-
D. Williams Rogers, D. Won, D. Koh, K. Hong, and
H. Lee,
"Optimal Satellite Constellation Configuration Design: A Collection of Mixed Integer
Linear Programs,"
Journal of Spacecraft and Rockets, doi: 10.2514/1.A36518, (Article in
Advance).
Abstract: Designing satellite constellation systems involves complex
multidisciplinary optimization in which coverage serves as a primary driver
of overall system cost and performance. Among the various design considerations,
constellation configuration, which dictates how satellites are placed and
distributed in space relative to each other, predominantly determines the
resulting coverage. In constellation configuration design, coverage may be
treated either as an optimization objective or as a constraint, depending
on mission goals. The state-of-the-art literature addresses each mission
scenario on a case-by-case basis, employing distinct assumptions, modeling
techniques, and solution methods. While such problem-specific approaches
yield valuable insights, users often face implementation challenges when
performing tradeoff studies across different mission scenarios, as each scenario
must be handled distinctly. In this paper, we propose a collection of five
mixed-integer linear programs that are of practical significance, extensible
to more complex mission narratives through additional constraints, and capable
of obtaining provably optimal constellation configurations. The framework
can handle various metrics and mission scenarios, such as percent coverage,
average or maximum revisit times, a fixed number of satellites, spatiotemporally
varying coverage requirements, and static or dynamic targets. The paper presents
several case studies and comparative analyses to demonstrate the versatility
of the proposed framework.
@article{WilliamsRogers2025,
author = {{Williams Rogers}, David O. and Won, Dongshik and Koh, Dongwook and Hong, Kyungwoo and Lee, {Hang Woon}},
title = {Optimal Satellite Constellation Configuration Design: A Collection of Mixed Integer Linear Programs},
journal = {Journal of Spacecraft and Rockets},
volume = {0},
number = {0},
pages = {1-18},
year = {0},
doi = {10.2514/1.A36518}
}
-
S. Paul and
H. Lee,
"Hybrid Sensing for Near-Earth Space Domain Awareness: Leveraging Space-Based Assets
for Augmenting Optical Ground Observations,"
The Journal of the Astronautical Sciences, vol. 73, no. 1, 2026, doi:
10.1007/s40295-025-00546-y.
Abstract: Because of recent advancements in space technologies, easier
and more economical access to space, and an increase in commercial interests,
the near-Earth space environment has witnessed an exploding number of objects
being put into orbit. In particular, the low Earth orbit (LEO) region is
at an increased risk of orbital collisions from large satellite constellation
projects. Thus, monitoring LEO objects for space domain awareness and space
traffic management has become increasingly imperative. In this paper, we
use the concept of limited-CDF (cumulative distribution function) surface
and mutual information for designing sensor tasking algorithms focusing on
regular observation of known catalog LEO objects (follow-up). Observations
are carried out using simulated ground-based optical telescope(s). The simulations
are representative of realistic observation processes. We investigate how
data from passive space-based sensors can be used to improve the follow-up
performance of the telescope(s). A sensor-tasking framework is developed
in which we conduct a comparative study to assess how different types of
satellite constellation patterns such as Walker-Delta and Walker-Star affect
the overall sensor tasking performance. Through several case studies, we
(1) analyze the appropriate characteristics of the parameters to be optimized
and their impact on the evolution of orbital state uncertainties, (2) compare
different traditional and non-traditional algorithms for sensor tasking problem,
(3) investigate the effect of measurements from different constellation configurations
of passive space-based sensor, and (4) identify a suitable coordinate system
for the limited-CDF surface construction.
@article{Paul2026,
author = {Paul, {Smriti Nandan} and Lee, {Hang Woon}},
title = {Hybrid Sensing for Near-Earth Space Domain Awareness: Leveraging Space-Based Assets for Augmenting Optical Ground Observations},
journal = {The Journal of the Astronautical Sciences},
volume = {73},
number = {1},
year = {2026},
doi = {https://doi.org/10.1007/s40295-025-00546-y}
-
B. Pearl,
J. Miller, and
H. Lee,
"Reconfigurable Earth Observation Satellite Scheduling Problem,"
Journal of Aerospace Information Systems, vol. 23, no. 2, pp. 136-154,
2026, doi: 10.2514/1.I011659.
Abstract: Earth observation satellites (EOSs) play a pivotal role in
capturing and analyzing planetary phenomena, ranging from natural disasters
to societal development. The EOS scheduling problem (EOSSP), which optimizes
the schedule of EOSs, is often solved with respect to nadir-directional EOS
systems, thus restricting the observation time of targets and, consequently,
the effectiveness of each EOS. This paper leverages state-of-the-art constellation
reconfigurability to develop the reconfigurable EOS scheduling problem (REOSSP),
wherein EOSs are assumed to be maneuverable, forming a more optimal constellation
configuration at multiple opportunities during a schedule. This paper develops
a novel mixed-integer linear programming formulation for the REOSSP to optimally
solve the scheduling problem for given parameters. Additionally, since the
REOSSP can be computationally expensive for large-scale problems, a rolling
horizon procedure (RHP) solution method is developed. The performance of
the REOSSP is benchmarked against the EOSSP, which serves as a baseline,
through a set of random instances where problem characteristics are varied
and a case study in which Hurricane Sandy is used to demonstrate realistic
performance. These experiments demonstrate the value of constellation reconfigurability
in its application to the EOSSP, yielding solutions that improve performance,
while the RHP enhances computational runtime for large-scale REOSSP instances.
@article{Pearl2025,
author = {Pearl, Brycen D. and Miller, Joseph M. and Lee, {Hang Woon}},
title = {Reconfigurable Earth Observation Satellite Scheduling Problem},
journal = {Journal of Aerospace Information Systems},
volume = {23},
number = {2},
pages = {136-154},
year = {2026},
doi = {10.2514/1.I011659}
}
-
A. Abdul-Hamid,
B. Pearl,
H. Lee, and H. Chen,
"Space Logistics Analysis and Incentive Design for Commercialization of Orbital
Debris Remediation,"
Journal of Spacecraft and Rockets, vol. 63, no. 1, pp. 218-230, 2026,
doi: 10.2514/1.A36465.
Abstract: As orbital debris continues to become a higher priority for
the space industry, there is a need to explore how partnerships between the
public and private space sectors may aid in addressing this issue. This research
develops a space logistics framework for planning orbital debris remediation
missions, providing a quantitative basis for partnerships that are mutually
beneficial between space operators and debris remediators. By integrating
network-based space logistics and game theory, we illuminate the high-level
costs of remediating orbital debris and the surplus that stands to be shared
as a result. These findings indicate significant progress toward the continued
development of a safe, sustainable, and profitable space economy.
@article{Abdu-Hamid2025,
author = {Abdul-Hamid, Asaad and Pearl, Brycen D. and Lee, {Hang Woon} and Chen, Hao},
title = {Space Logistics Analysis and Incentive Design for Commercialization of Orbital Debris Remediation},
journal = {Journal of Spacecraft and Rockets},
volume = {63},
number = {1},
pages = {218-230},
year = {2026},
doi = {10.2514/1.A36465}
}
-
D. Williams Rogers,
M. Fox, P. Stysley, and
H. Lee,
"Optimal Placement and Coordinated Scheduling of Distributed Space-Based Lasers
for Orbital Debris Remediation,"
Advances in Space Research, vol. 76, no. 9, pp. 5265-5293, 2025, doi:
10.1016/j.asr.2025.07.093.
Abstract: The significant expansion of the orbital debris population
poses a serious threat to the safety and sustainability of space operations.
This paper investigates orbital debris remediation through a constellation
of collaborative space-based lasers, leveraging the principle of momentum
transfer onto debris via laser ablation. A novel delta-v vector analysis
framework quantifies the cumulative effects of multiple concurrent laser-to-debris
(L2D) engagements by utilizing the vector composition of the imparted delta-v
vectors. The paper formulates the Concurrent Location-Scheduling Optimization
Problem (CLSP) to optimize the placement of laser platforms and the scheduling
of L2D engagements, aiming to maximize debris remediation capacity. Given
the computational intractability of the CLSP, a decomposition strategy is
employed, yielding two sequential subproblems: (1) determining optimal laser
platform locations via the Maximal Covering Location Problem, and (2) scheduling
L2D engagements using a novel integer linear programming approach to maximize
debris remediation capacity. Computational experiments evaluate the efficacy
of the proposed framework across diverse mission scenarios, demonstrating
critical constellation functions such as collaborative and controlled nudging,
deorbiting, and just-in-time collision avoidance. A sensitivity analysis
further explores the impact of varying the number and distribution of laser
platforms on debris remediation capacity, offering insights into optimizing
the performance of space-based laser constellations.
@article{WilliamsRogers2025,
author = {{Williams Rogers}, David O. and Fox, Matthew C. and Stysley, Paul R. and Lee, {Hang Woon}},
title = {Optimal placement and coordinated scheduling of distributed space-based lasers for orbital debris remediation},
journal = {Advances in Space Research},
volume = {76},
number = {9},
pages = {5265-5293},
year = {2025},
doi = {https://doi.org/10.1016/j.asr.2025.07.093}
}
-
E. Gkaravela,
H. Lee, and H. Chen,
"Distributed Space Resource Logistics Architecture Optimization under Economies
of Scale,"
Journal of Spacecraft and Rockets, vol. 62, no. 5, pp. 1654-1666, 2025,
doi: 10.2514/1.A36271.
Abstract: This paper proposes an optimization framework for distributed
resource logistics system design to support future multimission space exploration.
The performance and impact of distributed in-situ resource utilization (ISRU)
systems in facilitating space transportation are analyzed. The proposed framework
considers technology trade studies, deployment strategy, facility location
evaluation, and resource logistics after production for distributed ISRU
systems. We develop piecewise linear sizing and cost estimation models based
on economies of scale that can be easily integrated into network-based mission
planning formulations. A case study on a multimission cislunar logistics
campaign is conducted to demonstrate the value of the proposed method and
evaluate key tradeoffs to compare the performance of distributed ISRU systems
with traditional concentrated ISRU. Finally, a comprehensive sensitivity
analysis is performed to assess the proposed system under varying conditions,
comparing concentrated and distributed ISRU systems.
@article{Gkaravela2024,
author = {Gkaravela, Evangelia and Lee, {Hang Woon} and Chen, Hao},
title = {Distributed Space Resource Logistics Architecture Optimization Under Economies of Scale},
journal = {Journal of Spacecraft and Rockets},
volume = {62},
number = {6},
pages = {1654-1666},
year = {2025},
doi = {10.2514/1.A36271}
}
-
B. Pearl,
L. Gold, and
H. Lee,
"Benchmarking Agility and Reconfigurability in Satellite Systems for Tropical
Cyclone Monitoring,"
Journal of Spacecraft and Rockets, vol. 62, no. 4, pp. 1138-1151, 2025,
doi: 10.2514/1.A36177.
Abstract: Tropical cyclones (TCs) are highly dynamic natural disasters
that travel vast distances and occupy a large spatial scale, leading to loss
of life, economic strife, and destruction of infrastructure. The severe impact
of TCs makes them crucial to monitor such that the collected data contribute
to forecasting their trajectory and severity, as well as the provision of
information to relief agencies. Among the various methods used to monitor
TCs, Earth observation satellites are the most flexible, allowing for frequent
observations with a wide variety of instruments. Traditionally, satellite
scheduling algorithms assume nadir-directional observations, a limitation
that can be alleviated by incorporating satellite agility and constellation
reconfigurability—two state-of-the-art concepts of operations (CONOPS) that
extend the amount of time TCs can be observed from orbit. This paper conducts
a systematic comparative analysis between both CONOPS to present the performance
of each relative to baseline nadir-directional observations in monitoring
TCs. A dataset of 100 historical TCs is used to provide a benchmark concerning
real-world data through maximizing the number of quality observations. The
results of the comparative analysis indicate that constellation reconfigurability
allowing plane-change maneuvers outperforms satellite agility in the majority
of TCs analyzed.
@article{Pearl2023,
author = {Pearl, Brycen D. and Gold, Logan P. and Lee, {Hang Woon}},
title = {Benchmarking Agility and Reconfigurability in Satellite Systems for Tropical Cyclone Monitoring},
journal = {Journal of Spacecraft and Rockets},
volume = {60},
number = {6},
pages = {1811-1824},
year = {2023},
doi = {10.2514/1.A36177}
}
-
T. H. Clareson,
M. Fox,
D. Amato, and
H. Lee,
"Embedded State Estimation for Optimization of Cislunar Space Domain Awareness
Constellation Design,"
Journal of Spacecraft and Rockets, vol. 62, no. 3, pp. 898-914, 2025,
doi: 10.2514/1.A36102.
Abstract: The traffic in cislunar space is expected to increase over
the coming years, leading to a higher likelihood of conjunction events among
active satellites, orbital debris, and noncooperative satellites. This increase
necessitates enhanced space domain awareness (SDA) capabilities that include
state estimation for targets of interest. Both Earth surface-based and space-based
observation platforms in geosynchronous orbit or below face challenges such
as range, exclusion, and occlusion that hinder observation. Motivated by
the need to place space-based observers in the cislunar space regime to overcome
these challenges, this paper proposes a cislunar SDA constellation design
and analysis framework that integrates state estimation into an optimization
problem for determining the placement of observers for optimal state estimation
performance on a set of targets. The proposed multiobserver placement optimization
problem samples from a range of possible target orbits. Upon convergence,
the optimized constellation is validated against a broader set of targets
to assess its effectiveness. Two comparative analyses are presented to evaluate
the effects of changes in the sensor tasking procedure and sensor fidelity
on the optimized constellation, comparing these to a single observer baseline
case. The results demonstrate that the optimized constellations can provide
accurate state estimation for various orbit families.
@article{Clareson2025,
author = {Clareson, Thomas H. and Fox, Matthew C. and Amato, Dominic K. and Lee, {Hang Woon}},
title = {Embedded State Estimation for Optimization of Cislunar Space Domain Awareness Constellation Design},
journal = {Journal of Spacecraft and Rockets},
volume = {62},
number = {3},
pages = {898-914},
year = {2025},
doi = {10.2514/1.A36102}
}
-
H. Lee,
D. Williams Rogers,
B. Pearl, H. Chen, and K. Ho,
"Deterministic Multistage Constellation Reconfiguration Using Integer Programming
and Sequential Decision-Making Methods,"
Journal of Spacecraft and Rockets, vol. 62, no. 1, pp. 206-222, 2025,
doi: 10.2514/1.A35990.
Abstract: This paper addresses the problem of reconfiguring Earth observation
satellite constellation systems through multiple stages. The Multistage Constellation
Reconfiguration Problem (MCRP) aims to maximize the total observation rewards
obtained by covering a set of targets of interest through the active manipulation
of the orbits and relative phasing of constituent satellites. This paper
considers deterministic problem settings in which the targets of interest
are known a priori. We propose a novel integer linear programming formulation
for MCRP, capable of obtaining provably optimal solutions. To overcome computational
intractability due to the combinatorial explosion in solving large-scale
instances, we introduce two computationally efficient sequential decision-making
methods based on the principles of a myopic policy and a rolling horizon
procedure. The computational experiments demonstrate that the devised sequential
decision-making approaches yield high-quality solutions with improved computational
efficiency over the baseline MCRP. Finally, a case study using Hurricane
Harvey data showcases the advantages of multistage constellation reconfiguration
over single-stage and no-reconfiguration scenarios.
@article{Lee2025,
author = {Lee, {Hang Woon} and Williams Rogers, David O. and Pearl, Brycen D. and Chen, Hao and Ho, Koki},
title = {Deterministic Multistage Constellation Reconfiguration Using Integer Programming and Sequential Decision-Making Methods},
journal = {Journal of Spacecraft and Rockets},
volume = {62},
number = {1},
pages = {206-222},
year = {2025},
doi = {10.2514/1.A35990}
}
-
M. Patel, Y. Shimane,
H. Lee, and K. Ho,
"Cislunar Satellite Constellation Design Via Integer Linear Programming,"
The Journal of the Astronautical Sciences, vol. 71, no. 26, 2024, doi:
10.1007/s40295-024-00445-8.
Abstract: Cislunar space domain awareness is of increasing interest to
the international community as Earth-Moon traffic is projected to increase,
which raises the problem of placing space-based sensors optimally in a constellation
to satisfy the space domain awareness demand in cislunar space. This demand
profile can vary over space and time, making the design optimization problem
challenging. This paper tackles the problem of satellite constellation design
for spatio-temporally varying coverage demand by leveraging an integer linear
programming formulation. The developed optimization formulation assumes the
circular restricted 3-body dynamics and attempts to minimize the number of
satellites required for the requested demand profile.
@article{Patel2024,
author = {Patel, Malav and Shimane, Yuri and Lee, {Hang Woon} and Ho, Koki},
title = {Cislunar Satellite Constellation Design via Integer Linear Programming},
journal = {The Journal of the Astronautical Sciences},
volume = {71},
number = {3},
pages = {26},
year = {2024},
doi = {10.1007/s40295-024-00445-8}
}
-
H. Lee and K. Ho,
"Regional Constellation Reconfiguration Problem: Integer Linear Programming
Formulation and Lagrangian Heuristic Method,"
Journal of Spacecraft and Rockets, vol. 60, no. 6, pp. 1828-1845, 2023,
doi: 10.2514/1.A35685.
Abstract: A group of satellites, with either homogeneous or heterogeneous
orbital characteristics and/or hardware specifications, can undertake a reconfiguration
process due to variations in operations pertaining to Earth observation missions.
This paper investigates the problem of optimizing a satellite constellation
reconfiguration process against two competing mission objectives: 1) the
maximization of the total coverage reward, and 2) the minimization of the
total cost of the transfer. The decision variables for the reconfiguration
process include the design of the new configuration and the assignment of
satellites from one configuration to another. We present a novel biobjective
integer linear programming formulation that combines constellation design
and transfer problems. The formulation lends itself to the use of generic
mixed-integer linear programming (MILP) methods such as the branch-and-bound
algorithm for the computation of provably optimal solutions; however, these
approaches become computationally prohibitive even for moderately sized instances.
In response to this challenge, this paper proposes a Lagrangian relaxation-based
heuristic method that leverages the assignment problem structure embedded
in the problem. The results from the computational experiments attest to
the near-optimality of the Lagrangian heuristic solutions and a significant
improvement in the computational runtime as compared to a commercial MILP
solver.
@article{Lee2023,
author = {Lee, {Hang Woon} and Ho, Koki},
title = {Regional Constellation Reconfiguration Problem: Integer Linear Programming Formulation and Lagrangian Heuristic Method},
journal = {Journal of Spacecraft and Rockets},
volume = {60},
number = {6},
pages = {1828-1845},
year = {2023},
doi = {10.2514/1.A35685}
}
-
H. Lee, S. Shimizu, S. Yoshikawa, and K. Ho,
"Satellite Constellation Pattern Optimization for Complex Regional Coverage,"
Journal of Spacecraft and Rockets, vol. 57, no. 6, pp. 1309-1327, 2020,
doi: 10.2514/1.A34657.
Abstract: The use of regional-coverage satellite constellations is on
the rise, urging the need for an optimal constellation design method for
complex regional coverage. Traditional constellations are often designed
for continuous global coverage, and the few existing regional constellation
design methods lead to suboptimal solutions for periodically time-varying
or spatially varying regional-coverage requirements. This paper introduces
a new general approach to design an optimal constellation pattern that satisfies
such complex regional-coverage requirements. To this end, the circular convolution
nature of the repeating ground-track orbit and common ground-track constellation
is formalized. This formulation enables a scalable constellation pattern
analysis for multiple target areas and with multiple subconstellations. The
formalized circular convolution relationship is first used to derive a baseline
constellation pattern design method with the conventional assumption of symmetry.
Next, a novel method based on binary integer linear programming is developed,
which aims to optimally design a constellation pattern with the minimum number
of satellites. This binary integer linear programming method is shown to
achieve optimal constellation patterns for general problem settings that
the baseline method cannot achieve. Five illustrative examples are analyzed
to demonstrate the value of the proposed new approach.
@article{Lee2020,
author = {Lee, {Hang Woon} and Shimizu, Seiichi and Yoshikawa, Shoji and Ho, Koki},
title = {Satellite Constellation Pattern Optimization for Complex Regional Coverage},
journal = {Journal of Spacecraft and Rockets},
volume = {57},
number = {6},
pages = {1309-1327},
year = {2020},
doi = {10.2514/1.A34657}
}
-
H. Chen,
H. Lee, and K. Ho,
"Space Transportation System and Mission Planning for Regular Interplanetary
Missions,"
Journal of Spacecraft and Rockets, vol. 56, no. 1, pp. 12-20, 2019, doi:
10.2514/1.A34168.
Abstract: This paper develops a computationally efficient and scalable
mission planning optimization method for regular space transportation missions,
defined as a set of repeating and periodic interplanetary transportation
missions over a long time horizon after one or a few setup missions. As more
long-term manned missions to Mars are being conceptualized, the need for
a sustainable interplanetary transportation system has become increasingly
prominent. However, planning regular transportation missions with existing
space mission planning optimization formulations has a limitation in computational
scalability in the time dimension. The proposed partially periodic time-expanded
network can address this limitation of the past studies; it is shown to be
computationally scalable and capable of generating solutions that are practically
preferred. Properties of the proposed partially periodic time-expanded network
are analyzed, and a case study reveals that the total initial mass in the
low Earth orbit of regular missions approaches to the theoretical lower bound
as the number of transportation missions increases.
@article{Chen2019,
author = {Chen, Hao and Lee, {Hang Woon} and Ho, Koki},
title = {Space Transportation System and Mission Planning for Regular Interplanetary Missions},
journal = {Journal of Spacecraft and Rockets},
volume = {56},
number = {1},
pages = {12-20},
year = {2019},
doi = {10.2514/1.A34168}
}
-
H. Lee, P. Jakob, K. Ho, S. Shimizu, and S. Yoshikawa,
"Optimization of Satellite Constellation Deployment Strategy Considering Uncertain
Areas of Interest,"
Acta Astronautica, vol. 153, pp. 213-228, 2018, doi: 10.1016/j.actaastro.2018.03.054.
Abstract: This paper presents an integrated framework to design a flexible
multi-stage telecommunication satellite configuration deployment strategy
considering the uncertainties in the evolution of the areas of interest over
time. The constructed stochastic demand model considers multiple possible
scenarios for the evolution of the areas of interest with probabilities based
on the market share growth in each area. The optimization aims to find each
stage's design with minimum expected lifecycle cost considering all possible
scenarios. Each stage of the constellation, assumed to be Flower constellation
with circular orbits, provides a regional coverage of the current area of
interest as well as additional coverage for the potential future areas of
interest. The proposed multi-stage satellite constellation enables the constellation
designer to react flexibly and efficiently to the uncertain future expansion
of the areas of interest. A case study reveals a reduction in the expected
lifecycle cost for an optimized system compared with the all-in-single-stage
system and global coverage constellation.
@article{Lee2018,
author = {Lee, {Hang Woon} and Jakob, Pauline C. and Ho, Koki and Shimizu, Seiichi and Yoshikawa, Shoji},
title = {Optimization of satellite constellation deployment strategy considering uncertain areas of interest},
journal = {Acta Astronautica},
volume = {153},
pages = {213-228},
year = {2018},
doi = {10.1016/j.actaastro.2018.03.054}
}