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Strofio Science Plan & Operations. Mihir Desai Southwest Research Institute [email protected] (210) 522-6754. Strofio - part of SERENA suite. What is Strofio?.

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Strofio Science Plan & Operations

Mihir Desai

Southwest Research Institute

[email protected]

(210) 522-6754

What is strofio
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.

Presentation topics
Presentation Topics

  • Science Objectives

  • MPO timeline

  • Strofio Pointing and Observing Strategy

  • Science & Engineering Modes

  • Data Collection and Telemetry

Science objectives measurements
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

Strofio flight operations overview
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.,

Strofio pointing ops planning

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

Strofio measurements
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)

Overview of mode transitions
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

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

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

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

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

Instrument commanding implementation
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

Instrument commanding strategy
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

Data acquisition
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.

Orbit definition
Orbit Definition

From EID-A sec