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At least 721 records · Page 40

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NASA NTRS1998

A Spaceflight Magnetic Bearing Equipped Optical Chopper with Six-Axis Active Control

This paper describes the development of an ETU (Engineering Test Unit) rotary optical chopper with magnetic bearings. An ETU is required to be both flight-like, nearly identical to a flight unit without the need for material certifications, and demonstrate structural and performance integrity. A prototype breadboard design previously demonstrated the feasibility of meeting flight performance requirements using magnetic bearings. The chopper mechanism is a critical component of the High Resolution Dynamics Limb Sounder (HIRDLS) which will be flown on EOS-CHEM (Earth Observing System-Chemistry). Particularly noteworthy are the science requirements which demand high precision positioning and minimal power consumption along with full redundancy of coils and sensors in a miniature, lightweight package. The magnetic bearings are unique in their pole design to minimize parasitic losses and utilize collocated optical sensing. The motor is of an unusual disk-type ironless stator design. The ETU design has evolved from the breadboard design. A number of improvements have been incorporated into the ETU design. Active thrust control has been added along with changes to improve sensor stability, motor efficiency, and touchdown and launch survivability. It was necessary to do all this while simultaneously reducing the mechanism volume. Flight-like electronics utilize a DSP (Digital Signal Processor) and contain all sensor electronics and drivers on a single five inch by nine inch circuit board. Performance test results are reported including magnetic bearing and motor rotational losses.

Blumenstock, K. A.↗

NASA NTRS1998

A Spaceflight Magnetic Bearing Equipped Optical Chopper with Six-Axis Active Control

Blumenstock, Kenneth A.↗

NASA NTRS1999

Miniature X-Ray Bone Densitometer

The purpose of the Dual Energy X-ray Absorptiometry (DEXA) project is to design, build, and test an advanced X-ray absorptiometry scanner capable of being used to monitor the deleterious effects of weightlessness on the human musculoskeletal system during prolonged spaceflight. The instrument is based on the principles of dual energy x-ray absorptiometry and is designed not only to measure bone, muscle, and fat masses but also to generate structural information about these tissues so that the effects on mechanical integrity may be assessed using biomechanical principles. A skeletal strength assessment could be particularly important for an astronaut embarking on a remote planet where the consequences of a fragility fracture may be catastrophic. The scanner will employ multiple projection images about the long axis of the scanned subject to provide geometric properties in three dimensions, suitable for a three-dimensional structural analysis of the scanned region. The instrument will employ advanced fabrication techniques to minimize volume and mass (100 kg current target with a long-term goal of 60 kg) of the scanner as appropriate for the space environment, while maintaining the required mechanical stability for high precision measurement. The unit will have the precision required to detect changes in bone mass and geometry as small as 1% and changes in muscle mass as small as 5%. As the system evolves, advanced electronic fabrication technologies such as chip-on-board and multichip modules will be combined with commercial (off-the-shelf) parts to produce a reliable, integrated system which not only minimizes size and weight, but, because of its simplicity, is also cost effective to build and maintain. Additionally, the system is being designed to minimize power consumption. Methods of heat dissipation and mechanical stowage (for the unit when not in use) are being optimized for the space environment.

Charles, Harry K., Jr.↗

NASA NTRS2004

Low-Cost, User-Friendly, Rapid Analysis of Dynamic Data System Established

An issue of primary importance to the development of new jet and certain other airbreathing combined-cycle powered aircraft is the advancement of airframe-integrated propulsion technologies. Namely, engine inlets and their systems and subsystems are required to capture, convert, and deliver the atmospheric airflow demanded by such engines across their operating envelope in a form that can be used to provide efficient, stable thrust. This must be done while also minimizing aircraft drag and weight. Revolutionary inlet designs aided by new technologies are needed to enable new missions. An unwanted byproduct of pursuing these inlet technologies is increased time-variant airflow distortion. Such distortions reduce propulsion system stability, performance, operability, and life. To countermand these limitations and fully evaluate the resulting configurations, best practices dictate that this distortion be experimentally measured at large scale and analyzed. The required measurements consist of those made by an array of high-response pressure transducers located in the flow field at the aerodynamic interface plane (AIP) between the inlet and engine. Although the acquisition of the necessary pitot-pressure time histories is relatively straight-forward, until recent years, the analysis has proved to be very time-consuming, tedious, and expensive. To transform the analysis of these data into a tractable and timely proposition, researchers at the NASA Glenn Research Center created and established the Rapid Analysis of Dynamic Data (RADD) system. The system provides complete, near real-time analysis of time-varying inlet airflow distortion datasets with report quality output. This fully digital approach employs Institute of Electrical and Electronics Engineers (IEEE) binary data file format standardization to establish data-acquisition-system-independent processing on low cost personal computers. Features include invalid instrumentation code-out, logging, and multiple replacement schemes as needed for each channel of instrumentation. The AIP pressure distribution can be interpolated to simulate measurements by alternate AIP probe arrays, if desired. In addition, the RADD system provides for the application of filters that can be used to focus the analysis on the frequency range of interest.

Arend, David J.↗

NASA NTRS1992

Lunar scout: A Project Artemis proposal

The results of a student project to design a lunar lander in the context of a specifically defined mission are presented. The Lunar Scout will be launched from Cape Canaveral, Florida onboard a Delta II launch vehicle. The Delta II will carry the lander and its payload to a 1367 km orbit. Once it reaches that altitude, a STAR 48A solid rocket motor will kick the spacecraft into a lunar trajectory. After burnout of the lunar insertion motor, it will be jettisoned from the spacecraft. The flight from the earth to the moon will take approximately 106.4 hours. During this time the battery, which was fully charged prior to launch, will provide all power to the spacecraft. Every hour, the spacecraft will use its sun sensors and star trackers to update its position, maintain some stabilization and relay it back to earth using the dipole antennas. At the start of its lunar trajectory, the spacecraft will fire one of its 1.5 N thrusters to spin in at a very small rate. The main reason for this is to prevent one side of the spacecraft from overheating in the sun. When the spacecraft nears the moon, it will orient itself for the main retro burn. At an altitude of 200 km, a 4400 N bipropellant liquid thruster will ignite to slow the spacecraft. During the burn, the radar altimeter will be turned on to guide the spacecraft. The main retro rocket will slow the lander to 10 m/s at an approximate altitude of 40 km above the moon. From there, the space craft will use four 4.5 N hydrazine vertical thrusters and 1.5 N horizontal thrusters to guide the spacecraft to a soft landing. Once on the ground, the lander will shutoff the radar and attitude control systems. After the debris from the impact has settled, the six solar panels will be deployed to begin recharging the batteries and to power up the payload. The feedhorn antenna will then rotate to fix itself on the earth. Once it moves, it will stay in that position for the spacecraft's lifetime. The payload will then be activated to begin the lunar mission.

Source record↗

NASA NTRS1994

Hydrodynamics of rotating stars and close binary interactions: Compressible ellipsoid models

We develop a new formalism to study the dynamics of fluid polytropes in three dimensions. The stars are modeled as compressible ellipsoids, and the hydrodynamic equations are reduced to a set of ordinary differential equations for the evolution of the principal axes and other global quantities. Both viscous dissipation and the gravitational radiation reaction are incorporated. We establish the validity of our approximations and demonstrate the simplicity and power of the method by rederiving a number of known results concerning the stability and dynamical oscillations of rapidly rotating polytropes. In particular, we present a generalization to compressible fluids of Chandrasekhar's classical results for the secular and dynamical instabilities of incompressible Maclaurin spheroids. We also present several applications of our method to astrophysical problems of great current interest, such as the tidal disruption of a star by a massive black hole, the coalescence of compact binaries driven by the emission of gravitational waves, and the development of instabilities in close binary systems.

Lai, Dong↗

NASA NTRSDate not supplied

Design Development of a Stable, Lightweight, Tall and Self-Deploying Lunar Tower

Deployable composite booms with spaceflight heritage are being investigated at the National Aeronautics and Space Administration (NASA) Langley Research Center (LaRC) and the Massachusetts Institute of Technology (MIT) Space Resources Workshop for their potential to be vertically deployed in the lunar gravity field, in support of the NASA Artemis campaign. This paper reports new design development results—after the original presentation at the NASA 2020 BIG Idea Challenge—for a 16.5-meter-tall, compact, self-deploying composite tower intended to support the exploration of lunar permanently shadowed regions by nearby robotic assets or humans. Possible applications include vertical solar arrays and the provision of elevated lines-of-sight to science or engineering payloads, in support of nearby targets operating in areas of interest that may be hard to reach. Useful elevated payloads include radio repeaters, remote sensing and imaging, navigation and power beaming systems. However, while these lightweight rollable booms have an excellent height to mass ratio, they typically exhibit axial curvature upon deployment resulting in appreciable lateral dead-load deflection of the tip mass relative to the tower base. This static deflection increases with tower height and tip mass, not only constraining the value delivered by the tower but also endangering its integrity. To develop a competitive, lightweight deployable composite boom tower, a capability to correct static deflections during and after deployment will be required. In this paper, a deployable guy wire stability system will be presented for the MIT / LaRC self-erecting composite boom lunar tower that provides real time measurements, maintains tension both actively (during deployment) and passively (post-deployment), and can serve as a reconfigurable platform to test and trade alternative stability system configurations, such as with added spreaders inspired by sailing boat masts. Using a calibrated photogrammetry system, the natural lateral deflection of the boom tip relative to the boom base at different deployed heights was recorded for different configurations. With real-time force measurements it was found that tensioned guy wires can significantly reduce the static tip deflection of a deployable composite boom under dead load and can dampen a dynamic oscillation in under a minute. It was also found that control authority is greatest where it is needed most, i.e., for the lever arm closest to being opposite the direction of deflection. For a tower height of at least 11 m and spreader length of at least 60 cm, a solution of differential tension in all three arms exists and, in principle, provides sufficient control authority to correct or significantly reduce boom tip deflections. Notably, natural deflections occur almost entirely normal to the seams of the boom cross-section, but the natural boom tip lateral deflection under dead load upon deployment was approximately 5% of boom deployed length, exceeding the manufacturing acceptance specification of 1%. Ongoing and future work includes the further investigation towards mitigating manufacture-caused lateral deflection, trading of alternative guy wire system designs, as well as the design development of a second-generation tower incorporating a more capable boom design with the learnings from the proof-of-concept system presented here.

deployable composite boom↗

NASA NTRS1974

Amplitude steered array

A spin stabilized satellite has an electronically despun antenna array comprising a multiplicity of peripheral antenna elements. A high gain energy beam is established by connecting a suitable fraction or array of the elements in phase. The beam is steered or caused to scan by switching elements in sequence into one end of the array as elements at the other end of the array are switched out. The switching transients normally associated with such steering are avoided by an amplitude control system. Instead of abruptly switching from one element to the next, a fixed value of power is gradually transferred from the element at the trailing edge of the array to the element next to the leading edge.

Dietrich, F. J.↗

NASA NTRS1980

Physical chemistry and evolution of salt tolerance in halobacteria

The cellular constituents of extremely halophilic bacteria not only tolerate high salt concentration, but in many cases require it for optical functioning. The characteristics affected by salt include enzyme activity, stability, allosteric regulation, conformation and subunit association. The salt effects are of two major kinds: electrostatic shielding of negative charges by cations at low salt concentration, and hydrophobic stabilization by salting-out type salts at high salt concentration. The composition of halobacterial proteins shows an excess of acidic amino acids and a deficiency of nonpolar amino acids, which accounts for these effects. Since the cohesive forces are weaker and the repulsing forces are stronger in these proteins, preventing aggregation in salt, these structures are no longer suited for functioning in the absence of high salt concentrations. Unlike these nonspecific effects, ribosomes in halobacteria show marked preference for potassium over sodium ions. To ensure the proper intracellular ionic composition, powerful ion transport systems have evolved in the halobacteria, resulting in the extrusion of sodium ions and their replacement by potassium. It is likely that such membrane transport system for ionic movements is a necessary requisite for salt tolerance.

Lanyi, J. K.↗

NASA NTRS1985

The use of active controls to augment rotor/fuselage stability

The use of active blade pitch control to increase helicopter rotor/body damping is studied. Control is introduced through a conventional nonrotating swashplate. State variable feedback of rotor and body states is used. Feedback parameters include cyclic rotor flap and lead-lag states, and body pitch and roll rotations. The use of position, rate, and acceleration feedback is studied for the various state variables. In particular, the influence of the closed loop feedback gain and phase on system stability is investigated. For the rotor/body configuration analyzed, rotor cyclic inplane motion and body roll-rate and roll-acceleration feedback can considerably augment system damping levels and eliminate ground resonance instabilities. Scheduling of the feedback state, phase, and gain with rotor rotation speed can be used to maximize the damping augmentation. This increase in lead-lag damping can be accomplished without altering any of the system modal frequencies. Investigating various rotor design parameters (effective hinge offset, blade precone, blade flap stiffness) indicates that active control for augmenting rotor/body damping will be particularly powerful for hingeless and bearingless rotor hubs.

Straub, F. K.↗

NASA NTRS1985

The use of active controls to augment rotor/fuselage stability

Straub, F. K.↗

NASA NTRS2009

Evaluation of Carbon Dioxide Sensors for the Constellation Space Suit Life Support System for Surface Exploration

This paper presents the findings of the trade study to evaluate carbon dioxide (CO2) sensing technologies for the Constellation (Cx) space suit life support system for surface exploration. The trade study found that nondispersive infrared absorption (NDIR) is the most appropriate high Technology Readiness Level (TRL) technology for the CO2 sensor for the Cx space suit. The maturity of the technology is high, as it is the basis for the CO2 sensor in the Extravehicular Mobility Unit (EMU). The study further determined that while there is a range of commercial sensors available, the Cx CO2 sensor should be a new design. Specifically, there are light sources (e.g., infrared light emitting diodes) and detectors (e.g., cooled detectors) that are not in typical commercial sensors due to cost. These advanced technology components offer significant advantages in performance (weight, volume, power, accuracy) to be implemented in the new sensor. The exact sensor design (light source, transmitting optics, path length, receiving optics and detector) will be specific for the Cx space suit and will be determined by the performance requirements of the Cx space suit. The paper further identifies specifications for some of the critical performance parameters as well as discussing the engineering aspects of implementing the sensor into the Portable Life Support System (PLSS). The paper then presents testing results from three CO2 sensors with respect to issues important to Extravehicular Activity (EVA) applications; stability, humidity dependence and low pressure compatibility. The three sensors include two NDIR sensors, one commercial and one custom-developed by NASA (for a different purpose), and one commercial electrochemical sensor. The results show that both NDIR sensors have excellent stability, no dependence on ambient humidity (when the ambient temperature is above the dew point) and operate in low pressure conditions and after being exposed to a full vacuum. The commercial electrochemical sensor was not suitable for the Cx space suit for surface exploration. Finally, the paper identifies a number of techniques currently under development that offer significant advantages for EVA applications. These include miniaturized, room temperature, solid electrolyte systems and advanced optical detectors.

Dietrich, Daniel L.↗

NASA NTRS1987

Stability/Instability Analysis of Rotating Machinery

Numerical index of stability calculated for nonlinear system. Technique for determining rotor stability or instability from analysis of measurements adapted for use with computer simulations of rotor motion. Involves calculation of log decrement or increment of vibration amplitude. Applicable to rotors mounted in loose bearings and to similar problems in which load-versus-deflection characteristics nonlinear. Developed for assessments of vibrational characteristics of turbopump rotors, technique also usable with such mechanisms as high-speed ball bearings.

Powers, Richard W.↗

NASA NTRS1991

Nimbus-7

The DSN (Deep Space Network) mission support requirements for Nimbus 7 are summarized. The basic Nimbus series spacecraft is attitude-stabilized in three axes, with the yaw axis always pointing towards the center of the Earth. The spacecraft provides a stable platform, power, command, and data handling support for active and passive sensors for daily global surveillance of the atmosphere, and for mapping details of the atmospheric structure and Earth surface from satellite altitudes. The Nimbus 7 mission objectives are outlined and the DSN support requirements are defined through the presentation of tables and narratives describing the spacecraft flight profile; DSN support coverage; S-band frequency assignments; support parameters for telemetry, command and support systems; and tracking support responsibility.

Foreman, M.↗

NASA NTRS1991

Reusable Reentry Satellite (RRS) system design study. Phase B, appendix E: Attitude control system study

A study which consisted of a series of design analyses for an Attitude Control System (ACS) to be incorporated into the Re-usable Re-entry Satellite (RRS) was performed. The main thrust of the study was associated with defining the control laws and estimating the mass and power requirements of the ACS needed to meet the specified performance goals. The analyses concentrated on the different on-orbit control modes which start immediately after the separation of the RRS from the launch vehicle. The three distinct on-orbit modes considered for these analyses are as follows: (1) Mode 1 - A Gravity Gradient (GG) three-axis stabilized spacecraft with active magnetic control; (2) Mode 2 - A GG stabilized mode with a controlled yaw rotation rate ('rotisserie') using three-axis magnetic control and also incorporating a 10 N-m-s momentum wheel along the (Z) yaw axis; and (3) Mode 3 - A spin stabilized mode of operation with the spin about the pitch (Y) axis, incorporating a 20 N-m-s momentum wheel along the pitch (Y) axis and attitude control via thrusters. To investigate the capabilities of the different controllers in these various operational modes, a series of computer simulations and trade-off analyses have been made to evaluate the achievable performance levels, and the necessary mass and power requirements.

Source record↗

NASA NTRS1994

Microgravity isolation system design: A modern control analysis framework

Many acceleration-sensitive, microgravity science experiments will require active vibration isolation from the manned orbiters on which they will be mounted. The isolation problem, especially in the case of a tethered payload, is a complex three-dimensional one that is best suited to modern-control design methods. These methods, although more powerful than their classical counterparts, can nonetheless go only so far in meeting the design requirements for practical systems. Once a tentative controller design is available, it must still be evaluated to determine whether or not it is fully acceptable, and to compare it with other possible design candidates. Realistically, such evaluation will be an inherent part of a necessary iterative design process. In this paper, an approach is presented for applying complex mu-analysis methods to a closed-loop vibration isolation system (experiment plus controller). An analysis framework is presented for evaluating nominal stability, nominal performance, robust stability, and robust performance of active microgravity isolation systems, with emphasis on the effective use of mu-analysis methods.

Hampton, R. D.↗

NASA NTRS1973

Precision pointing thrustor.

A satellite experiment to test the predicted relativistic precession of a gyroscope moving through a gravitational field has been under development at Stanford University for a number of years. The instruments will be located in a liquid helium bath to insure dimensional stability and to permit using superconducting types of circuitry for readout of the gyro orientation. Heat leaks in the system cause the helium to boil and the resultant helium gas is used for attitude control. The principal subject of the paper is the design and experimental evaluation of an electromagnetically actuated differential thrustor which was built and tested at Stanford University. The results are unique because most propulsion systems operate on-off in order to utilize propellant efficiently. In this case, the gas must flow continually to provide cooling, and the requirements are primarily for low power, small volume, and high reliability.

Bull, J. S.↗

NASA NTRS1980

Large scale model tests of a new technology V/STOL concept

An ejector design concept for V/STOL aircraft, featuring a double-delta configuration with two large chordwise ejector slots adjacent to the fuselage side and a tailplane or canard for longitudinal control is examined. Large scale model tests of the concept have shown that ejector systems are capable of significant thrust augmentation at realistic supply pressures and temperatures, so that power plant size and weight can be reduced accordingly. A thrust augmentation of at least 1.75 can be achieved for the isolated ejector, not making allowance for duct and nozzle losses. Substantial reductions in velocity, temperature and noise of the lifting jet are assured due to mixing within the ejector - this lessens the severity of ground erosion and the thrust loss associated with reingestion. Consideration is also given to the effect of ground proximity, longitudinal aerodynamic characteristics, transition performance, and lateral stability.

Whittley, D. C.↗