strofio science plan & operations

14-17 May 2013 SERENA-HEWG Workshop, Key Largo, Fl,, USA Desai - 1

Strofio: Analysis of Mercury’s Exosphere

Strofio Science Plan & Operations

Mihir DesaiSouthwest Research Institute

[email protected](210) 522-6754



Strofio - part of SERENA suite



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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.


Strofio: Analysis of Mercury’s ExospherePresentation Topics

Science Objectives MPO timeline Strofio Pointing and Observing Strategy Science & Engineering Modes Data Collection and Telemetry



Science Objectives & Measurements

Science ObjectivesDetermine Exospheric CompositionStudy Exosphere-Magnetosphere InteractionsStudy Exosphere-Surface InteractionsDerive Surface Composition

Measurement Strategy Identify major (He, O, Na etc) and rare (e.g., Mg,

Ar, Ne isotopes) exospheric neutralsMeasure their temporal and spatial variations


Strofio: Analysis of Mercury’s ExosphereStrofio 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.,



Timeline of Flight Operations



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



Exospheric Asymmetries day/night

Aphelion Perihelion



Strofio Measurements Aphelionthe 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 Engineering Modes

Stand-by ModeDiagnostic ModeSafe ModePre-Science Mode

Science Survey ModeNormal mode

interleaved with 4 Sub-modes

Calibration Mode



Stand-By Mode After Power-onAfter Power On Reset

Diagnostic Mode After Stand-ByCheck Strofio health,

checksums, S/W & H/WHV, Filaments, RF off FSW Enabled

Safe ModeAutomatic in case of

instrument or system failureGround Intervention

required to de-activate

Pre-Science Mode Used for filament changeSource Voltages onMCP bias below operationalFilament 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

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

Nominal commanding – timeline basedNo real-time commands

Timeline & Command Strategy based onBepiColombo mission phase Orbit orientationPeriodic Feedback Types of science investigations Science coordination with other instrumentsPower ManagementDuty cycling


Strofio: Analysis of Mercury’s ExosphereScience Operations Plan



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.



Data Description & Telemetry AllocationData

ProductDescription

Bins or Bytes

Bits/bin

Integration Time (s)

Bitrate (bits/s)

Percent (%)

ADetailed Mass Histogram (Ultra-High Mass Resolution events)

2048 10 120 170.6 28.4

BMass Histogram (High Position Resolution)

64 10 10 64.0 10.7

CMass Histogram (Low Position Resolution)

64 10 10 64.0 10.7

D Single Events 106000 24 9000 282.7 47.1

Telemetry Before Compression (not including Housekeeping data)

581.3

Compression Factor 3.0

Telemetry After Compression (not including Housekeeping data)

193.8

E1Uncompressed Housekeeping (Temperature fields)

6 8 30 1.6 0.8

E2Uncompressed Housekeeping (in Bytes)

350 2800 600 4.6 2.3

Total Telemetry After Compression (bits/s)

200.0 100.0



Data Products and DeliveryTable 3: Strofio Data Product Summary Data Level

Responsibility Description Time Lag

L-0b BMOC Input telemetry stream Immediately

L-1b SGS (ESOC Science Ground Segment)

Raw time-ordered data, checksum validated data in scientific units, including label files

Immediately

L-2 SGS (1) Strofio GDS (2)

Time-ordered and calibrated data, including attitude and ephemeris information and label files

Immediately (1)

After reprocessing (2)

L-3 Strofio GDS Higher-order Strofio data (e.g., time-ordered mass histograms, densities organized by latitude and longitude), complementary SERENA and BepiColombo (MPO and MMO) data, relevant theoretical models of the surface-exosphere-magnetosphere interactions, appropriate laboratory measurements and modeling.

As available



BACKUP SLIDESMission Operations & Data Analysis



Science Overview



135°

45°

315°

225°

180°

170°

60°

300°

315°

45°

190°

Aphelion = 32 days

Reduced P/L ops.8 days (120 W)

during GS with Ka


during GS with Ka

Full P/L ops.27 days (179 W)

Full P/L ops.27 days (179 W)


during GS with Ka

Reduced P/L ops.16 days

111 W outside GS contact5 W during GS with X

(no Ka band during this period)

Terminator = 20 days

Terminator = 20 days

Perihelion = 16 days

MPO Timeline (from ESA)



Orbit Definition

RadiatorFrom EID-A sec 2.4.6.2



Timeline Assumptions

Launch 7/19/2014

Perihelion 5/12/2020

11/13/2020 Orbit insertion

Aphelion 6/25/2020

7/21/2020 Start of commissioning

Perihelion 8/8/2020

2/19/2021 Start Science Ops

Aphelion 9/21/2020



Exospheric Asymmetries dawn/dusk



Timeline of Flight Operations

strofio science plan & operations

Documents