Design and Evaluation of Distributed Spacecraft Missions for Multi-Angular Earth Observation

243 Pages·2015·15.5 MB·English

Design and Evaluation of Distributed Spacecraft Missions
for Multi-Angular Earth Observation

by
Sreeja Nag

B.S. Exploration Geophysics, Indian Institute of Technology, Kharagpur, 2009
M.S. Exploration Geophysics, Indian Institute of Technology, Kharagpur, 2009
S.M. Aeronautics and Astronautics, Massachusetts Institute of Technology, 2012
S.M. Technology and Policy, Massachusetts Institute of Technology, 2012

Submitted to the Department of Aeronautics and Astronautics
in Partial Fulfillment of the Requirements for the Degree of
Doctor of Philosophy in Aeronautics and Astronautics Engineering

at the
Massachusetts Institute of Technology
June 2015
© 2015 Massachusetts Institute of Technology. All rights reserved.

Signature of Author _________________________________________________________________________
Department of Aeronautics and Astronautics
April 17, 2015

Certified by _______________________________________________________________________________
Olivier L. de Weck
Professor of Aeronautics and Astronautics and Engineering Systems
Thesis Supervisor

Certified by _______________________________________________________________________________
David W. Miller
Professor of Aeronautics and Astronautics
Thesis Committee Member

Certified by _______________________________________________________________________________
Kerri L. Cahoy
Assistant Professor of Aeronautics and Astronautics
Thesis Committee Member

Certified by _______________________________________________________________________________
Charles K. Gatebe
Senior Research Scientist at NASA Goddard Space Flight Center
Thesis Committee Member

Accepted by ______________________________________________________________________________
Paulo Lozano
Associate Professor of Aeronautics and Astronautics
Chair, Graduate Program Committee
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Design and Evaluation of Distributed Spacecraft Missions
for Multi-Angular Earth Observation

by
Sreeja Nag

Submitted to the Department of Aeronautics and Astronautics
On April 17, 2015 in Partial Fulfillment of the Requirements for the Degree of

Doctor of Philosophy in Aeronautics and Astronautics Engineering

ABSTRACT
Distributed Spacecraft Missions (DSMs) are gaining momentum in their application to Earth science
missions owing to their ability to increase observation sampling in spatial, spectral and temporal dimensions.
This thesis identifies a gap in the angular sampling abilities of monolithic spacecraft in Earth observation
missions and proposes to use distributed spacecraft to address this gap. The science performance metric is
chosen to be Bidirectional Reflectance-Distribution Function (BRDF), which describes the directional and
spectral variation of reflectance of an optically thick surface element at any time instant. Airborne instruments
are the gold standard for BRDF estimation (e.g. Cloud Absorption Radiometer/CAR). They can collect
thousands of reflectance measurements at the same ground spot, but are localized in space and time.
Spaceborne platforms estimate BRDF by combining angular measurements over time, made along-track, cross-
track or by autonomous pointing. However, their plane of data acquisition is very restricted with respect to the
sun and the target itself might change over time of acquisition. Formations with spectrometer payloads can
make multi-spectral reflectance measurements of a ground target, at many zenith and azimuthal angles
simultaneously and estimate the angular signature of the surface. Constellations with overlapping ground spots
can capture the angular components of global and temporally varying science products.
This work demonstrates the performance impact and feasibility of a BRDF estimation mission using a
systems engineering tool (driven by model based systems engineering or MBSE), intricately coupled with a
science evaluation tool (driven by observing system simulation experiments or OSSEs). Formations and
payload pointing strategies are optimized to maximize angular spread and minimize estimation errors. The
effect of angular spread on spatial, spectral and radiometric sampling dimensions is quantified for available
spectrometer payloads that fit within the 6U CubeSat standard. Technical feasibility within 6U is verified for
attitude determination and control, propulsion, communication and onboard processing modules. DSM
architectures are generated and compared to each other and monoliths, in terms of BRDF, albedo, gross
primary productivity and total outgoing radiation. Performance is benchmarked with respect to data from
previous airborne campaigns (NASA CAR), tower measurements (AMSPEC II) and ideal values from radiative
transfer or climate models (UMGLO, COART); and accepted BRDF models.
A formation of 6 small satellites produces lesser average error (21.82%) than larger monoliths (23.2%)
over extended time periods, purely in terms of angular sampling benefits. The monolithic albedo error of 3.6%
is shown to be outperformed by a formation of 3 satellites (1.86%), when arranged optimally and by a formation
of 5 satellites (3.36%) when arranged in any way. An 8-satellite formation pushes albedo errors to 0.67% and
reduces gross primary productivity errors from 89.77% (monolithic) to 78.69%.

Thesis Supervisor: Olivier L. de Weck
Title: Professor of Aeronautics and Astronautics and Engineering Systems

Thesis Committee Member: David W. Miller
Title: Professor of Aeronautics and Astronautics

Thesis Committee Member: Kerri L. Cahoy
Title: Assistant Professor of Aeronautics and Astronautics
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Thesis Committee Member: Charles K. Gatebe
Title: Senior Research Scientist at NASA Goddard Space Flight Center

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Everything I am and ever hope to be, I owe to my mother.

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Acknowledgements

First and foremost, I want to sincerely thank my advisor, Prof. Olivier de Weck, for consistent belief
in my capabilities and for his guidance. I am particularly grateful to him for going out of his way on many
occasions to provide unwavering support of my pursuit of unexpected opportunities and ever-evolving
interests. His dedication to the topics of his students’ interests, irrespective of whether they align with his
personal research goals, is very admirable and deeply appreciated.

The quality of this dissertation would not have been what it currently is without the mentorship and
invaluable advice from each of my PhD committee members, readers and advisors, Prof. David Miller, Prof.
Kerri Cahoy, Prof. Jeffrey Hoffman and Prof. Dava Newman at MIT; and Dr. Charles Gatebe and Dr.
Jacqueline LeMoigne at NASA Goddard Space Flight Center (GSFC). A special mention for Prof. Anantha
Chandrakasan for being a very supportive mentor, especially during academically difficult times. I began my
PhD research by showing up at GSFC for the summer of 2012. All I knew back then was that I wanted to make
an impact in the Earth Sciences with large numbers of small satellites. I had the lucky privilege of meeting Dr.
Warren Wiscombe, a senior scientist at GSFC and an MIT alum, who introduced to me to “BRDF” and asked
me to go solve the “BRDF problem”. It has been nearly three years and every time I meet Warren, I learn
something brand new in earth science.

I am indebted to my Goddard family for the quality of my PhD: To Charles for giving me my GSFC
break without ever having met me, for being a mentor whenever I needed and for a comprehensive introduction
to Science@NASA; To Shana for sharing her home with me every time I visited for extended periods; To
Jacqueline for supporting me at work ever so cherubically, for consistent mentorship and for taking me to my
first launch (LADEE at Wallops); To Christine Chiu, Bert Pasquale, Tilak Hewagama, Shahid Aslam, Alexis
Lyapustin, Georgi Georgiev, Crystal Schaaf and Miguel Roman for teaching me about algorithms and
instruments in spite of their busy schedule; To Thomas Hilker and Forrest Hall for sharing their data and
invaluable advice on photosynthetic measurements; To Jonathan Fentzke and Lars Dyrud for introducing me
the world of dynamic and next-gen space entrepreneurship.

Very deep thanks to Sangram Ganguly, Steve Hipskind and Chad Frost at NASA Ames Research
Center (ARC) for giving me an opportunity to move to the wonderful San Francisco Bay Area. I have loved
every bit of being here and hope the adventure continues. Starting life in a new place didn’t feel as difficult as
they say out to be, thanks to Abhishek (owner of the Batmobile); Christina (the super mom); Fan, Jan, Jamie
and Andres; Anirudh, Moumita, Archi, Annapoorna mashi and everyone else who smoothened my move.

Generous funding for my work and study for my 3 years of PhD pursuit has come from the
Schlumberger Faculty for the Future Fellowship, NASA Earth and Space Science Fellowship, MIT
Zakhartchenko Fellowship, Zonta Amelia Earhart Fellowship, Draper Laboratory and the NASA InVEST
Program, NASA GSFC’s Internal Research and Development (IRAD) Grant, USRA’s GESTAR program at
NASA GSFC and BAERI’s ARC-CREST program at NASA ARC. Consistent funding from evaluators and
mentors who believed in my projects and me enabled my PhD journey to be a smooth-sailing but intellectually
challenging joyride. MIT’s International Students’ Office has been indispensable in my life of infinite paperwork
as a green-horned, non-resident alien in the US of A. Marilyn Good and Julie Finn, you should take a bow for
the years and years of very appreciated support you have provided to the SSL and SERG.

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Work can never be satisfying through content alone. I got to travel so much during grad school and I
could say that alone taught me a universe. While not during my PhD period, I shall always be grateful to Leopold
Summerer for hosting me at ESA/ESTEC in summer 2010 and opening doors to many future trips and
collaborations with Europe. Colleagues have played an integral part of my educational experience. Thank you,
Dani (now Prof. Daniel Selva) for support whenever I called for it, Farah for teaching me boatloads about
Aero/Astro as a social environment, Morgan for being my first host at Cambridge and continuing to make me
feel at home always, Danielle for introducing me to Charles Gatebe, Sydney for manning SERG and 33-409
almost as long as I did, James for keeping my TPP connections alive, Tom for teaching me tons about the
international space tech business, Evan, Maria, Alessandra, Laura, Jillian and Weston for listening to my last-
minute review requests, Koki, Narek, Ioana and many other SSLers and SERGers for making my association
with the two groups a very memorable one.

Finally, and most importantly, I would like to thank my family and friends for being my rock through
the turbulent sea of excitement and the directionless free-fall called Grad School. Big hugs for Diviya and
Rachel for being my Cambridge family; Cindy for being the best roommate one can ever hope to find on
Craiglist!; Arish for teaching me true feminism and for always believing in me; Sahil for showing me a whole,
new world; Mudit for brainstorming about careers; Abhik for sharing “Being not-so Bengali”, Sonam, Grace,
Morgan, Sheekha, Adity, Nihit, Harshad, Srinath, DC, Sisir, Murthy, Amrit, Vilas for being great company as
well as friends in need. My world would be incomplete without Mumu/mommy, Mashoon/aunt,
Didoon/grandma and Dadoon/grandpa. I owe the contented solace behind my energy and passion to them.

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Table of Contents

Acknowledgements ............................................................................................................................................................. 7
Table of Contents ............................................................................................................................................................... 9
Table of Figures ................................................................................................................................................................ 13
Table of Tables .................................................................................................................................................................. 17
Glossary .............................................................................................................................................................................. 19
Table of Symbols .............................................................................................................................................................. 21
I. Introduction............................................................................................................................................................... 23
I-1. Distributed Spacecraft Missions ................................................................................................................... 23
I-2. Space-based Earth Observation ................................................................................................................... 23
I-3. Angular Sampling in Earth Observation .................................................................................................... 24
II. Problem Statement and Research Objectives ................................................................................................. 27
II-1. Problem Statements ....................................................................................................................................... 27
II-2. Thesis Scope .................................................................................................................................................... 27
II-3. Thesis Objectives ............................................................................................................................................ 28
II-4. Thesis Outline ................................................................................................................................................. 29
III. Literature Review ................................................................................................................................................ 31
III-1. Gap Analysis in current Multi-Angular Acquisition ................................................................................. 31
III-1.1. BRDF Importance and Applications ................................................................................................. 31
III-1.2. BRDF Modeling .................................................................................................................................... 34
III-1.3. Current Multi-Angular Acquisition Methods .................................................................................... 37
III-1.4. Gap Identification #1 ........................................................................................................................... 40
III-2. Distributed Mission Design Methodologies .............................................................................................. 40
III-2.1. Small Satellite Nomenclature ............................................................................................................... 41
III-2.2. Model-Based Systems Engineering (MBSE) ..................................................................................... 43
III-2.3. Observing System Simulation Experiments (OSSE) ....................................................................... 43
III-2.4. Gap Identification #2 ........................................................................................................................... 44
III-3. Application of DSMs for Multi-Angular Acquisition ............................................................................... 44
III-3.1. Formation Flight Solutions .................................................................................................................. 44
III-3.2. Constellation Design ............................................................................................................................. 48
III-3.3. Payload Customization ......................................................................................................................... 49
III-3.4. Supporting Small Satellite Technologies ............................................................................................ 51
III-3.5. Gap Identification #3 ........................................................................................................................... 55
III-4. Cost Models for Small Satellite DSMs ........................................................................................................ 56
III-4.1. Existing Cost Models ............................................................................................................................ 56
III-4.2. Costing multiple copies in DSMs ....................................................................................................... 58
III-4.3. Launch Cost Modeling ......................................................................................................................... 58
III-4.4. Risk and Uncertainty Assessment ....................................................................................................... 59
III-4.5. Capturing Complexity ........................................................................................................................... 60
III-4.6. System Dynamics................................................................................................................................... 61
III-4.7. Gap Identification #4 ........................................................................................................................... 62
III-5. Chapter Summary ........................................................................................................................................... 62
IV. Approach and Methodology.............................................................................................................................. 65
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IV-1. Overall Approach ........................................................................................................................................... 65
IV-2. Systems Engineering Model (MBSE-driven) ............................................................................................. 66
IV-2.1. Constellation and Formation Flight Design...................................................................................... 69
IV-2.2. Imaging Modes ...................................................................................................................................... 70
IV-2.3. Payload Customization ......................................................................................................................... 71
IV-2.4. Cost Model and Results from Development .................................................................................... 76
IV-3. Science Performance Evaluation Model (OSSE-driven) ......................................................................... 85
IV-3.1. Radiation Integration and Spherical Harmonics .............................................................................. 87
IV-3.2. Data from Cloud Absorption Radiometer ........................................................................................ 89
IV-3.3. Data from AMSPEC II - the Automated Multi-angular SPECtro-radiometer ........................... 92
IV-3.1. Radiative Transfer Model data modulated with CAR data ............................................................. 94
IV-3.2. Formations applied to Snow Albedo and Vegetation BRDF ........................................................ 95
IV-4. Chapter Summary ......................................................................................................................................... 102
V. Results for Orbit and Observing System Simulation Sensitivity ............................................................... 105
V-1. Sensitivity Analysis of Science Models ...................................................................................................... 105
V-1.1. Sensitivity to Wavelength ................................................................................................................... 106
V-1.2. Sensitivity to BRDF Models .............................................................................................................. 107
V-1.3. Sensitivity to Measurement Angular Spread per Surface type ...................................................... 110
V-1.4. Dependence on Solar Zenith Angle ................................................................................................. 113
V-1.5. Dependence on Number of Satellites .............................................................................................. 114
V-2. Streamlining the Formation Flight Architectures .................................................................................... 116
V-3. Impact of Imaging Modes in Formations................................................................................................. 127
V-3.1. Baseline Formation Comparison (Mode #1) .................................................................................. 128
V-3.2. Changing the Reference Satellites (Mode #2) ................................................................................ 131
V-3.3. Impact of Tracking Ground Spots (Mode #3) ............................................................................... 133
V-4. Streamlining Constellation Architectures ................................................................................................. 138
V-5. Impact of Constellations in measuring Global Radiation ...................................................................... 143
V-6. Chapter Summary ......................................................................................................................................... 145
VI. Results for Payload and Subsystem Feasibility ............................................................................................. 147
VI-1. Concept of Operations ................................................................................................................................ 147
VI-2. Imager Payload .............................................................................................................................................. 148
VI-2.1. Spectral Element Options and Customization ............................................................................... 149
VI-2.2. Modeling Results ................................................................................................................................. 155
VI-2.3. Payload System Performance ............................................................................................................ 163
VI-2.4. Communication System Constraints on Performance .................................................................. 170
VI-3. Attitude Determination and Control ......................................................................................................... 170
VI-3.1. Overlapping Ground Spots for Co-Pointing .................................................................................. 172
VI-3.2. Slewing Maneuvers for Co-Pointing ................................................................................................ 175
VI-3.3. Control against Secular Disturbances .............................................................................................. 178
VI-4. Propulsion ...................................................................................................................................................... 178
VI-4.1. Distributed Satellite Initialization ..................................................................................................... 178
VI-4.2. Maintenance against Relative Secular Disturbances ...................................................................... 181
VI-4.3. Preliminary Propulsion Budget ......................................................................................................... 188
VI-5. Communication ............................................................................................................................................ 189
VI-5.1. Available Ground Stations and Frequency Bands ......................................................................... 189
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