Science

Strategic Science

As a dedicated science mission focusing on the physics of space weather sources, SULIS will compliment international operational space weather missions (such as ESAs potential future Lagrange mission to L5, NASA’s L1 follow-on to DISCOVR and the ASPIICS/PROBA-3 missions) paving the way for future space weather instruments.

 

  • Objective I Overview:

 

By providing measurements of coronal magnetic fields, SULIS will have an unprecedented ability to address a range of key questions about fundamental plasma processes. Determining the mechanisms responsible for the heating of the solar corona and accelerating the solar wind remain long-standing ambitions in solar physics (e.g. white paper). Magnetic fields shape the temperature and density structure of the corona and underpin all dynamic eruptions such as flares and CMEs. The energy released in dynamic eruptions is stored in the coronal magnetic field. Measurements of the surface magnetic field have limited utility for space weather forecasting, therefore, precise knowledge of the 3D properties of the coronal magnetic field is critical.

Scientific Relevance: To date, only two direct measurements of the coronal magnetic field have been made and both publications* are led by Prof Lin. The unambiguous determination of 3D coronal magnetic fields over the solar disk is challenging and requires co-temporal space-based observations of polarised spectral lines from multiple viewpoints, utilising the collective power of stereoscopy to disambiguate 3D field vectors.

Spectropolarimeter: Diffraction-grating spectrographs simultaneously observe several visible and near-IR spectral lines over multiple slits across the solar disk. The massively-multiplexed 99-slit coronal spectropolarimeter enables determination of magnetic fields, temperatures, and densities from emission line polarization (linear and circular). Inversion of the Fe XIII 1.075µm and He I 1.083µm spectra yield the magnetic field vectors through normal and saturated Hanle and Zeeman Effects. Two InGaAs cameras capture spectral observations from 99 adjacent slits spanning the full solar disk and out to 1.5 solar radii. Slit configurations with 20  x 20 arcsec binning, covering the full disk, can achieve a magnetic field detection down to a remarkable 2 Gauss sensitivity. Utilising simultaneous observations from the other CubeSats enables tomographic inversions of spectral lines, thus gaining a 3D mapping of the field and plasma structure. Clusters of small ~15 cm telescopes (suitable for CubeSat’s) operating collectively can achieve the same magnetic field sensitivity as a large ~1 m telescope, but at a significant cost saving.

*Lin, H. et al., 2000, “A new precise measurement of the coronal magnetic field strength”, Astrophysical Journal, 541:L83

*Lin, H. et al., 2004, “Coronal magnetic field measurements”, Astrophysical Journal, 613:L177

 

  • Objective II Overview:

 

Predicting the impact of CMEs on Earth is a key goal for space weather forecasting**. A CME’s effect at Earth primarily depends upon its magnetic field and kinematics. A CME with a dominant southward-oriented magnetic field has a larger chance of significantly disrupting the Earth’s magnetic field and producing magnetic storms. Following CME eruption, multi-viewpoint coronagraphs will perform 3D tracking of the kinematics of the CME. Direct measurement of CME magnetic and kinetic properties will enable an accurate early characterisation of the potential geoeffectiveness of the CME.

International Context: Understanding the physics of space weather sources is fundamental to protecting critical infrastructures in every sector of societyas shown below.

space_diagram_320

 

Space weather events occur frequently, with measurable effects on critical infrastructure systems and technologies (e.g. GPS, power grids and aviation). In the 2003 storms, a major airline rerouted six polar flights requiring fuel stops in Japan and Anchorage. In September 2015, air traffic radar jammed in Sweden for 1 hour. The UK’s latitude, long coast line and geology lead to increased risks from space weather.

SULIS will enable us to better understand the drivers of space weather.  The cost of space weather impact is enormous: The failure of the Hydro-Quebec system in 1989 during a solar storm took 9 hours to restore 80% of operations leaving 5 million people without power costing ~C$2 billion in economic losses. The definitive extreme space weather scenario is the famous 1859 Carrington event. Lloyd’s of London (2013)+ estimated the cost of a similar event today would be £1-2 trillion, based on calculations examining disruption to the global supply chain++. Insurers’ pricing models offer a robust methodological approach to economic cost quantification.

Coronagraph spectrometer: This instrument will provide simultaneous images for CME tracking whilst collecting spectra across the extended corona. The emission line spectra will infer electron temperatures, ion densities, bulk flow speeds and non-thermal heating, and link these to the spectropolarimeter magnetic field measurements. The figure below illustrates synoptic observations from both kinds of instruments. This instrument will simultaneously collect high-resolution spectral data of several coronal emission lines along a spatial slit, and will provide coverage of the whole corona by scanning across the corona. To provide context and high-resolution imagery, the spectrometer entrance slit is mirrored producing ‘slitjaw’ images through a unique broadband hyperspectral system. This system rapidly scans the visible range across the extended corona, providing a spectral profile for the corona’s broadband continuum. This is a scattered redistribution of the Sun’s known blackbody spectrum, providing constraints on the density and velocity distribution of coronal electrons. No other space- or ground-based mission will routinely collect data of this clarity in the range of 1.5–5 solar radii from the Sun. The high-resolution spectrometer component of the coronagraph instrument has input from inventor and project partner Prof Ding.

corona_slit

**Judge, P.G., 1998, Astrophysical Journal, 500, 1009

**Casini, R. & Judge, P.G., 1999, Astrophysical Journal, 522, 524

**Lin, H., Casini, R., 2000, Astrophysical Journal, 542, 528

++Eastwood, J. P. et al., 2017, “The Economic Impact of Space Weather: Where Do We Stand?”, Risk Analysis, 37, 2

+Lloyd’s. Solar Storm Risk to the North American Electric Grid. London UK: Lloyd’s, 2013

 

  • Objective III Overview:

 

SULIS offers bespoke UK technology demonstration with a wide range of applications, benefitting society and industry across many sectors: Next-generation Power-by-light Optical Wireless Communications (OWC) technology will be demonstrated in space for the first time. SULIS will demonstrate optical power transmission (offering mark-up data transfer rates compared with X-band antenna transmission) characteristic of Power-by-Light systems, an elegant method for powering PV solar cells across large distances, using laser light. Aside from communications upgrade, OWC can be coupled with advanced radiation-hardened PV solar cells to significantly elevate power capability of CubeSat’s. Laser light can also achieve very precise alignment of formation-flying smart CubeSats, critically important for maintaining a functioning coronagraph. SULIS will demonstrate autonomous CubeSat clusters which self-consistently control precision manoeuvres. Objective III will see:

Li-Fi The future of communications technology (Northumbria University): The demand for high-speed internet services has driven emergent technologies capable of delivering ultra-high data rates to end users1. Demand in radio frequency Wi-Fi communication is outstripping the available bandwidth leading to spectrum congestion. One solution to these restrictions is Visible Light Communications (VLC), a subset of OWC, which optimises visible-light wavebands (so-called Li-Fi). The application of high-speed data transfer using light is highly advantageous for SULIS given that VLC reduces the payload mass. Li-Fi technology is a novel solution for limited CubeSat bandwidth (VLC offers expansive bandwidth), connectivity (Li-Fi is highly energy efficient in monochromatic laser light) and range (VLC can transfer ethernet internet speeds).

New radiation-hardened large-format PV systems development (Swansea University in collaboration with Northumbria University): The CESR group at Swansea University developed the world’s first thin film solar cell (TFSC) to be deposited directly onto glass and deployed in space2. Depositing on glass allows for extremely high power-to-weight ratio, crucial for spaceflight. With CubeSat onboard power and outbound communications improvements, onboard control systems will be developed by the NUPV group at Northumbria University. A distinctive characteristic of NUPV is complete photovoltaic cell fabrication from substrate to device for unique application to CubeSat’s demonstrating and advanced form of power exchange.

Mission Launch & Operations: This mission will require launch capability in collaboration with the UK Space Agency and the Satellite Application Catapult. SULIS CubeSat construction will be managed by industrial partners SSTL. SSTL delivers complete mission solutions for remote sensing, science, exploration, navigation and telecommunications, as well as designing and building a wide range of satellite platforms, subsystems and optical instruments, and supplying avionics suites and ground infrastructure. The data downlink ground station segment for post-launch mission control and operations will be facilitated by STFC-RAL Space in collaboration with SSTL.

Data Centre Requirements: A processing centre will host data pipeline and analysis. Data communications from CubeSat’s to Earth is challenging. The spectropolarimeter will have a maximum data rate of ~100 Mbps per detector. The coronagraph, considering the lack of polarimetry and long exposure times (due to lower signal to noise) requires ~5 Mbps per detector. Thus the Li-Fi communication will rapidly redistribute the data between each CubeSat pair, before transmission to the Earth-orbiting CubeSat pair at ~100 Mbps each (in 2001, a 50 Mbps link was successfully established between the ARTEMIS geostationary satellite and the SPOT-4 satellite). The deployment of a CubeSat constellation enables a sharp reduction of the relay communication path length. The Earth orbiting CubeSat pair will require a downlink transfer at ~600 Mbps (in 2013, NASA’s lunar laser communication demonstration achieved an impressive downlink rate of 622 Mbps).

1Zabih Ghassemlooy et al., 2017, “Visible Light Communications: Theory and Applications”, CRC Press, ISBN 9781498767538

2Applied to the 3U CubeSat AlSat Nano mission, developed by the UK and Algerian Space Agencies.