February 18, 1997

Explorer Program
Office of Space Science
NASA Headquarters

Approved by:
Dr. G. Withbroe, Science Program Director, Sun-Earth Connection

Dr. R. L. Carovillano, IMAGE Program Scientist

W. T. Huddleston, IMAGE Program Executive


  1. Purpose
  2. Program Requirements
  3. Mission Overview
  4. Level 1 Science Requirements
  5. Level 1 Development Requirements
  6. Level 1 Mission Operations Requirements
  7. Level 1 Resource Policy and Requirements
  8. Acronyms

1. Purpose

This document contains the Level 1 requirements for the development of the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) investigation. Concurrent with the initiation of the development phase, the Level 1 requirements will be incorporated into the IMAGE Program Plan as approved by the Associate Administrator for the Office of Space Science (OSS) and the Director of the Goddard Space Flight Center (GSFC).

2. Program Requirements

In implementing the IMAGE program, the following principles apply:

3. Mission Overview

3.1 Contributions of IMAGE to Magnetospheric Science

In-situ measurements made for the past 35 years have yielded a wealth of statistical information about the magnetosphere and its constituent plasma regimes. These measurements have also provided many examples of dynamic changes of magnetospheric plasma parameters at specific times and places in response to changes in the solar-wind input and to internal disturbances related to substorms. However, statistical global averages and individual events are not sufficient to understand the dynamics and interconnections of this highly dynamic system. Fundamental questions concerning plasma entry into the magnetosphere, global plasma circulation and energization, and the global response of the magnetospheric system to internal and external forcing functions remain unanswered. Furthering our understanding of the physical processes that affect the magnetosphere requires the nearly instantaneous measurement of its topology, that is, magnetospheric imaging.

The overall objective of the IMAGE mission is to determine the global response of the magnetosphere to changing conditions of the solar wind. To address these basic questions, IMAGE will provide imaging of three general magnetospheric regions: a) the magnetopause, boundary layer, cusp, and auroral zone; b) the plasmasphere; and c) the inner plasma sheet, ring current, and trapped radiation. IMAGE will also provide images of near-Earth interplanetary space. The data acquired in each of these regions will be used to determine the global structure of the magnetosphere, characterize the connectivity between magnetospheric regions, and place results in a global context with previous in-situ measurements.

Significant international participation is planned as follows:
Institution Provision
Institute of Space and Astronautical Science,
Tokyo, Japan
Microchannel plate detector systems for the MENA instrument
Rutherford Appleton Laboratories,
High-voltage power supplies for MENA
University of Bern,
Design and test of conversion surface in LENA
Liege Space Center,
Optical and mechanical design of the FUV SI
University of Calgary,
Design of the FUV WIC instrument housing and optics and calibration of WIC
Observatoire de Paris,
Meudon, France
Provide antenna couplers for RPI
Max Planck Institute for Aeronomy,
Lindau, Germany
Provide geocorona oxygen cells (GEO) for FUV

3.2 IMAGE Mission Structure

The P.I., Dr James Burch, is accountable to NASA for the scientific success of the investigation. In accordance with NASAšs transfer of program management responsibility to its Centers, Explorer program management responsiblility has been assigned to GSFC. In this role, GSFC is responsible for the exercise of NASAšs fiduciary responsibility to ensure that Explorer missions are achieved in compliance with committed cost, schedule, performance, reliability, and safety requirements. The Principal Investigator and his support team at Southwest Research Institute (SwRI), will be responsible for the overall management of the investigation. With the assistance from the Co-Investigator institutions, SwRI will be responsible for the following elements of the overall program:

GSFC will be responsible for the following elements of the IMAGE program:

4. Level 1 Science Requirements

4.1 Scientific Objectives

The overall science objective of IMAGE is the determination of the global response of the magnetosphere to changing conditions in the solar wind. Three fundamental questions which must be addressed by IMAGE to accomplish its primary objective are: IMAGE will address these objectives in unique ways using neutral atom imaging (NAI) over an energy range from 10 eV to 200 keV, far ultraviolet imaging (FUV) at 121-190 nm, extreme ultraviolet imaging (EUV) at 30.4 nm, and radio plasma imaging (RPI) over the density range from 0.1 to 105 cm-3 throughout the magnetosphere.

4.2 Approach for Accomplishing Science Objectives

The IMAGE approach to accomplishing the science objectives listed above include the following key steps:

4.3 Allocation of Mission Time

The IMAGE mission will operate with a near 100% duty cycle with all instruments in their baseline operational modes. The minimum time resolution for all instruments except the RPI will be set by the spacecraft spin period of two minutes. Longer-term average images over multiple spin periods can be constructed on the spacecraft or later on the ground. The IMAGE Science Team will have the responsibility to collect and validate the data but claim no proprietary data rights, and the mission will therefore operate in a facility mode.

4.4 Minimum Mission Success Criteria

To meet its minimum success criteria, IMAGE will require the MENA and HENA instruments, the EUV instrument, and either the FUV Spectrographic Imager (SI) or the Wideband Imaging Camera (WIC) to function properly and meet the science objectives as stated in Table 1. With this complement of core instruments, IMAGE will be able to accomplish essential science objectives identified for the mission. With the data provided by the core instruments, IMAGE will be able to obtain images of the ring current as it builds up and decays over the course of magnetic storms. It will also obtain images of the plasmasphere, the outer portions of which are stripped away during magnetic storms and subsequently replenished from the ionosphere. The FUV images will provide the dynamical context by the determination and mapping of the global auroral activity that accompanies the magnetic storms. Achievement of these objectives during a single magnetic storm will constitute the minimum success criterion for IMAGE.

5. Level 1 Development Requirements

5.1 Flight Segment

5.1.1 Spacecraft Mission and Instrument Support
Requirements for the IMAGE spacecraft have been specified in SwRI document 8089-SPEC-01, Spacecraft Functional Performance Specification. The spacecraft must be spin stabilized (~0.5 rpm) in order to provide the fields of view needed by the instruments to image the magnetosphere. The spacecraft must provide power, telemetry and command resources needed to support the IMAGE science payload operation in an orbit of approximately 1000 km perigee by a 7 Earth radii apogee. The spacecraft is required to accommodate a science instrument deck plate of approximately 2.2 m diameter. All seven IMAGE instruments (Far Ultraviolet Spectrographic Imager, Far Ultraviolet Wideband Imaging Camera, Extreme Ultraviolet Imager, High Energy Neutral Atom Imager, Medium Energy Neutral Atom Imager, Low Energy Neutral Atom Imager, and Radio Plasma Imager) and a Central Instrument Data Processor (CIDP) will be mounted to the deck plate. The deck plate must be mechanically secured to the spacecraft bus structure. Thermal control of the integrated deck plate must be provided by the spacecraft thermal control system. An integrated purge manifold secured to the deck plate will maintain a steady purge on the instruments up to launch. Performance Assurance
A headquarters mission classification will not be issued for the IMAGE mission. Performance assurance requirements for the spacecraft are specified by NASA documents GSFC-410-MIDEX-001, and GSFC-410-MIDEX-002. The spacecraft will withstand the radiation dose accumulated during the 2-year mission with at least a 50% margin.
5.1.2 Science Instrumentation
The types of instrumentation needed for IMAGE to meet its science objectives (see Paragraph 4.1 for a discussion of science objectives) are listed in Table 1 below.
Image Measurement Critical Measurement Requirements
NAI Neutral atom composition and energy-resolved images over three energy ranges:
10-300 eV (LENA)
1-30 keV (MENA)
10-200 keV (HENA)
FOV: 90° 90 (image ring current at apogee).
Angular Resolution: 8 8.
Energy Resolution (E/E): 0.8 (trade resolution for sensitivity).
Composition: distinguish H and O in magnetospheric and ionospheric sources, interstellar neutrals and solar wind.
Image Time: 5 minutes (resolve substorm development).
Sensitivity: effective area 1 cm2
EUV 30.4 nm imaging of plasmasphere He+ column densities. FOV: 90° 90 (image plasmasphere from apogee).
Spatial Resolution: 0.1 Earth radius from apogee.
Image Time: several minutes to hours (resolve plasmaspheric processes).
FUV Far ultraviolet imaging of the geocorona (Geocorona Oxygen Cell) and the aurora at lambda = 140-190 nm (Wideband Imaging Camera, WIC) and lambda = 121.6 and 135.6 nm (Spectrographic Imager, SI) FOV: 16° for aurora (image full Earth from apogee), 60° for geocorona.
Spatial Resolution: 70 km (wideband camera),90 km (spectrographic imager)
Spectral Resolution: separate cold geocorona H from hot proton precipitation (Delta-lambda~0.2 nm near 121.6 nm); reject 130.4 nm and select 135.6 nm electron aurora emissions.
Image Time: 2 minutes (resolve auroral activity).
RPI Remote sensing of electron densities and magnetospheric boundary locations using radio sounding. Density range: 0.1-105 cm-3 (determine electron density from inner plasmasphere to magnetopause).
Spatial resolution: 500 km (resolve density structures at the magnetopause and plasmapause).
Image Time: 1 minute (resolve changes in boundary locations).
Table 1. Instrumentation Required to Meet Science Objectives NAI Instrument Performance Requirements (LENA,MENA,HENA)
Science instrumentation for IMAGE consists of the 7 instruments and the CIDP mentioned above in paragraph The performance requirements for the NAI instruments are shown in Table 2 below.
Energy range [keV] 0.1-0.3 1-30 10-500
Energy resolution [Delta-E/E] 0.8 E 0.8 E 3 keV
Instantaneous FOV [degrees] 8 x 90 4 x 107 90 x 120
Total FOV [degrees] 90 x 360 107 x 360 120 x 360
Pixel resolution [degrees] 88 48 44
Total G-factor [cm2-sr] 0.2 0.07 1.6
Pixel sensitivity
7 x 10-4 4 x 10-3 4.5 x 10-3
Image time [s] 120 120 120
Pixel array dimensions* 2M4E11A 2M16E32A 4M16E32A
UV rejection 10-7 10-7 10-9
Electron rejection 10-10 10-5 10-5
Ion rejection 10-8 10-5 10-5
Table 2. NAI Instrument Performance Parameters Photon Imagers (EUV,FUV)
There are three photon imagers required by IMAGE. The EUV instrument images resonantly scattered solar emissions from plasmaspheric He+ at 30.4 nm. Two FUV instruments, SI (Spectrographic Imager) and WIC (Wideband Imaging Camera) image the Earthšs electron and proton auroral emissions. The Geocorona Oxygen Cell (GOC) images the hydrogen geocorona. General characteristics of the imagers are listed in Table 3 below.
Inst. Measurement Type Focal Length (mm) Aperture (mm2) Wavelength (nm) Wavelength Resolution (nm) Instant FOV (deg) Total FOV (deg) Pixel FOV (deg) Sensitivity (c/R/pixel) Time Res. (min) Spatial Res. at 7RE (km/pix)
EUV Plasmaspheric He+ 30.4 nm 75 25 (3) 30.4 5.0 30 x 90 90 x 360 0.5 x 0.5 2.4 2 640 x 640
FUV/SI Auroral LBH (narrow band), Lyman-alpha 68 112 121.8, 135.6 0.2, 3 15 x 15 15 x 360 0.11 0.05 2 90 x 90
FUV/WIC Auroral LBH (broad band) 22.4 60.8 140 - 190 N/A 30 x 22.5 22.5 x 360 0.09 0.1 2 70 x 70
GEO Geocoronal Lyman-alpha 60 132 121.6 0.2 1 x 1 (3 cells) 60 x 360 1 0.1 2 N/A
Table 3. Photon Imager Instrument Performance Parameters Radio Plasma Imager (RPI)
The performance parameters for the radio plasma imager to meet science objectives are listed in Table 4 and Table 5 below.
Measurement Nominal Resolution Limits
Echo Range 500 km 0.1 to 5 RE
Angle-of-Arrival 1° at 40 dB S/N resolution = 2/[S/N]
Doppler 0.125 Hz 75 Hz
Time 8 sec./frequency 4 sec./frequency
Table 4. RPI Measurement Performance Parameters

Parameter Nominal Limits
RF Power 10 W 10 W
Pulse Width 53 ms 3.2 - 125 ms
Receiver Bandwidth 300 Hz fixed
Pulse Rate 2 pps 1 - 5 pps
Frequency Range 10 - 100 kHz 3 kHz - 3 MHz
Frequency Steps 5% >= 100 Hz
Coherent Integration Time 8 s >2 s
Table 5. RPI Instrument Performance Parameters

5.2 Launch Segment

The launch vehicle for IMAGE will be a Delta 7326, three-stage, expendable launch vehicle. The launch site will be NASAšs Western Test Range (WTR) at Vandenberg AFB, California. The launch date for IMAGE will be no later than March 2000. IMAGE will be launched into an orbit of approximately 1000 km perigee by 7 Earth radii apogee.

5.3 Ground Segment

The Science and Mission Operations Center for IMAGE will be located at the GSFC with support from the National Space Science Data Center (NSSDC). The mission will require the use of the 34-meter deep space network.

6. Level 1 Mission Operations Requirements

After launch and initial activation of the IMAGE spacecraft systems, the attitude determination and control system (ADAC) will orient the spacecraft spin axis perpendicular to the orbit plane to within 1. The ADAC will maintain a spin rate of at least 0.5 rpm while deploying the four radial wire antennas. At a time to be determined, the spacecraft will deploy the two axial antennas. The full deployment of the antennas should take <50 days.

After antenna deployment IMAGE will remain in an inertially fixed orbit for the full two years of the planned mission. No maneuvers will be required to maintain solar aspect for the duration of the mission. Commanding of IMAGE instruments will be required once per week after initial activation and checkout. Ground contact after initial activation will be once per orbit for a period of approximately 30 minutes each.

7. Level 1 Resource Policy and Requirements

7.1 Cost Containment Agreement

The IMAGE P.I. has agreed to cap the cost of the IMAGE investigation excluding launch vehicle at 68.0M in FY94 dollars for all activities through launch plus 30 days. Mission Operations and Data Analysis activities (MODA) are capped at $15M in FY94 dollars.

7.2 Scope Reduction

If necessary to keep IMAGE costs within the cost cap, the P.I. has developed to a two-tier descoping process. The first tier of descoping will take place if an individual instrument or subsystem experiences a cost or schedule problem. This descoping option is specified in Table 6 below. Further descoping will require Tier 2 descope options shown in Table 7 below. Any scope reductions will be implemented only after consultation with the Mission Manager and the Mission Scientist. Any potential scope reductions affecting Level 1 Requirements will require approval by OSS NASA headquarters prior to their execution.
Descope Science Impact Latest Date
Elimination of Z and/or Y axis antennas Loss of three (3) dimensional imaging capability CDR
Elimination of mass analysis from LENA or MENA Loss of composition information in neutral atom images CDR for maximum savings
Restriction of MENA energy range Reduction of overlap of energy ranges of MENA and HENA Anytime, but CDR for maximum savings
Elimination of solid-state detectors from HENA Reduction of mass resolution CDR
Table 6. Tier 1 Descoping Options

Descope Science Impact Latest Date
Elimination of RPI Loss of magnetopause topology
Loss of plasmasphere total ion contours
Loss of continuous monitor of cusp location
Anytime, but in order to save most cost the decision to execute this option should be made prior to CDR
Elimination of LENA Loss of NAI images of cusp ion fountain Same as above
Elimination of either SI or WIC Loss of SI would result in loss of high spectral resolution.
Loss of WIC would result in inability to image aurora well during very quiet times.
Same as above
Table 7. Tier 2 Descoping Options

7.3 Key Position

The following individuals are key to the success of IMAGE and will not be changed without agreement from GSFC and the OSS: Principal Investigator recommended changes in co-investigators requires evaluation by the mission project office and OSS approval.


ADAC      Attitude Determination and Control System
C&DH      Command and Data Handling
CDR       Critical Design Review
CCSDS     Consultative Committee for Space Data Systems
CIDP      Central Instrument Data Processor
COTS      Commercial Off-The-Shelf
DPS       Digisonde Portable Sounder
DSN       Deep Space Network
EEE       Electrical, Electronic, Electromechanical
EMC       Electromagnetic Compatibility
EMI       Electromagnetic Interference
EOL       End of Life
EUV       Extreme Ultraviolet Imager
FOV       Field of View
FSS       Fan Sun Sensor
FUV       Far Ultraviolet Imager
GSFC      Goddard Space Flight Center
HENA      High-Energy Neutral Atom Imager
IMAGE     Imager for Magnetopause-to-Aurora Global Exploration
LBH       Lyman-Birge-Hopfield (bands of FUV emissions from N2
LENA      Low-Energy Neutral Atom Imager
LEO       Low Earth Orbit
MCP       Microchannel Plate
Med-Lite  Medium-Light Expendable Launch Vehicle
MENA      Medium-Energy Neutral Atom Imager
MET       Mission Elapsed Time
MI        Magnetosphere Imager
MIDEX     Medium Explorer
NAI       Neutral Atom Imager
NASA      National Aeronautics and Space Administration
PA        Performance Assurance
QA        Quality Assurance
QAE       Quality Assurance Engineer
RAAN      Right Ascension of the Ascending Node
RE        Earth Radius
RPI       Radio Plasma Imager
S/C       Spacecraft
SI        Far Ultraviolet Spectrographic Imager
SMOC      GSFC Science and Mission Operations Center
S/N       Signal-to-Noise
SSD       Solid State Detector
SwRI      Southwest Research Institute
VME       Versamodule Europe
WIC       Far Ultraviolet Wideband Imaging Camera