Sara Susca

Robust multi-sensor, day/night 6-DOF pose estimation for a dynamic legged vehicle in GPS-denied environments

We present a real-time system that enables a highly capable dynamic quadruped robot to maintain an accurate 6-DOF pose estimate (better than 0.5m over every 50m traveled) over long distances traversed through complex, dynamic outdoor terrain, during day and night, in the presence of camera occlusion and saturation, and occasional large external disturbances, such as slips or falls. The system fuses a stereo-camera sensor, inertial measurement units (IMU), and leg odometry with an Extended Kalman Filter (EKF) to ensure robust, low-latency performance. Extensive experimental results obtained from multiple field tests are presented to illustrate the performance and robustness of the system over hours of continuous runs over hundreds of meters of distance traveled in a wide variety of terrains and conditions.

Fully self-contained vision-aided navigation and landing of a micro air vehicle independent from external sensor inputs

Direct-lift micro air vehicles have important applications in reconnaissance. In order to conduct persistent surveillance in urban environments, it is essential that these systems can perform autonomous landing maneuvers on elevated surfaces that provide high vantage points without the help of any external sensor and with a fully contained on-board software solution. In this paper, we present a micro air vehicle that uses vision feedback from a single down looking camera to navigate autonomously and detect an elevated landing platform as a surrogate for a roof top. Our method requires no special preparation (labels or markers) of the landing location. Rather, leveraging the planar character of urban structure, the landing platform detection system uses a planar homography decomposition to detect landing targets and produce approach waypoints for autonomous landing. The vehicle control algorithm uses a Kalman filter based approach for pose estimation to fuse visual SLAM (PTAM) position estimates with IMU data to correct for high latency SLAM inputs and to increase the position estimate update rate in order to improve control stability. Scale recovery is achieved using inputs from a sonar altimeter. In experimental runs, we demonstrate a real-time implementation running on-board a micro aerial vehicle that is fully self-contained and independent from any external sensor information. With this method, the vehicle is able to search autonomously for a landing location and perform precision landing maneuvers on the detected targets.

Real-time pose estimation of a dynamic quadruped in GPS-denied environments for 24-hour operation

We present a real-time system that enables a highly capable dynamic quadruped robot to maintain an accurate six-degree-of-freedom pose estimate (within a 1.0% error of distance traveled) over long distances traversed through complex, dynamic outdoor terrain, during day and night, in the presence of camera occlusion and saturation, and occasional large external disturbances, such as slips or falls. The system fuses a stereo-camera sensor, inertial measurement unit, leg odometry, and optional intermittent GPS position updates with an extended Kalman filter to ensure robust, low-latency performance. To maintain a six-degree-of-freedom local positioning accuracy alongside the global positioning knowledge, two reference frames are used; a local reference frame and a global reference frame, with the former benefiting obstacle detection and mapping and the latter for operator-specified and autonomous way-point following. Extensive experimental results obtained from multiple field tests are presented to illustrate the performance and robustness of the system over hours of continuous runs and hundreds of kilometers of distance traveled in a wide variety of terrains and conditions.

A framework for extending the Science Traceability Matrix: Application to the planned europa mission

One of the most critical functions of the systems engineering requirements process for a large multi-instrument science-driven space mission is to successfully communicate customer expectations into a comprehensive and traceable science requirements flowdown. These requirements are essential to communicating the constraints on the scope of the science investigations and clarifying how multiple instruments contribute to a given science goal. They also provide insight into how the science goals of the whole mission are affected by design choices. There is little specific guidance available on best practices for developing this science-driven flowdown. A unified Science Traceability Matrix (USTM) contains a significant amount of information that can be leveraged for that purpose, but the USTM was not designed to directly produce a complete science requirements flowdown. Thus, starting with the principles codified in a USTM, the authors propose a framework that directly maps into the requirements flowdown and supports broader systems engineering processes while retaining its meaning to the science team. This Science Traceability and Alignment Framework, or STAF, defines a set of common definitions and valid relationships to structure communication across the project. In addition, STAF populates a network of information that can be useful to support complex mission analysis activities such as fault protection. This work discusses the highest-level implementation of the STAF, the project-domain or P-STAF, which describes an approach to decomposing customer requirements into science requirements. The planned Europa Mission is used as a case study for the implementation of this framework and its potential benefits to a project.

Thermal, Structural, and Optical Analysis of a Balloon-Based Imaging System

The Subarcsecond Telescope And BaLloon Experiment, STABLE, is the fine stage of a guidance system for a high-altitude ballooning platform designed to demonstrate subarcsecond pointing stability, over one minute using relatively dim guide stars in the visible spectrum. The STABLE system uses an attitude rate sensor and the motion of the guide star on a detector to control a Fast Steering Mirror in order to stabilize the image. The characteristics of the thermal-optical-mechanical elements in the system directly affect the quality of the point spread function of the guide star on the detector, and so, a series of thermal, structural, and optical models were built to simulate system performance and ultimately inform the final pointing stability predictions. This paper describes the modeling techniques employed in each of these subsystems. The results from those models are discussed in detail, highlighting the development of the worst-case cold and hot cases, the optical metrics generated from the finite element model, and the expected STABLE residual wavefront error and decenter. Finally, the paper concludes with the predicted sensitivities in the STABLE system, which show that thermal deadbanding, structural preloading and self-deflection under different loading conditions, and the speed of individual optical elements were particularly important to the resulting STABLE optical performance.

Use of Model Payload for Europa Mission development IEEE aerospace conference

During the long early development of the Europa Mission concept, the team used a hypothetical, straw-man payload, called the Model Payload, to assist in the development of a complete mission design. The Model Payload comprised a suite of science instruments, and was structured to meet the science objectives of the mission. The science objectives were defined in terms of a set of specific physical measurements that would need to be made, including quality attributes such as resolution, accuracy, coverage, etc. The Model Payload was designed to acquire these data with the required attributes. A set of notional instruments was chosen to be able to meet the full set of science objectives. Each notional instrument was based on current capabilities and technologies of actual, similar instruments, and modeled with enough detail to be able to estimate aspects of the instrument such as power usage, pointing stability needs, thermal accommodation needs, etc. This paper discusses the basis for the Model Payload and how it was used to develop the mission design, observation and data acquisition strategy, needed spacecraft capabilities, spacecraft-payload interface needs, mission system requirements, and operational scenarios. Then we present a comparison of the Model Payload to the actual payload, recently selected by NASA for the proposed Europa Mission. The focus is on how well this process enveloped and constrained the design space and guided the development and analysis of not only instrument requirements, but also those of the flight system and the mission operations system. Specifically, we discuss those areas in which the Selected Payload drove the mission design and which areas remained unchanged. Lastly, we present lessons learned from the use of a Model Payload.

Characterization of a commercial, front-illuminated interline transfer CCD camera for use as a guide camera on a balloon-borne telescope.

We report results obtained during the characterization of a commercial front-illuminated progressive scan interline transfer CCD camera. We demonstrate that the unmodified camera operates successfully in temperature and pressure conditions (-40C, 4mBar) representative of a high altitude balloon mission. We further demonstrate that the centroid of a well-sampled star can be determined to better than 2% of a pixel, even though the CCD is equipped with a microlens array. This device has been selected for use in a closed-loop star-guiding and tip-tilt correction system in the BIT-STABLE balloon mission.

A framework for writing measurement requirements and its application to the planned europa mission

Science-engineering communication is critical to the success of any science-driven mission. The process of building this understanding relies on a shared language for communicating science needs and engineering results, which can be particularly difficult on large space-science missions where many different institutions contribute to the science team. The Science Traceability Matrix can be used to formalize this communication pathway, but it has limited use in the development of the science requirements flowdown, and varies in format, scope and content from mission to mission. There are many guidelines on developing well-constructed requirements in general, but very little is published on how to actually write these science-driven requirements in a systematic way. This paper discusses the measurement-domain science traceability and alignment framework, or M-STAF, which was developed to help frame the conversation between scientists and engineers in the development of measurement requirements. The M-STAF provides a common language that can be used to ensure consistency across instruments, completeness in the coverage of the requirements, and traceability of the engineering work to the science objectives of the project. This work discusses the framework in the context of other communication tools and its implementation on a flight project. The general framework is presented through the lens of its potential application on the planned Europa Mission.

A sub-arcsecond pointing stability fine stage for a high altitude balloon platform

High-altitude balloons (HABs) are platforms for collecting astrophysical and planetary science data that offer a number of advantages compared to conventional ground-based or space-based systems. However, they also pose a set of new environmental challenges that must be addressed in order to offer a viable alternative to ground-or space-based assets. In particular, maintaining science-quality pointing stability is a critical challenge for HAB platforms. For these missions, dynamic errors must be limited to a fraction of the observation wavelength, so as the wavelength becomes smaller, it becomes more difficult to meet the needed performance. As a result, there are very few existing pointing stabilization solutions that use visible-spectrum guide stars, despite their relatively wide distribution across the sky. This paper describes the results achieved with the STABLE (Sub-arc second Telescope And BaLloon Experiment) project whose goal is to provide the fine pointing stage for a balloon-borne platform observing in the visible wavelength.