an Extreme UV (EUV) imaging spectrometer with a slit-jaw imaging system called EUV High-Throughput Spectroscopic Telescope (EUVST) as the mission principal payload.

EUVST is designed to take a fundamental step towards answering how the plasma universe is created and evolves, and how the Sun influences the Earth. In 2020, SOLAR-C_EUVST was down-selected as the fourth in the series of the competitively chosen M-class mission to be launched with an Epsilon launch vehicle in 2028. The mission underwent the Mission Design Review in 2021.

The second instrument onboard SOLAR-C is the Solar Spectral Irradiance Monitor (SoSpIM) and is led by PMOD/WRC. It will provide “Sun-as-a-star” spectral irradiance measurements over two bands that overlap with EUVST, the Short EUV and Lyman-Alpha bands. This provides both scientific and cross-characterisation capabilities.

SoSpIM and EUVST will work hand-in-hand. While EUVST will deliver spectral observations from the chromosphere to the corona, tracking the energy flow on small spatial scales, SoSpIM will measure the integrated irradiance over the bands of interest, not just those within the EUVST field-of-view. The SoSpIM instrument provides the connectivity between the flare processes captured in detail on the Sun by EUVST and the impact of those irradiance changes in different layers of the Earth’s atmosphere.

PMOD/WRC Instrument: The Solar Spectral Irradiance Monitor (SoSpIM)

SoSpIM will provide ‘Sun-as-a-star’ measures in two wavelength bands also covered by EUVST. This provides measurements of all solar flares visible from Earth, not only those within the EUVST field-of-view. SoSpIM provides the connectivity between the flare processes captured in detail on the Sun by EUVST and the impact of that irradiance changes in different layers of Earth’s atmosphere.

SoSpIM aims to specifically address two aspects:

• Understand how the solar atmosphere becomes unstable, releasing the energy that drives solar flare which will be achieved through probing fast time cadence solar flare variations.
• Measuring solar irradiance that impacts the Earth’s thermosphere and the mesosphere, linking to spatially resolved measurements of the solar atmosphere with EUVST.

In order to achieve these goals, the SoSpIM instrument will monitor the spectrally resolved solar irradiance with sub-second time cadence. There will be two channels with redundancy in the following bands:

• Channel 1: covering 170-215 Å (Al/Zr/Al filter combination)
• Channel 2: covering 1115-1275 Å (MgF2 filter)

A key advantage of having a ‘Sun-as-astar’ instrument onboard the mission is that all solar flares visible from Earth can be observed. SoSpIM will allow the direct connection to the impact on the Earth. The two channels on SoSpIM will probe the effects on the ionosphere/ thermosphere (mainly with Channel 1)  and the mesosphere and stratosphere (with Channel 2).

Achievements and Status

The SoSpIM Phase A2B development kicked-off in November 2020 after confirmation of SSO PRODEX funding support. During 2021, the SoSpIM instrument architecture was defined, the required specifications were detailed, and the principal interfaces with the Solar-C were also defined. The instrument’s thermo-mechanical structure concept was also defined. SoSpIM sub-systems were defined and specified. Special attention was given to performance-relevant sub-systems, such as:

• The cold-trap for contamination management.
• The digital acquisition board for accurate acquisition.
• The control board and onboard software steering the instrument operations.

The Preliminary Design Review (PDR) is planned in Q1/2023 in alignment with the Solar-C mission PDR and its outcomes. During this definition period, several industry work packages and related tasks will be defined and specified. Swiss Industry will be invited to participate in the instrument consortium and provide different sub-units to SoSpIM. The implementation of an EM is planned in 2023 – 2024.

Collaboration Partners: SoSpIM Instrument

Royal Observatory of Belgium (ROB), Brussels, Belgium
Japanese Aerospace Exploration Agency (JAXA), Japan
National Astronomical Observatory of Japan (NAOJ), Japan
Physikalisch-Meteorologisches Observatorium Davos (PMOD/WRC), Davos, Switzerland

Swiss Scientific Contact

Prof. Louise Harra (PMOD/WRC)

Source and credits: ESA, NASA, JAXA, PMOD/WRC

SoSpIM Science Meeting 2024

Download PDFs of talks (password protected) →
Please contact Krzysztof Barczynski for access

Mission Facts

Source and credits: ESA, NASA, JAXA, PMOD/WRC