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Simulation

Fig. 1: Rendering of a simulated MER rover in simulated terrain.
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Fig. 1: Rendering of a simulated MER rover in simulated terrain.
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The JPL Mobility and Robotic Systems Section has a broad spectrum of modeling and simulation capabilities in support of surface and near-surface robotic-exploration technologies and missions. A family of models supports mission domains that include surface exploration- with planetary rovers, sample acquisition, entry/descent/landing, safe landing, legged mobility platforms, aerobots, and subsurface exploration. The simulations are used in a number of ways:

  • Early system design and technology development,
  • Algorithm development,
  • Mission analysis and design,
  • Onboard-software integration and testing,
  • System verification and validation, and
  • Surface mission operations.

New concept and technology-development activities typically develop models to assist in the design trades and performance analysis of the robotic system. CAD models are used for platform design of systems such as rover vehicles and manipulators.

Fig. 2: Plan view of terrain evaluation from the MER GESTALT navigation algorithm running under simulation.
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Fig. 2: Plan view of terrain evaluation from the MER GESTALT navigation algorithm running under simulation.
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Algorithm development for autonomous navigation, manipulation, safe-landing and aerobot systems are developed and evaluated using physics-based models. The simulations for these cases can involve optimization (e.g. genetic algorithm) techniques for tuning the performance on workstations and high-performance clusters.

Mission analysis has been used for landing, where Monte Carlo simulation is used to derive statistical performance metrics. Simulation models of sensors, mobility-platform kinematics and dynamics, atmospheric and surface environments, cameras, sensors and actuators, and terrain environments are all used as components of integrated models.

When algorithms are implemented as onboard software, they are run on robotic hardware platforms and test beds as a key part of their performance evaluation. However, such testing can be time-consuming and expensive, and is often limited to a narrow spectrum of environments. Closed-loop simulations complement such hardware test beds, and provide a cost-effective way to test and integrate the onboard software across a wide range of operational scenarios.

Fig. 3: Elevation map of a terrain patch in front.
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Fig. 3: Elevation map of a terrain patch in front.
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The simulators are also designed to provide good real-time performance for verification and validation, where interfaces must be faithful to the hardware platforms. Thus, minimal effort is needed to switch the onboard software between the physical and simulation test beds.

Simulation models are also used extensively during surface-mission operations. They are integrated into the rover-control workstations as well as into science-activity planning tools, and allow operators to design command sequences. The models help the evaluation of resource needs and sequence timing, as well as risks prior to upload and execution. The downlink telemetry is used to update the models with information about the environment and the rover state for use in the day-to-day mission cycles. Recognizing the importance of field tests in evaluating technologies and preparing for mission operations, the section is also supporting the development of a "virtual field testing in a box" capability. Such capability can provide platforms for training scientists and operators, and also allow missions to evaluate and tune operations concepts.

Fig. 4: Screen capture of simulation of entry and descent of a Mars capsule. From upper left and clockwise: entry spacecraft over simulated terrain, steps of entry phase, grid of landing area, plots of altitude and acceleration experienced.
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Fig. 4: Screen capture of simulation of entry and descent of a Mars capsule. From upper
left and clockwise: entry spacecraft over simulated terrain, steps of entry phase,
grid of landing area, plots of altitude and acceleration experienced.
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