SPACE BORNE ATTITUDE MEASUREMENT UNITS

Air data inertial reference system (ADIRS) receive the data from air data unit, inertial reference unit and global positioning system which hybridizing out the basic flight parameters. After giving the examples of accidents causing from ADIRS output data, the hybridization computation of basic parameters is analyzed, and give the new opinion of hybridization computation considering pitot probe fault, for getting more accurate data and avoiding accident.

With a view towards reducing cost and complexity for spacecraft early mission support at the NASA Goddard Space Flight Center (GSFC), efforts are being made to automate the attitude sensor calibration process. This paper addresses one of the major components needed by such a system. The beneficiaries of an improved calibration process are missions that demand moderate to high precision attitude knowledge or that need to perform accurate attitude slews. Improved slew accuracy reduces the time needed for re-acquisition of fine-pointing after each attitude maneuver, Rapid target acquisition can be very important for astronomical targeting or for off-nadir surface feature targeting by Earth-oriented spacecraft. The normal sequence of on-orbit calibration starts with alignment calibration of the star trackers and possibly the Sun sensor. Their relative alignment needs to be determined using a sufficiently large data set so their fields of view are adequately sampled. Next, the inertial reference unit (IRU) is calibrated for corrections to its alignment and scale factors. The IRU biases are estimated continuously by the onboard attitude control system, but the IRU alignment and scale factors are usually determined on the ground using a batch-processing method on a data set that includes several slews sufficient to give full observability of all the IRU calibration parameters. Finally, magnetometer biases, alignment, and its coupling to the magnetic torquers are determined in order io improve momentum management and occasionally for use in the attitude determination system. The detailed approach used for automating calibrations will depend on whether the automated system resides on the ground or on the spacecraft with an ultimate goal of autonomous calibration. Current efforts focus on a ground-based system driving subsystems that could run either on the ground or onboard. The distinction is that onboard calibration should process the data sequentially rather than in a single large batch since onboard computer data storage is limited. Very good batch- processing calibration utilities have been developed and used extensively at NASA/GSFC for mission support but no sequential calibration utilities are available. To meet this need, this paper presents the mathematical description of a sequential IRU calibration system. The system has been tested using flight data from the Rossi X-ray Timing Explorer (RXTE) during a series of attitude slews. The paper also discusses the current state of the overall automated system and describes plans for adding sequential alignment calibration and other additions that will reduce the amount of analyst time and input.

This paper describes a novel low-cost inertial reference unit (IRU) developed for spin-stabilized sounding rockets, as well as a method to calibrate the IRU using a one-axis rate table. The IRU contains three orthogonally mounted microelectromechanical system (MEMS) gyros and is intended for use in a low-cost system for attitude determination of sounding rockets. The high spin velocity of the rockets (4-6 r/s) causes sensor misalignments and scale factor errors to have a large effect on the gyro outputs. The performance of the IRU is considerably improved by detailed calibration, including temperature compensation. For sounding rocket applications, the total rate error is typically reduced by more than one order of magnitude. The calibration procedure uses a ramp profile calibration maneuver input at all three sensor axes and a Kalman filter to estimate the 12 error parameters.

The Cassini-Huygens mission is a flagship class NASA/ESA mission to the planet Saturn. Launched in 1997, Cassini is still successfully operating after 16 years of flight and the telemetry from the attitude control hardware on Cassini has produced an immense dataset that allows the Cassini operations team to report on the long-term performance of several commercially available GNC hardware components in the space environment. This investigation summarizes the in-flight performance of the two inertial reference units aboard Cassini. Each of the two Cassini inertial reference units contains four hemispherical quartz resonator gyros. The Cassini operations team previously reported on the performance of the inertial reference units in 2007, and this paper provides an update with an additional 6 years of flight experience at Saturn.

Significant technical considerations prompted the start of an evolution, twenty years ago, from the use of the floated, rate- integrating gyro to the dynamically tuned gyro (DTG) for the precision, three-axis attitude control of spacecraft. DTG's have since then been widely applied in U.S. spacecraft. The anticipated advent of smaller, lower cost spacecraft prompted the development of a new generation, lower cost, low weight (3.6 lb/1.8 kg), moderate performance inertial reference unit (IRU) for such applications by making use of the miniature CONEX DTG. The resulting two-axis rate assembly has already been qualified and delivered to two programs. In parallel, development of a miniature, three-axis ring laser gyro has proceeded to the point where an inertial measurement unit has entered the early phase of production for a tactical missile program. Simple modification of the hardware will provide a production-based IRU or IMU design at a cost advantage for spacecraft applications.

Research on inertial reference units prescribed performance integral sliding mode angle control

ABSTRACTPresent trends in space vehicles are leading to smaller platforms which present a new set of challenges andrequirements. For instance, because of their smaller inertias, these vehicles are likely to be more sensitive todisturbances and experience higher levels of attitude jitter. This higher frequency motion may be unacceptablefor some scientific instruments and require compensation. Hence, the bandwidth of inertial reference units mayneed to be enhanced if it is desired to control the high-frequency attitude jitter. In the case of line-of-sight typeinstruments, attitude jitter can be mitigated by incorporating a fast steering mirror into the system. To take fulladvantage of these devices, the spacecraft attitude needs to be measured at sufficiently high bandwidth, well beyond what is commonly provided by inertial reference units. Furthermore, due to cost and/or power considerations, it may be desirable to replace conventional gyros with accelerometers or quartz rate sensors, andstar trackers with UPS receivers configured to measure attitude. This paper explores various ways to obtainhigher bandwidth attitude measurements for the purpose of jitter control, and provides a practical solution.Keywords: sensor fusion, gyros, accelerometers, high-bandwidth attitude determination

In this paper, an autonomous relative navigation and joint attitude determination algorithm in asteroid exploration descent stage is researched based on feature point information of perpendicular asteroid surface image observed by optical navigation camera, distance vectors from spacecraft to asteroid measured by three angled installed lidars and relative velocity increment measured by accelerometer when the relative distance vector to the centroid of asteroid can not be obtained. The inertial attitude of spacecraft is determined by sun vector, star vectors and inertial angular velocity respectively measured by sun sensor, star trackers and inertial reference unit. Also, in order to obtain measurement error model transferred from sensor noise, a covariance matrix solver considering error correlation is presented via the error model of normalized vector to first order. Numerical simulation and improved observability evaluation of filtering are undertaken to discuss the results of complete sensor observation and weak observation of lidars, and verify the effectiveness of the presented relative navigation and attitude determination algorithm.

Next generation navigation systems demand performance enhancements to support new applications with longer range capabilities, provide robust operation in severe thermal and vibration environments while simultaneously reducing weight, size and power dissipation. Compact, inexpensive, advanced guidance components are essential for such applications. In particular, Inertial Reference Units (IRUs) that can provide high-resolution stabilization and accurate inertial pointing knowledge are needed. For space applications, an added requirement is radiation hardening up to 300 krad over 5 to 15 years. Manufacturing specifications for the radiation-induced losses are not readily available and empirical test data is required for all components in order to optimize the system performance. Interferometric Fiber-Optic Gyroscopes (IFOGs) have proven to be a leading technology for tactical and navigational systems. The sensors have no moving parts. This ensures high reliability and a long life compared to the mechanical gyroscopes and dithered ring laser gyroscopes. However, the available architectures limit the potential size and cost of the IFOG. The work reported here describes an innovative approach for the design, fabrication, and testing of the IFOG and enables the production of a small, robust and low cost gyro with excellent noise and bandwidth characteristics with high radiation tolerance. The development is aimed at achieving a sensor volume < 5 cubic inches. The new IFOS gyro uses an open loop configuration, utilizes extremely small diameter radiation-hard fiber with customized all-digital signal processing. The optics is packaged using a combination of highly-integrated optical component assemblies with an allfiber approach that leads to a more flexible yet lower cost optical design. The IFOS gyro prototypes are implemented using a distributed architecture, where the light source, electronics and receiver are integrated in an external package, while the sensor head is integrated in a robust and environmentally rigid package. The sensor package design is compatible with the most severe environmental requirements foreseen for the target applications. This paper presents the current state-of-the-art performance of the prototype gyros and the potential for further reduction of size with improved performance. The gyro sample and data rates are extremely high and can be close to the modulation frequency (up to 80 kHz). IFOS has shown that the noise at high frequencies is not flattening out and extremely high bandwidth operation is possible without any degradation of the operational stability. IFOS has also demonstrated the potential for a future, smaller and extremely robust IFOG. The next phase design will include highly radiation-resistant integrated, compact optical circuits based on InP technology that includes the light source, splitter and receiver in one package, a gyro coil that utilizes small diameter, radiation-hard fiber and a small fiber phase modulator with > 300 krad radiation tolerance. This gyro offers the low noise, low drift, low vibration sensitivity, high accuracy, high bandwidth and high radiation tolerance solution required for next generation systems. We will present both theoretical modeling and experimental results obtained to date

For over ten years, Al Cielo Inertial Solutions (ACIS) has been supplying Israeli and international customers with high-performance, reliable inertial solutions based on closed-loop FOGs. This technology has been proven over the past few decades as a growing number of IMU systems based on FOG technology have been successfully deployed. FOG systems are found in tactical and in strategic IMUs, providing a range of solutions for navigation and control. IMUs, as well as systems-gyroscopes-only inertial reference units (IRUs), are also used for high-precision attitude referencing. This chapter is most, but not exclusively, relevant to this application.

Both airborne and space-based high-energy laser weapon systems present interesting challenges for precision line-of-sight control. Sub-microradian to microradian pointing accuracies are required against dynamic targets. In addition, “absolute” pointing and accurate inertial angular rate measurement are required to support mission requirements. This paper addresses these unique directed-energy weapon (DEW) precision-pointing requirements and their associated implementation alternatives in the context of strapdown and stable platform inertial reference technologies. The contributions of this paper consider the broader issues of DEW requirement drivers, integration of the stabilization system with the rest of the optical system, and design tradeoffs between stable platform and strapdown stabilization mechanizations. Both types of mechanisms are mounted to the gimbal of an imaging system using gryo sensors (gyros) and accelerometers to maintain a desired orientation in inertial space independent of the craft motion. Although both can include an optical reference that propagates through the optical path for optical alignment and jitter control, only in the stable platform is the optical reference stabilized. When combined on the same platform with a stabilized inertial measurement system and closed-loop stabilization with the optical reference, the mechanism becomes a stabilized inertial reference unit, which provides a stabilized optical reference to the electro-optical/laser pointing and jitter control systems.

ORNL FY 2016 Annual Summary of Laboratory Directed Research and Development Program (LDRD) Completed Projects. The Laboratory Directed Research and Development (LDRD) program at ORNL operates under the authority of DOE Order 413.2C, “Laboratory Directed Research and Development” (October 22, 2015), which establishes DOE’s requirements for the program while providing the Laboratory Director broad flexibility for program implementation. The LDRD program funds are obtained through a charge to all Laboratory programs. ORNL reports its status to DOE in March of each year.

The Ernest Orlando Lawrence Berkeley National Laboratory (LBNL or Berkeley Lab) Laboratory Directed Research and Development Program FY 1998 report is compiled from annual reports submitted by principal investigators following the close of the fiscal year. This report describes the supported projects and summarizes their accomplishments. It constitutes a part of the Laboratory Directed Research and Development (LDRD) program planning and documentation process that includes an annual planning cycle, projection selection, implementation, and review. The LBNL LDRD program is a critical tool for directing the Laboratory's forefront scientific research capabilities toward vital, excellent, and emerging scientific challenges. The program provides the resources for LBNL scientists to make rapid and significant contributions to critical national science and technology problems. The LDRD program also advances LBNL's core competencies, foundations, and scientific capability, and permits exploration of exciting new opportunities. All projects are work in forefront areas of science and technology. Areas eligible for support include the following: Advanced study of hypotheses, concepts, or innovative approaches to scientific or technical problems; Experiments and analyses directed toward ''proof of principle'' or early determination of the utility of new scientific ideas, technical concepts, or devices; and Conception and preliminary technical analyses of experimental facilities or devices.

In the last 20 years NASA has worked in collaboration with industry to develop enabling technologies needed to make aircraft safer and more affordable, extend their lifetime, improve their reliability, better understand their behavior, and reduce their weight. To support these efforts, research programs starting with ideas and culminating in full-scale structural testing were conducted at the NASA Langley Research Center. Each program contained development efforts that (a) started with selecting the material system and manufacturing approach; (b) moved on to experimentation and analysis of small samples to characterize the system and quantify behavior in the presence of defects like damage and imperfections; (c) progressed on to examining larger structures to examine buckling behavior, combined loadings, and built-up structures; and (d) finally moved to complicated subcomponents and full-scale components. Each step along the way was supported by detailed analysis, including tool development, to prove that the behavior of these structures was well-understood and predictable. This approach for developing technology became known as the approach. In the Advanced Composites Technology Program and the High Speed Research Program the building-block approach was used to develop a true understanding of the response of the structures involved through experimentation and analysis. The philosophy that if the structural response couldn't be accurately predicted, it wasn't really understood, was critical to the progression of these programs. To this end, analytical techniques including closed-form and finite elements were employed and experimentation used to verify assumptions at each step along the way. This paper presents a discussion of the utilization of the building-block approach described previously in structural mechanics research and development programs at NASA Langley Research Center. Specific examples that illustrate the use of this approach are included from recent research and development programs for both subsonic and supersonic transports.

OVERVIEW: The challenge for research management is to drive research projects forward without stifling creativity. At W. R. Grace, this challenge is met with a project tracking system to manage a research program consisting of approximately 100 research projects. The tracking system consists of three features: (1) A two-page Fact Sheet summaries key project commercial and technical information; (2) milestones establish technical goals; (3) performance against milestones is used to evaluate progress. The tracking system is effective for monitoring individual research projects as well as measuring performance of the overall research program. The system has become a useful communication tool with operating divisions and a means to establish and maintain credibility with corporate management. Research and development programs, by their very nature, are difficult to monitor and control. With too much control, creativity is stifled, innovation suffers and goals are set to be easily met. On the other hand, without control, programs can languish, drift away from their intended objectives, or create unrealistic expectations. The challenge for research management is to strike a balance between these two extremes to develop a workable and productive system to manage projects. At W. R. Grace & Co., a project tracking system has been developed which, over the last ten years, has evolved into an effective management tool to track and measure performance of research programs. This system has been instrumental in establishing credibility for the RD the system can then be used as a tool to measure the performance of the organization and of researchers and managers on their projects. The system can also be used to identify poorly performing projects. In addition to these internal needs, new product development requires close communication between the research organization and the operating divisions. A tracking system provides a mechanism for discussing and formalizing projects. Project success depends on mutual understanding of project objectives and the specifications of the products to be developed. Credibility with top corporate management is a key requirement of any research organization. Having formal documents with clearly defined objectives and timetables, against which performance can be measured, helps to create and sustain credibility. With a project tracking system, results of research can be forecast based on established performance rather than unfounded speculation. CORPORATE RESEARCH IN W. R. GRACE W. R. Grace & Co. is a specialty chemical and health care company comprised of global product lines. To support the technology needs of the corporation, Grace has a Corporate Research organization that accounts for approximately one-third of the total R&D activity within the company. The mission of Corporate Research is to develop new products through applications-oriented research. Corporate Research is an interdisciplinary organization with approximately 600 scientists, technicians and support staff working in three locations. The organization maintains close working relationships with the product lines within Grace. The broad skill base and diverse product line orientations within Corporate Research help to create synergies that can lead to new product concepts. An example is a progesterone test kit for the dairy industry, which will be described to illustrate the tracking system in detail. …