**University of California**

**Project Data Management Plan**

**for the HESSI Mission**

[\_\_\_\_\_\_\_\_\_\_\_\_]{.underline}

Prepared by: Dr. Gordon Hurford (GSFC 682.0 / UCB) Date

HESSI Co-Investigator

[\_\_\_\_\_\_\_\_\_\_\_\_]{.underline}

Prepared by: Dr. Richard Schwartz (GSFC 682.3 / ITSS) Date

HESSI Associated Investigator

[\_\_\_\_\_\_\_\_\_\_\_\_]{.underline}

Concurrence: Dr. Robert P. Lin (UCB) Date

HESSI Principal Investigator

[\_\_\_\_\_\_\_\_\_\_\_\_]{.underline}

Concurrence: Dr. Brian R. Dennis (GSFC 682.0) Date

HESSI Mission Scientist

[\_\_\_\_\_\_\_\_\_\_\_\_]{.underline}

Concurrence: Dr. William Wagner (NASA HQ Code SR) Date

HESSI Program Scientist

[\_\_\_\_\_\_\_\_\_\_\_\_]{.underline}

Concurrence: Mr. Frank Snow (GSFC 410.0) Date

HESSI Mission Manager

TABLE OF CONTENTS

1.0 Introduction [1](#introduction)

1.1 Purpose and Scope [1](#purpose-and-scope)

1.2 PDMP Development, Maintenance, and Management Responsibility
[1](#pdmp-development-maintenance-and-management-responsibility)

2.0 Project Overview [1](#project-overview)

2.2 Data Acquisition and Access Overview
[2](#data-acquisition-and-access-overview)

2.3 Summary of Mission Operations [2](#summary-of-mission-operations)

3.0 Science Instrumentation [4](#science-instrumentation)

4.0 IMAGE End-to-End Data Flow [5](#hessi-end-to-end-data-flow)

4.3 Data Products and Access Overview [9](#__RefHeading___Toc457042840)

4.3.1 Level-0 Data [10](#level-0-data-primary-science-data)

4.3.2 Level-1 Data [10](#level-1-data)

4.3.3..Orbital Files [11](#orbital-files)

4.5 Archival Data Volume [11](#archival-data-volume)

4.6 Archive Data Access [11](#archive-data-access)

Acknowledgments [11](#acknowledgments)

Appendix A- Acronym List [12](#section-2)

# HESSI

**SMEX Mission**

**Project Data Management Plan**

# 1.0 Introduction

This document describes the Project Data Management Plan (PDMP) for the
High Energy Solar Spectroscopic Imager (HESSI) mission. HESSI is a NASA
Small Explorer (SMEX) mission with launch scheduled for July 4, 2000.

## Purpose and Scope

This PDMP is designed to be consistent with the HESSI Level-1
Requirements Definition document. It will describe the generation and
delivery of HESSI science data products to the Solar Data Analysis
Center (SDAC) and elsewhere, institutional responsibilities for data
analysis, and the transfer of archival data products to the National
Space Science Data Center (NSSDC). Covered in this plan are:

> 1\. Brief description of the instruments
>
> 2\. Description of the data flow
>
> 3\. Description of the science data products
>
> 4\. Processing requirements and facilities
>
> 5\. Policies for access and use of HESSI data
>
> 6\. Data product documentation

## 1.2 PDMP Development, Maintenance, and Management Responsibility

The HESSI Principal Investigator, Dr. Robert Lin[^1], is responsible for
the development, maintenance, and management of the PDMP through the
life of the mission. The point of contact for the PDMP is Dr. Gordon
Hurford[^2], HESSI Co-Investigator. The HESSI PDMP will be modified and
updated as required in accordance with the Configuration Management Plan
for SMEX Missions.

# 2.0 Project Overview

The HESSI mission was selected in October 1997 as a result of
AO-97-OSS-03 for SMEX missions. The lead American institutions for the
development of HESSI are the University of California at Berkeley and
Goddard Space Flight Center. The Paul Scherrer Institut in Switzerland
is developing and integrating the imager and aspect systems. Spectrum
Astro is developing the spacecraft.

The Phase B study began on February 23, 1998 and the Mission
Confirmation Review was held on August 17, 1998. Mission Confirmation
was granted on October 2, 1998. The HESSI mission is scheduled to be
launched July 4, 2000.

## 2.1 Science Objectives 

The primary scientific objective of the HESSI is to understand particle
acceleration and explosive energy release in the magnetized plasmas at
the Sun, processes that also occur at many other sites in the universe.
The Sun is the most powerful particle accelerator in the solar system,
accelerating ions up to tens of GeV and electrons to hundreds of MeV.
Solar flares release up to 10^32^-10^33^ ergs in 10^2^-10^3^ s. The
accelerated 10-100 keV electrons (and possibly \>\~1 MeV/nucleon ions)
appear to contain a significant fraction, perhaps the bulk, of this
energy, indicating that the particle accele­ration and energy release
processes are intimately linked. How the Sun releases this energy,
presumably stored in the magnetic fields of the corona, and how it
rapidly accelerates electrons and ions with such high efficiency, and to
such high energies, is presently unknown.

The hard X-ray/-ray continuum and -ray lines are direct signatures of
energetic electrons and ions, respectively, at the Sun. HESSI will
provide the first hard X-ray imaging spectroscopy, the first
high-resolution spectroscopy of solar -ray lines, the first imaging
above 100 keV, and the first imaging of solar -ray lines. HESSI combines
an imaging system consisting of 9 rotating modulation collimators
(RMCs), with a high-resolution spectrometer consisting of 9 germanium
detectors (GeDs) covering energies from soft X-rays (3 keV) to
high-energy -rays (15 MeV). HESSI's hard x-ray imaging spectroscopy
provides spectral resolution of \~1 keV, spatial resolution down to \~2
arcsec, and temporal resolution as short as tens of milliseconds. These
parameters are, for the first time, commensurate with physically
relevant scales for energy loss and transport of the \>\~10 keV
electrons that are believed to con­tain much of the energy released in
flares.

HESSI\'s -ray imaging spectroscopy will provide the first imaging of
energetic protons, heavy ions, relativistic electrons, neutrons, and
positrons; the first information on the angular distribution of
accelerated ions; and detailed information on elemental abundances for
both the ambient plasma and the accelerated ions.

With the fleet of spacecraft (SOHO, Wind, ACE, Ulysses, TRACE, GOES,
Yohkoh, SAMPEX, CGRO, etc.)[^3] that are already in place, a HESSI
launch in mid-2000 will provide the high energy measurements needed for
comprehensive studies of the solar maximum.

## 2.2 Data Acquisition and Access Overview

The HESSI mission will operate with an 85% duty cycle with the
imager/spectrometer in its baseline operational mode. Operationally, the
only difference between day and night will be the night-time absence of
attitude control and solar aspect data. The remaining 15% of operations
will differ only in the suppression of science data acquisition during
passage through the South Atlantic Anomaly. The HESSI Level-0 data will
be processed into Level-1 and Level-2 data (Quick-look Browse Products)
within 24 hours after their receipt in the Mission Operations Center and
Science Operations Center (MOC/SOC) at UCB. These Level 0-2 data
products will be transferred to the Solar Data Analysis Center (SDAC) at
GSFC and to the Swiss co-investigator institution, Eidgen"ossische
Technische Hochschule (ETH), in Zurich where they will be posted
immediately on the World Wide Web for use by the HESSI team, the
international community of scientists, and the public.

## Summary of Mission Operations

The HESSI Mission uses a single instrument consisting of an Imaging
System, Spectrometer and Instrument Electronics, all mounted in a
Sun-pointed, spin-stabilized spacecraft. The HESSI mission summary is
shown Table 1.

**Table 1** HESSI Mission Summary

+-------------------------------+---------------------------------------+
| **Orbit Description**         | Inclination: 38º                      |
|                               |                                       |
|                               | Apogee: 600 km                        |
|                               |                                       |
|                               | Perigee: 600 km                       |
|                               |                                       |
|                               | Period: 96 min.                       |
+-------------------------------+---------------------------------------+
| **Launch Date**               | 4 July 2000                           |
+-------------------------------+---------------------------------------+
| **Launch Vehicle**            | Pegasus XL (SELSV II)                 |
+-------------------------------+---------------------------------------+
| **Nominal Mission Duration**  | 2 years                               |
+-------------------------------+---------------------------------------+
| **Potential Mission Life**    | Over 10 years                         |
+-------------------------------+---------------------------------------+
| **Spacecraft + Instrument     | \~260 kg                              |
| Mass**                        |                                       |
+-------------------------------+---------------------------------------+
| **Spin Rate**                 | 15 rpm                                |
+-------------------------------+---------------------------------------+
| **Attitude Control Accuracy** | spin axis: 0.2º from Sun center       |
+-------------------------------+---------------------------------------+
| **Attitude determination**    | Instrument SAS gives spin axis        |
|                               | attitude to 1.5 arcsec; RAS gives     |
|                               | roll angle to 3 arcmin.               |
+-------------------------------+---------------------------------------+
| **On-Board Data Storage       | 4 Gbytes                              |
| Capacity**                    |                                       |
+-------------------------------+---------------------------------------+
| **Typical Data Acquisition    | 100 kbits/sec                         |
| Rate**                        |                                       |
+-------------------------------+---------------------------------------+

HESSI will be launched in mid-2000 on a small-fairing Pegasus XL (SELVS
II) vehicle into a 600-km circular, 38 inclination orbit. The launch
configuration will have the spacecraft ON and the instrument OFF
(detectors warm). Following injection into orbit, the spacecraft will
reorient towards the Sun, deploy its solar arrays, and spin up to 15
RPM.

Once the operational attitude, orientation and spin rates have been
achieved, the instru­ment electronics and cryocooler will be pow­ered.
Using a preprogrammed thermal pro­file, the cryocooler will cool the
spec­tro­meter to operational temperatures within a few days. This will be
followed by a brief de­tector checkout period in which high vol­tages are
turned on before normal operations begin.

Meanwhile the spacecraft will transition from coarse to Fine Sun Sensor
(FSS) pointing. The Imager's Solar Aspect System (SAS) and Roll Aspect
Sensor (RAS) will be activated and the analysis of initial data will
result in commands to electronically align the FSS with the optical axis
of the imager. Fine mechanical adjustment of the solar panel orientation
will be used to coalign the principle moment with the optical axis.
Normal operations for the remainder of the mission will consist of the
spacecraft using its FSS aspect in a fully-automated closed-loop
magnetic-torquing control system to keep the axis of rotation within 0.2
degrees of Sun center.

In normal operation the germanium detectors (GeDs) are cooled to 75 K;
GeD high voltage is on; and observations are taken continuously. Because
of the large thermal mass of the GeDs the cryocooler can be cycled over
time scales of hours if needed. Normal data acquisition is based on
storage of the energy and arrival time of every detected photon,
together with instrument SAS and RAS aspect information. These data are
stored in the spacecraft's 4 Gbyte mass memory until telemetered. Ground
data systems will convert these data into X-ray and -ray images and
spectra.

An 11-m ground station from Allied Signal and EMP, currently under
construction at UCB, will provide command transmission and data
reception. The Mission Operations Center and Science Operations Center
at UCB will operate the spacecraft and instrument, write the data onto
CD-ROMs, and distribute the data to the Solar Data Analysis Center
(SDAC) at GSFC and the High Energy Data Center (HEDC) in Zurich. The
SDAC will archive and distribute both data and analysis software to
outside users in the U.S., and coordinate access to context observations
from other space­craft and ground instruments. The HEDC will perform the
same functions in Europe. A pro­gram of ground observations is supported
directly by HESSI to provide the most critical context data. All users
will have equal access to the ground-based data.

# 3.0 Science Instrumentation

The HESSI scientific objectives will be achieved with high resolution
imaging spectroscopy observations from soft X‑rays to ‑rays, using a
single instrument consisting of an Imaging System, a Spectrometer, and
Instrument Electronics. The Imaging System is made up of nine Rotating
Modulation Collimators (RMCs), each consisting of a pair of widely
separated grids mounted on the rotating spacecraft. Pointing information
is provided by the Solar Aspect System (SAS) and Roll Angle System
(RAS).

The Spectrometer has nine segmented GeDs, one behind each RMC, to detect
photons from 3 keV to 15 MeV. Each detector is made from a single
germanium crystal, which is electrically divided into independent front
and rear segments to provide an optimum response for low and high energy
photons, respectively. The GeDs are cooled to \<\~75 K by a
space-qualified long-life mechanical cryo­cooler to achieve the highest
spectral reso­lution (Table 2) of any presently available -ray detector.
As the spacecraft rotates, the RMCs convert the spatial information from
the source into temporal modulation of the photon counting rates of the
GeDs. The Instrument Electronics amplify, shape, and digitize the GeD
signals, provide low-voltage power and GeD high voltage, format the
data, and interface to the spacecraft electronics.

Specific HESSI instrument performance parameters are given in Table 2.

**Table 2** HESSI Instrument Performance Parameters

+------------------------------------+---------------------------------+
| **Number of Germanium Detectors**  | 9                               |
+------------------------------------+---------------------------------+
| **Number of Independent Detector   | 18                              |
| Segments**                         |                                 |
+------------------------------------+---------------------------------+
| **Front Segment Detector           | 6.1 cm                          |
| Diameter**                         |                                 |
+------------------------------------+---------------------------------+
| **Rear Segment Detector Diameter** | 7.1 cm                          |
+------------------------------------+---------------------------------+
| **Front Detector Segment           | 1.5 cm                          |
| Thickness**                        |                                 |
+------------------------------------+---------------------------------+
| **Rear Detector Segment            | 6.5 cm                          |
| Thickness**                        |                                 |
+------------------------------------+---------------------------------+
| **Energy Range**                   | 3 keV to 15 MeV                 |
+------------------------------------+---------------------------------+
| **Energy Resolution (FWHM)**       | 0.5 keV to 30 keV               |
|                                    |                                 |
|                                    | increasing to 2 keV at 1 MeV,   |
|                                    |                                 |
|                                    | 5 keV at 15 MeV                 |
+------------------------------------+---------------------------------+
| **Imaging Technique**              | Fourier-transform imaging with  |
|                                    | rotating modulation collimators |
+------------------------------------+---------------------------------+
| **Angular Resolution**             | 2.3 arcsec to 40 (or 300) keV   |
|                                    |                                 |
|                                    | 7 arcsec to 400 keV             |
|                                    |                                 |
|                                    | 36 arcsec to 2.2 MeV            |
+------------------------------------+---------------------------------+
| **FOV**                            | Full Sun                        |
+------------------------------------+---------------------------------+
| **Range of Collimator Resolutions  | 2.3 -- 189 arcsec               |
| (FWHM)**                           |                                 |
+------------------------------------+---------------------------------+
| **Time-averaged Sensitive Area**   | up to 118 cm^2^                 |
+------------------------------------+---------------------------------+
| **Temporal Resolution**            | Tens of ms for basic image      |
|                                    |                                 |
|                                    | 2 s for detailed image          |
+------------------------------------+---------------------------------+
| **Max Photon-tagged Event Rate**   | 50,000 events/sec/segment       |
+------------------------------------+---------------------------------+
| **Time Resolution**                | Events recorded with 1s         |
|                                    | relative,                       |
|                                    |                                 |
|                                    | 1 ms absolute accuracy          |
+------------------------------------+---------------------------------+
| **Attenuators**                    | On-board logic selects one of 4 |
|                                    | states                          |
+------------------------------------+---------------------------------+
| **Rate Mode**                      | Activated by on-board logic     |
+------------------------------------+---------------------------------+

## 

## 3.1 Data Acquisition 

The primary science data will be returned in event data packets,
indicated in Table 3 along with other packet types. The contents of
these packets include the time, energy and detector-segment
identification of each detected event. The relative time resolution of 1
s is sufficient that coincident events are indicated by identical
time-tags, instead of conventional flags. Aspect data from SAS and RAS
are included with sufficient time resolution that the instantaneous
aspect associated with each detected event can be inferred.

To help accommodate the large dynamic range expected in flare count
rates as a function of time and energy, instrument logic will control
the mechanical insertion of either or both of two x-ray attenuators
between the lower grids and detectors. As an additional measure, in
large flares, should the memory and/or data storage rates approach their
limits, on-board instrument logic will apply increasingly stringent
energy criteria to favor the retention of high energy photons, along
with an unbiassed subset of the more numerous low energy photons. At
exceptionally high rates, time-tagging of each detected event in the
front segment detectors will be replaced by recording in Fast Rate
Counters with sufficient time resolution to permit imaging, albeit with
lower spectral resolution. In all cases, Monitor Rates with lower time
resolution are used to provide an overview of detector performance and
as input to support on-board decision-making.

**Table 3** HESSI Data Packets

  -----------------------------------------------------------------------
  **HESSI PACKET TYPES**

  State-of-Health Packets

  Event data

  SAS Data

  RAS Data

  Fast Rates data

  Monitor Rates

  Diagnostic IDPU Memory dump
  -----------------------------------------------------------------------

# 4.0 HESSI End-to-End Data Flow

## 4.1 Overview

Design and operations planning for space-based telescopes typically
require difficult tradeoffs among time resolution, spectral range and
resolution, spatial resolution, image quality, etc. Instead of
transmitting such a preselected subset of potential images and spectra,
the HESSI telemetry includes all of the information about each detected
photon. Thus, the data analyst can make these tradeoffs during the data
analysis phase, as opposed to during the instrument design or operations
planning phase. By making these decisions on a case-by-case basis *in
response to* the unique characteristics of the solar event under study
and the relevant scientific objectives, the scientific return from the
observations will be significantly enhanced*. Therefore a key driver of
our data analysis approach is the pre­servation of this flexibility for
use by the data analyst*.

To maintain this flexibility, the generation of extensive secondary
databases will be minimized. Instead, most scientific analysts will use
the primary database with the most current calibration information, and
be provided with the software necessary to apply such calibration data
to yield images and spectra with the time, spatial and spectral
resolution and range most appropriate to their objectives.

The data flow will follow the FAST model that was designed to minimize
interfaces and the production of extensive secondary databases. Data
will be telemetered directly from the spacecraft to the MOC/SOC at UCB,
where the raw telemetry files will be reformatted into a primary
database and where health, safety and spacecraft and instrument status
will be confirmed using automated algorithms.

The primary database includes the following principal elements:
time-tagged photons, SAS and RAS data, Monitor Rates, Fast Rate Counter
output (when appropriate), housekeeping data and "catalog" information
(discussed below). Except for the catalog, the primary database has no
"value-added". This catalog includes pointers to make the primary
database appear as a sequence of time-ordered, non-duplicated, and
quality-flagged data; a summary of spacecraft/instrument status;
detector rates above representative energy thresholds; a list of
identified flares; orbital averages of full-resolution spectra and, for
solar events, sets of representative images and spatially integrated
spectra. As with FAST, to ensure prompt preparation, the primary
database is generated without routine operator intervention.

The primary database and catalog will be made available at UCB by
network access using a CD-ROM jukebox, and will be shipped daily to GSFC
and ETH on CD-ROMs and/or via the Internet.

At GSFC, the HESSI solar data analysis, distribution, and archiving
tasks will be conducted under the auspices of the Solar Data Analysis
Center (SDAC). We will take full advantage of the SDAC facilities and
experienced personnel developed through the coordinated analysis of data
from SMM, Yohkoh, CGRO, and SOHO. In addition to HESSI data, SDAC and
ETH will also maintain a database of other relevant spacecraft and
ground-based observations.

The time line for these activities is given in Table 4. The primary
database and the quick-look data products will be available on line,
typically within 30 hours of receipt at UCB. (Longer latencies can be
anticipated during non-routine periods where support from additional
ground stations is used, as described in the next section.) While this
telemetry-driven latency may limit the role of HESSI data in
'now-casting' solar activity, the HESSI database should prove valuable
in the context of Space Weather research.

All data products, including the latest analysis software and
calibration data, will be shipped to the NSSDC on high-density magnetic
tape or CD-ROM's for archiving within 2 months of real time.

Table 4 Data Timeline

  ------------- ------------------ ------------------------- -------------------
  **Process**                                                **Time Required**

  1\.           Data telemetered                             0-48 hrs
                to UCB                                       

  2\.           Reformat primary                             6 hrs
                database and                                 
                generate catalog                             

  3\.           Generate CDs and                             24 hrs
                ship to GSFC and                             
                ETH. Data on line                            
                at UCB                                       

  4\.           Data products to                             2 months
                NSSDC                                        
  ------------- ------------------ ------------------------- -------------------

The HESSI mission will maintain a series of World Wide Web (WWW) pages
that provide the latest information about all aspects of HESSI
operations, including the type and accessibility of HESSI data. These
pages are located at the following URL: http://hessi.ssl.berkeley.edu/

## 4.2 Science and Mission Operations Center

The HESSI mission operations scenario is simple and efficient. Both the
spacecraft and the instrument are fully autonomous during normal
operations. No commands need be sent to the spacecraft for days or even
weeks at a time, other than those required to activate the transmitter
and dump data during each ground-station pass. Thus, once all spacecraft
and instrument functions have been activated and verified in the
Post-Launch and Early Orbit phase, the normal mission operations
scenario consists merely of reading out science data from the onboard
memory each orbit and verifying the health and safety of the mission.

We are installing an autonomous dedicated ground station at Berkeley for
command transmission and data reception. The HESSI Mission Operations
Center (MOC) and Science Operations Center (SOC) will be co-located at
the Space Sciences Laboratory on the campus of the University of
California at Berkeley. Figure 1 is a block diagram of the Ground Data
System.

To satisfy mission operations requirements, HESSI will use the
Integrated Test and Operations System (ITOS) and other Commercial Off
the Shelf Software (COTS). Science operations requirements will be
satisfied by using the same type of system used by the FAST Science
Operations Center. For most of the mission both the MOC and SOC
facilities will perform their required functions autonomously with a
minimal 5 day per week dayshift staffing to monitor system performance,
perform off-line trending and analysis of the spacecraft and instrument,
and perform system maintenance and upgrades.

**Normal Operations (MO&DA).** HESSI science observations will occur
continuously with data stored on-board and dumped periodically to the
UCB ground station. Each of the 5 to 6 ground station contacts per day
at UCB will collect approximately 100 to 300 Mbytes of data, consisting
of limited coverage provided by of real-time engineering and science
data (VC0 and VC2 respectively) and full coverage from the stored
engineering and science data (VC1 and VC3).

**Real-Time Operations.** The MOC will autonomously configure the
necessary ground communication and control elements for each contact.
The ground station will forward real-time engineering data (VC0) to the
MOC, which will autonomously receive, process, and perform limit
checking on all telemetry points. Configuration monitors will respond to
anomalous spacecraft conditions by paging key personnel or executing
STOL procedures. Access to the real-time data will be available via the
HESSI WWW site.

The ground station will also route stored engineering data (VC1) to the
MOC, which will run autonomous off-line trending and analysis procedures
using pre-defined parameters and configurations. Access to the output of
these procedures will also be available through the HESSI WWW site.

Prepared command loads and procedures will be forwarded to the ground
station during designated contacts for uplink to the spacecraft or will
be forwarded to the ground station prior to contact with the ground
station uplinking the command load at the designated time.

**Mission Planning.** The HESSI orbital elements will be downloaded
periodically from NORAD and used to produce spacecraft ephemeris, the
ground station contact schedule, and antenna acquisition angles. The
antenna acquisition angles and contact schedule will be forwarded to the
UCB ground station for automated antenna control. The contact schedule
and spacecraft ephemeris will be used to produce the spacecraft Absolute
Time Sequence (ATS) load, which will include transmitter on/off commands
and commands to dump telemetry data. The spacecraft ATS load will be
combined with the science ATS load and forwarded prior to or during a
ground station contact for uplink to the spacecraft. Other table and
software loads will also be produced and uplinked periodically.

Additional ground station support is expected during increased solar
activity periods or during a UCB ground station outage. Contacts will be
scheduled on an as-needed basis. Data communication will occur with
engineering data being shipped over a dial-up ISDN line to the MOC with
the Internet as backup and science data will be recorded to tape at the
ground station and delivered to UCB SOC.

**Database Maintenance.** The telemetry and command database will
require periodic updates and maintenance with distribution to all
required ground support elements.

**Science Operations.** Initially, real-time science data (VC2) will be
routed to the SOC and quick-look summary data will be produced, with
access via the HESSI WWW site at UCB**.**

The ground station will then route the stored engineering and science
data to the SOC. Upon reception of data, autonomous Level Zero
Processing will occur to sort the data by Application Identification
(APID). Following this, catalog and summary data will be produced with
access to the summary data via the HESSI WWW site.

**Science Planning.** HESSI will use a modified version of the FAST
science ATS command generation software. This will use spacecraft
ephemeris, contact schedule, and rules files to produce a series of
time-tagged commands which will control instrument data collection. For
example, time-tagged on/off commands would control science data
acquisition during predicted

SAA passages. The science ATS load will be passed over to the MOC
mission planning system for combining with the spacecraft ATS load in
preparation for transmission to the spacecraft.

4.3 Data Products and Access Overview[]{#__RefHeading___Toc457042840
.anchor}

This section discusses all the HESSI data products, how and where they
are generated, and how and when they will be accessible.

### 4.3.1 Level-0 Data -- Primary Science Data

The primary data product of the HESSI mission is what is normally
considered to be Level 0 data. Following the discussion in section 4.1,
the approach of the HESSI data analysis is to create a robust data
analysis system which will allow the routine production of Level 2
quality images and spectra by any scientist given the Level-0 data, the
calibration database, and the software installation. Scientists on the
PI team will interact with the data set in the same way.

Each Level-0 data file (available from the SDAC and ETH) will consist of
a complete set of time-ordered source data packets and a standard file
header in CCSDS format. The packets will be organized into FITS files up
to 50 Mbytes in length or of the duration of a single orbit between
local midnights. The telemetry packets will be completely preserved
within the FITS file, that structure only being used to facilitate the
documentation and the addition of autonomously generated browse
products. These browse products will consist of several FITS extensions.
The first extension will be a table of the packet number, packet type,
and time range included. The second extension will be an observing
summary which includes broadband rates and ephemerides. The third
extension will include any autonomously created quick-look products for
flares observed during the file's duration.

The Level-0 FITS files will be collected daily and imprinted on CDROMs
for distribution to GSFC and ETH. Also, as each FITS file is completed
by the MOC/SOC, the file will be transmitted to GSFC and ETH over the
Internet as well. By the time of the mission we expect that this means
of transmission will be the primary method of data dissemination.

### 4.3.2 Level-1 Data

In order to accomplish the HESSI scientific goals, the ability to
quickly survey the large number of flares observed is essential. The
result of Level-1 data processing in the MOC/SOC will typically be
referred to as a Quick-look Product (QLP). All QLP data sets are created
as FITS files and browser viewable image formats such as GIF. The SOC
will post the most recent QLP data on the HESSI web pages. On the web
page any user will be able to easily access the entire QLP archive for
either image or FITS files. Additionally, a simple summary event catalog
will be available for browse and for search via a web page. The
browser-viewable products are well-suited to public access, since no
special analysis skills or HESSI-specific software will be required. The
Quick-look Product summaries for the HESSI instrument mission are given
in Table 5.

**Table 5** Level 1 Data Products (Browse Products)

  ------------------------ -------------------------- -------------------
  **Quick Look Product**   **Estimated number/day**   **Data Volume**

  Flare Images             10                         36 kbyte

  Flare Light Curves       20                         20 kbyte

  Flare Spectra            20                         20 kbyte
  ------------------------ -------------------------- -------------------

The software algorithms for the QLP production will be built from the
most robust algorithms (especially for imaging) within our software
library. The QLP software will operate without human intervention by
first identifying flares on the basis of rotation-averaged fluxes during
solar observations. This software, as with all the HESSI software, will
be documented and included as a living document with the SolarSoftWare
(SSW) package available at the SDAC.

### 

### 4.3.3 Orbital Files

A daily or orbital attitude history file will be produced in the SOC.
From this file and the software within the HESSI segment of SSW, it will
be possible to reconstruct the orbit to within 10 km at any time during
the mission. The orbital files will appear on the CDROMs distributed to
and archived at UCB, SDAC, and ETH.

## 4.4 Data Archiving and Distribution

Once a designated amount of VC2 and VC4 data is received at the SOC, it
will be copied to CD-ROM along with associated ephemeris, catalog, and
summary data. At least three copies of each CD data set will be produced
with copies being distributed to SDAC and HEDC. At UCB on-line data
access from the SOC will be via either a RAID or a CD-ROM jukebox
system. The HESSI CD-ROM production system will be the same as that used
by the FAST mission, a fully autonomous system producing multiple copies
of data sets for distribution. At GSFC, all data products, including the
latest analysis software and calibration data, will be converted to
high-density magnetic tape and shipped to the NSSDC for archiving within
2 months of real time.

## 4.5 Archival Data Volume

The estimated volume of mission data acquired over nominal 2-year
lifetime is approximately 1 Tbyte based on 700 days at 1.5 Gbyte/day.
The QLP are a small fraction of the volume of the Level 0 data files.
Based on these estimates the total HESSI Mission data volume to be
archived at the NSSDC will be approximately 1 Terabyte over the 2-year
lifetime of the mission.

## 4.6 Archive Data Access

The SDAC's on-line archive will be used for rapid access to all the
archived HESSI data. At the SDAC we expect to create an archive capable
of holding up to 250 Gbytes for immediate on-line access either through
direct Telnet, FTP, or web interface. While this is a large database
capable of holding the most important events observed with HESSI, it
will not hold the entire database including all of the ancillary
observations, both ground and space based. Additionally, we expect the
availability of a 10 Tbyte near-line (\<1 minute) archive at ETH. Both
of these data archives will be open for public use without reservation.

# Acknowledgments

The preparation of this document was greatly aided by the assistance of
Kate Harps, Dave Curtis and David Smith.

##### Appendix A - Acronym List 

##### 

ACE - Advanced Composition Explorer

APID - Application Identification

ATS - Absolute Time Sequence

CD-ROM - Compact Disk - Read Only Memory

CGRO - Compton Gamma Ray Observatory

COTS - Commercial Off-The-Shelf

ETH - Eidgen"ossische Technische Hochschule

FAST - Fast Auroral SnapshoT

FITS - Flexible Image Transport System

FOV - Field of View

FSS - Fine Sun Sensor

FTP - File Transfer Protocol

FWHM - Full Width at Half Maximum

GeD - Germanium Detector

GIF - Graphic Interchange Format

GOES - NOAA's Geostationary Operational Environmental Satellite

GSFC - Goddard Space Flight Center

HEDC - High Energy Data Center at ETH

HESSI - High Energy Solar Spectroscopic Imager

ISDN - Integrated Services Digital Network

ITSS - Information Technology Scientific Services

ITOS - Integrated Test and Operations System

MO&DA - Mission Operations and Data Analysis

MOC - Mission Operations Center

NASA - National Aeronautics and Space Administration

NORAD - North American Air Defense Command

NSSDC - National Space Science Data Center

PI - Principal Investigator

PDMP - Project Data Management Plan

QLP - Quick Look Product

RAS - Roll Angle System

RMC - Rotating Modulation Collimator

SAMPEX - Solar Anomalous and Magnetospheric Particle EXplorer

SAS - Solar Aspect System

SDAC - Solar Data Analysis Center

SELSV II - Small Expendable Launch Vehicle Services II

SMEX - SMall EXplorer

SOC - Science Operations Center

SOHO - SOlar and Heliospheric Observatory

SSW - Solar SoftWare

TRACE - Transition Region And Corona Explorer

UCB - University of California, Berkeley

URL - Uniform Resource Locator

VCn - Virtual Channel n

WWW - World Wide Web

[^1]: Space Sciences Lab, University of California, Berkeley CA 94720.
    rlin@ssl.berkeley.edu (510) 642-1149

[^2]: Code 682.0, NASA/GSFC, Greenbelt MD 20771.
    ghurford@pop600.gsfc.nasa.gov (301) 286-4255

[^3]: See List of Acronyms in Appendix I-4.