SEARCH · Engineering Papers
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Analytical methods defining location of reference horizons in earth horizon radiance profile
Feasibility design of instrument system to collect data of horizon radiance profile in carbon dioxide absorption band
Earth infrared horizon definition for space guidance, navigation, control, and pointing systems - feasibility study
Explore the source record for details and available documents.
Explore the source record for details and available documents.
A major limitation on the use of infrared horizon sensors for attitude determination is the variability of the height of the infrared Earth horizon. This variation includes a climatological component and a stochastic component of approximately equal importance. The climatological component shows regular variation with season and latitude. Models based on historical measurements have been used to compensate for these systematic changes. The stochastic component is analogous to tropospheric weather. It can cause extreme, localized changes that for a period of days, overwhelm the climatological variation. An algorithm has been developed to compensate partially for the climatological variation of horizon height and at least to mitigate the stochastic variation. This method uses attitude and horizon sensor data from spacecraft to update a horizon height history as a function of latitude. For spacecraft that depend on horizon sensors for their attitudes (such as the Total Ozone Mapping Spectrometer-Earth Probe-TOMS-EP) a batch least squares attitude determination system is used. It is assumed that minimizing the average sensor residual throughout a full orbit of data results in attitudes that are nearly independent of local horizon height variations. The method depends on the additional assumption that the mean horizon height over all latitudes is approximately independent of season. Using these assumptions, the method yields the latitude dependent portion of local horizon height variations. This paper describes the algorithm used to generate an empirical horizon height. Ideally, an international horizon height database could be established that would rapidly merge data from various spacecraft to provide timely corrections that could be used by all.
The aerosol scattering coefficient as a function of height can be recovered from a direct inversion of the single-scattering horizon radiance provided the sun is above the horizon and an independent measurement of extinction as a function of height is made. Aerosol detection is effected by means of spacecraft measurements of the horizon radiance made during periods of spacecraft twilight. A solar occultation technique which allows the twilight measurements to be made when the sun is still above the horizon greatly reduces the complexity of the inversion problem. The second part of the paper reports on the use of a coronograph aboard Skylab to photograph the horizon just before spacecraft twilight in order to monitor the aerosol component above the tropopause. The coronograph picture, centered on 26.5 degrees E longitude and 63.0 degrees S latitude, shows that the aerosol layer peaks at a height of 48 plus or minus 1 km.
The work performed by the Attitude Determination and Control Section at the National Aeronautics and Space Administration/Goddard Space Flight Center in analyzing and evaluating the performance of infrared horizon sensors is presented. The results of studies performed during the 1960s are reviewed; several models for generating the Earth's infrared radiance profiles are presented; and the Horizon Radiance Modeling Utility, the software used to model the horizon sensor optics and electronics processing to computer radiance-dependent attitude errors, is briefly discussed. Also provided is mission experience from 12 spaceflight missions spanning the period from 1973 to 1984 and using a variety of horizon sensing hardware. Recommendations are presented for future directions for the infrared horizon sensing technology.
Recently substantial progress has been made towards design building and testifying remotely piloted Micro Air Vehicles (MAVs). This progress in overcoming the aerodynamic obstacles to flight at very small scales has, unfortunately, not been matched by similar progress in autonomous MAV flight. Thus, we propose a robust, vision-based horizon detection algorithm as the first step towards autonomous MAVs. In this paper, we first motivate the use of computer vision for the horizon detection task by examining the flight of birds (biological MAVs) and considering other practical factors. We then describe our vision-based horizon detection algorithm, which has been demonstrated at 30 Hz with over 99.9% correct horizon identification, over terrain that includes roads, buildings large and small, meadows, wooded areas, and a lake. We conclude with some sample horizon detection results and preview a companion paper, where the work discussed here forms the core of a complete autonomous flight stability system.
NASA's Orion Project has sparked a renewed interest in horizon-based optical navigation(OPNAV) techniques for spacecraft in the Earth-Moon system. Some approaches have begun to explore the geometry of horizon-based OPNAV and exploit the fact that it is a conic section problem. Therefore, the present paper focuses more deeply on understanding and leveraging the various geometric interpretations of horizon-based OPNAV. These results provide valuable insight into the fundamental workings of OPNAV solution methods, their convergence properties, and associated estimate covariance. Most importantly, the geometry and transformations uncovered in this paper lead to a simple and non-iterative solution to the generic horizon-based OPNAV problem. This represents a significant theoretical advancement over existing methods. Thus, we find that a clear understanding of geometric relationships is central to the prudent design, use, and operation of horizon-based OPNAV techniques.
Planetary rovers navigate in extreme environments for which a Global Positioning System (GPS) is unavailable, maps are restricted to relatively low resolution provided by orbital imagery, and compass information is often lacking due to weak or not existent magnetic fields. However, an accurate rover localization is particularly important to achieve the mission success by reaching the science targets, avoiding negative obstacles visible only in orbital maps, and maintaining good communication connections with ground. This paper describes a horizon solution for precise rover orientation estimation. The detected horizon in imagery provided by the on board navigation cameras is matched with the horizon rendered over the existing terrain model. The set of rotation parameters (roll, pitch yaw) that minimize the cost function between the two horizon curves corresponds to the rover estimated pose.
We present Jovian zonal wind speeds measured during the Cassini and New Horizons Jupiter flybys in 2000 and 2007, respectively. We performed our cloud tracking wind measurements using an automated, two-dimensional correlation imaging velocimetry technique. We analyzed all LORRI panchromatic images from the New Horizons Jupiter flyby dataset. This LORRI measurement documents the state of Jupiter’s zonal mean wind speed in 2007 and extends the historical record of Jupiter’s winds that serve as useful points of comparison for Juno observations. Among the Cassini ISS images, we analyzed the CL1CL2, CB2, UV3, BL1, BL2, GRN, RED, IR1, IR2, IR3, IR4, MT2, and MT3 filters. Our Cassini measurements provide valuable context to understand the altitudes probed by LORRI. Comparing the panchromatic LORRI measurements against past wind measurements using images captured with various narrow and wide-band camera filters is not straightforward. Because the Cassini ISS CL1CL2 “clear” filter’s performance is similar to that of LORRI, comparing CL1CL2 winds against LORRI results will help determine if the New Horizons measurements represent Jupiter’s cloud-top zonal wind speeds or if they are sensitive to different altitudes. In addition to placing our New Horizons measurements in altitudinal context, the Cassini ISS's IR4, IR2, RED, GRN, and BL1 filters are similar to those on Europa Clipper EIS camera. Wind measurements performed using those ISS filters will enable comparison to future missions, including anticipated observations to be taken by Europa Clipper.
We present Jovian zonal wind speeds measured during the Cassini and New Horizons Jupiter flybys in 2000 and 2007, respectively. We performed our cloud tracking wind measurements using an automated, two-dimensional correlation imaging velocimetry technique. We analyzed all LORRI panchromatic images from the New Horizons Jupiter flyby dataset. This LORRI measurement documents the state of Jupiter’s zonal mean wind speed in 2007 and extends the historical record of Jupiter’s winds. Among the Cassini ISS images, we processed the CL1CL2, CB2, UV3, BL1, BL2, GRN, RED, IR1, IR2, IR3, IR4, MT2, and MT3 filters. Our Cassini measurements provide valuable context to understand the altitudes probed by LORRI. Comparing the panchromatic LORRI measurements against past wind measurements using images captured with various narrow and wide-band camera filters is not straightforward. Because the Cassini ISS CL1CL2 “clear” filter’s performance is similar to that of LORRI, comparing CL1CL2 winds against LORRI results will help determine if the New Horizons measurements represent Jupiter’s cloud-top zonal wind speeds or if they are sensitive to different altitudes. In addition to placing our New Horizons measurements in altitudinal context, the Cassini ISS's IR4, IR2, RED, GRN, and BL1 filters are similar to those on Europa Clipper EIS camera. Wind measurements performed using those ISS filters will enable comparison to future missions, including anticipated observations to be taken by Europa Clipper
Two different experimental manipulations, namely head tilt and the viewing of a visual display rotating around the line of sight, induce torsional displacements of the eyes and a tilting of the apparent horizon. The present study examines the routes by which visual (field rotation) and otolith-proprioceptive (head tilt) sources of afference influence horizon judgments. In particular, the relationship between torsional eye movements and horizon estimates is addressed. The results indicate that visual and otolith-proprioceptive information sum directly in their influence on eye torsion, but interact more complexly in horizon estimates, indicating a dissociation of their central determinants.
A modified earth horizon sensor design is proposed for the Mars Observer mission. The horizon sensor modification are based on Mars horizon radiance profiles. Attention is given to the Mars Observer's attitude control system, whose primary mode is horizon sensor-based and therefore obviates the use of an onboard spacecraft ephemeris; control accuracy of the order of 10 mrad 3sigma/axis is achieved. The attitude control system's second, celestial-backup mode, wich requires greater operational effort, employs an onboard celestial sensor as the spacecraft ephemeris; its control accuracy is of the order of 8 mrad 3sigma/axis.
Two experiments were conducted in actual flight operations to evaluate an audio artificial horizon display that imposed aircraft attitude information on pilot-selected music. The first experiment examined a pilot's ability to identify, with vision obscured, a change in aircraft roll or pitch, with and without the audio artificial horizon display. The results suggest that the audio horizon display improves the accuracy of attitude identification overall, but differentially affects response time across conditions. In the second experiment, subject pilots performed recoveries from displaced aircraft attitudes using either standard visual instruments, or, with vision obscured, the audio artificial horizon display. The results suggest that subjects were able to maneuver the aircraft to within its safety envelope. Overall, pilots were able to benefit from the display, suggesting that such a display could help to improve overall safety in general aviation.
A new image processing method for automated horizon detection is presented in this paper. This method was developed for the Mars Exploration Rovers mission’s surface operations to aid in determining orbiter visibility periods for downlink data, and is now being considered for all Mars surface missions and for a variety of applications. Starting with images received from Mars rovers or landers, the horizon pixel location is found by (1) obtaining the gradient images using the Sobel operator, (2) calculating the preliminary horizon locations by optimizing the maximum difference between sky and ground regions in the gradient domain, and (3) applying a multi-variable thresholding method. The results are analyzed using a variety of images from the Mars rovers, as an example one dataset’s results were categorized as 94.2% Good, 4.11% Okay, and 1.65% Poor. The pixel location corresponding to the found horizon in an image is converted to azimuth and elevation values using the camera model. The elevation of the terrain surrounding the rover or lander directly affects the duration orbiters are visible for downlink data volume, and when the sun is visible for image quality or solar energy consumption. Having an automated process to detect the elevation of the terrain allows the operation team to better predict the outcome of the plan, reducing heath and safety risks and allowing new operational limits to be defined.
This research focuses on the strategic deconfliction of unmanned aircraft systems (UAS) in an urban package delivery environment with two depots and multiple drop-off locations. Since the formulated mixed-integer nonlinear programming (MINLP) problem is non-deterministic polynomial-time (NP) hard, a heuristic algorithm called "rolling horizon with k-position search (KPS)" is used to compute the departure sequence and scheduled time of departure (STD) of each UAS at a depot, considering temporal constraints at en-route crossing waypoints and depots for strategic deconfliction. The simulation studies show that an increase in the value of k (local neighborhood search) in the KPS reduces the average ground delay at the cost of an increase in the computation time for a given number of UAS, size of the rolling horizon window, and number of depots involved in the local neighborhood search. The studies also show that for a given rolling horizon window, the computation time increases exponentially with an increase in the total number of UAS flights when serial processing the local neighborhood search of KPS (with k > 1) and drops by an order of magnitude upon performing the local neighborhood search of KPS using parallel processing instead of serial processing. The computation time drops with the reduction in air traffic complexity of a scenario for a given number of flights, k (local neighborhood search), and rolling horizon window.