Scott R. Ploen

Bio: Scott R. Ploen is an academic researcher from California Institute of Technology. The author has contributed to research in topics: Spacecraft & Orbital station-keeping. The author has an hindex of 10, co-authored 21 publications receiving 1487 citations. Previous affiliations of Scott R. Ploen include Analysis Group & Jet Propulsion Laboratory.

A survey of spacecraft formation flying guidance and control. Part II: control

Abstract: Formation flying is defined as a set of more than one spacecraft whose states are coupled through a common control law. This paper provides a comprehensive survey of spacecraft formation flying control (FFC), which encompasses design techniques and stability results for these coupled-state control laws. We divide the FFC literature into five FFC architectures: (i) multiple-input multiple-output, in which the formation is treated as a single multiple-input, multiple-output plant, (ii) leader/follower, in which individual spacecraft controllers are connected hierarchically, (iii) virtual structure, in which spacecraft are treated as rigid bodies embedded in an overall virtual rigid body, (iv) cyclic, in which individual spacecraft controllers are connected non-hierarchically, and (v) behavioral, in which multiple controllers for achieving different (and possibly competing) objectives are combined. This survey significantly extends an overview of the FFC literature provided by Lawton, which discussed the L/F, virtual structure and behavioral architectures. We also include a brief history of the formation flying literature, and discuss connections between spacecraft FFC and other multi-vehicle control problems in the robotics and automated highway system literatures.

Convex programming approach to powered descent guidance for mars landing

Abstract: We present a convex programming algorithm for the numerical solution of the minimum fuel powered descent guidance problem associated with Mars pinpoint landing. Our main contribution is the formulation of the trajectory optimization problem, which has nonconvex control constraints, as a finite-dimensional convex optimization problem, specifically as a second-order cone programming problem. Second-order cone programming is a subclass of convex programming, and there are efficient second-order cone programming solvers with deterministic convergence properties. Consequently, the resulting guidance algorithm can potentially be implemented onboard a spacecraft for real-time applications.

A survey of spacecraft formation flying guidance and control (part 1): guidance

Abstract: This paper provides a comprehensive survey of spacecraft formation flying guidance (FTG). Here by the term guidance we mean both path planning and optimal, open loop control design.

High accuracy inertial sensors from inexpensive components

Abstract: An analytical apparatus for optimally combining measurements from N individual rate sensing devices or gyros into a single rate estimate significantly improves performance over that of any individual component device. Kalman filtering is used to combine rate sensed devices optimally in the sense of minimizing the variance of the rate error. The Riccati differential equation (RDE) associated with combining a collection of rate sensed devices is completely and exactly solved to derive to the matrix RDE. This analytic solution serves as the key for understanding all of the theoretical properties of the optimal filter, and provides a complete characterization of the final virtual rate sensed performance. In addition, the analytic RDE solution allows many practical problems to be solved that have proved essential for developing successful filter implementations. A discrete-time minimum variance filter implementation combines sensor measurements optimally.

A Comparison of Powered Descent Guidance Laws for Mars Pinpoint Landing.

Abstract: I. Abstract In this paper, we formulate and compare a number of powered terminal descent guidance algorithms for Mars pinpoint landing (PPL). The PPL guidance problem involves finding a trajectory that transfers the spacecraft from any g iven state at engine ignition to a desired terminal state (usually within 100m of a desired target) without violating fuel limits or any state constraints and control constraints. Sp ecifically, we first formulate the fuel-optimal guidance problem and show that a direct method can be used to reduce it to a finite-dimensional convex program. Modern interior point methods can then be used to find the global solution to any desired level of accuracy. Nex t, we discuss a class of suboptimal guidance laws based on simple polynomial basis functions. The performance of the sub-optimal guidance laws under a variety of realistic mission constraints are compared to the global fuel-optimal solution.

A survey of multi-agent formation control

Abstract: We present a survey of formation control of multi-agent systems. Focusing on the sensing capability and the interaction topology of agents, we categorize the existing results into position-, displacement-, and distance-based control. We then summarize problem formulations, discuss distinctions, and review recent results of the formation control schemes. Further we review some other results that do not fit into the categorization.

ECOS: An SOCP solver for embedded systems

Abstract: In this paper, we describe the embedded conic solver (ECOS), an interior-point solver for second-order cone programming (SOCP) designed specifically for embedded applications. ECOS is written in low footprint, single-threaded, library-free ANSI-C and so runs on most embedded platforms. The main interior-point algorithm is a standard primal-dual Mehrotra predictor-corrector method with Nesterov-Todd scaling and self-dual embedding, with search directions found via a symmetric indefinite KKT system, chosen to allow stable factorization with a fixed pivoting order. The indefinite system is solved using Davis' SparseLDL package, which we modify by adding dynamic regularization and iterative refinement for stability and reliability, as is done in the CVXGEN code generation system, allowing us to avoid all numerical pivoting; the elimination ordering is found entirely symbolically. This keeps the solver simple, only 750 lines of code, with virtually no variation in run time. For small problems, ECOS is faster than most existing SOCP solvers; it is still competitive for medium-sized problems up to tens of thousands of variables.

A survey of spacecraft formation flying guidance and control. Part II: control

Abstract: Formation flying is defined as a set of more than one spacecraft whose states are coupled through a common control law. This paper provides a comprehensive survey of spacecraft formation flying control (FFC), which encompasses design techniques and stability results for these coupled-state control laws. We divide the FFC literature into five FFC architectures: (i) multiple-input multiple-output, in which the formation is treated as a single multiple-input, multiple-output plant, (ii) leader/follower, in which individual spacecraft controllers are connected hierarchically, (iii) virtual structure, in which spacecraft are treated as rigid bodies embedded in an overall virtual rigid body, (iv) cyclic, in which individual spacecraft controllers are connected non-hierarchically, and (v) behavioral, in which multiple controllers for achieving different (and possibly competing) objectives are combined. This survey significantly extends an overview of the FFC literature provided by Lawton, which discussed the L/F, virtual structure and behavioral architectures. We also include a brief history of the formation flying literature, and discuss connections between spacecraft FFC and other multi-vehicle control problems in the robotics and automated highway system literatures.

Mars Exploration Entry, Descent, and Landing Challenges

Abstract: The United States has successfully landed five robotic systems on the surface of Mars. These systems all had landed mass below 0.6 metric tons (t), had landed footprints on the order of hundreds of km and landed at sites below -1 km MOLA elevation due the need to perform entry, descent and landing operations in an environment with sufficient atmospheric density. Current plans for human exploration of Mars call for the landing of 40-80 t surface elements at scientifically interesting locations within close proximity (10's of m) of pre-positioned robotic assets. This paper summarizes past successful entry, descent and landing systems and approaches being developed by the robotic Mars exploration program to increased landed performance (mass, accuracy and surface elevation). In addition, the entry, descent and landing sequence for a human exploration system will be reviewed, highlighting the technology and systems advances required.

Convex programming approach to powered descent guidance for mars landing

Abstract: We present a convex programming algorithm for the numerical solution of the minimum fuel powered descent guidance problem associated with Mars pinpoint landing. Our main contribution is the formulation of the trajectory optimization problem, which has nonconvex control constraints, as a finite-dimensional convex optimization problem, specifically as a second-order cone programming problem. Second-order cone programming is a subclass of convex programming, and there are efficient second-order cone programming solvers with deterministic convergence properties. Consequently, the resulting guidance algorithm can potentially be implemented onboard a spacecraft for real-time applications.