THEMIS

Project Data Management Plan

THM-SYS-012

07/15/2004

Timothy Quinn, THEMIS Science Operations Manager

Dr. Tai Phan, THEMIS Data Analysis Software Lead

Dr. Manfred Bester, THEMIS Mission Operations Manager

Dr. Ellen Taylor, THEMIS Mission Systems Engineer

Peter Harvey, THEMIS Project Manager

# Document Revision Record {#document-revision-record .unnumbered}

  ---------- ------------ ------------------------------------ -------------
  **Rev.**   **Date**     **Description of Change**            **Approved
                                                               By**

  1          12/03/2003   Preliminary Draft                    \-

  2          06/07/2004   Second Draft                         \-

  3          06/13/2004   Signature Version                    See
                                                               Signatories

                                                               

                                                               
  ---------- ------------ ------------------------------------ -------------

# Distribution List {#distribution-list .unnumbered}

  ----------------------------------- ----------------------------------------------------------
  **Name**                            **Email**

  Timothy Quinn, U.C. Berkeley        teq@ssl.berkeley.edu

  Dr. Tai Phan, U.C. Berkeley         phan@ssl.berkeley.edu

  Dr. Manfred Bester, U.C. Berkeley   manfred@ssl.berkeley.edu

  Dr. Ellen Taylor, U.C. Berkeley     ertaylor@ssl.berkeley.edu

  Peter Harvey, U.C. Berkeley         prh@ssl.berkeley.edu

  Dr. Vassilis Angelopoulos, U.C.     [vassilis@ssl.berkeley.edu](mailto:prh@ssl.berkeley.edu)
  Berkeley                            

  Dr. Dave Sibeck, NASA GSFC          david.g.sibeck@nasa.gov

  Dr. William Peterson, NASA          william.k.Peterson@nasa.gov
  Headquarters                        
  ----------------------------------- ----------------------------------------------------------

# TBD List {#tbd-list .unnumbered}

  --------------- -------------------------------------------------------
  Identifier      Description

  --------------- -------------------------------------------------------

Table of Contents

[Document Revision Record 2](#document-revision-record)

[Distribution List 2](#distribution-list)

[TBD List 2](#tbd-list)

[1. Introduction. 7](#introduction.)

[1.1 Purpose and Scope. 7](#purpose-and-scope.)

[1.2 Applicable Documents. 7](#applicable-documents.)

[2. Project Overview. 8](#project-overview.)

[2.1 Science Objectives. 8](#science-objectives.)

[2.2 Mission Summary. 8](#mission-summary.)

[3. Probe Description. 10](#probe-description.)

[3.1 Overview 10](#overview)

[3.2 Subsystem Descriptions. 11](#subsystem-descriptions.)

[3.2.1 RF and Communications Subsystem (RFCS).
11](#rf-and-communications-subsystem-rfcs.)

[3.2.2 Guidance Navigation and Control (GN&C)
11](#guidance-navigation-and-control-gnc)

[3.2.3 Command and Data Handling Subsystem (CDHS).
11](#command-and-data-handling-subsystem-cdhs.)

[3.2.4 Power. 12](#power.)

[3.2.5 Structural/Mechanical & Thermal.
12](#structuralmechanical-thermal.)

[3.2.6 Bus Avionics Unit (BAU). 13](#bus-avionics-unit-bau.)

[3.2.7 Probe Carrier Configuration and Launch.
13](#probe-carrier-configuration-and-launch.)

[4. Instrument Descriptions. 14](#instrument-descriptions.)

[4.1 Overview 14](#overview-1)

[4.2 Fluxgate Magnetometer 14](#fluxgate-magnetometer)

[4.2.1 Science Requirements 14](#science-requirements)

[4.2.2 Specification 15](#specification)

[4.2.3 Calibration 15](#calibration)

[4.2.4 Boom Deployment 15](#boom-deployment)

[4.3 Electrostatic Analyzers (ESA). 16](#electrostatic-analyzers-esa.)

[4.3.1 Science Requirements 16](#science-requirements-1)

[4.3.2 Specifications 16](#specifications)

[4.3.3 Calibration 16](#calibration-1)

[4.3.4 Aperture Cover Release 17](#aperture-cover-release)

[4.4 Solid State Telescope (SST). 17](#solid-state-telescope-sst.)

[4.4.1 Science Requirements. 17](#science-requirements.)

[4.4.2 Specifications 17](#specifications-1)

[4.4.3 Calibration 17](#calibration-2)

[4.4.4 Attenuator Operation 18](#attenuator-operation)

[4.5 Search Coil Magnetometer 18](#search-coil-magnetometer)

[4.5.1 Science Requirements 18](#science-requirements-2)

[4.5.2 Specifications 18](#specifications-2)

[4.5.3 Calibration 18](#calibration-3)

[**4.5.4** Boom Deployment 18](#boom-deployment-1)

[4.6 Electric Field Instrument (EFI) 19](#electric-field-instrument-efi)

[4.6.1 Science Requirements 19](#science-requirements-3)

[4.6.2 Specifications 19](#specifications-3)

[4.6.3 Calibration 20](#calibration-4)

[4.6.4 Deployment Operations 20](#deployment-operations)

[4.7 Instrument Data Processing Unit (IDPU)
20](#instrument-data-processing-unit-idpu)

[4.8 Ground Observations 21](#ground-observations)

[4.8.1 Ground Based Observatories (GBO)
21](#ground-based-observatories-gbo)

[4.8.2 E/PO Ground Magnetometers (E/PO-GMAGS)
27](#epo-ground-magnetometers-epo-gmags)

[5. Ground Data System (GDS) Description
28](#ground-data-system-gds-description)

[5.1 Overview 28](#overview-2)

[5.2 Ground Stations 28](#ground-stations)

[5.2.1 Berkeley Ground Station (BGS) 28](#berkeley-ground-station-bgs)

[5.2.2 Secondary and Backup Ground Stations
28](#secondary-and-backup-ground-stations)

[5.2.3 Telemetry Files 29](#telemetry-files)

[5.3 Mission Operations Center (MOC) 29](#mission-operations-center-moc)

[**5.3.1** **Mission Operations** 29](#mission-operations)

[5.4 Flight Dynamics Center (FDC) 31](#flight-dynamics-center-fdc)

[5.4.1 Overview 31](#overview-4)

[5.4.2 Software Tools 31](#software-tools)

[5.4.3 Operations 31](#operations)

[5.5 Flight Operations Team (FOT) 32](#flight-operations-team-fot)

[5.6 Science Operations Center (SOC) 32](#science-operations-center-soc)

[5.6.1 Overview 32](#overview-5)

[6. Project Data Flow 33](#project-data-flow)

[6.1 Overview 33](#overview-6)

[6.2 Probe Instrument Data 33](#probe-instrument-data)

[6.2.1 Collection -- Time T0 34](#collection-time-t0)

[6.2.2 Recovery -- Time T1 (T0+8 Days Maximum)
34](#recovery-time-t1-t08-days-maximum)

[6.2.3 Delivery to SOC -- T1+1Hr 34](#delivery-to-soc-t11hr)

[6.2.4 Level Zero Processing -- Time T1+2Hrs
35](#level-zero-processing-time-t12hrs)

[6.2.5 CDF Processing -- Time T1+3Hrs 35](#cdf-processing-time-t13hrs)

[6.2.6 Diagnostic Plot Creation -- T1+4Hrs
35](#diagnostic-plot-creation-t14hrs)

[6.2.7 Browse/Key Parameter (K0) Data Creation -- T1+24Hrs
35](#browsekey-parameter-k0-data-creation-t124hrs)

[6.2.8 K1 Data Creation -- T1+1Month 35](#k1-data-creation-t11month)

[6.2.9 K2 Data Creation -- T1+6Months 36](#k2-data-creation-t16months)

[6.3 GBO Data 37](#gbo-data)

[6.3.1 Collection -- Time T0 37](#collection-time-t0-1)

[6.3.2 Thumbnail Image Recovery by UC -- T0+1min
38](#thumbnail-image-recovery-by-uc-t01min)

[6.3.3 Health and Safety (H&S) Data Recovery -- T0+1min
38](#health-and-safety-hs-data-recovery-t01min)

[6.3.4 Thumbnail Image Copied to UCB -- T0+5mins
38](#thumbnail-image-copied-to-ucb-t05mins)

[6.3.5 Raw Magnetometer Data Recovered by UC and Copied to UCLA, UA, and
UCB - T0+27hrs
39](#raw-magnetometer-data-recovered-by-uc-and-copied-to-ucla-ua-and-ucb---t027hrs)

[6.3.6 UCLA Produces Processed GMAG Data -- T0+28hrs
39](#ucla-produces-processed-gmag-data-t028hrs)

[6.3.7 Keogram Recovery and Distribution -- T0+30Hrs
39](#keogram-recovery-and-distribution-t030hrs)

[6.3.8 Inclusion in Key Parameter Data -- T0+30Hrs
39](#inclusion-in-key-parameter-data-t030hrs)

[6.3.9 Recovery and Distribution of Full Resolution Images -- T0+6Months
39](#recovery-and-distribution-of-full-resolution-images-t06months)

[6.4 E/PO GMAG Data 39](#epo-gmag-data)

[6.4.1 Collection -- Time T0 39](#collection-time-t0-2)

[6.4.2 Recovery -- Time T0+27Hrs 39](#recovery-time-t027hrs)

[6.4.3 Processed GMAG Data Produced and Distributed
39](#processed-gmag-data-produced-and-distributed)

[6.5 SPASE Collaboration 39](#spase-collaboration)

[7. Instrument Command and Control 40](#instrument-command-and-control)

[7.1.1 Overview 40](#overview-7)

[7.1.2 Instrument Commissioning 40](#instrument-commissioning)

[7.1.3 Normal Operations 40](#normal-operations-1)

[7.2 GBO Installation, Monitoring, Control, and Maintenance
41](#gbo-installation-monitoring-control-and-maintenance)

[7.3 E/PO GMAG Control 41](#epo-gmag-control)

[8. Science Data Products 42](#science-data-products)

[8.1 Instrument Data CDF Files 42](#instrument-data-cdf-files)

[8.2 Instrument Data Calibration Files
42](#instrument-data-calibration-files)

[8.3 Key Parameter Data 43](#key-parameter-data)

[8.4 GBO Data and Products 44](#gbo-data-and-products)

[8.4.1 ASI 44](#asi)

[8.4.2 GMAG 44](#gmag)

[8.5 E/PO GMAG Data Products 44](#epo-gmag-data-products)

[9. Data Access 46](#data-access)

[9.1 THEMIS Data Analysis Software Package File Search Tool
46](#themis-data-analysis-software-package-file-search-tool)

[9.2 Website 46](#website)

[10. Data Analysis Software 46](#data-analysis-software)

[10.1 Overview 46](#overview-8)

[10.2 File Search Tool 47](#file-search-tool)

[10.3 Moments & Fields Tool 47](#moments-fields-tool)

[10.4 Reading and Writing Tools 47](#reading-and-writing-tools)

[11. Data Archiving and Distribution
47](#data-archiving-and-distribution)

[12. Appendix A. Instrument Data Quantities
49](#appendix-a.-instrument-data-quantities)

[13. Appendix B. Instrument Data Rates
50](#appendix-b.-instrument-data-rates)

[14. Appendix C. Instrument Data Volumes
51](#appendix-c.-instrument-data-volumes)

# Introduction.

## Purpose and Scope.

This document provides the Project Data Management Plan (PDMP) for the
Time History of Events and Macroscale Interactions during Substorms
(THEMIS) Explorer Mission. The PDMP describes all of the activities
associated with the flow of THEMIS scientific data from collection on
the spacecraft through production, distribution and access, and
archiving of data and data products. This also includes extensive ground
based imager and magnetometer measurements taken by 20 Ground Based
Observatories (GBO\'s) spread across Alaska and Canada, and 10 Education
and Public Outreach (E/PO) magnetometers spread across the northern
continental United States.

## Applicable Documents.

1.  THM-SYS-102 THEMIS Command Format Specification

2.  THM-SYS-115 THEMIS Telemetry Data Format Specification

3.  THM-SYS-116 THEMIS Telemetry Data Packet Format Specification

4.  THM-SYS-114 THEMIS Radio Frequency Interface Control Document

5.  THM-SYS-013 THEMIS Mission Operations Plan

6.  THM-SYS-018 THEMIS Launch and Early Orbit Operations Plan

7.  THM-SYS-019 THEMIS Contingency Plan

# Project Overview.

## Science Objectives.

The primary objective for the THEMIS project is to understand the onset
and macroscale evolution of magnetospheric substorms. A substorm is an
instability in the circulation of magnetic flux and plasma through the
solar wind magnetospheric system ultimately linked to the familiar
auroral eruptions on the Earth\'s polar ionosphere. Understanding the
substorm instability is crucial for space science, basic plasma physics,
and space weather, and has been identified by the National Research
Council (NRC) as one of the main strategic questions in space physics.
THEMIS will determine for the first time when and where in the
magnetosphere substorms start, and how they evolve macroscopically. It
will do so by timing well-known plasma particle and field signatures at
several locations in the Earth's magnetotail while simultaneously
determining the time and location of substorm onset at Earth using a
dense network of ground observatories.

![](media/image1.png){width="5.678346456692913in"
height="2.5708661417322833in"}

> Figure 1. Science Objectives

## Mission Summary.

The THEMIS science objectives are achieved by five space probes, P1 --
P5, in High Earth Orbits (HEO) with similar perigee altitudes (1.16 to
1.5 earth radii, Re) and varying apogee altitudes. P1 has an apogee of
\~30 Re, P2 at \~20 Re, and P3 - P5 at \~12 Re, with corresponding
orbital periods of \~4, 2, and 1 days, respectively. This choice of
periods results in multi-point conjunctions at apogee, allowing the
probes to simultaneously measure substorm signatures over long distances
along the magneto tail, while simplifying ground communications and
scheduling. The probe conjunctions are tightly coordinated with the
ground-based observatories within a 4-month primary observing season per
year, centered on mid-February and carried out each year during a 2-year
baseline mission. A store-and-forward data flow scheme retrieves prime
conjunction plasma and fields data during substorm events with simple,
automated science operations.

The ground observations will be carried out by 20 Ground Based
Observatories (GBO) spread across Alaska and Canada. Each GBO will use
an All Sky Imager (ASI - camera) and ground magnetometer (GMAG) to
monitor the auroral light and ionospheric currents in order to localize
the time, location, and evolution of the auroral manifestation of the
substorm. A second ground network will include 10 Education and Public
Outreach (E/PO) Ground Magnetometers located in schools at sub-auroral
latitudes in the U.S.

+-------------+--------------------------------------------------------+
| **Launch**  | **Vehicle: Delta II Eastern Range**                    |
|             |                                                        |
|             | **Injection: 1.1x12Re, 9 degrees inclination**         |
|             |                                                        |
|             | **Date: October, 2006**                                |
+-------------+--------------------------------------------------------+
| **Space     | **Spacecraft: 5 spinning probes with fuel for          |
| Segment**   | orbit/attitude adjust**                                |
|             |                                                        |
|             | **Instruments: 3-Axis E-Field and B-Field, 3-D Ion and |
|             | electron particle detectors**                          |
|             |                                                        |
|             | **Orbit Periods: 1, 2, and 4 days**                    |
|             |                                                        |
|             | **Spin Axis Orientation: Ecliptic normal**             |
+-------------+--------------------------------------------------------+
| **Ground    | **Ground Based Observatories (GBO): 20 sites in Alaska |
| Segment**   | (4) and Canada (16) containing All Sky Imagers (ASI)   |
|             | and Ground Magnetometers (GMAG)**                      |
|             |                                                        |
|             | **E/PO GMAGS: 10 GMAGS placed in schools located in    |
|             | Northern Latitude U.S.**                               |
+-------------+--------------------------------------------------------+
| **O         | **Phases: I&T, L&EO (2 mo), Campaigns                  |
| perations** | (December-March), De-orbit**                           |
|             |                                                        |
|             | **Lifetime: 2 years**                                  |
+-------------+--------------------------------------------------------+

> Table 1. THEMIS Mission Summary

# Probe Description.

## Overview

THEMIS employs 5 simple, identical, high heritage space probes (P1, P2,
P3, P4, & P5) in coordinated orbits. Each probe consists of the probe
bus (probe) and the instrument suite. The probe bus subsystems include
Structural/Mechanical, Thermal, Power, RF and Communications (RFCS),
Command and Data Handling (CDHS), and Guidance Navigation & Control
(GN&C). The GNCS consists of the Attitude Control Subsystem (ACS) and
the Reaction Control (propulsion) Subsystem (RCS). The electronics
associated with the Power, CDHS, ACS, and RCS reside in the Bus Avionics
Unit (BAU). The probe bus has a simple, low-rate S-band communications
system with a store-and-forward (near perigee) strategy. It is supported
by the General Dynamics ColdFire processor, hosting heritage software to
perform data handling and minor fault detection activities. The power
system is comprised of simple body-mounted solar panels and a small
battery charged by a direct energy transfer controller. The probes are
spin-stabilized and the Attitude Control System (ACS) uses a
fault-tolerant cross-strapped monopropellant hydrazine blow-down system
to control orbit, spin rate, and spin axis attitude. ACS is simplified
by ground based attitude determination performed at UCB by the Flight
Dynamics Center (FDC). All maneuver sequences are planned, checked (via
a spacecraft simulator), uploaded, and executed during real-time ground
communications.

![](media/image3.png){width="3.65in" height="2.225in"}

![](media/image4.png){width="3.390277777777778in"
height="2.1930555555555555in"}

Figure 2. THEMIS Probe

## Subsystem Descriptions.

### RF and Communications Subsystem (RFCS).

The RFCS utilizes a NASA standard 5-Watt S-Band transponder for Command
and Telemetry communications with a single cylindrical FAST-like antenna
with a toroidal gain pattern. The transponder allows two-way Doppler
ranging for accurate orbit determination. All probes use the same
frequency pair for telemetry and commanding. Communications are
established with one probe at a time. Command and telemetry protocols
for the probes follow standard CCSDS procedures \[1\]. Downlink
telemetry rates are selectable and available to optimize probe
monitoring and telemetry recovery as a function of probe range. The
nominal rate is 524.288 kbps, and the expected data volume during a
science dump is 480 - 640 Mbits. The command uplink rate is fixed at 1
kbps.

+-----------------------------------+-----------------------------------+
| Frequency                         | Downlink -- 2282.5 MHz            |
|                                   |                                   |
|                                   | Uplink -- 2101.8 MHz              |
+-----------------------------------+-----------------------------------+
| Polarization                      | Left-Hand Circular Polarized      |
|                                   | (LHCP)                            |
+-----------------------------------+-----------------------------------+
| Modulation                        | Downlink -- BPSK (4 highest data  |
|                                   | rates)                            |
|                                   |                                   |
|                                   | PCM/PSK/PM (6 lowest data rates)  |
|                                   |                                   |
|                                   | Uplink - PCM/PSK/PM               |
+-----------------------------------+-----------------------------------+
| Encoding                          | Downlink -- Reed-Solomon +        |
|                                   | Rate-1/2 Convolution              |
+-----------------------------------+-----------------------------------+
| Compression Scheme (VC3 only)     | Differencing and truncation or    |
|                                   | Huffman (TBR)                     |
+-----------------------------------+-----------------------------------+
| Bit Rates                         | 1.024, 4.096, 8.192, 16.384,      |
|                                   | 32.768, 65.536, 131.072, 262.144, |
|                                   | 524.288, 1048.576 kbps            |
+-----------------------------------+-----------------------------------+
| Virtual Channels                  | 0-3, 6                            |
+-----------------------------------+-----------------------------------+
| Data Volume per Orbit per Probe   | 480 - 640 Mbits                   |
+-----------------------------------+-----------------------------------+

Table 2. RF and Communications Subsystem Summary

### Guidance Navigation and Control (GN&C)

The GN&C subsystem includes the Attitude Control Subsystem (ACS) and the
Reaction Control Subsystem (RCS).

The ACS utilizes a thruster interface driven by ground-processed
estimation and command algorithms with on-board limit and time-out
protection. Attitude data collected from a Miniature Spinning Sun Sensor
(MSSS) and the science Fluxgate Magnetometer (FGM) are sampled at 10 Hz
and telemetered to the ground for standard, 3-axis, post-processing
estimation. Ground generated thruster command sequences are tested in a
high-fidelity probe simulator (I&T test bed migrated to MOC) prior to
any upload. Also, two single-axis gyros, transverse to the spin plane,
provide short-term attitude verification (prior to orbit maneuvers). The
on-board protection logic monitors real-time sun aspect angle and spin
period, comparing them to a ground commanded reference uploaded for each
maneuver. If thresholds are exceeded, the maneuver is terminated.

The RCS includes two fuel tanks, a pressurization tank, a pyro valve,
two latch valves, fuel line and fuel filters, and four 5-N thrusters: 2
oriented axially, (Both along +Z) for primary orbit placement ∆V and
attitude control; and 2 oriented tangentially for spin up/down control
and minor ∆V side thrusting for orbit fine tuning. The minimum thruster
pulse duration is 50 milliseconds.

### Command and Data Handling Subsystem (CDHS).

The CDHS provides real-time and stored command capability for the bus
subsystems and instruments, collects, formats, and transmits to the
ground data from the bus subsystems and instruments, provides
engineering data storage, distributes time to the IDPU, and implements
autonomous fault protection features to ensure the health and safety of
the probe. The CDHS functions are implemented in flight software and
hardware that reside in the BAU.

CDHS receives uplink commands from the RFCS at a fixed rate of 100 bps
using CCSDS telecommand protocols that guarantee correct, in-sequence
delivery of variable-length command packets (embedded in command
transfer frames) to the probe. Command transfer frames are
authenticated. The CDHS is capable of accepting hardware commands
(commands that do not require processor involvement) to perform critical
operations such as hardware reconfiguration from the ground. Stored
command capability in the form of Absolute Time Sequence (ATS) and
Relative Time Sequence (RTS) loads is available for controlling the
probe and instruments outside of a ground station contact.

CDHS data may involve real-time engineering, playback engineering, and
real-time or playback science (from the IDPU). The CDHS collects and
packetizes engineering data from the bus subsystem and instruments and
either delivers these data to the RFCS in real-time for downlink (VC0),
or stores the data locally in the BAU for playback at a later time
(VC1).The CDHS will also route real-time (VC2) and stored (VC3) science
data to the RFCS for downlink. The THEMIS telemetry format is based on
CCSDS standards and data structures. The telemetry link is encoded using
concatenated rate-1/2 (K=7) convolutional and Reed-Solomon (255,223,I=5)
coding to allow for error correction. Also, the VC3 packet data are
compressed, as described in \[3\].

  ------------ ----------------------------------------------------------
  VC ID        Description

  0            Real-time Engineering Data (Probe and Instruments)

  1            Stored Engineering Data (Probe and Instruments)

  2            Real-time Science Data

  3            Stored Science Data

  6            Event Data

  7            Fill Data
  ------------ ----------------------------------------------------------

Table 3. Virtual Channel Summary

### Power.

The Power Subsystem is a Direct Energy Transfer (DET) system with the
battery and solar array connected directly to the power bus. The solar
array consists of eight panels, four on each side, and two on each deck.
At nominal attitudes, approximately 59 Watts EOL are provided by the
side panels and 21 Watts EOL by the top and bottom panels. Accounting
for battery recharging, increased eclipse heater power, and power
control efficiencies, the minimum load power available is 41.7 Watts,
easily achieving energy balance for the required load power of 29.2
Watts. Eclipse and peak transient loads (i.e., transmitter operation)
are balanced with an 11.8 A-hr, 28V Lithium-Ion battery. Thermal
management using heaters and thermistors keeps the battery temperature
at -5 to +25 degrees C.

### Structural/Mechanical & Thermal.

The probe consists of a lower deck, an upper deck, and four corner and
side panels. The lower deck is the primary mounting surface for most of
the instruments and probe components. The upper deck, corner, and side
panels close out the probe internal cavity. The FGM and SCM mount to the
upper deck; solar cells utilize the exterior surface of the probe side
panels as their substrate. The ESA and SST instruments, the sun sensor,
and thruster brackets mount to two of the corner panels for a clear
Field of View (FOV). The mechanical and thermal designs provide a low
conductance composite structure for isolation of the body-mounted solar
panels, minimizing thermal energy effects between full-sun and shadow
operations.

### Bus Avionics Unit (BAU).

The BAU includes a SMEX-Lite heritage uplink/downlink communications
card, a processor card (identical to the IDPU processor card), and a
Direct Energy Transfer (DET) power control card with SMEX-Lite and EO-1
heritage. The flight software is derived from prior SMEX mission modules
(in C-language) and is hosted by the heritage CMX-RTX Real-Time
Operating System (RTOS). Instrument and bus housekeeping data are stored
in the local bus memory, while science data are stored in the IDPU.
During a ground station contact, housekeeping data are transmitted
directly by the BAU while science data stored in the IDPU memory are
sent to the BAU. The latter in turn merges these into the telemetry
stream (bent pipe flow), similar to the FAST implementation.

### Probe Carrier Configuration and Launch.

THEMIS will use a standard Delta sequence to directly inject the Probe
Carrier Assembly (PCA) into the target insertion orbit. The PCA does not
separate from the third stage. The probes separate from the probe
carrier immediately after third stage burnout and yo-yo despin. The
probes are electrically independent; each imitates separation based on
built-in sequence timers and ELV separation signals, thereby eliminating
any credible single point failure. For contingency, the separation can
also be initiated by ground command. Multiple timers (hardware and
software) are provided to protect against premature probe separation.

# Instrument Descriptions.

## Overview

Each probe contains an instrument complement that will measure DC and AC
electric and magnetic fields as well as electron and ion energies and
distributions. A detailed list of the instrument data quantities, data
rates, and data volume is given in Appendix A, B, and C, respectively.
The instruments and their probe placement and configuration are detailed
in Figure 3 below.

![](media/image5.png){width="6.820138888888889in"
height="4.196527777777778in"}

Figure 3. Instrument/Probe Configuration

## Fluxgate Magnetometer 

A tri-axial fluxgate magnetometer will measure the 3D ambient magnetic
field in the frequency bandwidth from DC to 64 Hz (Nyquist).

### Science Requirements

1)  Measure DC and low frequency perturbations of the magnetic field

2)  Time wave and structure propagation between probes

3)  Provide information on plasma currents based on instantaneous
    magnetic field differences on two or more probes, separated by \>0.2
    Re.

### Specification

The unit consists of two orthogonal ring core elements of different
diameter, fixed with a bobbin. The unit is mounted on a 2-meter
double-hinge carbon epoxy boom. The electronics consist of the driver
and control circuits on a board within the IDPU. The controller controls
digital excitation, data acquisition, feedback, and compensation, making
the device low power. Its low noise permits easy inter-calibration with
the search-coil magnetometer at frequencies of approximately 10 Hz.

![](media/image6.jpeg){width="2.120138888888889in"
height="2.745833333333333in"}

Figure 4. Fluxgate Magnetometer

### Calibration 

Although a 1 nT absolute accuracy requirement is achievable with
independent sensor calibration, it is important to ascertain that two
separate probes provide identical values when properties of the medium
are steady. As required (near each apogee, perigee or both), calibration
data will be collected at 32 Hz to determine (on individual probes) zero
levels, gains, and sensor orientation. The magnetometers on all 5 probes
will also be inter-calibrated during the early part of the mission
(L&EO) using traversals of current-free (or low current density) regions
of the magnetosphere. Also, as required during the second year of the
mission, magnetometer data from probes P3, P4 and P5 will be collected
at high rates outside of burst-mode triggers, in order to perform
inter-calibration of their relative orientation and offsets in
current-free regions. The validity of a divergence-free assumption (a
theoretical necessity) will be used to ascertain the validity of the
current-free approximation. If the divergence-free approximation cannot
be easily met then time-tagged data from the probes traversing the same
region will be compared for trend-recognition after long-term averaging.

### Boom Deployment

During L&EO, once the FGM and SCM are operating, the magnetometer booms
will be deployed by ground command. First the FGM data rate is set to 32
Hz and FGM data are monitored in the real-time telemetry stream (VC2).
The prime and secondary boom release mechanisms are then commanded in
succession. The FGM axis rotation is verified during deployment.

## Electrostatic Analyzers (ESA).

The Electrostatic Analyzers will measure thermal ions and electrons in
the range 5 eV - 30 keV.

### Science Requirements

1)  Plasma moments to within 10%, at high time resolution (10s or
    better) for inter-probe timing studies.

2)  Instantaneous differences in velocity and ion pressure between
    probes, to estimate the scale size of transport, the size and
    strength of flow vortices and the pressure gradient.

3)  Distribution functions of ions and electrons, to ascertain the
    presence of free energy sources.

### Specifications

Both the ion and electron ESA have a look direction of 180 degrees in
elevation, split in eight 22.5-degree bins (one per anode). Measurements
over 4π steradian are made once per spin. The particles are selected in
E/q (where q is the charge) by a sweeping potential applied in 32 steps,
32 times/spin (32 azimuths) between the outer (0 kV and the inner (\~3
kV) concentric spheres in a Chevron configuration. On-board moment,
pitch angle, and averaging computations are implemented at the IDPU.
These operations routinely utilize FGM and SST data (to ensure correct
values when the peak flux extends beyond the plasma instrument energy
range). Even with onboard averaging, the ESAs generate nearly 3 kbytes
of data each spin and thus require onboard moment calculations to obtain
spin period data. 3-D distributions will be transmitted at a much lower
cadence except during event bursts that will contain spin period
distributions.

![](media/image7.jpeg){width="1.820138888888889in"
height="1.8416666666666666in"}

![](media/image8.png){width="4.579861111111111in"
height="1.7027777777777777in"}

> Figure 5. ESA

### Calibration

The science requirement of 10% accuracy on moment computation can be met
by independent calibration of the ESAs. However, by inter-calibrating
hour-long averages of routinely collected particle distributions during
quiet-time probe-conjunctions it is expected to surpass the accuracy
obtained from independent ESA calibration.

An automated calibration procedure performs a complete angle/energy
calibration of an instrument stack in less than 1 day. Calibration
determines:

1)  Analyzer constant, uniformity of energy/angle response

2)  Hemisphere concentricity

3)  Optimum MCP voltage

4)  Sweep voltage verification

5)  Relative geometric factors

6)  Flight mode validation

Absolute geometric factor values are determined from computer
simulations and calibrations with a Ni^63^ beta source.

### Aperture Cover Release

During L&EO the ESA entrance aperture covers will be removed. This
process will be commanded from the ground and the cover release is
performed using a Shaped Metal Alloy (SMA) device.

## Solid State Telescope (SST).

The Solid State Telescope (SST) measures the angular distribution (\~3π
steradian coverage) of super thermal ions and electrons. The detectors
are identical to the SST pairs flown on the WIND spacecraft. Each probe
carries two telescope pairs.

### Science Requirements. 

1)  Perform remote sensing of the tail-ward moving current distribution
    boundary (at P3, P4, P5)

2)  Measure the time-of-arrival of super thermal ions and electrons
    (30-300 keV, at 10s resolution or better) during injections, and
    ascertain the Rx onset time (P1, P2).

### Specifications

Each of the two SSTs consists of a telescope pair with double-ended
sensors, as shown in Figure 6. Individual sensors comprise three
stacked, fully depleted, passivated, ion-implanted, 1.5 cm^2^ silicon
detectors. The center (T) detector is 600 μm thick, while the outside (O
& F) detectors are 300 μm thick. Each of the four sensors measures ions
and electrons via opposing sides of its detector. The two telescope
pairs are mounted such that one pair of sensor aperatures points above
the spin plane at 25 and 55 deg, and the other pair below the spin plane
at --25 and --55 deg, respectively.

![](media/image9.jpeg){width="2.7597222222222224in"
height="2.2840277777777778in"}

Figure 6. The Solid State Telescope (SST)

### Calibration

Absolute calibration points are determined by monitoring the highest
energy of protons stopped and by placing the pairs (or triplets) of
detectors in coincidence and monitoring the minimum ionizing energy for
penetrating particles. Such practices have led to superb agreement
between SST and ESA fluxes on WIND, and result to \<10% absolute flux
uncertainty. Inter-probe calibration will also be performed at times of
low plasma sheet activity, when the flux anisotropy is low.

### Attenuator Operation

The SST attenuator is controlled by the IDPU. It will be operated when a
probe approaches the radiation belts based on measured flux levels.
Sufficient (\~10min) hysteresis is built into the design.

## Search Coil Magnetometer

The SCM measures the 3D magnetic field in the frequency bandwidth from 1
Hz to 4 kHz. It will extend with appropriate sensitivity the
measurements of the FGM beyond the 1 Hz range.

### Science Requirements

The science requirements derive from the need to measure with
appropriate sensitivity (\<1 pT/√Hz @ 10 Hz): the cross-field current
disruption waves (\~0.1 fLH) at least as close to Earth as 8Re
(fLH-60Hz).

### Specifications

The SCM measures the variation of the magnetic flux threading three
orthogonal high permeability μ−metal rods. The unit sensitivity is 0.5
pT/√Hz @ 10 Hz. A flux feedback loop is employed to ensure phase
stability.

The signals from the three sensors are pre-amplified and then processed
together with the EFI data at the IDPU.

![](media/image10.jpeg){width="2.8097222222222222in"
height="2.907638888888889in"}

Figure 7. The Search Coil Magnetometer (SCM)

### Calibration

Absolute amplitude and phase calibration takes place with calibration
coils that create a known AC pseudo-random noise consisting of a series
of discrete frequencies covering most of the bandwidth (10 Hz -- 4 kHz).
Calibration switch-on is commanded by the IDPU according to a
pre-scheduled sequence.

### Boom Deployment

See FGM boom deployment.

## Electric Field Instrument (EFI)

The EFI measures the 3D electric field in the frequency range from DC to
300 KHz. The three-dimensional EFI experiment consists of 4 spin-plane
spherical sensors each suspended on its own 20 mm deployable cable 20
meters away from the probe center. Two axial tubular sensors, each 1 m
long, are mounted on a 4 m-long stacer element.

### Science Requirements

Determine the time of onset at 8-10 Re by measuring:

1)  The plasma pure convection motion, i.e., without the effects of
    diamagnetic drifts that ESA measurements are subject to.

2)  The low frequency (T\~1min) wave mode and pointing flux.

The inner probes will determine the axial component independently from
the axial boom measurement and provide both a method for calibration of
the axial measurement and a backup solution.

### Specifications

Boom electronics located at the EFI housing perform stub and guard
voltage control and sphere biasing. Signal processing takes place in the
IDPU, together with the SCM. Routine waveforms (32 samples/s) or burst
waveforms (128-8192 samples/s) are captured and processed just as for
the SCM data. Spectral processing of the low frequency (\< 8 kHz) data
occurs in the DSP in a fashion identical to the SCM. The wire booms will
be deployed with near real-time monitoring of a release and spin-up
sequence, each lasting 1-2 hours/probe. Alternating between different
THEMIS probes in science and sphere-release phase, mission-total EFI
deployment lasts \< 10 days.

![](media/image11.jpeg){width="5.1097222222222225in"
height="3.8118055555555554in"}

Figure 8. The Electric Field Instrument (EFI)

### Calibration

The aforementioned individual probe calibration results in absolute DC
measurement accuracy of 0.1 mV/m, i.e. \<10% of the field value
anticipated during fast flows. Increased confidence in the measurements
will be obtained from inter-spacecraft calibration during quiet times.

### Deployment Operations

The EFI requires operational commands to govern boom deployment and
adjustment as well as science commands to control sensor bias voltages,
data sample rates, filter settings, and spectral resolution control. As
in previous missions, a typical mode can be specified with \~200
commands valid over a typical operational period of \~1 month once
deployment and checkout phases have been completed.

Three phases:

1)  Deployment alternatively extending the wire boom pair in
    predetermined increments. During radial wire boom deployment and at
    each stop, sphere potentials are monitored in order to characterize
    probe charging affects, plasma environment, and EFI status. After
    the radial boom deployment, the axial booms are each deployed to
    their final lengths using one initiator event per boom.

2)  Checkout: Assuming nominal potential measurements and probe spin
    rate, the checkout phase begins with final adjustments in wire boom
    lengths to verify that each pair deployed symmetrically relative to
    the probe body. These occur in near real-time sessions, monitoring
    the release and spin-up sequence, each lasting 1-2 hours/probe.
    Alternating between different THEMIS probes in science data
    collection and sphere-release phase, mission-total EFI deployment
    lasts \< 10 days. After boom deployment, an EFI early-checkout phase
    begins in which the photo-currents are characterized and the guards,
    stubs, and bias adjusted accordingly, requiring a new command load
    roughly once per week, per probe. Science quality data are returned
    during this phase which lasts \~1 month.

3)  During the nominal science phase, the EFI is configured roughly once
    each month through a command sequence.

## Instrument Data Processing Unit (IDPU)

This unit is the heart of the instrument package: it provides instrument
power, controls instrument functions, receives instrument commands and
obtains housekeeping and science data, stores and processes the data and
transmits data to the probe bus electronics. It is the interface between
the instrument sensors and the probe BAU. The IDPU uses an 8085
processor and 256 Mbytes of memory to store science data.

The IDPU collects, compresses, and stores instrument data and transmits
the data to the ground upon command with a nominal downlink rate of
524.288 kbps or 1,048.576 kbps. The command uplink protocol is a 1 kbps,
COP-1 compliant system, with commands relayed by the bus processor.
Instrument data are yielded to the IDPU at continuous rates governed by
the overall system mode (survey, particle burst, wave burst I or II).
The data format is 24-bits consisting of an 8-bit application process
identifier (APID) followed by 16 bits of data. Data compression and
complete packetization is performed by the processor, prior to storage
in the IDPU memory. The IDPU-to-bus C&DH telemetry requirement is a 1
Mbps serial data stream. The IDPU can mix and prioritize engineering and
science frames according to operational preferences at downlink time.

During nominal operation, the IDPU provides instrument housekeeping
packets to the probe-BAU, which are combined with its data into CCSDS
frames for downlink. Stored science data are transmitted separately
after engineering data over the high-speed link to the BAU when
commanded from the ground.

The IDPU is responsible for monitoring instrument science data and using
pre-defined measurement quantities as criteria for the overall
instrument data rates. Using a command upload table, the processor
steers instrument quantities into a trigger buffer section of memory
based on a trigger APID list. A real-time evaluation of a single
measurement level or weighted linear combinations of several
measurements are compared to pre-set thresholds as criteria for survey,
particle burst, or wave burst instrument rates.

Mode definition tables are large macros used by the IDPU to configure
instruments appropriate to the region of space being examined. The IDPU
will be programmed with a number of mode definitions that are selected
by an ATS command or on-board triggering logic. Assuming 32 macros of
512 bytes each, a full reload would require 16 kbytes. ESA and SST
Moment Tables are calculated by IDPU FSW at system startup and loaded
into the ESA and SST moment circuitry. For contingency operations, these
tables are also directly loadable from the ground. EFI biasing, FGM and
SCM parameter modes are expected to be small and are included in the
mode definitions.

## Ground Observations

Ground observations and measurements will be made of the aurora and
earth\'s magnetic field by two networks of instruments. The first will
be 20 Ground Based Observatories (GBO\'s) spread across Alaska (4) and
Canada (16). The GBO\'s will contain All Sky Imagers (ASI) and Ground
Magnetometers (GMAGs). The second network will be 10 Education and
Public Outreach (E/PO) GMAGs located in schools at sub-auroral latitudes
in the U.S. The locations of both networks are shown below in Figure 9.

### Ground Based Observatories (GBO)

The THEMIS mission times substorm signatures on the ground and in space
with a time resolution of better than 30 seconds. The comprehensive
THEMIS approach to solving the substorm problem calls for monitoring the
night side auroral oval with fast (\<1s exposures), low cost, and robust
white-light All Sky Imagers (ASI) and high-time resolution (1s) Ground
Magnetometers (GMAGS). These instruments will produce auroral images and
Earth magnetic field measurements. In addition to the ASI and GMAG data,
the GBO will produce health and safety data for evaluating the status of
the site. The ASI\'s are provided by UCB and the GMAGs are supplied by
UCLA. GBO locations are shown below in Figure 9.

![](media/image12.pct)

Figure 9. Ground Based Observatory (GBO) Locations

Some of the GBO's will take advantage of infrastructure and
instrumentation which are part of existing ground based networks. Each
of the 20 sites will house a UCB ASI, however, only 10 sites will house
a UCLA GMAG. Two of the Alaska sites will rely on magnetometers supplied
and operated by the Geophysical Institute at the University of Alaska,
Fairbanks. The remaining 8 sites in Canada will rely on magnetometers
supplied and operated by Canadian Geospace Monitoring (CGSM) and Natural
Resources Canada (NRCAN). Table 2 lists the type of magnetometer at each
site as well as the geographic coordinates.

![](media/image13.wmf)

Table 4. GBO Information

Figure 10 shows the major components of the GBO. The Computer System
Enclosure (CSE) consists of an external insulated environmental
enclosure and an internal rack mount. The rack mount will contain the
system computer, hot swappable hard drive, GMAG interface electronics,
Power Control Unit (PCU), CD10X Datalogger and battery, ASI power
supply, and an Uninterruptible Power Supply (UPS).

![](media/image14.jpeg){width="5.529861111111111in"
height="3.397222222222222in"}

Figure 10. GBO Components

The CSE will operate under external ambient temperatures of --50 degrees
C to 40 degrees C. It provides a dust free method of cooling via a solid
state air conditioner and heating via small space heaters (see Figure
11). It provides access for external cables, maintenance, hot swapping
of hard drives.

![](media/image15.jpeg){width="4.939583333333333in"
height="2.204861111111111in"}

Figure 11. GBO CSE Heating and Cooling

The PCU provides control of both temperature and instrument power. The
temperature in the CSE and ASI will be maintained at 20 degrees Celsius
+/- 10 degrees Celsius. Also, the PCU provides a graceful shutdown of
the system computer in the event of a loss of power or temperature.

![](media/image16.jpeg){width="4.0in" height="2.4375in"}

Figure 12. GBO PCU

The CR10X Datalogger is a "smart" controller with simple programming and
data logging capability, and takes the place of a regular thermostat. It
provides analog and digital I/O for the system computer, and is always
operating and always accessible for re-programming via the internet or
Iridium modem. It has an extended operating range of --55 degrees
Celsius to 85 degrees Celsius. Due to lower power consumption, it can
operate for months on battery power.

Remote access to the GBO's will typically be through an internet
connection made possible by one of the following:

-   Hardwired using a local LAN connection

-   Telesat HSi (Canada) or Starband 480 (Alaska)

    -   Can provide fixed IP address

    -   Minimum 10 kbps uplink rate

-   Backup connection via an Iridium modem

    -   2400 bps

![](media/image17.jpeg){width="3.2194444444444446in"
height="2.0319444444444446in"}

Figure 13. Prime Data Communications Link

![](media/image18.jpeg){width="4.279861111111111in" height="1.95in"}

Figure 14. Backup Data Communications Link

#### All Sky Imagers (ASI)

The ASI design uses commercially available components, and is based on
heritage ASI's used at AGO sites in Antarctica. The basic components
include a Charged Couple Device (CCD) camera and an all sky (fish-eye)
lens (Figure 15).

![](media/image19.jpeg){width="3.589583333333333in"
height="1.7173611111111111in"}

Figure 15. All Sky Imager (ASI)

The ASI is housed in a heated environmental enclosure topped with a
polycarbonate/acrylic dome (Figure 16). The enclosure is hermetically
sealed with a nitrogen purge. The enclosure is designed to operate with
external ambient temperatures in the range of --50 degrees Celsius to 40
degrees Celsius. The internal temperature is maintained at 20 degrees
Celsius, +/- 10 degrees Celsius

.

![](media/image20.jpeg){width="3.709722222222222in"
height="1.8819444444444444in"}

Figure 16. ASI Mounting and Enclosure

An internal sun shield will protect the ASI UV radiation damage during
non-operation periods (figure 17).

![](media/image21.jpeg){width="5.419444444444444in" height="2.175in"}

Figure 17. ASI Sun Shield

#### Ground Magnetometers (GBO-GMAGs)

There are 10 GBO\'s (2 in Alaska, 8 in Canada) that will house Ground
Magnetometers (GMAGs) developed by UCLA. These units are also referred
to as Fluxgate Magnetometers. The GMAGs are small, low power units, and
have a ruggedized all weather sensor design. The GMAG processor card is
located in the CSE and has a USB interface for data retrieval and
firmware uploads.

![](media/image22.jpeg){width="5.3in" height="2.092361111111111in"}

Figure 18. GMAG Sensor

The sensor has a +/-72KnT dynamic range @ 0.01nT resolution, and will
produce 2 vectors per second. Each vector consists of three quantities:
Bx, By, and Bz, which are measurements of the magnetic field strength
along each axis. The data output is expected to be 86.4 kbytes/hour with
approximately 100 bytes/hour for housekeeping and log data. The raw
magnetometer data are recorded in raw format, and calibration is applied
when products are compiled for distribution. Data are recovered with the
ASI data.

#### Health & Safety - System Status

The GBO will log approximately 10 kbytes of health and safety data every
5 minutes, or 100 kbytes/hour. Essential information is recorded at a
much lower rate, approximately 20 bps, yielding a data volume of 10
Kbytes/hour.

### E/PO Ground Magnetometers (E/PO-GMAGS)

UCLA will also build and install 10 additional GMAGs in selected K-12
schools located in sub-auroral latitudes in the U.S. (blue dots in
figure 9). The UCB Education and Public Outreach (E/PO) group will
manage this effort in order to promote inquiry-based and theme-based
instruction as well as allow hands-on student participation.

![](media/image23.jpeg){width="4.679861111111111in"
height="3.6069444444444443in"}

Figure 19. E/PO GMAG Locations

ASCII conversion routines will process the raw magnetometer data at the
sites. Working with E/PO personnel, students and teachers will use
standard Windows software packages (Excel import of ASCII data) to view
and analyze data. Web-based download functions will make the data
accessible to other schools and the general public. Data will also be
copied to UCLA and UCB. At UCB, the data will be integrated into the
data access and retrieval system as well as folded into the summary plot
production system.

# Ground Data System (GDS) Description

## Overview

The THEMIS GDS consists of several functional segments: The Ground
Stations (GS) to communicate with the probes on-orbit, the Mission
Operations Center (MOC) for probe telemetry and command control, the
Flight Dynamics Center (FDC) for probe orbit and attitude determination,
and the Science Operations Center (SOC) for instrument data collection,
processing, archiving, and distribution functions as well as planning
and generating commands for instrument operations. The Berkeley Ground
Station (BGS), MOC, FDC, and SOC are all co-located at the Space
Sciences Laboratory on the UCB campus. A general description of each GDS
segment is given below as well as their operational responsibility.

## Ground Stations

### Berkeley Ground Station (BGS)

The primary ground station for THEMIS is the Berkeley Ground Station
(BGS). The BGS employs front-end processors for bit synchronization,
Viterbi decoding, frame synchronization, Reed-Solomon decoding, and
CCSDS channel routing. Data streams that carry real-time engineering and
science data are routed directly into the MOC for real-time
state-of-health monitoring and control functions. In addition, all
received telemetry data are stored locally at the ground station in
separate files for each virtual channel and are automatically
transferred to the MOC and SOC via FTP once the support is complete.

Commanding of the probes is initiated from the ITOS workstations in the
MOC and follows standard CCSDS procedures \[1\]. Individual commands or
entire command loads are divided up into CLTUs and are forwarded to the
front-end processors via secure TCP/IP network socket connections. The
command data stream is then transmitted in real-time at a rate of 1 kbps
and BPSK modulated onto a 16-kHz subcarrier. The subcarrier is in turn
PM modulated onto the RF carrier with a modulation index of 1.0 rad. The
CCSDS COP-1 protocol is used to verify command reception on the probe.
Once a command is transmitted to the probe, ITOS monitors the Command
Link Control Word (CLCW) that is attached to each telemetry frame,
indicating the command verification status on-board the probe. ITOS
automatically initiates retransmission of commands that are not
verified.

Each probe contains a coherent STDN compatible transponder, thus
allowing two-way Doppler ranging for accurate orbit determination. All
probes use the same frequency pair for telemetry and commanding.
Communications are established with one probe at a time.

### Secondary and Backup Ground Stations

Secondary ground station support will be provided by NASA/GN stations
WGS 11-m, MILA 9-m, AGO 9-m, and HBK 10-m. TDRSS support is baselined
for the Launch and Early Orbit (L&EO) phase of the mission to monitor
probe release, aid in maneuver operations, and recovery from anomalous
conditions.

Real-time telemetry and command data are carried between the ground
station and MOC via a T1 line. Telemetry data stored on the ground are
transferred to the MOC and SOC via the open Internet. During Launch and
Early Orbit (L&EO) operations, TDRSS S-Band Single Access (SSA) mode
allows communications with each of the probes at a low data rate at
times when the individual probes are within communications range of a
TDRS spacecraft.

Pass schedule requests generated by the MOC are submitted to the
respective scheduling office associated with each ground station
network. Confirmed pass schedules are used to perform mission planning
and build command loads. All real-time command and telemetry connections
between the MOC and ground stations are carried over secure network
links. Tracking data are transferred from all ground stations to the FDC
to perform orbit determination in order to generate updated ephemeris
products. Attitude sensor data received from the probes through the MOC
are routed to the FDC to obtain ground based attitude solutions. Once
verified, ephemeris products and attitude solutions are used to plan
orbit maneuvers.

### Telemetry Files

The ground station telemetry file transfer protocols and file formats
are listed in reference document \[4\]. The file naming convention is
listed below:

Telemetry File Naming Conventions:

> Format:

-   FACILITY.PROBE_BUS_NAME.TLM_VCN.YYYY_DDD_HHMMSS.dat

> Examples:

-   BGS.THEMIS_A.TLM_VC0.2007_028_060312.dat

-   WGS.THEMIS_B.TLM_VC1.2007_029_012031.dat

-   MIL.THEMIS_C.TLM_VC2.2007_038_102319.dat

-   AGO.THEMIS_D.TLM_VC3.2007_032_151745.dat

-   HBK.THEMIS_E.TLM_VC6.2007_034_234512.dat

-   WSC.THEMIS_A.TLM_VC0.2006_301_001834.dat

## Mission Operations Center (MOC)

The THEMIS Mission Operations Center (MOC) will perform mission planning
functions, commanding, and state of health monitoring of the 5 probes,
recovery of science and engineering data, data trending and anomaly
resolution. The UCB Flight Operations Team (FOT) will carry out these
activities.

### **Mission Operations** 

#### Overview

The main operational modes or phases include Pre-Launch, Launch and
Early Orbit (L&EO), Nominal Science Operations, Maneuvers, and
End-of-Mission. The probes are powered with the receiver on during
Pre-Launch and L&EO modes with all deployable appendages stowed during
the Probe Carrier (PC) dispense operation. The probes are passively
spin-stabilized upon release (even under dispense fault conditions) and
full command and telemetry operations commence, initiated by ground
command, to each probe using unique identification codes. Deployment of
all booms, checkout, and power-up of each instrument is accomplished at
the appropriate stages of the In-orbit Checkout (IOC) phase (part of
L&EO) to verify key instrument functions and extract body (FGM), sheath
(EFI), and field (SCM) calibration data for each unique configuration
during these deployments. This allows for independent decoupling and
characterization of the probe body effects for use in subsequent science
data analysis. While all probes are self-sufficient the FDC will carry
out orbit and attitude determination using the Berkeley Flight Dynamics
System (BFDS). All maneuvers will take place during a ground station
contact. A passively spin-stabilized control scheme, 4π steradian power
positive body-mounted solar panels and a near omni directional
communications coverage allow any probe to fail-safe with no required
maneuvers.

#### Pre-launch, Launch and Early Orbit (L&EO) Operations

Pre-launch operations include end-to-end data flow tests, rehearsals,
and full mission simulations, integrating and operating all of the GDS
elements. During the launch sequence the Delta II injects the PCA into
the target insertion orbit, initiating the release of the probes from
the PCA. At this time operational command and control authority
transitions from the LV controllers to the MOC at UCB. Subsequently each
probe is polled via ground station contacts in a round-robin scheme to
evaluate state-of-health and to obtain telemetry and tracking data for
initial orbit and attitude determination. Once the orbits are well
established, the MOC generates the first set of command loads that are
uplinked to each probe. Further on-orbit checkout commences with
deployment of the FGM/SCM magnetometer booms, which undergo a
simultaneous deploy, followed by the power up sequence of all science
instruments. As soon as all probes are checked out, the final
designation of probe constellation IDs, i.e. P1, P2, P3, P4 and P5 is
performed based on functional test results and magnetic signature
levels. This scheme allows for implementation of mission redundancy and
a probe replacement strategy that minimizes impact from off-nominal
science instrument performance.

Final orbit injection begins after all probes are re-spun to a spin rate
of 20 rpm. Calibration of the tangential thrusters is part of the
re-spin sequence. The orbits of each probe are then adjusted in one
(P3-P5) or two (P1-P2) discrete pairs of apogee and perigee maneuvers,
using the axial thrusters. Each individual maneuver is followed by
accurate orbit and attitude determination, allowing for a calibration of
the axial thrusters. Proper thruster firing is verified in real-time by
monitoring telemetry data from the RCS temperature sensors, tank
pressure gauges, and attitude sensors. Once placed in their final
mission orbits, the probes are commanded to deploy the radial EFI wire
booms and subsequently the axial EFI booms. Calibration measurements of
the probe potentials are performed as part of the step-by-step deploy
sequence. Once the radial wire booms have been deployed, the EFI
axial-boom pair undergoes a simultaneous deploy. Finally, the spin rate
on all probes is adjusted to 20 rpm.

#### Normal Operations

Normal operations begin with preparation for the conjunction season.
During normal operations, communications with each probe are established
at least once per day via the primary ground station (BGS) to monitor
the probe health and safety, to recover stored engineering data, and to
collect tracking data for precise orbit determination.

Science data are stored on-board and are transmitted to the primary or
secondary ground station during a 15-30 min pass near perigee. Data
transmissions are initiated by time sequence commands stored on-board
each probe. These commands are part of an Absolute Time Sequence (ATS)
load generated individually for each probe using the Mission Planning
System (MPS). ATS loads are uploaded several times per week and cover at
least 8 days for P1, 4 days for P2, and 3 days for P3, P4, and P5. The
ground stations will transfer to the MOC health and safety data in
real-time (VC0) as well as a subset of science data (VC2) for monitoring
instrument performance. Stored engineering (VC1) and science (VC3) data
are saved in files and are delivered post-pass to the MOC and the SOC.

During normal operations, the orbits of P1, P2, and P5 are adjusted in a
few (2-4/year depending on probe) intervals to optimize conjunctions.
These short duration adjustments are nominally performed with side
thrusting. Additionally, orbit maneuvers are performed once per year
with P1 and P2 to compensate the lunar perturbations on inclination,
thus avoiding long shadow periods while optimizing science conjunction
time. These longer duration burns for P1 and P2 take place outside the
main science season and are performed with axial thrusting.

The Berkeley Emergency & Anomaly Response System (BEARS) is used to
contact FOT members if probe/instrument telemetry out-of-limits
conditions are detected or other GDS conditions arise that require
immediate attention. The BEARS will parse through log files generated by
ITOS during real-time passes and playback of stored engineering data,
and automatically checks for yellow and red telemetry limit violations.
The BEARS will also act on email warning messages sent to it from other
GDS elements. If a limit violation or other GDS anomaly is detected,
on-call FOT members are alerted via 2-way email pagers in order to
access and resolve the problem.

#### End of Mission

After the second year of operations the probes will be positioned for
re-entry course.

## Flight Dynamics Center (FDC)

### Overview

The FDC is responsible for supporting all orbit dynamics and maneuver
functions, such as generation of ephemeris and mission planning
products, orbit determination, ACS sensor calibration, attitude
determination, maneuver planning, and analysis and calibration of
thruster performance.

### Software Tools

Four major software tools are used to generate all ephemeris and mission
planning products, perform orbit and attitude determination, and carry
out maneuver planning functions. These tools are the Goddard Trajectory
Determination System (GTDS), the General Maneuver Program (GMAN), and
the Multi-mission Spin Axis Stabilized Spacecraft (MSASS) attitude
determination systems were all developed at GSFC. SatTrack is a
Commercial-off-the-Shelf (COTS) product. Probe conjunction analysis is
accomplished with a combination of GTDS and an Interactive Data Language
(IDL) based software library that was developed in-house at SSL.

### Operations

The four major functions of these software tools are described below:

#### Orbit Determination

GTDS performs high-precision orbit propagation and orbit determination
functions for THEMIS. For orbit-determination, GTDS ingests two-way
Doppler tracking data collected from the ground stations in UTDF format.
These tracking data are obtained during regular science data
transmissions at ranges of 30,000 km or less, and during additional
passes at other parts of the orbit for each probe. GTDS estimates new
state vectors for the five probes and generates an updated ephemeris.
Once state vectors have been updated, new mission planning products are
generated, and the updated vectors are distributed to the ground
stations to generate new acquisition angles for upcoming pass supports.
Routine NORAD orbit determination using radar tracking data provides a
back up for the primary orbit determination.

#### Mission Planning Products

Mission planning products are generated by SatTrack based on GTDS
ephemeris output. These include ground station view periods, link access
periods, eclipse entry and exit times, and other orbit events required
as input to MPS. Other tools in the SatTrack software suite distribute
real-time event messages to various ground system elements such as ITOS
and the BGS in a fully autonomous client/server network environment

#### Attitude Determination

Ground based attitude determination of the probes utilizes MSASS to
ingest raw sensor data from the telemetry stream that are converted into
vectors expressed in spacecraft body coordinates. The suite of attitude
sensors on each probe comprises a V-slit sun sensor, two mini-gyros, and
the dual-use three-axis FGM. FGM data are utilized during the near-Earth
portion of the probe orbits to cross-calibrate the other sensors.
Reference vectors for conversion from the body frame to the inertial
frame are obtained from the spacecraft, solar, lunar, and planetary
ephemeris, and from the most current International Geophysical Reference
Model (IGRF) of Earth\'s magnetic field. Based on these inputs, the
MSASS estimator determines the inertial attitude vector at any given
time for each probe.

#### Maneuver Planning

The GMAN tool performs all maneuver planning functions. Based on probe
propulsion plus current and target state vectors, GMAN generates an
optimized mission profile that includes spin-axis reorientation and
orbit adjustment maneuvers with coast periods between thruster firings.
A typical maneuver scenario includes a reorientation of the probe from
its mission attitude to the orbit maneuver attitude, followed by the
orbit maneuver itself and the reorientation maneuver returning attitude
back to nominal. Attitude reorientation maneuvers may be performed near
perigee to take advantage of the magnetometer data that allow for
independent confirmation of the correct attitude for the subsequent
orbit maneuver. Orbit maneuvers are executed near perigee and apogee for
operational mission orbit insertion and periodic orbit maintenance.
Maneuver planning functions are performed at the FDC in consultation
with GSFC/FDAB.

## Flight Operations Team (FOT)

The MOC, FDC, and BGS systems are controlled and maintained by the UCB
operations personnel. In the MOC, the Flight Operations Team (FOT) uses
the Integrated Test and Operations System (ITOS) for probe command,
control, and Health and Safety (H&S) monitoring. The use of ITOS from
I&T through on-orbit operations allows FOT members to be trained in bus
and instrument operations early on, facilitating a smooth transition
from I&T to normal operations.

## Science Operations Center (SOC)

### Overview

The THEMIS Science Operations Center (SOC) is responsible for Probe and
GBO instrument data collection, processing, archiving, and distribution
functions as well as planning and generating commands for instrument
operations. The SOC works closely with the co-located MOC to guarantee a
seamless transfer and processing of probe instrument telemetry data, and
proper control and configuration of the instruments. The SOC will work
with the GBO team in a similar fashion.

#  Project Data Flow

## Overview

The following sections detail the flow of THEMIS Project Data from probe
and GBO instrument collection through ground processing and product
production and availability.

![](media/image24.png){width="4.0in" height="5.229166666666667in"}

Figure 20. THEMIS SOC Data Flow

## Probe Instrument Data

Figure 14 and 15 detail the major processing steps and timeline
associated with the probe instrument data and the products produced from
them. Please refer to them while reading the following sections.

![](media/image25.png){width="5.992361111111111in"
height="2.1118055555555557in"}

Figure 21. Instrument Data Collection and Processing Timeline

### Collection -- Time T0

The data flow begins with collection on board the probe. Collection
rates vary based on orbital position and local plasma conditions. See
Appendix B for details on the exact collection rates. The engineering
data are stored as VC1, and science data as VC3.

### Recovery -- Time T1 (T0+8 Days Maximum)

The stored engineering and science data (VC1 and VC3) are transmitted to
the ground during a 15 to 30 minute long ground station contact near
perigee. After data have been collected on the spacecraft, it could take
up to 8 days to recover a complete orbits worth of data. This takes into
account the probe with the longest orbit period (P1 -\> 4 days), the
number of instrument data transmissions per orbit (1 transmission per
orbit for P1), and the maximum number of transmissions it might take to
recover the full orbit (2 transmissions for P1).

In addition to the stored data, the probe will transmit real-time
engineering data (VC0) and a subset of the science data (VC2). The
transmission of the data is controlled by stored commands the FOT had
previously loaded and/or ground command. The ground stations transfer
the VC0 and VC2 to the MOC in real-time. All VCs are saved in files and
are delivered to the MOC and the SOC approximately 1 hour after the end
of the ground station contact.

VC2 will contain a subset of the instrument science data in real-time,
which will be useful during Integration and Testing (I&T) and Launch and
Early Orbit (L&EO) operations when the instruments will be heavily
tested and configured for normal operations. Also, VC2 will give the FOT
an additional avenue for checking that instruments are operating
properly on a day-to-day basis. The VC0 and VC2 data will undergo limit
checking by ITOS and will be archived to files that will be available
for post-pass processing. The results of the limit checking are recorded
to a file and passed on to the BEARS for error detection and personnel
notification.

### Delivery to SOC -- T1+1Hr

At approximately 1 hour after the completion of the ground station
contact, the VC1 and VC3 files will be sent via FTP to the SOC. The VC1
file is also sent to the MOC where it is processed automatically by an
ITOS workstation for back-orbit limit checking. Corresponding log files
are passed to BEARS for error detection and operator notification. The
reception of the VC files at the SOC will initiate autonomous processing
of the data. This includes data quality checks and statistics generation
to determine if data gaps have occurred both within files and between
prior data transmissions. Also, these data files will be immediately
available to data analysis tools (SDT and IDL routines) used to
thoroughly checkout instrument operation during I&T and the L&EO
instrument turn on and commissioning phase. The VC files will remain
accessible from hard-drive and are backed up on to DVD.

### Level Zero Processing -- Time T1+2Hrs

Following the initial quality checks and statistics generation, the data
undergo Level Zero Processing, which includes sorting by Application
(Packet) Identifier, time ordering, and then mapping the time ordered
packets into 24 hour Level Zero (L0) data files. Each 24 hour L0 data
file will contain all engineering and science (slow survey, fast survey,
burst) collected during that period. The L0 files are stored locally,
archived to DVD, and made available to data analysis tools.

### CDF Processing -- Time T1+3Hrs

Once a L0 file is created or updated, it will be converted into Common
Data Format (CDF) or Level 1 (L1) data. Level 1 CDF files contain raw
data from all instruments at the highest temporal resolution. Particle
moments and distributions and field quantities are obtained by
converting raw data into physical quantities using instrument
calibration data

### Diagnostic Plot Creation -- T1+4Hrs

The completion of CDF processing will trigger the creation of instrument
diagnostic plots (T1+4hrs). Each day the THEMIS Operations Scientist
(Tohban) will review these plots in order to validate nominal operation
and calibration of each instrument. This includes daily checks of (i)
the overall data quality, (ii) housekeeping data trends (e.g., detector
efficiencies and offsets) and (iii) identification and tabulation of
geophysical events of special interest.

### Browse/Key Parameter (K0) Data Creation -- T1+24Hrs

The completion of CDF processing will also trigger the creation of
Browse or Key Parameter (K0) Data which will be available to the public
via the UCB website approximately 1 day after instrument data are
initially received at the SOC (T1+24hrs). Space-based instrument key
parameter data includes (all provided in physical units and at 3-s
resolution):

-   3-D magnetic field, DC waveforms and AC spectrograms.

-   3-D electric field, DC waveforms and AC spectrograms.

-   Core (10eV-40 keV) ion density and velocity moments, temperature and
    pressure tensor, energy spectrogram.

-   Core (5 eV-30 keV) electron temperature and pressure tensor, energy
    spectrogram.

-   Energetic ion and electron fluxes.

-   Indications when burst data has been collected

The browse data are designed for monitoring the large-scale particle and
field dynamics and for selecting time periods of interest. These data
are created using IDL scripts provided by instrument investigators and
are available as both plots (GIFS) and CDF files. They are not routinely
checked for accuracy and are subject to revision as new data are
received and/or updates to calibration and orbit data occur. Key
parameter data associated with the GBO and E/PO ground based
observations will also be produced.

### K1 Data Creation -- T1+1Month

At approximately 1 month (T1+1month) after data reception at the SOC,
the first key parameter set (K1) is delivered to the Sun-Earth
Connection Active Archive (SECAA) and the National Space Science Data
Center (NSSDC) via the internet. This incorporates updates to data
content, calibrations, and orbit data.

### K2 Data Creation -- T1+6Months

At approximately 6 months (T1+6months) after data reception at the SOC,
the definitive key parameter set (K2) is delivered to SECAA and NSSDC.

## GBO Data

In general, the University of Calgary (UC) shall serve as the primary
data distribution hub for the UCB All Sky Imager (ASI) and UCLA Ground
Magnetometer (GMAG) data, as well as the GBO health and safety (H&S)
data. The University of Alberta (UA) will recover and process the CGSM
and NRCan magnetometer data and make it available for download.

![](media/image26.jpeg){width="5.0125in" height="3.3631944444444444in"}

Figure 22. Ground Based Data Flow

### Collection -- Time T0

#### ASI Data

The ASI will produce full images (Stream2) in PNG format at a frequency
of 1-image/5 seconds (nighttime only). Each image is made up of 256x256
16-bit values (pixels). PNG compression reduces this to 90 Kbytes/frame
(70%). A 5-second frame rate will produce 150 kbps or 60 Mbytes/hour or
720 images/hour. For Stream 2, the expected data volume is **220-290
gigabytes/year/site uncompressed**.

Smaller, low resolution "thumbnail" images (Stream 1) in PGM format will
be derived from the full images. Each thumbnail is comprised of 20x20
8-bit values (pixels) plus header information (roughly 50 bytes) for a
total of \~450 bytes. GZIP compression reduces this to 270 bytes/frame
(60%). A 5-second frame rate will produce 430 bps or 190 Kbytes/hour.

Stream 1 and 2 are stored locally on a hard drive connected to the
system computer.

#### GMAG Data

The GMAG will generate 2 mag vectors every second. Each vector consists
of three quantities: Bx, By, and Bz, which are measurements of the
magnetic field strength along each axis. The data output is expected to
be 86.4 Kbytes/hour.

GBO data collection is summarized in the table below.

+-----------+-------------------+-------------------------------------+
| **Ins     | **Collection      | **Description**                     |
| trument** | Rate**            |                                     |
+-----------+-------------------+-------------------------------------+
| ASI       | 1 image every 5   | **Stream 1**: "Thumbnail" low       |
|           | seconds           | resolution image. 20x20 8-bit       |
|           |                   | values (pixels) plus header         |
|           |                   | information (roughly 50 bytes) for  |
|           |                   | a total of \~450 bytes. PGM Format. |
|           |                   |                                     |
|           |                   | **Stream 2**: Raw image frames.     |
|           |                   | 256x256 16-bit values (pixels). PNG |
|           |                   | format.                             |
+-----------+-------------------+-------------------------------------+
| GMAG      | 2 mag vectors     | Each vector consists of three       |
|           | every second      | quantities: Bx, By, and Bz.         |
+-----------+-------------------+-------------------------------------+

Table 5. GBO Data Acquisition

### Thumbnail Image Recovery by UC -- T0+1min

Stream 1 (thumbnail frames) is transmitted to UC daily and complies with
the needs of THEMIS to determine the substorm onset to better than 0.5
hours in MLT. Primary means of stream 1 data retrieval is through the
Internet provider Telesat HIs using a typical TCP/IP connection, with
the expected throughput rate of 50 kbps. Stream 1 should arrive at UC
within a few seconds of acquisition and be available for download after
review and movement to central storage (\~5minutes). A fraction of the
high-resolution data (Stream 2) will be recovered with Stream 1 (\<10%).
An Iridium telephone backup is available for recovery of stream 1 and
health and safety data as well as controlling GBO operations. The
Iridium phone link operates at 2400 bps.

As soon as ASI data arrives at UC, it will also enter a sophisticated
data access and retrieval system developed for NORSTAR\'s filter camera
images and based on keogram summary plots (image North-South slices as a
function of time). With this interactive system, a user calls up a
customized summary of data from one or more stations.

### Health and Safety (H&S) Data Recovery -- T0+1min

Health and safety monitoring of sites will also occur over the Telesat
Internet link as well as via a back link using an Iridium telephone. The
H&S data will be available for review from the UC website. This will
include the following items:

-   CPU and motherboard temperatures, fan speeds

-   Hard drive temperature, error rates

-   Clock status (NTP)

-   Network status

-   Power status (UPS)

-   Free disk space, memory

-   Web-cam

### Thumbnail Image Copied to UCB -- T0+5mins

Once the stream 1 data is moved to central storage at UC it will be
mirrored to UCB, where it will be available for download via the UCB
website and incorporated into Browse Data.

### Raw Magnetometer Data Recovered by UC and Copied to UCLA, UA, and UCB - T0+27hrs

The raw magnetometer data is saved to a file every hour, and these files
will then be recovered by UC once per day. Once at UC, it will be copied
to UCB, UCLA, and UA.

### UCLA Produces Processed GMAG Data -- T0+28hrs

Once UCLA acquires the raw mag data, it will convert it into a more
easily used format. This processed data will be copied to UCB and UA.

### Keogram Recovery and Distribution -- T0+30Hrs

While the ASI is off (daytime), keograms will be created. These will be
recovered and made available from the UC website. They will be copied to
UCB where they will also be available via the UCB website.

### Inclusion in Key Parameter Data -- T0+30Hrs

The ASI and GMAG data will be included in the Key Parameter data
beginning with the Browse data.

### Recovery and Distribution of Full Resolution Images -- T0+6Months

Full recovery of stream 2 data requires physically swapping out GBO hard
drives and returning the units to UC for disk integrity and status
checks and offloading of data to central storage. This will occur once
or twice a year. The total image data volume (stream 2) amounts to
**220-290 gigabytes/year/site uncompressed**. The full image data set
will be copied to UCB.

## E/PO GMAG Data

UCLA is responsible for collecting the raw GMAG data from the schools
sites and processing the data into a more usable format for the science
community.

### Collection -- Time T0

The E/PO GMAGS will collect data at the same frequency as the GBO GMAGS
-- 2 mag vectors per second.

### Recovery -- Time T0+27Hrs

UCLA will copy the raw GMAG data from the sites once per day. The raw
data will be copied to UCB also.

### Processed GMAG Data Produced and Distributed

UCLA will produce processed GMAG once the raw data is received which
will then be copied to UCB and UA.

## SPASE Collaboration

The THEMIS Project Data set will be described in the terms spelled out
by the Space Physics Archive Search and Exchange (SPASE) data model,
which is used by SEC. Much work has been done on the Virtual Solar
Observatory (VSO) and Virtual Space Physics Observatory (VSPO) and
Virtual Observatories in other areas are expected to be established in
the near future as well. SPASE will be working with each of these groups
to unify access within the whole of the space physics community.

# Instrument Command and Control

### Overview

The Flight Operation Team (FOT) carries out instrument command and
control functions from the Mission Operations Center (MOC) under the
direction of the PI and instrument Co-Is in consultation with pertinent
subsystem engineers. Probe and instrument operation are reviewed and
planned in weekly team meetings.

One of the science team members assumes the rotating role of the
scientist-on-duty (Tohban) who forms the point of contact between the
THEMIS science team and the FOT. The Tohban is responsible for
overseeing day-to-day science operations, including instrument
configuration, data recovery and data processing.

Command and control of the instruments is separated into (4) different
operational phases:

1.  Instrument Commissioning (L&EO)

2.  Normal Operations

3.  Conjunction

4.  Maneuvers

### Instrument Commissioning

Instrument commissioning begins with the IDPU turn-on as soon as the
probe power system is stable and temperatures are below maximum
operating limits. From there the instruments are powered up and
configured based on the THEMIS Launch and Early Orbit Operations Plan
\[6\].

### Normal Operations

The instruments will be operated in 4 basic science modes:

-   Slow Survey (SS)

-   Fast Survey (FS)

-   Particle Burst (PB)

-   Wave Burst (WB)

Selection of these modes is controlled by either stored commands or
on-board triggers.

#### Slow Survey to Fast Survey

The transition between these two modes will be controlled by instrument
commands in the probe Absolute Time Sequence (ATS) load. The load is
built by the Mission Planning System (MPS) using the ITOS Command
Database. The timing of the commands will be taken from a special
ephemeris event file supplied by the FDC and ingested by the MPS.

#### Particle & Wave Burst Triggers

For the triggers, the IDPU FSW continuously samples science data in the
SSR (e.g., ESA/SST Peak Flux, DFB V1-V6 voltages, FGM Bx-Bz) and
evaluates the data at 1 spin resolution against a pre-loaded threshold
value. When the threshold is exceeded, it then calculates a Quality
value using 8 selectable functions and tags the resulting burst data
collected with a value ranging from 0-255. This quality value decides
whether the burst is kept or overwritten as subsequent bursts are
collected. Also, the quality value determines the memory readout
priority. The particle and wave burst trigger setting will be fine tuned
early in the mission using ground commands to the IDPU.

#### Conjunction Operations

During conjunction season, the FOT will uplink predicted conjunction
times to the IDPU. The FSW will increase the Quality evaluation near the
conjunction. Also, conjunction duration and bias settings are
configurable.

#### Maneuver Operations

During maneuvers the ESA high voltage will be disabled and the SST
placed in attenuated mode.

The probe orbit placement is designed for maximum science return during
the prime tail season, a four month period centered on February 21 of
each year. Over the course of the mission, the orbits of P1 and P2 are
optimized periodically by small orbit trim maneuvers to maximize
conjunction time. Also, P1 and P2 undergo inclination change maneuvers
to counteract lunar perturbations. The orbital period of P5 is changed
from initially 4/5 days to 8/7 and 8/9 days to optimize dayside
measurements during the first and second year, respectively. P3 and P4
remain in the same orbits throughout the mission. Fuel budgets for P3
and P4 allow these probes to replace P1 or P2 in the unlikely event of a
probe loss.

After the second year of operations the probes are positioned for
re-entry course. All maneuvers occur while in contact with a ground
station with full a priori and a posteriori (near-real-time) attitude
and orbit determination.

## GBO Installation, Monitoring, Control, and Maintenance

Responsibilities for the various sites are shared between UCB, UC, UCLA,
and UA. A breakdown of these responsibilities is listed below:

1.  UC physically installs and maintains the Canadian GBO\'s.

2.  UCB physically installs and maintains the Alaskan GBO\'s.

3.  UC collects all GBO data (UCB ASI, UCLA GMAG, H&S) and GBO team
    (UCLA, UCB, UA) picks up data from UC.

4.  UA recovers CGSM and NRCAN GMAG data. UCB picks up data from UA.

5.  UC will have a notification system in place that will react to all
    high level GBO H&S issues. UCB acts in backup capacity for this
    role.

6.  UC maintains the physical status and responds to H&S of the Canadian
    GBO\'s

7.  UCB maintains the physical status and responds to H&S of the Alaskan
    GBO\'s

8.  UCLA monitors the data quality of the GMAG data and directs UC to
    make any configuration or calibration changes. Changes are discussed
    and approved by GBO team.

9.  UC monitors the quality of the Canadian ASI data. UC will make
    changes to instrument configuration/calibration after consulting
    with the GBO team (if the action is not already specified in the ops
    doc). 

10. UCB monitors the quality of the Alaskan ASI data and directs UC to
    make changes to instrument configuration/calibration.  

11. UCLA will recover the E/PO data. UCB picks up data from UCLA.

12. UCLA will validate data and respond to any H&S issues.

## E/PO GMAG Control

UCLA will be responsible for the overall installation of the E/PO GMAGs.
Site control, operation and data retrieval will be the responsibility of
local schools under the guidance of UCLA and UCB. Depending on internet
access, UCLA will perform configuration and software changes as
necessary. The schoolteachers associated with each site will carry out a
limited degree of maintenance of the units under the direction of UCB
and UCLA E/PO personnel. Data collection will be the responsibility of
UCB and a mirror site will be established at UCLA.

# Science Data Products

UCB will receive and process probe instrument telemetry, GBO data, and
E/PO GMAG data, producing a variety of data products that will be
available to the projects scientists and the general public. These
include:

-   Instrument Data CDF Files

-   Instrument Calibration CDF Files

-   Key Parameter Data

-   GBO ASI Data and Products

-   GBO GMAG Data and Products

-   E/PO GMAG Data and Products

## Instrument Data CDF Files

The raw probe engineering and science data that has undergone level zero
processing will be used to produce daily data CDF files. These files
will contain all of the VC1 and VC3 data collected for a GMT day (00:00
-- 23:59:59). These files are stored locally at UCB.

> Directory Structure:
>
> **/data/cdf/probe_id/yyyy/mm/dd**
>
> File Naming Convention:
>
> **probe_id.yyyymmdd_sv_pv.cdf**
>
> **where:**
>
> **probe_id = THEMIS_A-\>THEMIS_E**
>
> **yyyy = year**
>
> **mm = month (01-12)**
>
> **dd = day (01-31)**
>
> **sv = Software version (00-99)**
>
> **pv = Processing version (00-99)**
>
> **cdf = Common Data Format**

## Instrument Data Calibration Files

Calibration files will exist for each instrument and will be used for
processing the raw data quantities that are transmitted in VC3. The
calibration files will be initially created based on ground based
instrument testing and evaluation during I&T.

The following calibration files are planned:

1)  **FGM Mounting Orthogonality and Gain**

2)  **FGM Boom Angles**

3)  **SCM Boom Angles**

4)  **SCM Gains**

5)  **ESA MCP Gains, one per anode for 16 anodes x 2 heads**

6)  **SST Gains, 3 per telescope x 4 telescopes x 2 shutter conditions
    (open/closed**

7)  **EFI 1 current and 3 voltages per sensor x 6 sensors**

A file will be produced for each day and will be associated with the
data for that day. The calibration file naming convention and directory
structure are listed below.

> **Directory Structure:**
>
> **/data/cal/probe_id/yyyy/mm/dd**
>
> **File naming convention:**
>
> **probe_id.type.yyyymmdd.pv.cal**
>
> **where:**
>
> **probe_id = THEMIS_A -\> THEMIS_B**
>
> **type = calibration type (e.g., SSTG for SST Gains)**
>
> **vv = processing version number**
>
> **cal = calibration**

Interprobe calibration will be performed in the early mission phase to
confirm individual probe calibrations but will not be part of the data
analysis efforts thereafter so as not to hold up data dissemination.

## Key Parameter Data

Instrument, calibration, and orbit data CDFs, plus GBO and E/PO data,
will be used to produce Key Parameter data products. The general
categories are:

**1) Keograms (GBO Image Data Overview)**

**2) Auroral Electrojet Indices (GBO Magnetometer Data Overview)**

**3) E/PO Ground Magnetometer Data Overview**

**4) P1 data (Probe Overview)**

**5) P2 data "**

**6) P3 data "**

**7) P4 data "**

**8) P5 data "**

**9) Mission Overview Plot**

The probe overview data will include (all provided in physical units and
at 3-s resolution):

-   3-D magnetic field, DC waveforms and AC spectrograms.

-   3-D electric field, DC waveforms and AC spectrograms.

-   Core (10eV-40 keV) ion density and velocity moments, temperature and
    pressure tensor, energy spectrogram.

-   Core (5 eV-30 keV) electron temperature and pressure tensor, energy
    spectrogram.

-   Energetic ion and electron fluxes.

-   Indications when burst data has been collected

All key parameter products will be available via the UCB website.

## GBO Data and Products

UCB will receive the raw image, GMAG, and calibration data and will
produce the following data products.

### ASI 

The ASI data and data products available at UCBerkeley will include the
following:

-   Image Thumbnail frames: 20x20 8-bit values (pixels) plus header
    information (roughly 50 bytes) for a total of \~450bytes. File
    format = PGM.

-   Raw Image Frames: 256x256 16-bit values (pixels). Approximately 131
    kbytes in size. File format = PNG

-   Calibration files

-   Keogram summary plots (latitude slice versus time - summary\'s of
    one or more stations)

-   Composite global views providing both quick overview of data
    availability and a portal to data selection, decommutation, and
    analysis

UC will also produce its own ASI data product set which will be
available from its own website. In addition to the raw image and
calibration data, this will include:

-   Site status info/plots

-   Keograms (latitude slice versus time) for each site

-   Merged intensity maps of all stream 1 data

-   Merged maps of stream 2 data

-   Estimates of visibility based on stars

-   Estimates of arc location and orientation (when viewing is good)

-   CDF for advanced data products

-   raw ASCII and PNG/JPEG for availability lists and summary plots

### GMAG

The GMAG data will include the following:

-   L0 (Level 0) Raw Vector Data

-   Calibration Files

-   L1 (Level 1 ) Processed Data

-   Auroral Electrojet Indices

Auroral Electrojet indices, already developed for Canopus, give similar,
synoptic ground magnetometer information (similar to the presentation of
NORSTAR data).

Both UA and UCLA will be producing their own GMAG data products that
will be available at their own websites.

## E/PO GMAG Data Products

When the E/PO GMAG data is received at UCB it will be used to produce
Auroral Electrojet Indices similar to those produced using the GBO GMAG
data. The data will also be folded into mission composite summary plots
that will display probe, GBO, and E/PO GMAG data. UCLA will also be
producing its own data product set.

-   L0 (Level 0) Raw Vector Data

-   Calibration Files

-   L1 (Level 1 ) Processed Data

-   Auroral Electrojet Indices

# Data Access 

Access to the THEMIS data and products will be through one of the
following:

1.  THEMIS Data Analysis Software Package File Search Tool

2.  THEMIS Website

## THEMIS Data Analysis Software Package File Search Tool

The File Search Tool (FST) is part of the Data Analysis Software Package
which will be available for download from the THEMIS website. The FST
will allow both internal and external users (with permission from PI) to
query for instrument data and calibration CDF files and associated GBO
and E/PO data based on probe ID, date, and time. The internal users will
copy files over the Local Area Network (LAN) while external users will
use secure FTP or COPY.

## Website

The THEMIS website will allow users to query for instrument data and
calibration CDF files, GBO ASI and GMAG raw and calibration files, E/PO
GMAG raw and calibration files, and all of the associated data products.

# Data Analysis Software

## Overview

UCB will produce and make available a software package for accessing and
processing the instrument data and calibration CDF files, GBO ASI and
GMAG data, and the E/PO GMAG data. For instrument data, including slow
survey, fast survey, and burst, science data analysis software exists in
the form of an extensive library of IDL programs and the Science Data
Tool (SDT) developed at SSL to analyze data from FAST, WIND, CLUSTER_II,
and POLAR. The decommutator functions that allow access to the raw and
CDF formatted data are adapted from those developed to for analysis of
FAST science data. In general, four IDL-based software suites are
planned:

1)  Single probe analysis software, is directly transferable to THEMIS
    from FAST and WIND.

2)  Multi-point data analysis software from ISTP and CLUSTER_II analysis
    to compute the flow shear/curl and pressure gradient along with
    their standard error will be directly implemented or modified for
    THEMIS

3)  Ancillary Data Software. An existing distributed database of such
    data will be upgraded with IDL decommutators for plotting them
    seamlessly, relative to THEMIS quantities

4)  Event Modeling. IDL codes that fly virtual probes within simulation
    run results under specific, idealized solar wind external conditions
    already exist. These will allow comparisons between models and
    observations.

For ASI and GMAG data, tools already exist for accessing, evaluating,
and comparing the ground observatory data with the space-borne
measurements. Data will be analyzed using standard IDL-Based routines
developed from years of experience with NORSTAR and other AGO\'s.

The different software for accessing and analyzing the variety of data
and data products will be integrated into one complete package that will
be distributed to Co-Is and guest investigators throughout the mission
as updates are made. Training sessions in the use of this software are
planned. The software package will also be freely available from the UCB
website.

## File Search Tool

The file search tool will be available in both a command line and GUI
form. The user will enter from 1 to 5 probe IDs and the time period of
interest. The tool will initially check the users local directory for
the data, and if not found will initiate a LAN copy or FTP session to
download the data. In addition to requesting probe data, the user can
request ASI and GMAG data for the same period. The user can also go down
a basic directory path either locally or from the website and download
data via local copy, remote copy, http, or ftp.

Once data is downloaded and available on the users workstation they can
engage the second layer of data decommutation software and/or data
analysis software described below.

## Moments & Fields Tool

This tool will take data from CDF files and covert them into an ASCII
file containing Density (N), Velocity (V), Temperature (T), Pressure
(P), Mag field (Bxyz), Electric Field (Exyz), and Position (X,Y,Z). For
the particle instruments, this tool will ingest the CDF file and produce
an ASCII file that includes:

-   N = Density

-   V = Velocity

-   T = Temperature

-   P = Pressure

> Partial ion density from the ESA: Niesa
>
> Partial electron pressure from SST: Pesst

For the Fluxgate Magnetometer, this tool will produce:

-   Bxyz

For the Electric Field Instrument, this tool will produce:

-   Exyz

The filter banks from the EFI and SCM will both produce 8 quantities at
spin resolution. The 8 quantities represent the electric field power in
8 frequency bins, as well as the magnetic field power in 8 freq bins.

## Reading and Writing Tools

These include:

-   Basic read routine

-   Basic write routine

-   Conversion routines like cdf2flat, cdf2asci, and cdf2cdf

-   Processing routines

-   Plotting routines like Specplot, dfplot, lineplot, tplot

# Data Archiving and Distribution

The following data will be available in its entirety on disk drives at
UCB as well as being backed up onto DVD media:

1.  VC1 and VC3 files from the ground stations

2.  24 hour LZP data files

3.  24 hour instrument CDF data files

4.  GBO Data (ASI & GMAG)

5.  E/PO GMAG

The DVD's containing the 24-hour instrument CDF data files will be
distributed to Co-I's and NSSDC on a monthly basis.

# Appendix A. Instrument Data Quantities

![](media/image27.pct){width="6.659722222222222in"
height="3.1486111111111112in"}

# Appendix B. Instrument Data Rates

![](media/image29.pct){width="7.709722222222222in"
height="2.188888888888889in"}

# Appendix C. Instrument Data Volumes

![](media/image30.pct){width="8.159722222222221in"
height="5.452083333333333in"}