Ben Hockman

ASL Publications

S. Newdick, T. G. Chen, B. Hockman, E. Schmerling, M. R. Cutkosky, and M. Pavone, “Designing ReachBot: System Design Process with a Case Study of a Martian Lava Tube Mission,” in IEEE Aerospace Conference, Big Sky, Montana, 2023.
[BibTeX] [Abstract]

Abstract: In this paper we present a trade study-based method to optimize the architecture of ReachBot, a new robotic concept that uses deployable booms as prismatic joints for mobility in environments with adverse gravity conditions and challenging terrain. Specifically, we introduce a design process wherein we analyze the compatibility of ReachBot’s design with its mission. We incorporate terrain parameters and mission requirements to produce a final design optimized for mission-specific objectives. ReachBot’s design parameters include (1) number of booms, (2) positions and orientations of the booms on ReachBot’s chassis, (3) boom maximum extension, (4) boom cross-sectional geome-try, and (5) number of active/passive degrees-of-freedom at each joint. Using first-order approximations, we analyze the relationships between these parameters and various performance metrics including stability, manipulability, and mechanical in-terference. We apply our method to a mission where ReachBot navigates and gathers data from a martian lava tube. The resulting design is shown in Fig. 1.
```
@inproceedings{NewdickChenEtAl2023,
  author = {Newdick, S. and Chen, T. G. and Hockman, B. and Schmerling, E. and Cutkosky, M. R. and Pavone, M.},
  title = {Designing ReachBot: System Design Process with a Case Study of a Martian Lava Tube Mission},
  booktitle = {{IEEE Aerospace Conference}},
  year = {2023},
  address = {Big Sky, Montana},
  month = mar,
  doi = {10.1109/AERO55745.2023.10115893},
  owner = {jthluke},
  timestamp = {2024-09-20},
  url = {https://arxiv.org/abs/2210.11534}
}
```
B. J. Hockman, “Robotic Mobility on Small Solar System Bodies: Design, Control, and Autonomy,” PhD thesis, Stanford University, Dept. of Mechanical Engineering, Stanford, California, 2018.
[BibTeX] [Abstract]

Abstract: In this thesis, we investigate the mobility challenges associated with robotic exploration of small solar system bodies, such as comets and asteroids. We open with a discussion on the surface environment of small bodies, and in particular, how their extremely weak gravity motivates hopping as a promising form of locomotion for long-distance traverses. We then propose an adaptable rover architecture called “Hedgehog”—a minimalistic, internally-actuated, hopping rover designed for targeted mobility in such low-gravity environments. By applying internal torques to three mutually-orthogonal flywheels, the rover’s chassis rotates, giving rise to ground reaction forces and various motion primitives, including long-range hopping, short precise tumbling, and small pose adjustments. We propose various models for analyzing the dynamics of these motion primitives and derive control laws for achieving desired motions. We then discuss various methods for conducting experiments in a reduced-gravity environment, including a custom six-degree-of-freedom laboratory test bed and parabolic flights. We validate our control laws in these test beds and demonstrate unprecedented motion accuracy for internally-actuated hoppers. Finally, we broaden our focus to general hopping platforms and consider various algorithmic tools for autonomous exploration. Specifically, we develop a suite of tools for motion planning, localization, and traversability analysis, with a careful attention on the various sources of model uncertainty and the complex dynamics of hopping trajectories. Despite the stochastic nature of bouncing dynamics, we demonstrate through high-fidelity simulations that a hopping rover can efficiently traverse highly irregular bodies that would otherwise be inaccessible to traditional rovers.
```
@phdthesis{Hockman2018b,
  author = {Hockman, B. J.},
  title = {Robotic Mobility on Small Solar System Bodies: {Design,} Control, and Autonomy},
  school = {{Stanford University, Dept. of Mechanical Engineering}},
  year = {2018},
  address = {Stanford, California},
  month = jun,
  url = {https://stacks.stanford.edu/file/druid:zg590cd2343/Hockman_PhD-augmented.pdf},
  owner = {bylard},
  timestamp = {2021-12-06}
}
```
B. Hockman and M. Pavone, “Traversability of Hopping Rovers on Small Solar System Bodies,” in Int. Symp. on Artificial Intelligence, Robotics and Automation in Space, Madrid, Spain, 2018.
[BibTeX] [Abstract]

Abstract: In this paper we explore notions of traversability for hopping rovers on small solar system bodies, such as asteroids and comets, with a focus on developing actionable tools for mission planning. We start with a discussion of hopping dynamics and the inherent differences between notions of “traversability” for hopping and traditional wheeled rovers. We then discuss various map-based tools for understanding the surface gravity environment and propose an algorithm that partitions the surface into locally traversable regions. Finally, we leverage dynamic simulations to estimate k-hop backwards reachable sets—that is the surface regions from which a particular point can be reached within k hops. A case study of comet 67P demonstrates that even extremely irregular bodies may be largely traversable with an appropriate hopper design.
```
@inproceedings{Hockman2018,
  author = {Hockman, B. and Pavone, M.},
  title = {Traversability of Hopping Rovers on Small Solar System Bodies},
  booktitle = {{Int. Symp. on Artificial Intelligence, Robotics and Automation in Space}},
  year = {2018},
  address = {Madrid, Spain},
  month = jun,
  url = {/wp-content/papercite-data/pdf/Hockman.Pavone.ISAIRAS18.pdf},
  owner = {bhockman},
  timestamp = {2018-05-25}
}
```
S. Chiodini, R. G. Reid, B. Hockman, I. A. D. Nesnas, S. Debei, and M. Pavone, “Robust Visual Localization for Hopping Rovers on Small Bodies,” in Proc. IEEE Conf. on Robotics and Automation, Brisbane, Australia, 2018.
[BibTeX] [Abstract]

Abstract: We present a collaborative visual localization method for rovers designed to hop and tumble over the surface of small Solar System bodies, such as comets and asteroids. In a two-phase approach, an orbiting primary spacecraft first maps the surface of a body by capturing images from various poses and illumination angles; these images are processed to create a prior map of 3D landmarks. In the second phase, a hopping rover is deployed to the surface where it uses the prior map and a camera to perform on-board visual simultaneous localization and mapping (SLAM). Small bodies present new challenges to existing visual SLAM algorithms. Rotation periods as short as 1-12 hours, in the absence of atmospheric scattering, create high-contrast shadows that move over the surface. The constantly changing illumination angles cause landmark outliers and increase pose uncertainty. Furthermore, in this collaborative visual SLAM problem, the scene scale between spacecraft and hopping rover varies by several orders of magnitude (kilometers to centimeters). In this work, we describe how to augment ORB-SLAM2 - a state of the art visual SLAM implementation - so that it combines prior images with multiple illumination angles to handle large illumination variations. We also demonstrate how a wide field of view (FOV) camera (e.g. on a hopping rover) can relocalize to prior maps captured by a narrow FOV camera (e.g. a spacecraft navcam) to handle large scale variations. To reduce pose and scale errors accumulated while exploring the surface, we show how the rover can perform large hops to capture views of the surface that it can match to the prior map. After relocalizing, the rover’s on-board estimates are updated with a pose graph optimization and bundle adjustment. We evaluate the proposed method with sequences of images captured around a mock asteroid; illumination angles are varied while narrow and wide FOV cameras are steered along trajectories representative of orbital and hopping motions. Trajectory estimates are compared and found to be consistent with ground truth data. Evaluations suggest this method is robust to large illumination variations, scene scale changes and off-nadir camera pointing angles.
```
@inproceedings{ChiodiniReidEtAl2018,
  author = {Chiodini, S. and Reid, R. G. and Hockman, B. and Nesnas, I. A. D. and Debei, S. and Pavone, M.},
  title = {Robust Visual Localization for Hopping Rovers on Small Bodies},
  booktitle = {{Proc. IEEE Conf. on Robotics and Automation}},
  year = {2018},
  address = {Brisbane, Australia},
  month = may,
  url = {/wp-content/papercite-data/pdf/Chiodini.Reid.Hockman.ea.ICRA18.pdf},
  owner = {bhockman},
  timestamp = {2018-01-16}
}
```
B. Hockman, R. G. Reid, I. A. D. Nesnas, and M. Pavone, “Gravimetric Localization on the Surface of Small Bodies,” in IEEE Aerospace Conference, Big Sky, Montana, 2018.
[BibTeX] [Abstract]

Abstract: The localization of landers on the surface of small bodies has traditionally relied on observations from a mothership (e.g. Rosetta’s Philae lander and Hayabusa 2’s MASCOT and MINERVA landers). However, when line-of-sight with the mothership is not always available, or for surface rovers that travel large distances, alternative mothership-independent localization techniques may be required. On-board vision-based techniques have demonstrated effective localization in terrestrial applications as well as for Mars rovers, but may be unreliable on small bodies where rovers must contend with fast-moving shadows, difficulties observing absolute scale, and issues acquiring images such as dust, sun blinding, tumbling and low albedo. We investigate the feasibility of an entirely new localization approach based on surface gravimetry, where a rover can constrain its location on the surface by precisely measuring the local gravity vector. This mothership-independent localization technique is well-suited to a class of hybrid rovers that can bounce and tumble over the surface of small bodies; it is insensitive to surface illumination, and even works at night. We develop a Bayesian framework for computing localization “likelihood maps” from gravimetry (and gradiometry) data, accounting for all sensor and model uncertainties. We then propose a method for deriving landing distributions of a bouncing rover from simulation data to serve as a prior for the localization estimate. Finally, we conduct a case study on the Philae lander, where we show how this approach could have helped reject localization hypotheses and significantly narrow the areas searched for the Philae lander.
```
@inproceedings{HockmanReidEtAl2018,
  author = {Hockman, B. and Reid, R. G. and Nesnas, I. A. D. and Pavone, M.},
  title = {Gravimetric Localization on the Surface of Small Bodies},
  booktitle = {{IEEE Aerospace Conference}},
  year = {2018},
  address = {Big Sky, Montana},
  month = mar,
  url = {/wp-content/papercite-data/pdf/Hockman.Reid.Nesnas.Pavone.AeroConf18.pdf},
  owner = {bhockman},
  timestamp = {2018-01-16}
}
```
B. Hockman and M. Pavone, “Stochastic Motion Planning for Hopping Rovers on Small Solar System Bodies,” in Int. Symp. on Robotics Research, Puerto Varas, Chile, 2017.
[BibTeX] [Abstract]

Abstract: Hopping rovers have emerged as a promising platform for the future surface exploration of small Solar System bodies, such as asteroids and comets. However, hopping dynamics are governed by nonlinear gravity fields and stochastic bouncing on highly irregular surfaces, which pose several challenges for traditional motion planning methods. This paper presents the first ever discussion of motion planning for hopping rovers that explicitly accounts for various sources of uncertainty. We first address the problem of planning a single hopping trajectory by developing (1) an algorithm for robustly solving Lambert’s orbital boundary value problems in irregular gravity fields, and (2) a method for computing landing distributions by propagating control and model uncertainties—from which, a time/energy-optimal hop can be selected using a (myopic) policy gradient. We then cast the sequential planning problem as a Markov decision process and apply a sample-efficient, off-line, off-policy reinforcement learning algorithm—namely, a variant of least squares policy iteration (LSPI)—to derive approximately optimal control policies that are safe, efficient, and amenable to real-time implementation on computationally-constrained rover hardware. These policies are demonstrated in simulation to be robust to modelling errors and outperform previous heuristics.
```
@inproceedings{HockmanPavone2017,
  author = {Hockman, B. and Pavone, M.},
  title = {Stochastic Motion Planning for Hopping Rovers on Small Solar System Bodies},
  booktitle = {{Int. Symp. on Robotics Research}},
  year = {2017},
  address = {Puerto Varas, Chile},
  month = dec,
  url = {/wp-content/papercite-data/pdf/Hockman.Pavone.ISRR17.pdf},
  owner = {bhockman},
  timestamp = {2018-01-16}
}
```
R. MacPherson, B. Hockman, A. Bylard, M. A. Estrada, M. R. Cutkosky, and M. Pavone, “Trajectory Optimization for Dynamic Grasping in Space using Adhesive Grippers,” in Field and Service Robotics, Zurich, Switzerland, 2017.
[BibTeX] [Abstract]

Abstract: Spacecraft equipped with gecko-inspired dry adhesive grippers can dynamically grasp objects having a wide variety of featureless surfaces. In this paper we propose an optimization-based control strategy to exploit the dynamic robustness of such grippers for the task of grasping a free-floating, spinning object. First, we extend previous work characterizing the dynamic grasping capabilities of these grippers to the case where both object and spacecraft are free-floating and comparably sized. We then formulate the acquisition problem as a two-phase optimal control problem, which is amenable to real time implementation and can handle constraints on velocity, control, as well as integer timing constraints for grasping a specific target location on the surface of a spinning object. Conservative analytical bounds on the set of initial states that guarantee persistent feasibility are derived.
```
@inproceedings{MacPhersonHockmanEtAl2017,
  author = {MacPherson, R. and Hockman, B. and Bylard, A. and Estrada, M. A. and Cutkosky, M. R. and Pavone, M.},
  title = {Trajectory Optimization for Dynamic Grasping in Space using Adhesive Grippers},
  booktitle = {{Field and Service Robotics}},
  year = {2017},
  address = {Zurich, Switzerland},
  month = sep,
  url = {/wp-content/papercite-data/pdf/MacPherson.Hockman.Bylard.ea.FSR17.pdf},
  owner = {bylard},
  timestamp = {2018-01-16}
}
```
A. Bylard, R. MacPherson, B. Hockman, M. R. Cutkosky, and M. Pavone, “Robust Capture and Deorbit of Rocket Body Debris Using Controllable Dry Adhesion,” in IEEE Aerospace Conference, Big Sky, Montana, 2017.
[BibTeX] [Abstract]

Abstract: Removing large orbital debris in a safe, robust, and cost-effective manner is a long-standing challenge, having serious implications for LEO satellite safety and access to space. Many studies have focused on the deorbit of spent rocket bodies (R/Bs) as an achievable and high-priority first step. However, major difficulties arise from the R/Bs’ residual tumble and lack of traditional docking/grasping fixtures. Previously investigated docking strategies often require complex and risky approach maneuvers or have a high chance of producing additional debris. To address this challenge, this paper investigates the use of controllable dry adhesives (CDAs), also known as gecko-inspired adhesives, as an alternative approach to R/B docking and deorbiting. CDAs are gathering interest for in-space grasping and manipulation due to their ability to controllably attach to and detach from any smooth, clean surface, including flat and curved surfaces. Such capability significantly expands the number and types of potential docking locations on a target. CDAs are also inexpensive, are space-qualified (performing well in a vacuum, in extreme temperatures, and under radiation), and can attach and detach while applying minimal force to a target surface, all important considerations for space deployment. In this paper, we investigate a notional strategy for initial capture and stabilization of a R/B having multi-axis tumble, exploiting the unique properties of CDA grippers to reduce maneuver complexity, and we propose alternatives for rigidly attaching deorbiting kits to a R/B. Simulations based on experimentally verified models of CDA grippers show that these approaches show promise as robust alternatives to previously explored methods.
```
@inproceedings{BylardMacPhersonEtAl2017,
  author = {Bylard, A. and MacPherson, R. and Hockman, B. and Cutkosky, M. R. and Pavone, M.},
  title = {Robust Capture and Deorbit of Rocket Body Debris Using Controllable Dry Adhesion},
  booktitle = {{IEEE Aerospace Conference}},
  year = {2017},
  address = {Big Sky, Montana},
  month = mar,
  url = {/wp-content/papercite-data/pdf/Bylard.MacPherson.Hockman.ea.AeroConf17.pdf},
  owner = {bylard},
  timestamp = {2017-03-07}
}
```
B. Hockman, R. G. Reid, I. A. D. Nesnas, and M. Pavone, “Experimental Methods for Mobility and Surface Operations of Microgravity Robots,” in Int. Symp. on Experimental Robotics, Tokyo, Japan, 2016.
[BibTeX] [Abstract]

Abstract: We propose an experimental method for studying mobility and surface operations of microgravity robots on zero-gravity parabolic flights - a test bed traditionally used for experiments requiring strictly zero gravity. By strategically exploiting turbulence-induced gravity fluctuations, our technique enables a new experimental approach for testing surface interactions of robotic systems in micro- to milli-gravity environments. This strategy is used to evaluate the performance of internally-actuated hopping rovers designed for controlled surface mobility on small Solar System bodies. In experiments, these rovers demonstrated a range of maneuvers on various surfaces, including both rigid and granular. Results are compared with analytical predictions and numerical simulations, yielding new insights into the dynamics and control of hopping rovers.
```
@inproceedings{HockmanReidEtAl2016,
  author = {Hockman, B. and Reid, R. G. and Nesnas, I. A. D. and Pavone, M.},
  title = {Experimental Methods for Mobility and Surface Operations of Microgravity Robots},
  booktitle = {{Int. Symp. on Experimental Robotics}},
  year = {2016},
  address = {Tokyo, Japan},
  month = oct,
  url = {/wp-content/papercite-data/pdf/Hockman.Reid.ea.ISER16.pdf},
  owner = {bylard},
  timestamp = {2017-03-07}
}
```
M. A. Estrada, B. Hockman, A. Bylard, E. W. Hawkes, M. R. Cutkosky, and M. Pavone, “Free-Flyer Acquisition of Spinning Objects with Gecko-Inspired Adhesives,” in Proc. IEEE Conf. on Robotics and Automation, Stockholm, Sweden, 2016.
[BibTeX] [Abstract]

Abstract: We explore the use of grippers with gecko-inspired adhesives for spacecraft docking and acquisition of tumbling objects in microgravity. Towards the goal of autonomous object manipulation in space, adhesive grippers mounted on planar free-floating platforms are shown to be tolerant of a range of incoming linear and angular velocities. Through modeling, simulations, and experiments, we characterize the dynamic “grasping envelope” for successful acquisition and derive insights to inform future gripper designs and grasping strategies for motion planning.
```
@inproceedings{EstradaHockmanEtAl2016,
  author = {Estrada, M. A. and Hockman, B. and Bylard, A. and Hawkes, E. W. and Cutkosky, M. R. and Pavone, M.},
  title = {Free-Flyer Acquisition of Spinning Objects with Gecko-Inspired Adhesives},
  booktitle = {{Proc. IEEE Conf. on Robotics and Automation}},
  year = {2016},
  address = {Stockholm, Sweden},
  doi = {10.1109/ICRA.2016.7487696},
  month = may,
  url = {/wp-content/papercite-data/pdf/Estrada.Hockman.Bylard.ea.ICRA16.pdf},
  owner = {bylard},
  timestamp = {2017-01-28}
}
```
B. Hockman, A. Frick, I. A. D. Nesnas, and M. Pavone, “Design, Control, and Experimentation of Internally-Actuated Rovers for the Exploration of Low-Gravity Planetary Bodies,” Journal of Field Robotics, vol. 34, no. 1, pp. 5–24, 2016.
[BibTeX] [Abstract]

Abstract: In this paper we discuss the design, control, and experimentation of internally-actuated rovers for the exploration of low-gravity (micro-g to milli-g) planetary bodies, such as asteroids, comets, or small moons. The actuation of the rover relies on spinning three internal flywheels, which allows all subsystems to be packaged in one sealed enclosure and enables the platform to be minimalistic, thereby reducing its cost. By controlling flywheels’ spin rate, the rover is capable of achieving large surface coverage by attitude-controlled hops, fine mobility by tumbling, and coarse instrument pointing by changing orientation relative to the ground. We discuss the dynamics of such rovers, their control, and key design features (e.g., flywheel design and orientation, geometry of external spikes, and system engineering aspects). We then discuss the design and control of a first-of-a-kind test bed, which allows the accurate emulation of a microgravity environment for mobility experiments and consists of a 3 DoF gimbal attached to an actively controlled gantry crane. Finally, we present experimental results on the test bed that provide key insights for control and validate the theoretical analysis.
```
@article{HockmanFrickEtAl2016,
  author = {Hockman, B. and Frick, A. and Nesnas, I. A. D. and Pavone, M.},
  title = {Design, Control, and Experimentation of Internally-Actuated Rovers for the Exploration of Low-Gravity Planetary Bodies},
  journal = {{Journal of Field Robotics}},
  volume = {34},
  number = {1},
  pages = {5--24},
  year = {2016},
  doi = {10.1002/rob.21656},
  url = {/wp-content/papercite-data/pdf/Hockman.Pavone.ea.JFR15.pdf},
  owner = {bylard},
  timestamp = {2017-08-11}
}
```
B. Hockman, A. Frick, I. A. D. Nesnas, and M. Pavone, “Design, Control, and Experimentation of Internally-Actuated Rovers for the Exploration of Low-Gravity Planetary Bodies,” in Field and Service Robotics, Toronto, Canada, 2015.
[BibTeX] [Abstract]

Abstract: In this paper we discuss the design, control, and experimentation of internally-actuated rovers for the exploration of low-gravity (micro-g to milli-g) planetary bodies, such as asteroids, comets, or small moons. The actuation of the rover relies on spinning three internal flywheels, which allows all subsystems to be packaged in one sealed enclosure and enables the platform to be minimalistic, thereby reducing its cost. By controlling flywheels’ spin rate, the rover is capable of achieving large surface coverage by attitude-controlled hops, fine mobility by tumbling, and coarse instrument pointing by changing orientation relative to the ground. We discuss the dynamics of such rovers, their control, and key design features (e.g., flywheel design and orientation, geometry of external spikes, and system engineering aspects). The theoretical analysis is validated on a first-of-a-kind 6 degree-of-freedom (DoF) microgravity test bed, which consists of a 3 DoF gimbal attached to an actively controlled gantry crane.
```
@inproceedings{HockmanFrickEtAl2015,
  author = {Hockman, B. and Frick, A. and Nesnas, I. A. D. and Pavone, M.},
  title = {Design, Control, and Experimentation of Internally-Actuated Rovers for the Exploration of Low-Gravity Planetary Bodies},
  booktitle = {{Field and Service Robotics}},
  year = {2015},
  address = {Toronto, Canada},
  doi = {10.1007/978-3-319-27702-8_19},
  url = {/wp-content/papercite-data/pdf/Hockman.Pavone.ea.FSR15.pdf},
  owner = {bylard},
  timestamp = {2017-01-28}
}
```

Contacts:

Ben Hockman

Awards:

ASL Publications