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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.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Determination of angles of attack and sideslip from radar data and a roll-stabilized platform

Equations for angles of attack and sideslip relative to both a rolling and nonrolling body axis system are derived for a flight vehicle for which radar and gyroscopic attitude data are available. The method is limited to application where a flat, nonrotating earth may be assumed. The gyro measures attitude relative to an inertial reference in an Euler angle sequence. In particular, a pitch, yaw, and roll sequence is used as an example in the derivation. Sample calculations based on flight data are presented to illustrate the method. Results obtained with the present gyro method are compared with another technique that uses onboard camera data.

Preisser, J. S.↗
NASA NTRS2018

High Fidelity Reconstructed Attitude Estimation Using Cassini Flight Telemetry

The Cassini Grand Finale capped the 20 year Cassini mission with 22 one-week-long orbits each with periapsis inside the ring plane just above Saturn’s cloud tops. One aspect of these remarkable orbits was unprecedented measurements of Saturn’s magnetic field very close to the planet. Processing this data required precise estimates of Cassini’s orientation during these ring plane crossings. These periods coincided with planned gyro-only attitude propagation due to the enormous bright bodies in the star tracker field-of-view. This paper describes how attitude reacquisition information, when the star tracker reacquires an absolute inertial reference, can be used to correct errors introduced during gyro-only propagation. The resulting high fidelity reconstruction significantly improves the extraction of Saturn’s magnetic field from the raw data obtained during gyro-only periods when Cassini’s changing orientation makes precise attitude estimation a challenge.

Burk, Thomas A.↗
NASA NTRS2005

Up, Up and Away: Arc Minute Pointing at 130,000 Feet

The InFOC-S X-ray telescope was launched September 16, 2004 aboard a 40 million cubic foot zero pressure high altitude balloon. Its primary objective was to demonstrate advances in hard X-ray focusing optics technology by flying an incident grazing mirror developed in cooperation between NASA Goddard Space Flight Center and Nagoya University, Japan. Launched from Ft. Sumner, NM and recovered near Wickenburg, AZ, the payload successfully collected photons from several X-ray sources during its 27 hour flight at a float altitude of 130,000 feet. To accommodate the instrument's narrow field of view, a precision arc-minute attitude determination and control systems was flown. This paper describes the application of a traditional spacecraft star tracker gyro based attitude determination and control system to the balloon problem. The control system architecture is presented, hardware identified, and software outlined. Simulated results are compared against actual flight data, with recommendations for enhanced performance identified.

Freesland, Doug↗
NASA NTRS1990

Inflight estimation of gyro noise

A method is described and demonstrated for estimating single-axis gyro noise levels in terms of the Farrenkopf model parameters. This is accomplished for the Cosmic Background Explorer (COBE) by comparing gyro-propagated attitudes with less accurate single-frame solutions and fitting the squared differences to a third-order polynomial in time. Initial results are consistent with the gyro specifications, and these results are used to determine limits on the duration of batches used to determine attitude. Sources of error are discussed, and guidelines for a more elegant implementation, as part of a batch estimator or filter, are included for future work.

Filla, O. H.↗
NASA NTRS1993

Resolution of the COBE Earth sensor anomaly

Since its launch on November 18, 1989, the Earth sensors on the Cosmic Background Explorer (COBE) have shown much greater noise than expected. The problem was traced to an error in Earth horizon acquisition-of-signal (AOS) times. Due to this error, the AOS timing correction was ignored, causing Earth sensor split-to-index (SI) angles to be incorrectly time-tagged to minor frame synchronization times. Resulting Earth sensor residuals, based on gyro-propagated fine attitude solutions, were as large as plus or minus 0.45 deg (much greater than plus or minus 0.10 deg from scanner specifications (Reference 1)). Also, discontinuities in single-frame coarse attitude pitch and roll angles (as large as 0.80 and 0.30 deg, respectively) were noted several times during each orbit. However, over the course of the mission, each Earth sensor was observed to independently and unexpectedly reset and then reactivate into a new configuration. Although the telemetered AOS timing corrections are still in error, a procedure has been developed to approximate and apply these corrections. This paper describes the approach, analysis, and results of approximating and applying AOS timing adjustments to correct Earth scanner data. Furthermore, due to the continuing degradation of COBE's gyroscopes, gyro-propagated fine attitude solutions may soon become unavailable, requiring an alternative method for attitude determination. By correcting Earth scanner AOS telemetry, as described in this paper, more accurate single-frame attitude solutions are obtained. All aforementioned pitch and roll discontinuities are removed. When proper AOS corrections are applied, the standard deviation of pitch residuals between coarse attitude and gyro-propagated fine attitude solutions decrease by a factor of 3. Also, the overall standard deviation of SI residuals from fine attitude solutions decrease by a factor of 4 (meeting sensor specifications) when AOS corrections are applied.

Sedler, J.↗
NASA NTRS2001

A Nonlinear Spacecraft Attitude Controller and Observer with an Unknown Constant Gyro Bias and Gyro Noise

A nonlinear control scheme for attitude control of a spacecraft is combined with a nonlinear gyro bias observer for the case of constant gyro bias, in the presence of gyro noise. The observer bias estimates converge exponentially to a mean square bound determined by the standard deviation of the gyro noise. The resulting coupled, closed loop dynamics are proven to be globally stable, with asymptotic tracking which is also mean square bounded. A simulation of the proposed observer-controller design is given for a rigid spacecraft tracking a specified, time-varying attitude sequence to illustrate the theoretical claims.

Deutschmann, Julie↗
NASA NTRS1978

Performance of ground attitude determination procedures for HEAO-1

Ground attitude support for HEAO 1 provided at GSFC by the HEAO 1 Attitude Ground Support System (AGSS) is described. Information telemetered from Sun sensors, gyroscopes, star trackers, and an onboard computer are used by the AGSS to compute updates to the onboard attitude reference and gyro calibration parameters. The onboard computer utilizes these updates in providing continuous attitudes (accurate to 0.25degree) for use in the observatory's attitude control procedures. The relationship between HEAO 1 onboard and ground processing, the procedures used by the AGSS in computing attitude and gyro calibration updates, and the performance of these procedures in the HEAO 1 postlaunch environment is discussed.

Fallon, L., III↗
NASA NTRS1990

Comparison and testing of extended Kalman filters for attitude estimation of the Earth radiation budget satellite

The testing and comparison of two Extended Kalman Filters (EKFs) developed for the Earth Radiation Budget Satellite (ERBS) is described. One EKF updates the attitude quaternion using a four component additive error quaternion. This technique is compared to that of a second EKF, which uses a multiplicative error quaternion. A brief development of the multiplicative algorithm is included. The mathematical development of the additive EKF was presented in the 1989 Flight Mechanics/Estimation Theory Symposium along with some preliminary testing results using real spacecraft data. A summary of the additive EKF algorithm is included. The convergence properties, singularity problems, and normalization techniques of the two filters are addressed. Both filters are also compared to those from the ERBS operational ground support software, which uses a batch differential correction algorithm to estimate attitude and gyro biases. Sensitivity studies are performed on the estimation of sensor calibration states. The potential application of the EKF for real time and non-real time ground attitude determination and sensor calibration for future missions such as the Gamma Ray Observatory (GRO) and the Small Explorer Mission (SMEX) is also presented.

Deutschmann, Julie↗
NASA NTRS1986

Space Telescope precision pointing control system

The Hubble Space Telescope has the most stringent pointing requirements imposed on any spacecraft to date. The overall HST stability shall not exceed 0.007 arc-seconds rms. The Pointing Control System utilizes fine guidance sensors and rate gyros for attitude reference and rate information. Control torques are provided by reaction wheels. A digital computer collects the sensor data, performs the control law computations, and sends torque commands to the reaction wheels. To attain this precision pointing, improvements were made to the rate gyros to lower their noise characteristics and to the reaction wheels to reduce their emitted vibration levels. The control system design was validated in a test sequence which progressed from model verification tests on an air-bearing to operations-oriented, closed loop testing on the assembled vehicle. A test system is described which allowed the simultaneous production of test case command loads for the flight computer and plots of predicted profiles to assist in test data analysis. Workarounds were required during system test to accommodate gyro biases and noise introduced into the closed loop system. Testing and analysis indicate that the HST will provide the capability to meet the requirements for precision pointing.

Beals, G. A.↗
NASA NTRS1975

A complementary filtering technique for deriving aircraft velocity and position information

An onboard navigation system which employed complementary filtering was developed to provide velocity and position information. The inputs to the mix filter included both acceleration inputs, which provided high-frequency position and velocity information, and radar position inputs, which provided the low-frequency position and velocity information. Onboard aircraft instrumentation, including attitude reference gyros and body-mounted accelerometers, was used to provide the acceleration information. An in-flight comparison of signal quality and accuracy showed good agreement between the complementary filtering system and an aided inertial navigation system. Furthermore, the complementary filtering system was proven to be satisfactory in control and display system applications for both automatic and pilot-in-the-loop instrument approaches and landings.

Niessen, F. R.↗
NASA NTRS1979

On-orbit control system performance of the HEAO-2 observatory

The on-orbit performance of the High Energy Astronomy Observatory is described. The control system utilizes precision gyros for attitude reference and skewed reaction wheels controlled by a reprogrammable computer. The observatory points at selected targets, maneuvers automatically and acquires guide stars for updating at each target. Performance data indicates maneuver accuracies less than one arc minute and pointing accuracies of 2-5 arc seconds. Use of 7th-9th magnitude guide stars has resulted in several improper updates caused by 'flat-field' stray light effects in the star trackers. The method used to discriminate true stars from the flat-field is also presented.

Rose, R. E.↗
NASA NTRS1988

Dynamics and control characteristics of a reference Space Station configuration

This paper describes the structural dynamic characteristics of a NASA reference space station configuration as defined in the November 1987 Space Station Program - Systems Engineering and Integration Engineering Data Book. The modes and frequencies of the station below 2.0 Hz were obtained and selected results along with rigid body properties are presented. A three-axis attitude control system using control moment gyros responding to attitude and attitude rate signals is used to regulate the orientation of the station. The stability of the control system with non-collocated sensors is investigated for both compensated and uncompensated control signals. Results from a closed-loop simulation of a commanded attitude change about three axes, and from a closed-loop simulation of the response of the station to an externally applied unit force impulse at the docking port are presented. These simulation results are used to evaluate the possible degree of control/structures interaction which could occur during normal operation of the station.

Sutter, Thomas R.↗
NASA NTRS1990

Comparison and testing of extended Kalman filters for attitude estimation of the Earth Radiation Budget Satellite

This paper presents the testing and comparison of two extended Kalman filters (EKFs) developed for the Earth Radiation Budget Satellite (ERBS). One EKF updates the attitude quaternion using a four-component additive error quaternion. This technique is compared to that of a second EKF, which uses a multiplicative error quaternion. Brief developments of the algorithms are included. The convergence properties, singularity problems, and normalization techniques of the two filters are addressed. Both filters are tested with simulated ERBS sensor data in addition to real ERBS sensor data. The results of the two filters are also compared to those from the ERBS operational ground support software, which uses a batch differential correction algorithm to estimate attitude and gyro biases.

Bar-Itzhack, Itzhack Y.↗
NASA NTRS1994

The use of a tactile interface to convey position and motion perceptions

Under normal terrestrial conditions, perception of position and motion is determined by central nervous system integration of concordant and redundant information from multiple sensory channels (somatosensory, vestibular, visual), which collectively yield vertical perceptions. In the acceleration environment experienced by the pilots, the somatosensory and vestibular sensors frequently present false information concerning the direction of gravity. When presented with conflicting sensory information, it is normal for pilots to experience episodes of disorientation. We have developed a tactile interface that obtains vertical roll and pitch information from a gyro-stabilized attitude indicator and maps this information in a one-to-one correspondence onto the torso of the body using a matrix of vibrotactors. This enables the pilot to continuously maintain an awareness of aircraft attitude without reference to visual cues, utilizing a sensory channel that normally operates at the subconscious level. Although initially developed to improve pilot spatial awareness, this device has obvious applications to 1) simulation and training, 2) nonvisual tracking of targets, which can reduce the need for pilots to make head movements in the high-G environment of aerial combat, and 3) orientation in environments with minimal somatosensory cues (e.g., underwater) or gravitational cues (e.g., space).

Rupert, A. H.↗
NASA NTRS1986

Inflight observability of gyro reference frame misalignment

The effect of gyro misalignment on the attitude knowledge error (AKE) in a strapdown environment is analyzed. The subject attitude knowledge is defined, and the equation of motion is derived considering only the initial AKE and the misalignment. These two error sources are shown to be different. The closed-form solution to the equation of motion is presented, and an important theorem concerning the error induced by the initial AKE and misalignment is proven. The observability of misalignment in an ideal update environment where three cases of AKE can be measured simultaneously is examined. The misalignment observability in an infinitesimal field of view line of sight sensor update design is discussed. It is concluded that attitude error in a strapdown gyro application due to gyro misalignment is a conservative function of the attitude only.

Huang, W. H.↗