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Deferred-Decision Trajectory Optimization

Purnanand Elango, Selahattin Burak Sarsilmaz, Behcet Acikmese

TL;DR

Deferred-Decision Trajectory Optimization (DDTO) addresses planning under unmodeled uncertainties by maintaining a collection of reachable targets and deferring target selection until more information is available. The authors formulate constrained reachability and show its equivalence to cardinality minimization, enabling tractable optimization-based solution methods. They develop three solution approaches—ddto-qcvx (quasiconvex), ddto-micp (mixed-integer convex), and ddto-scp (sequential convex programming)—that produce trunk-and-branch trajectory structures for discrete-time affine and continuous-time nonlinear systems, demonstrated on quadrotor motion planning problems. The work provides a deterministic, information-gavorable framework with practical relevance to robust autonomous navigation and safe landing in uncertain environments, and outlines future extensions to fully closed-loop perception-driven decision-making.

Abstract

We present DDTO--deferred-decision trajectory optimization--a framework for trajectory generation with resilience to unmodeled uncertainties and contingencies. The key idea is to ensure that a collection of candidate targets is reachable for as long as possible while satisfying constraints, which provides time to quantify the uncertainties. We propose optimization-based constrained reachability formulations and construct equivalent cardinality minimization problems, which then inform the design of computationally tractable and efficient solution methods that leverage state-of-the-art convex solvers and sequential convex programming (SCP) algorithms. The goal of establishing the equivalence between constrained reachability and cardinality minimization is to provide theoretically-sound underpinnings for the proposed solution methods. We demonstrate the solution methods on real-world optimal control applications encountered in quadrotor motion planning.

Deferred-Decision Trajectory Optimization

TL;DR

Deferred-Decision Trajectory Optimization (DDTO) addresses planning under unmodeled uncertainties by maintaining a collection of reachable targets and deferring target selection until more information is available. The authors formulate constrained reachability and show its equivalence to cardinality minimization, enabling tractable optimization-based solution methods. They develop three solution approaches—ddto-qcvx (quasiconvex), ddto-micp (mixed-integer convex), and ddto-scp (sequential convex programming)—that produce trunk-and-branch trajectory structures for discrete-time affine and continuous-time nonlinear systems, demonstrated on quadrotor motion planning problems. The work provides a deterministic, information-gavorable framework with practical relevance to robust autonomous navigation and safe landing in uncertain environments, and outlines future extensions to fully closed-loop perception-driven decision-making.

Abstract

We present DDTO--deferred-decision trajectory optimization--a framework for trajectory generation with resilience to unmodeled uncertainties and contingencies. The key idea is to ensure that a collection of candidate targets is reachable for as long as possible while satisfying constraints, which provides time to quantify the uncertainties. We propose optimization-based constrained reachability formulations and construct equivalent cardinality minimization problems, which then inform the design of computationally tractable and efficient solution methods that leverage state-of-the-art convex solvers and sequential convex programming (SCP) algorithms. The goal of establishing the equivalence between constrained reachability and cardinality minimization is to provide theoretically-sound underpinnings for the proposed solution methods. We demonstrate the solution methods on real-world optimal control applications encountered in quadrotor motion planning.

Paper Structure

This paper contains 23 sections, 12 theorems, 57 equations, 7 figures, 2 tables, 2 algorithms.

Key Result

Lemma 1

Consider a trajectory $x_1,\ldots,x_N$. Then, the following statements hold:

Figures (7)

  • Figure 1: A Mars landing example where deferring decision is useful. The black trajectory segments keep a collection of candidate landing sites reachable (colored nodes). Each black node serves as a decision point beyond which reachability to one of the landing sites is lost. While the spacecraft follows the black segment, it can learn more about the terrain to determine the most viable landing site. The background image (taken by the Perseverance rover in December 2023 mars2020week149) shows examples of a priori unknown irregularities on the Martian surface which can potentially make landing sites infeasible.
  • Figure 2: A trajectory of horizon length $7$ from $z^0$ to $\mathcal{Z}^i$ passing through $\mathcal{R}^j_4$ at the fourth time node. The arguments of $\mathcal{F}_{k}$ and $\mathcal{B}_{k}$, for $k\in{[0\!:\!3]}$, are omitted for brevity.
  • Figure 3: Trajectories forming a tree-like structure (shown above) are optimal (with respect to problems \ref{['prb:gJmax']}, \ref{['prb:l0min-i']}, and \ref{['prb:l0min-best']}) whereas the trajectories with irregular clumping (shown below) are not.
  • Figure 4: Algorithms \ref{['alg:ddtoqcvx']} and \ref{['alg:ddtoscp']} recursively compute trunk and branch trajectories connected by branch points while adhering to the given target prioritization.
  • Figure 5: Algorithm \ref{['alg:ddtoqcvx']} applied to the discrete-time convex optimal control example in Appendix \ref{['app:ocp-eg-dt-cvx']}.
  • ...and 2 more figures

Theorems & Definitions (39)

  • Definition 1
  • Definition 2
  • Lemma 1
  • Proof
  • Remark 1
  • Definition 3
  • Definition 4: $\bm{k}$-reach set
  • Lemma 2
  • Proof
  • Definition 5
  • ...and 29 more