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NASA NTRS2002

Skeletal muscle plasticity: cellular and molecular responses to altered physical activity paradigms

The goal of this article is to examine our current understanding of the chain of events known to be involved in the adaptive process whereby specific genes and their protein products undergo altered expression; specifically, skeletal muscle adaptation in response to altered loading states will be discussed, with a special focus on the regulation of the contractile protein, myosin heavy chain gene expression. This protein, which is both an important structural and regulatory protein comprising the contractile apparatus, can be expressed as different isoforms, thereby having an impact on the functional diversity of the muscle. Because the regulation of the myosin gene family is under the control of a complex set of processes including, but not limited to, activity, hormonal, and metabolic factors, this protein will serve as a cellular "marker" for studies of muscle plasticity in response to various mechanical perturbations in which the quantity and type of myosin isoform, along with other important cellular proteins, are altered in expression.

Non-NASA Center↗

NASA NTRS2007

Exploration Challenges: Transferring Ground Repair Techniques to Space Flight Application

Fulfilling NASA's Vision for Space Exploration will demand an extended presence in space at distances from our home planet that exceed our current experience in space logistics and maintenance. The ability to perform repairs in lieu of the customary Orbital Replacement Unit (ORU) process where a faulty part is replaced will be elevated from contingency to routine to sustain operations. The use and cost effectiveness of field repairs for ground based operations in industry and the military have advanced with the development of technology in new materials, new repair techniques and new equipment. The unique environments, accessibility constraints and Extra Vehicular Activity (EVA) issues of space operations will require extensive assessment and evolution of these technologies to provide an equivalent and expected level of assurance to mission success. Challenges include the necessity of changes in design philosophy and policy, extremes in thermal cycling, disruptive forces (such as static charge and wind entrainment) on developed methods for control of materials, dramatically increased volatility of chemicals for cleaning and other compounds due to extremely low pressures, the limits imposed on dexterity and maneuverability by current EVA equipment and practices, and the necessity of unique verification methodology. This paper describes these challenges in and discusses the effects on the established ground techniques for repair. The paper also describes the leading repair methodology candidates and their beneficial attributes for resolving these issues with the evolution of technology.

McLemore, Carole A.↗

NASA NTRS2013

Thermal Performance of ATLAS Laser Thermal Control System Demonstration Unit

The second Ice, Cloud, and Land Elevation Satellite mission currently planned by National Aeronautics and Space Administration will measure global ice topography and canopy height using the Advanced Topographic Laser Altimeter System {ATLAS). The ATLAS comprises two lasers; but only one will be used at a time. Each laser will generate between 125 watts and 250 watts of heat, and each laser has its own optimal operating temperature that must be maintained within plus or minus 1 degree Centigrade accuracy by the Laser Thermal Control System (LTCS) consisting of a constant conductance heat pipe (CCHP), a loop heat pipe (LHP) and a radiator. The heat generated by the laser is acquired by the CCHP and transferred to the LHP, which delivers the heat to the radiator for ultimate rejection. The radiator can be exposed to temperatures between minus 71 degrees Centigrade and minus 93 degrees Centigrade. The two lasers can have different operating temperatures varying between plus 15 degrees Centigrade and plus 30 degrees Centigrade, and their operating temperatures are not known while the LTCS is being designed and built. Major challenges of the LTCS include: 1) A single thermal control system must maintain the ATLAS at 15 degrees Centigrade with 250 watts heat load and minus 71 degrees Centigrade radiator sink temperature, and maintain the ATLAS at plus 30 degrees Centigrade with 125 watts heat load and minus 93 degrees Centigrade radiator sink temperature. Furthermore, the LTCS must be qualification tested to maintain the ATLAS between plus 10 degrees Centigrade and plus 35 degrees Centigrade. 2) The LTCS must be shut down to ensure that the ATLAS can be maintained above its lowest desirable temperature of minus 2 degrees Centigrade during the survival mode. No software control algorithm for LTCS can be activated during survival and only thermostats can be used. 3) The radiator must be kept above minus 65 degrees Centigrade to prevent ammonia from freezing using no more than 135 watts of heater power. 4) The LHP reservoir control heater power is limited to 15 watts with a 70 percent duty cycle. 5) The voltage of the power supply can vary between 26 volts direct current and 34 volts direct current during the spacecraft lifetime. A design analysis shows that a single LTCS can satisfy these requirements. However, shutdown of· the LHP is particularly challenging and the shutdown heater must be wired in series with two reservoir thermostats and two CCHP thermostats at different set points. An LTCS demonstration unit has been tested to verify these performance characteristics experimentally prior to proceeding to the final LTCS design and fabrication. Test results showed that the LHP shutdown scheme would be able to shut down the LHP as designed and the reservoir control heater can maintain the ATLAS mass simulator within the plus or minus 1 degrees Centigrade accuracy under various combinations of the heat load, sink temperature, and power supply voltage.

Ku, Jentung↗

NASA NTRS1997

IV and V Issues in Achieving High Reliability and Safety in Critical Control System Software

Risk analysis and integrated verification and validation are two important elements in a plan for ensuring the safety of critical software systems. We describe an approach we are currently developing for integrating risk analysis, and metrics analysis, and propose a fault predictor that would integrate the results of these activities. Practical difficulties associated with our approach are also discussed, as are limitations of the proposed predictor. We conclude with a discussion of what as been learned to date, and with suggestions for future work.

validation software reliability software risk asse↗

NASA NTRS1983

Bringing AI up to the space challenge

The state of the art in automated systems for working in environments hostile to humans is assessed, together with the technological advancements necessary to meet NASA goals. Since completely automated operations are not possible with the current level of artificial intelligence (AI), the operator must have access to remote television access and interactive computerized controls. A proximal system exists when the teleoperated mechanism is close enough so that negligible time passes between operator and servocontrolled activation and feedback. An additional constraint is the complexity of the signal. Further development areas have been identified as limiting the necessary communication, compensating for technical limitations of communication with remote systems, such as bandwidth, error rate, and equipment response time, and to build-in fault tolerance, self-diagnosis, and self-maintenance capabilities. An AI expert system is being developed at JPL to provide an expert knowledge base and a decision-making capability. It is suggested that only thorough questioning of mission and spacecraft experts, as well as searching the large volume of project documentations, will provide the necessary data for establishing an expert data base for AI implementation.

Heer, E.↗

NASA NTRS1997

Structural Verification of the Space Shuttle's External Tank Super LightWeight Design: A Lesson in Innovation

The Super LightWeight Tank (SLWT) team was tasked with a daunting challenge from the outset: boost the payload capability of the Shuttle System by safely removing 7500 lbs. from the existing 65,400 lb. External Tank (ET). Tools they had to work with included a promising new Aluminum Lithium alloy, the concept of a more efficient structural configuration for the Liquid Hydrogen (LH2) tank, and a highly successful, mature Light Weight Tank (LWT) program. The 44 month schedule which the SLWT team was given for the task was ambitious by any measure. During this time the team had to not only design, build, and verify the new tank, but they also had to move a material from the early stages of development to maturity. The aluminum lithium alloy showed great promise, with an approximately 29% increase in yield strength, 15% increase in ultimate strength, 5 deg/O increase in modulus and 5 deg/O decrease in density when compared to the current 2219 alloy. But processes had to be developed and brought under control, manufacturing techniques perfected, properties characterized, and design allowable generated. Because of the schedule constraint, this material development activity had to occur in parallel with design and manufacturing. Initial design was performed using design allowable believed to be achievable with the Aluminum Lithium alloy system, but based on limited test data. Preliminary structural development tests were performed with material still in the process of iteration. This parallel path approach posed obvious challenges and risks, but also allowed a unique opportunity for interaction between the structures and materials disciplines in the formulation of the material.

Otte, Neil↗

NASA NTRS1994

Development of an Advanced Animal Habitat for Spaceflight

It is necessary to fly a group-housed animals for many Life Science spaceflight studies. Currently, group-housed rodents are flown aboard the shuttle in the Animal Enclosure Module (AEM). Although the AEM has been used successfully for a number of flights, it has significant limitations in the number of animals it can accommodate, limited flight duration, passive temperature control and limited in flight data acquisition capability. An Advanced Animal Habitat (AAH) is being developed, which can be flown on the shuttle middeck, both spacelab and spacehab shuttle payload modules, and the space station. The AAH is designed to house 12 rats or 30 mice for up to 30 days. The AAH will have active temperature control, a window mechanism to facilitate video monitoring/recording of the animals, and biotelemetry capabilities. In addition, the design will permit access to the animals for experimental manipulations in space. The AAH can be refitted to experiment-specific requirements as needed. In initial 7-day hardware tests 12 male rats and 10 female mice show no adverse affects with respect to final body and organ weights as compared to vivarium. controls. The Advanced Animal Habitat will provide the science community opportunities to perform a greater variety of studies for longer duration in the microgravity environment than the current Animal Enclosure Module.

Baer, L.↗

NASA NTRS2004

Development of a Self-calibrating Dissolved Oxygen Microsensor Array for the Monitoring and Control of Plant Growth in a Space Environment

Plant experiments in space will require active nutrient delivery concepts in which water and nutrients are replenished on a continuous basis for long-term growth. The goal of this study is to develop a novel microsensor array to provide information on the dissolved oxygen environment in the plant root zone for the optimum control of plant cultivation systems in the space environment. Control of water and oxygen is limited by the current state-of-the-art in sensor technology. Two capabilities of the new microsensor array were tested. First, a novel in situ self-diagnosis/self-calibration capability for the microsensor was explored by dynamically controlling the oxygen microenvironment in close proximity to an amperometric dissolved oxygen microsensors. A pair of integrated electrochemical actuator electrodes provided the microenvironments based on water electrolysis. Miniaturized thin film dissolved oxygen microsensors on a flexible polyimide (Kapton(Registered Trademark)? substrate were fabricated and their performances were tested. Secondly, measurements of dissolved oxygen in two representative plant growth systems were made, which had not been performed previously due to lack of proper sensing technology. The responses of the oxygen microsensor array on a flexible polymer substrate properly reflected the oxygen contents on the surface of a porous tube nutrient delivery system and within a particulate substrate system. Additionally, we demonstrated the feasibility of using a 4-point thin film microprobe for water contents measurements for both plant growth systems. mechanical flexibility, and self-diagnosis. The proposed technology is anticipated to provide a reliable sensor feedback plant growth nutrient delivery systems in both terrestrial environment and the microgravity environment during long term space missions. The unique features of the sensor include small size and volume, multiple-point sensing,

Kim, Chang-Soo↗

NASA NTRS2010

Interplanetary Transit Simulations Using the International Space Station

We evaluated the space life sciences utility of the International Space Station (ISS) to simulate the outbound transit portion of missions to Mars and Near Earth Asteroids (NEA) to investigate biomedical and psychological aspects of such transits, to develop and test space operation procedures compatible with communication delays and outages, and to demonstrate and validate technologies and countermeasures. Two major categories of space life sciences activities can capitalize on ISS capabilities. The first includes studies that require ISS (or a comparable facility), typically for access to prolonged weightlessness. The second includes studies that do not strictly require ISS but can exploit it to maximize their scientific return more efficiently and productively than in ground-based simulations. For these studies, ISS offers a high fidelity analog for fundamental factors on future missions, such as crew composition, mission control personnel, operational tasks and workload, real-world risk, and isolation, and can mimic the effects of distance and limited accessibility. In addition to conducting Mars- and NEA-transit simulations on 6-month ISS increments, extending the current ISS increment duration from 6 months to 9 or even 12 months will provide opportunities for enhanced and focused research relevant to long duration Mars and NEA missions. Increasing the crew duration may pose little additional risk to crewmembers beyond that currently accepted on 6-month increments, but additional medical monitoring capabilities will be required beyond those currently used for ISS operations. Finally, while presenting major logistical challenges, such a simulation followed by a post-landing simulation of Mars exploration could provide quantitative evidence of capabilities in an actual mission. Thus, the use of ISS to simulate aspects of Mars and NEA missions seems practical. If it were to be implemented without major disruption of on-going ISS activities, then planning should begin soon, in close consultation with all international partners.

Charles, John B.↗

NASA NTRS1976

Arc discharge supply component protection circuitry

In a mercury-bombardment ion engine, the discharge supply is a high-current low-voltage one that maintains an arc or discharge inside the engine. In a 30-cm engine the supply provides up to 45 volts at about 13 amperes and is referenced at approximately 1100 volts above ground. Due to the engine discharge characteristics, a very slow feedback control loop is required. A high-speed current limit must be used to protect the components in the power conditioner, a pulse-width-modulated bridge inverter. A high-speed cycle-by-cycle current-limit circuit which allows the inverter to continue running in an overcurrent condition is used to protect it. The high-speed current sensing allows the inverter to be turned off each half cycle before the current in the primary of the inverter exceeds a safe level. This permits the inverter to continue to provide current into a discharge or a fault condition, until the feedback control system can actively control the current.

Ahrens, A. F.↗

NASA NTRS1989

Overview of computational control research at UT Austin

An overview of current research activities at UT Austin is presented to discuss certain technical issues in the following areas: (1) Computer-Aided Nonlinear Control Design: In this project, the describing function method is employed for the nonlinear control analysis and design of a flexible spacecraft equipped with pulse modulated reaction jets. INCA program has been enhanced to allow the numerical calculation of describing functions as well as the nonlinear limit cycle analysis capability in the frequency domain; (2) Robust Linear Quadratic Gaussian (LQG) Compensator Synthesis: Robust control design techniques and software tools are developed for flexible space structures with parameter uncertainty. In particular, an interactive, robust multivariable control design capability is being developed for INCA program; and (3) LQR-Based Autonomous Control System for the Space Station: In this project, real time implementation of LQR-based autonomous control system is investigated for the space station with time-varying inertias and with significant multibody dynamic interactions.

Bong, Wie↗

NASA NTRS1991

Roll plus maneuver load alleviation control system designs for the active flexible wing wind-tunnel model

Three designs for controlling loads while rolling for the Active Flexible Wing (AFW) are discussed. The goal is to provide good roll control while simultaneously limiting the torsion and bending loads experienced by the wing. The first design uses Linear Quadratic Gaussian/Loop Transfer Recovery (LQG/LTR) modern control methods to control roll rate and torsional loads at four different wing locations. The second design uses a nonlinear surface command function to produce surface position commands as a function of current roll rate and commanded roll rate. The final design is a flutter suppression control system. This system stabilizes both symmetric and axisymmetric flutter modes of the AFW.

Moore, Douglas B.↗

NASA NTRS1981

A decoupled control system for improved flight performance in wind shear

A fixed-base simulation study has been made to compare the approach and landing performance of a decoupled longitudinal control system and the velocity-vector control-wheel steering (VCWS) system that currently exists on the NASA Terminal Configured Vehicle (TCV). The decoupled control system employed constant prefilter and feedback gains to provide steady-state decoupling of flight-path angle, pitch angle, and forward velocity using symmetric spoilers, throttle, and elevator as active control elements. In severe wind shear, of the Kennedy-type, the decoupled control system improved both approach performance and touchdown performance even when the spoiler deflection was limited to 16 deg. On a 10-point rating scale, three research pilots rated the approach and landing task with decoupled controls as much as 3 to 4 increments better than the use of the VCWS system in severe winds

Miller, G. K., Jr.↗

NASA NTRS2001

Baseline Validation of Unstructured Grid Reynolds-Averaged Navier-Stokes Toward Flow Control

The value of the use of the Reynolds-averaged Navier-Stokes methodology for active flow control applications is assessed. An experimental flow control database exists for a NACA0015 airfoil modified at the leading edge to implement a fluidic actuator; hence, this configuration is used. Computational results are documented for the baseline wing configuration (no control) with the experimental results and assumes two-dimensional flow. The baseline wing configuration has discontinuities at the leading edge, trailing edge, and aft of midchord on the upper surface. A limited number of active flow control applications have been tested in the laboratory and in flight. These applications include dynamic stall control using a deformable leading edge, separation control for takeoff and landing flight conditions using piezoelectric devices, pulsed vortex generators, zero-net-mass oscillations, and thrust vectoring with zero-net-mass piezoelectric-driven oscillatory actuation. As yet, there is no definitive comparison with experimental data that indicates current computational capabilities can quantitatively predict the large aerodynamic performance gains achieved with active flow control in the laboratory. However, one study using the Reynolds-averaged Navier-Stokes (RANS) methodology has shown good quantitative agreement with experimental results for an isolated zero-net-mass actuator. In addition, some recent studies have used RANS to demonstrate qualitative performance gains compared with the experimental data for separation control on an airfoil. Those quantitative comparisons for both baseline and flow control cases indicated that computational results were in poor quantitative agreement with the experiments. The current research thrust will investigate the potential use of an unstructured grid RANS approach to predict aerodynamic performance for active flow control applications building on the early studies. First the computational results must quantitatively match experiments for the no-control case before proceeding to the time-dependent flow control case. This paper documents the baseline (no-control) case using an unswept airfoil configuration. The next section describes the configurations used for the computations and the experimentals. The computational approach is then described followed by results and concluding remarks.

Joslin, Ronald D.↗

NASA NTRSDate not supplied

ETM: Upper Class E Traffic Management

This is a slide set as part of a meeting series with members of a working group aimed at the development of a concept that addresses needs and gaps in the management of high-altitude airspace operations. This concept leverages elements developed through the UAS Traffic Management project with respect to a cooperative, service-based approach that provides services and capabilities in areas (e.g., Upper Class E airspace) that currently receive no or limited service from Air Traffic Control. This concept is meant to provide a safe, fair, and scalable approach to management of Upper Class E operations that reduces the burden on ATC while providing the flexibility and access desired by current and new users of the airspace. This set of slides includes an overview of discussions and industry news covering the time since the previous group meeting, an overview of relevant activities by NASA's Airborne Science Program, a review of the 2023 ETM Workshop, a placeholder for a presentation on an approach to an International Framework for operations, and an update on NASA's preparations for upcoming simulations.

Upper E↗

NASA NTRS1997

Optical Design of the Developmental Cryogenic Active Telescope Testbed (DCATT)

In the summer of 1996, three Study teams developed conceptual designs and mission architectures for the Next Generation Space Telescope (NGST). Each group highlighted areas of technology development that need to be further advanced to meet the goals of the NGST mission. The most important areas for future study included: deployable structures, lightweight optics, cryogenic optics and mechanisms, passive cooling, and on-orbit closed loop wavefront sensing and control. NASA and industry are currently planning to develop a series of ground testbeds and validation flights to demonstrate many of these technologies. The Deployed Cryogenic Active Telescope Testbed (DCATT) is a system level testbed to be developed at Goddard Space Flight Center in three phases over an extended period of time. This testbed will combine an actively controlled telescope with the hardware and software elements of a closed loop wavefront sensing and control system to achieve diffraction limited imaging at 2 microns. We will present an overview of the system level requirements, a discussion of the optical design, and results of performance analyses for the Phase 1 ambient concept for DCATT,

Davila, Pam↗

NASA NTRS2010

Analysis and Design of Phase Change Thermal Control for Light Emitting Diode (LED) Spacesuit Helmet Lights

LED Helmet Extravehicular Activity Helmet Interchangeable Portable (LEHIP) lights for the Extravehicular Mobility Unit (EMU) have been built and tested and are currently being used on the International Space Station. A design is presented of the passive thermal control system consisting of a chamber filled with aluminum foam and wax. A thermal math model of LEHIP was built and correlated by test to show that the thermal design maintains electronic components within hot and cold limits for a 7 hour spacewalk in the most extreme EVA average environments, and do not pose a hazard to the crew or to components of the EMU.

Bue, Grant C.↗

NASA NTRS1993

In-flight simulation of high agility through active control: Taming complexity by design

The motivation for research into helicopter agility stems from the realization that marked improvements relative to current operational types are possible, yet there is a dearth of useful criteria for flying qualities at high performance levels. Several research laboratories are currently investing resources in developing second generation airborne rotorcraft simulators. The UK's focus has been the exploitation of agility through active control technology (ACT); this paper reviews the results of studies conducted to date. The conflict between safety and performance in flight research is highlighted and the various forms of safety net to protect against system failures are described. The role of the safety pilot, and the use of actuator and flight envelope limiting are discussed. It is argued that the deep complexity of a research ACT system can only be tamed through a requirement specification assembled using design principles and cast in an operational simulation form. Work along these lines conducted at DRA is described, including the use of the Jackson System Development method and associated Ada simulation.

Padfield, Gareth D.↗