1. Assessment of the payload for space weather monitoring missions situated at the L1 & L5 Lagrangian points
Yulia Bogdanova1, Jackie Davies1, Richard Harrison1, Mario Bisi1, Mike Hapgood1, Mark Gibbs2, David Jackson2, Oliver Turnbull3, David Riley3, Reuben Wright3, Alessandro Grasso4, Marc Scheper4
RAL Space, STFC, UK; (2) Met Office, UK;
(3) Deimos Space UK Ltd, UK; (4) OHB System AG, Germany

2. Talk Outline Motivation L1 & L5 mission objectives
Recommended payload and its performance

3. Motivation/justification
Provision of services to the users and customers
Satellite designers / builders
Satellite operators
Human spaceflight
Launch providers / operations
Trans‐ionospheric radio communications, satellite navigation, data relay
Space Surveillance and Tracking Services
General Data Services
Non‐space systems operators
• Aviation
• Power grid operators
• Oil drilling/exploration
• Road transport
• Tourism
Services include: forecasting, activity warnings, nowcasting, post-event analysis and archives.
The mission payload assessment was based on the analysis of the ESA SSA Customer Requirements, System Requirements and Product Specification Documents .

4. L1 and L5 Missions L1
In-situ observations & solar monitoring for space weather forecasting L5
Remote sensing & in-situ observations to improve SWE forecasting capabilities
Observational requirements for each mission was assessed as for stand-alone mission.
Synergies between two missions also have been considered.

5. L1 mission objectives Primary Secondary
Geomagnetic storm forecasting with lead times of up to 12 hours (sufficient to forecast the arrival of a very fast Coronal Mass Ejections (CMEs) with ≤ 18 hour transit time) -> decide on mitigation actions
Identification of the launch of Earth directed CMEs, and their motion away from the Sun, including the prediction of arrival times at Earth
Provision of improved inputs to heliospheric models, including estimates of the background solar wind and CME parametrisation, to improve CME arrival time and solar wind predictions at Earth
Measurement of vector components of the Interplanetary Magnetic Field (IMF)
Measurement of speed, density and temperature of solar wind
Monitoring of low energy ion precursors of CME shock arrival at Earth
Monitoring of solar energetic particles impacting the terrestrial system
Enable real‐time assessment of Earth‐directed CMEs
Secondary
Monitoring of developing solar activity with potential Earth impact
Provision of stable, continuous space weather data (model development and
underpinning space weather research)

6. L5 mission objectives Primary Secondary
Geomagnetic storm forecasting with lead times of up to 12 hours (as for L1)
Improvement of assessment of CME motion and density, in the corona and heliosphere, using a different observational perspective to the L1 observations
Provision of improved inputs to heliospheric models to improve CME arrival time and solar wind predictions at Earth
Measurement of vector components of the IMF and the speed, density and temperature in solar wind features (e.g., SIRs) rotating towards Earth.
Monitoring of active regions development up to 4‐5 days beyond the East limb identify developing solar activities with potential for Earth‐impact
Enable real‐time assessment of Earth‐directed CMEs
Secondary
Monitoring of low energy ion signatures at L5 as indicate an Earth‐directed CME shock
Provision of stable, continuous space weather data (model development and underpinning space weather research)
Enhancing: ‘To provide a broader view of solar energetic particle events occurring in the inner solar system’

7. Observational requirements
PSD Ref
Measurement L1 L5
L1-008-M
Interplanetary Magnetic Field C
L1-009-M
Solar Wind Bulk Velocity
L1-010-M
Solar Wind Bulk Density
L1-011-M
Solar Wind Temperature
L1-001-M
>10 MeV solar wind protons E
L1-005-M
30 keV/nuc -1 MeV/nuc solar wind ions
L1-003-M
1-10 MeV solar wind protons O
N/R
L1-007-M
30 keV – 8 MeV solar wind electrons
SU-005-M
Photospheric Solar-Disk Magnetic-Field
SU-017-M
Photospheric Solar-Disk White-light Images
SU-015-M, SU-021-M
EUV Images of the Sun
SU-025-M, SU-022-M
White-light wide-angle Coronagraph Images
SU-032-M
Heliospheric Images
SU-027-M
Solar X-ray flux
SU-026-M
Solar Radio spectrographic Observations
L1-006-M
2-50 MeV solar wind electrons
L1-004-M
1-10 MeV/nuc solar wind ions
L1-002-M
> 10 MeV/nuc solar wind ions
PSD Ref

8. SWE instruments – general requirements
The instruments should be optimised for the space weather monitoring:
Robust, radiation tolerant, continuous operation 24/7
Based on proven design and techniques
Easy to operate and calibrate
Fast downlink for nowcasting
Should measure extreme behaviour accurately
Limitations on the telemetry, mass & power budget.
Assessment of the instruments requirements for two levels:
Threshold - satisfies the basic need of the customer and is required to maintain current capability of the services.
Goal - provides substantial improvements in the Space Weather services capability.
Steenburgh et al., 2014

9. Magnetograph Mandatory : L1 and L5 Justification:
To provide basis data on which to model the background solar wind (including SIRs/CIRs) for arrival time prediction of CMEs at Earth.
To inspect the magnetic field in order to provide advanced warning of developing activity.
To monitor white-light Sun to provide an indicator of sunspot activity, and their potential complexity and development.
Performance requirements:
FoV: 42.6 x 42.6 arcmin centred on Sun centre
Spatial resolution: 5 arcsec (T), 2 arcsec (G)
Dynamic range: ± 4 kG , 12 bits
Accuracy: 10-3 of continuum intensity
T: the line of sight magnetograph; G: vector magn.
Pointing stability: 0.5/0.2 arcsec over 30 s (T, G)
Cadence: 30 min (T), 10 min (G) 
Latency: 60 min (T),10/30 min (L1/L5 G)
Heritage/baseline: PHI instrument on Solar Orbiter

10. EUV Imager Mandatory: L1 and L5 Justification:
To monitor the chromosphere/corona for impending Earth-affecting solar activity (occurrence of prominence eruption, situation of coronal holes, etc.), particularly on the region of the Sun that is yet to rotate to the longitude of Earth.
Performance requirements:
T: Full disk image in Fe XII 193 A line
G: Full disk image in Fe XII 193 A, He II 304 A, Fe IX 171 A and Fe XIV 211 A
FoV: 42.6 x 42.6 arcmin image centred on Sun centre
Spatial resolution: 5 arcsec (T), 2 arcsec (G)
Dynamic range: 14 bits
Pointing stability: 0.5/0.2 arcsec (T/G) over 5 s
Cadence: 5/20 min ( L1/L5 T), 5/10 min (L1/L5 G)
Latency: 10/60 min (L1/L5 T), 10/30 min (L1/L5 G)
Heritage/baseline: SOHO/EIT, SDO/AIA, STEREO/EUVI, ESIO (EUV Solar Imager for Operations)

11. Coronagraph Mandatory: L1 and L5 Justification:
To enable definitive, early and critical identification of Earth-directed CMEs and to enable forecasting, with the longest possible lead time, of their arrival at Earth.
To provide the basis of the characterisation of CMEs for inclusion into the majority of current operational modelling endeavours to predict their Earth arrival.
Performance requirements:
FoV: 3-22 Rs (T); Rs (G)
Spatial resolution: 2 arcmin
Dynamic range: 16 bits
Sensitivuty: detection of signal to 2 x Bo
Accuracy: 20% of CME signal; SNR > 2 (T),
SNR > 4 (G)
Cadence: 10 min (T); 5 min (G)
Latency: 15/25 min (L1/L5 T), 5/15 min (L1/L5 G)
Heritage/baseline: LASCO C2 & C3 and COR, SCOPE (Solar Coronagraph for OPErations) instrument.

12. Heliospheric Imager Mandatory: L1 and L5 Justification:
To enable tracking of Earth-directed CMEs over much of their propagation path, in order to mitigate deficiencies in arrival times predictions based on the use alone of near-Sun data.
To provide information on the background solar wind.
Performance requirements:
FoV: deg (L1, T), 4-60 deg (L1 G, L5) elongation coverage from Sun-centre along ecliptic.
Two cameras required for higher FoV
Two instruments (L1), one instrument (L5)
Spatial resolution: < 4 arcmin
Dynamic range: 24 bits
Sensitivity: detection of intensity down to ~ Bo (T), 3x Bo (G)
Accuracy: 20% of CME signal
Cadence: 60 min (T), 30 min (G)
Latency: 20/25 min (L1/L5 T), 10/15 min (L1/L5 G)
Heritage/baseline: HI on STEREO

13. X-ray sensor Mandatory: L1 and L5 Justification:
To monitor flare activity in integrated 1-8 Angstrom band. This measurement provides important information in order to predict HF radio wave absorption in the upper atmosphere D-region.
Performance requirements:
Intergrated solar X-ray flux
Range: 1-8 Å (T), Å (G)
Dynamic range: to cover events in range 2x10-8 – 2x10-3 W/m2
Accuracy: 15%
Cadence: 1 min
Latency: 10/20 min (L1/L5 T); 5/15 min (L1/L5 G)
Heritage/baseline: SMART-1 XSM, BepiColombo SIXS

14. Radio-burst Spectrometer
Enhancing: L1 and L5
Justification:
To track shocks in the inner heliosphere (Type II). Observations from the one location can confirm what type of radio bursts is observed, e.g., Type II or Type IV.
To identify a shock, its distance from the Sun and speed, these data in combination with other data sets can be used for definition of the CME direction.
Performance requirements:
Frequency range: 40 kHz - 10 MHz (T); 10 kHz-60 MHz (G)
Dynamic range depends on the frequency range, /110 dB
Cadence: 30 s (T); For G: < 150 kHz - 10 s; > 150 kHz - 1 s; > 30 MHz - 0.1s
Latency: 40 min (T), 10/15 min (L1/L2 G)
Heritage/baseline: STEREO S/WAVES instrument.

15. Magnetometer Mandatory: L1 and L5 Justification:
To provide a short lead-time forecast and nowcast.
To define the geoeffectiveness of the CMEs (on L1) and SIRs (on L1 and L5).
To provide data for the magnetospheric dynamics forecast models.
Performance requirements:
IMF vector with 3-components
Range: 0.1 – 200 nT for every component
Accuracy: ± 1nT (T); ± 0.5 nT (G)
Cadence: 1 min (T); 1 sec ( G ) 
Latency: 5/20 min (L1/L5 T); 1/15 min (L1/L5 G)
2 sensors: one in-board and other out-board.
Heritage/baseline: BepiColombo, Juice, Rosetta, VEX, Cluster, MAG on Solar Orbiter, triaxial fluxgate magnetometer

16. Solar Wind Analyser Mandatory: L1 and L5 Justification:
To provide measurements of the solar wind density, velocity and temperature. crucial in prediction and analysis of the impacts of the geomagnetic storms on the magnetosphere, ionosphere and atmosphere.
To provide a short lead-time forecast of the arrival of the CMRs and SIRs at Earth.
To provide data for the magnetospheric dynamics forecast models.
Performance requirements:
Velocity:
Range: km/s (T); km/s (G)
5% relative accuracy
Density:
Range: 0.1 – 150 cm-3 (T); cm-3 (G)
5% absolute accuracy
Temperature
Range: 40,000-1,000,000 K (T); 10,000 – 2,000,000 (G)
Byrne et al, 2010

17. Solar Wind Analyser Performance requirements:
Top-hat electrostatic analyser with segmented anode combined with aperture deflection plates.
Instrument should produce 3D phase space density data and produce on-board moments (velocity, density and temperature).
FoV: 45⁰ (azimuthal) x ± 22.5⁰ (elevation)
Angular resolution: 5⁰ x5⁰, 9 azimuthal bins and 9 polar bins
Number of energy bins: 30 bins
Energy range: 70 eV/q – 32.6 keV/q (T), ~ 50 eV/q – 47 keV/q (G)
∆E/E =~10%
Dynamic range: x1010 #/(cm2-sec-sr)
Cadence: 1 min (T); 1 sec (G)
Latency: 5/20 min (L1/L5 T); 1/15 min (L1/L5 G)
Heritage/baseline: HIA-CIS on Cluster, SWA-PAS and SWA-EAS on Solar Orbiter

18. Energetic particle instruments
Justification:
To provide early warning on the CME shock propagation.
To monitor radiation storms and its effects, including disruption and damage of the sensitive exposed to space systems such as solar panels and sensors. e.g., through single event effects, radiation damage and dielectric discharge.
To monitor high-energy components of the radiation storms which can affect aircraft (if > 150 MeV) and ground systems (if > 500 MeV).

19. In-situ payload
Classification
Instrument
Observations
Instrument requirements
Heritage
L1: Mandatory
L5: Enhancing
Low energy ion detector
30 keV/nuc- 1 MeV/nuc ions
Ions:
p+, alpha, CNO groups and Fe
p+, alpha, CNO groups, Si/Ne, Fe, Ni and single measurement for heavy ions
FoV: 60deg half-width
1 (2) sensors, along and opposite to Parker spiral
Limited dynamic range targeting SEP fluxes
Accuracy: ±15% relative accuracy, ±50% (±40%) absolute accuracy
4 (5) energy bins
SIT on STEREO
L1: Enhancing
Medium energy ion detector
1-10 MeV/nuc ions
5 (10) energy bins
LET on STEREO
High energy ion detector
> 10 MeV/nuc ions
Range: (1000) MeV/nuc
HET on STEREO
Medium energy proton detector
1-10 MeV protons
3 (5) energy bins
SEPT and LET on STEREO,
NGRM
High energy proton detector
> 10 MeV protons
Range: (1000) MeV
SGPS on GOES-R, HET on STEREO NGRM
Low & medium energy electron detector
30 keV – 8 MeV electrons
8 (10) energy bins
SEPT on STEREO, NGRM
High energy electron detector
2-60 MeV electrons
1 energy bin > 2 MeV
3 energy bins, 1-50 MeV
NGRM, HET on STEREO
L1: Combination of 6 detectors needed to cover all species and energies.
L5: Combination of 2 detectors, NGRM and STEREO SIT.

20. Summary
A dedicated monitoring mission, providing timely observations of conditions on the Sun and in the solar wind, is essential in mitigating against the effects of space weather.
Short summary of the assessment of the SWE missions at L1 & L5 is presented, including:
Missions objectives.
Analysis and classification of the observational requirements.
Space weather mission payload definition. The mission payload is developed in order to accommodate ESA SSA SWE monitoring service requirements.
Acknowledgement: ESA Contract No /15/D/MPR, Enhanced Space Weather Monitoring System, ESA's SSA Programme.