Strofio Science Plan & Operations

1. Strofio Science Plan & Operations Mihir Desai Southwest Research Institute mdesai@swri.edu (210) 522-6754

2. Strofio - part of SERENA suite

3. What is Strofio? • Strofio is a scientific investigation of the Hermean exosphere based on a novel mass spectrograph that determines the mass-per-charge (m/q) of low-energy (~1 eV) neutral atoms by a time-of-flight (TOF) technique. • The name comes from the Greek word Strofi, which means “to rotate”: the phase of a rotating electric field “stamps” a start time on the particles’ trajectory. The detector records the hit position (hence the start time) and the stop time. • Strofio achieves high-sensitivity (0.14 counts/s when the density is 1 particle/cm3) within limited resources (~2 kg). • The mass resolution (m/m≥ 60) is achieved by fast electronics and does not require tight mechanical tolerances.

4. Presentation Topics • Science Objectives • MPO timeline • Strofio Pointing and Observing Strategy • Science & Engineering Modes • Data Collection and Telemetry

5. Science Objectives & Measurements • Science Objectives • Determine Exospheric Composition • Study Exosphere-Magnetosphere Interactions • Study Exosphere-Surface Interactions • Derive Surface Composition • Measurement Strategy • Identify major (He, O, Na etc) and rare (e.g., Mg, Ar, Ne isotopes) exospheric neutrals • Measure their temporal and spatial variations

6. Strofio Flight Operations - Overview • Cruise Phase – ~6.5 years • Activation and Check out • Calibration and Voltage Optimization • Background Rejection Tests & Characterization • Commissioning Phase – ~90 days • Power off (orbit insertion) ~72 days • Same as Cruise Phase ~6 days • Normal Science Mode ~11 days • Science Operations Phase – 2 years • Timeline-based • Power off +/-3 days at Eclipse • Engineering Modes during safing, thruster firing etc.,

7. Timeline of Flight Operations

8. Primary source points into +X direction Strofio collects Mercury gas when the spacecraft velocity is pointing in +X direction Going with Mercury, away from the Sun (from Perihelion to aphelion), RAM is from the –X direction, hence the secondary source is active From Aphelion to Perihelion, RAM is in the +X direction and so the Primary Source is active Strofio pointing & Ops Planning

9. Exospheric Asymmetries day/night Aphelion Perihelion

10. Strofio Measurements • Aphelionthe pericenter is on the dayside, close to local noon, where the PSD has its maximum Measurement Strategy • Perihelion  the pericenter is at midnight; Strofio has best observing chances for meteorite impact vaporization (MIV)

11. Overview of Mode Transitions • Engineering Modes • Stand-by Mode • Diagnostic Mode • Safe Mode • Pre-Science Mode • Science Survey Mode • Normal mode interleaved with 4 Sub-modes • Calibration Mode

12. Stand-By Mode After Power-on After Power On Reset Diagnostic Mode After Stand-By Check Strofio health, checksums, S/W & H/W HV, Filaments, RF off FSW Enabled Safe Mode Automatic in case of instrument or system failure Ground Intervention required to de-activate Pre-Science Mode Used for filament change Source Voltages on MCP bias below operational Filament Heaters ~10-20% of operational levels Engineering Modes

13. Normal Science Mode Measure ~50 meV/AMU exospheric neutrals Default data collection mode Ionizing Electron Energy range: -90 – -110 V Interleaved with one of the following four sub-modes Sub-Mode 1: Ion Mode Measure ions between 0.5-10 eV Switch filament off Heater at <5% of operational levels Science Survey Mode

14. Sub-Mode 2: Molecular Mode Measure molecular species, H2O, CO2, O2, N2 etc. Vary ionizing electron energy between -40 – -60 V Sub-Mode 3: High Energy Mode Measure higher energy exospheric neutrals Scan above ~5-10 eV energy range Sub-Mode 4: Background Mode Measure instrument background Switch Filament from Ram to anti-Ram direction Science Modes...cont’d

15. Independent Calibration Mode Parameters are updated to perform calibration functions such as: Check Instrument performance Adjust MCP gain Tune and Optimize Voltages Optimize ionizing source performance Strofio collects raw, double coincidence paired-event data (TOF: position & sync.) Calibration Mode

16. Instrument Commanding Implementation • Simple Mode/State Transitions implemented through Flight Software macros • Macros based on Engineering, Science (sub-modes) and calibration modes • Extensive Tests and Verification of all commands and macros on ground

17. Instrument Commanding Strategy • Nominal commanding – timeline based • No real-time commands • Timeline & Command Strategy based on • BepiColombo mission phase • Orbit orientation • Periodic Feedback • Types of science investigations • Science coordination with other instruments • Power Management • Duty cycling

18. Science Operations Plan

19. Data Acquisition • 1 particle creates 1 event ==> 25-bit word • 11 + 1 bits for ToF and its validity • 11 + 1 bits for position and its validity • 1 bit = Identify hit location hemisphere of the annulus • FPGA creates 24-bit word for 1 VALID event • 11 bits for ToF • 11 bits for position • 1 bit = Identify hit location hemisphere of the annulus • 1 bit for high or low position resolution • Use lookup tables to fill 2048 or 64 bins • The 64 bins or counters correspond to major masses of interest (He, Na, O, Mg…), and background and guard channels.

20. Data Description & Telemetry Allocation

21. Data Products and Delivery

22. Mission Operations & Data Analysis BACKUP SLIDES

23. Science Overview

24. MPO Timeline (from ESA)

25. Orbit Definition From EID-A sec 2.4.6.2 Radiator

26. Timeline Assumptions

27. Exospheric Asymmetries dawn/dusk

28. Timeline of Flight Operations