KEYWORDS: Space operations, LIDAR, Telescopes, Space telescopes, Backscatter, Doppler effect, Satellites, Weather forecasting, Aerospace engineering, Control systems
There is an important need for accurate measurements of tropospheric wind altitude profiles. These wind systems have
long been recognized as one of the primary unknowns limiting weather forecasting over timescales of several days.
Typical measurement architectures have focused primarily on space-based approaches, using a high-powered and highly
effective Light Detection and Ranging (lidar) system.
This paper discusses architectures for low-altitude space missions. The architectures are analyzed in the context of a
weather forecasting system for the Gulf of Mexico region during hurricane season. The architecture studies were
developed by collaboration between a class of engineers who are part of the University of Michigan's new Space
Engineering program and Michigan Aerospace Corporation, a University of Michigan spin-off company specializing, in
part, in lidar systems.
A near space, high-altitude balloon mission (BalloonWinds) is planned to demonstrate the performance of a direct detection wind LIDAR instrument. The program is a NOAA-funded initiative to demonstrate direct detection, fringe imaging Doppler Wind LIDAR (Light Detection and Ranging) technology. BalloonWinds will involve a series of high altitude missions (~30km), each lasting 8-10 hours, scheduled for launch in 2006 to validate wind LIDAR technology from a near space platform. With the promise of responsive, affordable launch vehicles and near space platforms, there is an opportunity to demonstrate launch-on-demand capability of low-cost instruments that can provide regional or global wind data. It has been well established that direct measurement of winds will improve weather forecasting accuracy and hurricane landfall prediction and would provide benefits to government agencies and the public at large. An overview of the BalloonWinds instrument design and near space flight plan is presented in this paper as well as a concept design for a low-cost, 6-12 month space mission. Instrument performance simulations are used to demonstrate the feasibility and effectiveness of the low-cost approach for global wind sounding compared to traditional mission concepts.
KEYWORDS: Sensors, Data modeling, 3D modeling, Space operations, 3D acquisition, Solid modeling, Algorithm development, Satellites, Image processing, Detection and tracking algorithms
Researchers at the Michigan Aerospace Corporation have developed accurate and robust 3-D algorithms for pose determination (position and orientation) of satellites as part of an on-going effort supporting autonomous rendezvous, docking and space situational awareness activities. 3-D range data from a LAser Detection And Ranging (LADAR) sensor is the expected input; however, the approach is unique in that the algorithms are designed to be sensor independent. Parameterized inputs allow the algorithms to be readily adapted to any sensor of opportunity. The cornerstone of our approach is the ability to simulate realistic range data that may be tailored to the specifications of any sensor. We were able to modify an open-source raytracing package to produce point cloud information from which high-fidelity simulated range images are generated. The assumptions made in our experimentation are as follows: 1) we have
access to a CAD model of the target including information about the surface scattering and reflection characteristics of the components; 2) the satellite of interest may appear at any 3-D attitude; 3) the target is not necessarily rigid, but does have a limited number of configurations; and, 4) the target is not obscured in any way and is the only object in the field of view of the sensor. Our pose estimation approach then involves rendering a large number of exemplars (100k to 5M), extracting 2-D (silhouette- and projection-based) and 3-D (surface-based) features, and then training ensembles of decision trees to predict: a) the 4-D regions on a unit hypersphere into which the unit quaternion that represents the
vehicle [QX, QY, QZ, QW] is pointing, and, b) the components of that unit quaternion. Results have been quite promising and the tools and simulation environment developed for this application may also be applied to non-cooperative spacecraft operations, Autonomous Hazard Detection and Avoidance (AHDA) for landing craft, terrain mapping, vehicle guidance, path planning and obstacle avoidance.
The Molecular Optical Air Data System (MOADS) is a compact instrument designed to measure aircraft airspeed as well as the density of the air surrounding the aircraft. Other air data products provided by the instrument include density altitude, angle of attack (AOA), angle of side-slip (AOS), and Mach number. MOADS is a direct-detection LIDAR that measures these air data products from fringe images derived from a Fabry-Perot etalon. Determination of airspeed and direction is achieved through three telescopes that view a fixed air volume ahead of the aircraft turbulent flow field. This method reduces the measurement error as compared to traditional measurements made from within this turbulent region. As a direct detection LIDAR instrument, MOADS is capable of collecting both molecular and aerosol LIDAR returns, which allows operation in clear air as well as in aerosol-filled atmospheric regions. A second prototype was designed, built and tested. This MOADS prototype has been validated in a laboratory wind tunnel. Presented here are the airflow velocity measurement results from ground testing and vibration test measurements.
KEYWORDS: Large telescopes, High power lasers, Atmospheric modeling, Doppler effect, LIDAR, Satellites, Wind measurement, Telescopes, Space telescopes, Space operations
Tropospheric wind measurements are of great meteorological and tactical value, but are presently not available on a global basis. The primary obstacle to a space-based Doppler wind LIDAR mission capable of obtaining these measurements has been the cost and risk associated with flying high power lasers and large telescopes in low-earth orbit. This paper presents an alternative approach that would result in a low-cost, low-risk responsive approach to deploying a global tropospheric wind measurement system.
During the development of an autonomous spacecraft docking mechanism, one of the primary areas of interest in the way the mechanism will behave in a micro-gravity environment. This issue is of particular interest when a flexible soft-dock cable is used to make initial capture, because ground-based testing does not adequately represent the environmental conditions that will be seen on orbit. To this end, Michigan Aerospace Corporation has recently conducted flight tests of its prototype autonomous satellite docking system in a micro-gravity environment on the KC-135 in conjunction with the Air Force Research Laboratory Space Vehicles Directorate and Microcosm, Inc. Though the first flight was primarily for the purpose of testing the core operating principles of the docking mechanism, several lessons were learned that will be applied toward developing a second, more advanced prototype and experimental setup intended for a second series of flights on the KC-135. Areas of improvement for the new flight test will be in the physical operation of the experimental apparatus and the data collection methods used. The use of redundant sensors as a means of eliminating noise will be explored, as will the merits of using a combination of coarse and fine sensors to collect data over a broader measurement range.
The past five years has witnessed a significant increase in the attention given to on-orbit satellite docking and servicing. Recent world events have proven how we have come to rely on our space assets, especially during times of crisis. It has become abundantly clear that the ability to autonomously rendezvous, dock, inspect and service both military and civilian assets is no longer a nicety, but a necessity. Reconnaissance and communications satellites, even the space shuttle and International Space Station, could benefit from this capability. Michigan Aerospace Corporation, with funding from the Defense Advanced Research Projects Agency (DARPA) and the Air Force Research Laboratory (AFRL), has been refining a compact, light, compliant soft-docking system. Earlier prototypes have been tested on the Marshall Space Flight Center (MSFC) flat-floor as well as on the Johnson Space Flight Center (JSC) KC-135 micro-gravity aircraft. Over the past year, refinements have been made to the mechanism based on the lessons learned from these tests. This paper discusses the optimal design that has resulted.
The Molecular Optical Air Data System (MOADS) is a compact optical instrument that can directly measure aircraft velocity, as well as the density of the air surrounding the aircraft. From these measurements, many air data products can be determined. Successful MOADS operation has been demonstrated in the laboratory using a wind tunnel. Recently, a MOADS prototype was designed and built in order to complete an upcoming flight experiment aboard a Beechcraft King Air 300. This flight program will be a significant milestone for direct detection lidar systems configured as an air data system aboard an aircraft. The background of the technology, ground experimentation summary of results, flight experiment approach, flight prototype design, and flight experiment planning are discussed.
In recent years, Michigan Aerospace has approached the problem of gentle autonomous spacecraft rendezvous and docking using a flexible soft-dock cable that is extended from the docking spacecraft to the target spacecraft. Because of the nature of a soft-dock cable, testing and validation of the technology is difficult in normal gravity. To properly emulate the behavior of this soft-dock cable, we have performed dynamic computer simulations so that the effects of micro-gravity could be simulated. The Autonomous Satellite Docking System (ASDS) was initially prototyped and tested at Marshall Space Flight Center’s air-bearing floor facility. The test data was compared to the simulations and used to validate the model. Once a good correlation between the simulation’s predicted results and the actual data was shown, the model was used to predict future performance of the ASDS mechanism on several potential spacecraft for the Orbital Express program. A new dynamic simulation model was created and compared to test data from a recent KC-135 flight test to further validate the modeling approach used. This paper will describe the methodology used in modeling and simulating the ASDS mechanism. Correlation between the models and the test data will be discussed.
Michigan Aerospace Corporation has developed a mechanism for microsatellite docking, which has been successfully demonstrated in a microgravity environment. This docking mechanism is specifically designed for soft-docking capability, tolerance to misalignment, and scalability. The current Autonomous Microsatellite Docking System (AMDS) design resulted from modifications to an earlier docking mechanism prototype that was tested at the Marshall Space Flight Center (MSFC) Flat Floor Facility.
The AMDS was tested in a microgravity environment through the NASA JSC Reduced Gravity Program, where a KC-135 turbo jet flies a series of parabolic maneuvers. The test objectives of the KC-135 flight were to determine the docking mechanism cable assembly behavior in zero-g, test the full range of the docking envelope in a six degree of freedom test setup and determine the undocking capability and stability. The nature of the Michigan Aerospace docking mechanism enabled the entire docking cycle, including soft dock, auto-alignment and hard dock, to be completed within the 20 seconds of 'zero-g' time. Complete end-to-end docking and undocking was performed under a variety of initial conditions and docking parameters. The data collected during the KC-135 testing will be used to validate dynamic simulation models of the docking mechanism. The intent of these dynamic models is to examine a number of docking scenarios between a chaser and target satellite. This paper will discuss the results of the KC-135 docking tests and docking simulations.
The Molecular Optical Air Data System (MOADS) is a compact optical instrument that can directly measure wind speed and direction, density, and temperature of the air surrounding an aircraft. From these measurements, a complete set of air data products can be determined. Single-axis wind tunnel testing of wind speed and density has just been completed for the current prototype. These wind tunnel measurements have shown that the current prototype meets wind speed accuracy predictions and initial results from density testing indicate a high level of correlation with absolute pressure transducer measurements. A preliminary design for the next generation instrument, the Joint Optical Air Data System (JOADS), has been completed and is intended to meet Joint Striker Fighter (JSF) requirements. Work is also underway to evaluate the application of MOADS to Unmanned Air Vehicles (UAVs), Reusable Launch Vehicles (RLVs), helicopters and weapon systems. Extensions of MOADS technology to wind shear, gust alleviation, and clear air turbulence detection for commercial aircraft are also being pursued. The basic instrument operation, preliminary ground testing (wind tunnel) results, comparison of these results to simulations, next generation instrument capabilities, and plans for a flight demonstration are discussed.
With the prospects of future Mars and lunar missions improving, the autonomous capabilities required to accomplish many of the proposed missions has been given considerable attention. As a result, it has been recognized that the sensing capability of spacecraft must be enhanced, not only for interplanetary missions, but for those in Earth orbit as well. NASA began addressing many technology development issues under the Pathfinder Program. A sensor trade-off study was performed at ERIM under two subprograms of Pathfinder: the Autonomous Lander Project, and Autonomous Rendezvous and Docking Project. This paper is based on that trade-off study, using the scenario of an autonomous landing on a planetary body and the associated autonomous rendezvous and docking operations which would precede and/or follow such a landing. Several sensor concepts are analyzed, including RF-based, laser- based, and passive optical techniques. For each concept, a brief description of the sensor operating principles is provided, and the results of a performance analysis are summarized along with performance drivers, operational constraints, and a state-of-the-art assessment.
This paper discusses the scenario of an autonomous landing like that required for the Mars Rover Sample Return Mission. An application of laser radar for conducting autonomous hazard detection and avoidance is discussed. A trade-study is performed to identify operational and implementation constraints as well as the state of the art in component technology.
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