Constellations have proven to be an effective and efficient way to acquire earth science data. By flying together, sensors on all satellites in a constellation take measurements of the same air, water, or land mass at essentially the same time. The sensors form a single "virtual satellite". The key to making a constellation effective and efficient is keeping the operations as independent as possible in order to minimize the operational burden and costs. The Earth Science Constellation (ESC) has been successful on all counts and continues to welcome new missions to continue its 18+ year record of coincidental earth science observations. The ESC also serves as a model for future constellation designs. This paper describes the ESC and its evolution from its initial launches in 1999 through the present and how new missions might benefit from joining the ESC

Case, Warren F.

Guit, William J.

Machado, Michael J.

NASA Technical Reports Server

1Leverage your science data return by 
flying with the International Earth 
Science Constellation (ESC)
Michael J. Machado*a, William J. Guita, Warren F. Caseb
aNASA Goddard Space Flight Center (GSFC), Greenbelt, Maryland USA 20771 
bArctic Slope Technical Services, Inc., GSFC, Greenbelt, Maryland USA 20771
https://ntrs.nasa.gov/search.jsp?R=20180007427 2019-08-31T18:27:00+00:00Z
2Agenda
• What is the Earth Science Constellation (ESC)?
– Overview and ESC Orbit Characteristics
– Morning and Afternoon Constellation Evolution
• What are the benefits of flying in the ESC?
• How can a mission benefit yet remain 
independent?
– What are control boxes?
– How do missions coordinate and communicate?
• What resources are available to ensure safe 
operations?
• What does the future of the ESC look like?
3Overview
The ESC has proven to be an effective and efficient 
way to acquire earth science data. 
By flying together:
• Sensors on ESC satellites in the constellation take 
measurements of the same air, water, or land mass
at essentially the same time. 
• The sensors form a single “virtual satellite”. 
4ESC Orbits
• 705 km nominal equatorial altitude
• Polar at 98 deg. Inclination
 Benefit: Provides near global coverage
• Repeating (233 orbits/16 days)
 Benefit: Easier to see changes
• Sun-synchronous
 Benefit: Consistent lighting
Morning Constellation ~10:30 a.m. at equator crossing
Afternoon Constellation ~1:30 p.m. at equator crossing
(The Afternoon Constellation is also known as the “A-Train”) 
• Satellites in close proximity
 Benefit: Near-simultaneous observations
• Follows the Worldwide Reference System-2 (WRS-2)
 Benefit: Observations overfly the same ground tracks
705 km 
altitude
10:00 
a.m. Sun-synchronous
(near constant lighting)
1:30 
p.m.
5199920002461137
Aqua
Aura
CALIPSO
CloudSat
GCOM-W1
OCO-2
PARASOL
Landsat 7
Landsat 8
Terra
SAC-C
EO-1
Morning 
Constellation
Afternoon 
Constellation
ESC’s Evolution
OCO
Glory Mission no 
longer 
operational
6The ESC Today
7Globally Distributed Science and 
Mission Operations
Project 
Scientists
Mission 
Operations
Aqua
GSFC
Greenbelt, MD
OCO-2
JPL
Pasadena, CA
Landsat 7
GSFC
Greenbelt, MD
Terra
GSFC
Greenbelt, MD
Aura
GSFC
Greenbelt, MD
Landsat 8
GSFC
Greenbelt, MD
CALIPSO
LaRC
Hampton, VA
CALIPSO
CNRS
Paris, France
GCOM-W1
JAXA
Tokyo, Japan
CALIPSO
MOCC at LaRC
Hampton, VA
Landsat-7
MOCC at GSFC
Greenbelt, MD
Aqua
EOC at GSFC
Greenbelt, MD
Aura
EOC at GSFC
Greenbelt, MD
Terra
EOC at GSFC
Greenbelt, MD
Landsat-8
MOCC at GSFC
Greenbelt, MD
OCO-2
Ops Facility
Dulles, VA
GCOM-W1
JAXA
Tsukuba, Japan
CALIPSO
SOCC at CNES
Toulouse, France
IGARSS 2009
8
Washington DC
USGS Map
13.5 km Aqua AIRS IR;  
AMSU & HSB µ wave
6 x 7 km PARASOL POLDER 
5.3 x 8.5 km Aura TES 
Cloud
0.5 km Aqua & Terra 
MODIS Band 3-7
0.09 km CALIPSO CALIOP
1. 4 km CloudSat CPR
OCO-2
1x1.5 km
“A-Train” Nadir Footprints
9Afternoon Constellation Coincidental Science
MODIS & CERES -
IR Properties of Clouds
AIRS - Temperature and 
H2O Sounding
AquaCloudSatPARASOL
PARASOL POLDER –
Aerosol and cloud polarization
CALIPSO CALIOP – Aerosol 
and cloud heights
CloudSat CPR - Cloud 
droplets
CALIPSOAura
OMI – Cloud heights
OMI & HIRDLS – Aerosols
MLS & TES – H2O & temp 
profiles
MLS & HIRDLS – Cirrus 
clouds
OCO-2
OCO-2  -
CO2 column
10
Constellation Benefit – Enhanced Science
Aqua, CALIPSO, and CloudSat
Observe Hurricane Debby
The Aqua satellite collects data on the 
geographical distribution of clouds and 
aerosols, atmospheric temperature, 
moisture content and the radiation 
balance at the top of the atmosphere.
CloudSat uses a radar to 
provide vertical profiles 
of thick clouds that lidar
cannot penetrate.
The CALIPSO satellite provides vertical, 
curtain-like images of the atmosphere on 
a global scale using a lidar.
8/24/2006
Credit: NASA Earth Observatory (https://earthobservatory.nasa.gov/Features/CALIPSO) and NASA/Goddard Space Flight Center Scientific Visualization Studio (https://svs.gsfc.nasa.gov/3437)
11
Constellation Benefit – Enhanced Science
Aqua, CALIPSO, and CloudSat data used for the GLOBE Program
The Global Learning and Observations to benefit the Environment (GLOBE) Program, is a worldwide 
program that brings together students, teachers, scientists and citizens to promote science and learning about 
the environment. Combining this with satellite observations will help address questions about changes in the 
water cycle and freshwater availability.
Aqua’s MODIS instrument 
provides a natural color view of 
clouds over a broad swath of the 
continent.
CALIPSO’s lidar by contrast 
measures the fine structural 
detail of the atmosphere above 
and between the clouds, but is 
attenuated very near the tops of 
thick cloud layers.
CloudSat’s Cloud Profiling 
Radar (CPR) can penetrate deep 
into the cloud layer, but it can 
miss the structure of thin clouds 
above thick cloud layers.
Credit: NASA Earth Observatory (https://earthobservatory.nasa.gov/Features/CALIPSO) and NASA/Goddard Space Flight Center Scientific Visualization Studio (https://svs.gsfc.nasa.gov/4524)
12
• Keep the operations as independent as possible in 
order to minimize the operational burden and costs
Effective and Efficient Operation
Key Goal:
• Coordination systems and procedures are in place
• Experienced teams are ready to lend a hand to new 
members
 Flight dynamics expertise
 Orbital debris collision avoidance interface
Institutional Advantages
13
Buffer
Control Boxes
• Control Boxes minimize the amount of coordination 
between missions
 As long as the spacecraft stays inside its control box, little 
or no daily coordination is required
 No complex interfaces
14
A-Train Control Box Configuration
(based on equator crossing times)
~270                 86                      ~343                    43 30  43          195              86        98        86             ~400   
sec                    sec sec sec sec sec sec sec sec sec sec
30 sec 15 sec
15
Agreements
• The agreement between Landsat-7 and Terra for coincident 
observations after their 1999 launches formed the basis for the 
Morning Constellation coordination
• The A-Train Mission Operations Working Group (MOWG) was 
established in 2003 comprising science and mission operations 
representatives
• The Morning and Afternoon constellation working groups were 
formally combined into a single ESC MOWG in 2015
• The MOWG developed policies and procedures that
 Handle contingencies
 Manage changes to the constellation configuration
 Define a conflict resolution process
 Setup communications guidelines
• The MOWG meets twice per year to review status and 
coordinate plans
16
Constellation Coordination System (CCS)
NASA’s Earth Science Mission Operations (ESMO) Project at 
Goddard Space Flight Center developed the CCS to facilitate 
coordination between the teams:
• Exchanges ephemeris data
• Monitors constellation
• Sends out alerts as required
• Generates plots and reports 
to analyze orbital safety and 
develop “what-if analysis”
• Performs ephemeris 
conversions and 
comparisons
CCS Analyses
• Ad Hoc Analysis
• Argument of Latitude
• Close Approach Analysis
• Control Box and Phasing Analysis
• Mean Local Time at the Nodes
• Phase Margin Analysis
• Phasing at the Poles
• Satellite Situational Awareness
• Single Orbit Altitude Versus Latitude
17
18
Recent changes
CloudSat and CALIPSO relocation
• CloudSat lowered its orbit on February 22, 2018
• CALIPSO plans to join CloudSat in September 2018 
• This continues their strong coincident science in a new orbit 
thereby forming the “C-Train”.  
Relative motion*
Aura                                 Aqua       GCOM-W1  OCO-2
CloudSat  CALIPSO
16.5 km
A-Train orbit
C-Train orbit
*Once CALIPSO and CloudSat are in place, they will pass underneath the A-Train every ~20 days
A-Train and C-Train Relationship
19
Future ESC Changes
New Missions The ESC has a process in place to accept new 
missions. For a new mission to join:
• It needs to enhance the overall science
• It requires approval from the existing 
MOWG teams and their space agencies
Constellation Exit All teams have to determine when to leave the 
ESC based on their fuel reserves or spacecraft 
health
For example:
December 2020 Landsat-9 launches and joins the Morning 
Constellation
Sometime in 2022 RESTORE-L spacecraft refuels Landsat-7 as 
part of a technology demonstration.  Landsat-7 
subsequently de-orbits.
20
• The ESC has been successful for nearly 2 decades 
providing a record of coincidental earth science 
observations
• The ESC serves as a model for future constellation 
designs
• The ESC continues to evolve and welcome new 
missions
Summary
If you have questions or requests . . .
Contact Michael.J.Machado@nasa.gov
21
Questions?
22
AIRS Atmospheric Infrared Sounder
AMSR-E Advanced Microwave Scanning Radiometer-EOS
AMSU Advanced Microwave Sounding Unit
AUX auxiliary
ASTER Advanced Spaceborne Thermal Emission and Reflection and Radiometer
CA California
CALIOP Cloud-Aerosol Lidar with Orthogonal Polarization
CALIPSO Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations
CCS Constellation Coordination System
CERES Clouds and the Earth’s Radiant Energy System
CIRA Cooperative Institute for Research in the Atmosphere
CNES Centre National D’Etudes Spatiales
CNRS Centre national de la recherche scientifique
CO carbon monoxide
CO2 carbon dioxide
CPR Cloud Profiling Radar
CVT Constellation Visualization Tool
dBZ decibel relative to Z (the equivalent reflectivity factor)
deg degree
DPC Data Processing Center
E east
EO-1 Earth Observing 1
EOC EOS Operations Center
EOS Earth Observing System
ESC Earth Science Constellation
ESMO Earth Science Mission Operations
ETM Enhanced Thematic Mapper
GCOM-W1 Global Change Observation Mission – Water 1
GEOPROF geometrical profile
gm gram
GSFC Goddard Space Flight Center
H2O water
HIRDLS High Resolution Dynamics Limb Sounder
HSB Humidity Sounder for Brazil
IIR Imaging Infrared Radiometer
IR infrared
IWC ice water content
JAXA Japan Aerospace Exploration Agency
JPL Jet Propulsion Laboratory
kg kilogram
km kilometer
LaRC Langley Research Center
Lat latitude
LIDAR Light Detection And Ranging
Log logarithm
Lon longitude
MD Maryland
MIS Multi-angle Imaging. Spectroradiometer
MLS Microwave Limb Sounder
MOCC mission operations control center
MODIS Moderate Resolution Imaging Spectroradiometer
MOPITT Measurement of Pollution in the Troposphere
MOWG Mission Operations Working Group
NASA National Aeronautics and Space Administration
Nov November
nm nanometer
OCO Orbiting Carbon Observatory
OLI Operational Land Imager
OMI Ozone Monitoring Instrument
Ops Operations
PARASOL Polarization and Anisotropy of Reflectances for Atmospheric 
Science coupled with Observations from a Lidar
POLDER Polarization and Directionality of the Earth's Reflectances
SAC-C Satelite de Aplicaciones Cientificas-C
sec second
SOCC Satellite Operations Control Center
TES Tropospheric Emission Spectrometer
TIRS Thermal Infrared Sensor
Tot total
USA United States of America
USGS United States Geological Survey
UTC Universal Time Coordinated
UTM Universal Transverse Mercato
VA Virginia
W west
WFC Wide Field Camera
WRS Worldwide Reference System
Acronyms and Abbreviations
23
Afternoon Constellation (A-Train)
(1 of 2)
Satellite Summary Of Mission Instruments Launch Responsible Organization
Aqua
Aqua is named for the large amount of
information that the mission is collecting about
the Earth's water cycle, including evaporation
from the oceans, water vapor in the atmosphere,
clouds, precipitation, soil moisture, sea ice, land
ice, and snow cover on the land and ice.
AIRS
AMSU-A
HSB
AMSR-E
CERES
MODIS
May 4, 
2002 NASA/GSFC
Aura
Aura (Latin for air) studies the Earth’s ozone, air
quality, and climate. It is designed exclusively to
conduct research on the composition, chemistry,
and dynamics of the Earth’s atmosphere. Limb
sounding and nadir imaging observations allow
studies of the horizontal and vertical distribution
of key atmospheric pollutants and greenhouse
gases and how these distributions evolve and
change with time.
HIRDLS
MLS
OMI
TES
July 15, 
2004 NASA/GSFC
CALIPSO
Observations from space-borne lidar, combined
with passive imagery, lead to improved
understanding of the role aerosols and clouds
play in regulating the Earth’s climate.
CALIOP
IIR
WFC
April 28, 
2006
NASA/GSFC 
NASA/LaRC
CNES
24
Afternoon Constellation (A-Train)
(2 of 2)
Satellite Summary Of Mission Instruments Launch Responsible Organization
GCOM-W1
The GCOM-W1 observes integrated water
vapor, integrated cloud liquid water,
precipitation, sea surface wind speed, sea
surface temperature, sea ice concentration, snow
water equivalent, and soil moisture.
AMSR-2 May 18, 2012 JAXA
OCO-2
Three grating spectrometers will make global,
space-based observations of the column-
integrated concentration of carbon dioxide, a
critical greenhouse gas.
Three grating 
spectrometers
July 2, 
2014 NASA/JPL
25
Morning Constellation
Satellite Summary Of Mission Instruments Launch Responsible Organization
Landsat-7
Provides global coverage, and spectral
characteristics to allow comparisons for global
and regional change detection and image data to
various international users throughout the world
during times of sudden global changes (e.g.,
earthquakes or floods).
ETM+ April 15, 1999
US Geological 
Survey 
(USGS)
Terra
Terra is a multi-national, multi-disciplinary
mission that will help us to understand how the
complex coupled Earth system of air, land, water
and life is linked.
MISR
CERES
MOPITT
ASTER
MODIS
December 
18, 1999 NASA/ GSFC
Landsat 8
Provides moderate-resolution measurements of
the Earth's terrestrial and polar regions in the
visible, near-infrared, short wave infrared, and
thermal infrared. Landsat 8 provides continuity
with the 45+ year Landsat land imaging data set.
OLI 
TIRS
February 
11, 2013 USGS
26
Worldwide Reference System-2
(Established for the Landsat Missions)
WRS-2 shown for ascending node orbits. Descending node orbit tracks are similar in nature.
https://landsat.usgs.gov/sites/default/files/images/wrs2.gif
27
Constellation Coordination System (CCS)
Detailed Analyses Descriptions
Ad Hoc Analysis Enables the user to create, save, and view custom plots and/or text reports of a variety of 
selectable orbit parameters for a mission for the span of a selected ephemeris. Users can 
select daily products, or can choose trending products by selecting the "view only trending 
products" check box.
Argument of 
Latitude
Enables the user to visualize the missions’ latitude at the end of its ephemeris (or the end of 
the ephemeris overlap for multiple missions). This is a 2-D visualization that only gives a basic 
representation, projecting all missions onto the same orbit plane.
Close Approach 
Analysis
Enables the user to screen several missions and determine whether a close approach situation 
is encountered. The radial, in-track, and cross-track separations are analyzed in order to 
determine if any specified Zone of Exclusion is violated.
Control Box and 
Phasing Analysis
Enables the user to visualize where an afternoon constellation mission is within its designated 
control box over a specific time period and determine if any violations will occur. Each missions 
control box and all associated data is referenced to the descending node of its orbit.
Mean Local Time at 
the Nodes
Enables user to conduct a trending analysis utilizing archived data and a predictive analysis 
utilizing predictive future data of the Mean Local Time of the Ascending and Descending Nodes 
of CCS defined Morning and Afternoon Constellation missions.
Phase Margin 
Analysis
Enables the user to save and view text reports detailing the difference in the descending node 
crossing times of two selected missions.
Phasing at the Poles Enables the user to conduct a phasing analysis of any two CCS defined Morning and Afternoon 
Constellation missions at the North and the South orbit plane intersection of the two satellites.
Satellite Situational 
Awareness
Provides a user customizable three dimensional and two dimensional visualization of the 
location of chosen satellites and their ground tracks with user controlled play speed. The three 
dimensional visualization also supports variable view angles.
Single Orbit Altitude 
Versus Latitude
Enables the user to have the ability to analyze the altitude versus the latitude relationship for a 
single orbit of any two CCS defined Morning and Afternoon Constellation missions.


Leverage Your Science Data Return by Flying with the International Earth Science Constellation (ESC)

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server