Peter Tchoryk

Dynamic simulation and validation of a satellite docking system

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.

Molecular optical air data system (MOADS) flight experiment

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.

Advancements in KC-135 microgravity testing of an autonomous satellite docking 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.

Advancements in design of an autonomous satellite docking system

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.

Space-based direct detection wind mission design

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 Michigans new Space Engineering program and Michigan Aerospace Corporation, a University of Michigan spin-off company specializing, in part, in lidar systems.

High-altitude balloon-based wind LIDAR demonstration: from near space to space

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.

3D sensor algorithms for spacecraft pose determination

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.

Low-cost mission architecture for global tropospheric wind measurements

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.