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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Development of Weigh-Out Process and Evaluations for Underwater Partial Gravity Simulations

For the upcoming Artemis lunar missions, astronauts will need to train in a spacesuit where partial gravity can be simulated such as the NASA Neutral Buoyancy Lab (NBL). At the NBL, dive weights and foam can be added around the spacesuit to attain a satisfactory center of buoyancy (CB) and center of gravity (CG) location to simulate the lunar gravity (1/6thG) effects. If CG and CB are not co-located properly, incorrect righting moments can be introduced, and both simulation quality and EVA task performance can be impaired. Based on the findings from the initial testing using xEMU spacesuits, it was observed that the weigh-out method (i.e., determination of the weights and foam quantities and position) needed further development to improve the simulation quality, especially for the subjects who experienced excessive instability. This paper aims to present the on-going effort to improve the weigh-out process for enabling NBL lunar EVA simulations. For this effort, a human-suit model was created to use suit CAD and 3D human body scans to estimate both CB and CG location for each suited subject. NBL weigh-out testing was performed to characterize the effects of CG and CB positioning, in which the 3D human-suit model was used to determine optimal weigh-out combinations of weights and foam. Postural, balance, and subjective feedback were gathered for each weigh-out configuration. The results indicated that, as the CB was shifted higher and the CB and CG located closer to each other, the subject tended to be more stable and their EVA performance improved. A high CB location was then prioritized across 4 additional subjects in both small and large size spacesuits. When compared to the initial xEMU test series, improved performance was observed across all subjects as the CB moved higher and aligned closer to the system CG.

Pouyan Sabahi↗
NASA NTRS1972

Testing relativistic gravity theories using radio tracking data from planetary orbiting spacecraft.

We present a thorough analysis of a computational method for determining the numerical values of the relativity and other related dynamical parameters using two-way Doppler and ranging data from planetary orbiting spacecraft. The computational method consists of two parts. From Doppler data we first determine the earth-planet components of the position of the orbiting spacecraft relative to the center of gravity of the planet to high accuracy; adding the observed spacecraft range yields a range value to the center of the planet. These constructed earth-planet range data, referred to as normal points, are then treated as raw data in a regression analysis combined with planetary radar delay and meridian circle measurements to solve for the significant solar system dynamical parameters. The major errors sources in the planetary orbiter process are enumerated and their individual effects on the overall accuracy of the normal point accuracies are presented. The accuracies of the parameter estimates as a function of time, data sampling, and a priori assumptions are illustrated.

Jordan, J. F.↗
NASA NTRS1986

New shape in the sky

The 'dual keel' design currently under consideration for NASA's Space Station program is of rectangular configuration to yield greater space along the truss structure for the attachment of payloads, by comparison with a previously considered single-keel truss design. The placing of the pressurized modules much nearer the center of gravity of this station configuration allows accelerations that are closer to 1 micro-g than the earlier alternative. The U.S. Servicing Facility and Telerobotic System, and the Canadian Mobile Servicing Center, will be incorporated in order to meet a large variety of Space Station servicing requirements.

Aaron, J. W.↗
NASA NTRS1974

Experimental determination of the principal moments of inertia of the Helios prototype spacecraft

The moment of inertia of the Helios Spacecraft about its spin axis was determined by use of a roll-fixture using two sets of crossed flexure pivots as elastic constraints. The test procedure entailed measurement of a system oscillation period with each of a set of added moment-of-inertia increments. The tare effect of the fixture was determined by a like process and was subtracted from the gross value to yield the spacecraft roll moment of inertia to an estimated accuracy of 0.2%. Lateral moments of inertia (i.e., about each of three axes normal to the spin axis) were determined by a gravity pendulum method that makes use of the fact that any physical pendulum has a minimum period of oscillation determined by a particular distance from the axis of rotation to the system center of gravity.

Gayman, W. H.↗
NASA NTRS1989

Tethered gravity laboratories study

The use is studied of tether systems to improve the lowest possible steady gravity level on the Space Station. Particular emphasis is placed by the microgravity community on the achievement of high quality microgravity conditions. The tether capability is explored for active control of the center of gravity and the analysis of possible tethered configurations.

Lucchetti, F.↗
NASA NTRS1987

Combustion of velcro in low gravity

An experimental program was conducted to investigate the low gravity burning characteristics on nylon and Nomex Velcro fastening tapes in an atmosphere of 30-percent oxygen, 70-percent nitrogen at a 70-kPa pressure. The tests were conducted using the NASA Lewis Research Center Zero Gravity Facility. The test results, as documented by high-speed cameras, indicate that both nylon and Nomex burn in low gravity for the full 5.18 sec test time but that Nomex burns less vigorously than nylon. Nylon melts as it burns, whereas Nomex forms a solid char. Nylon also sputters burning droplets as it burns. Thus, from these limited tests, it appears that Nomex Velcro is less hazardous than nylon Velcro for spacecraft applications. The results also show that residual gas velocities, and by analogy spacecraft air circulation, can enhance the low-gravity combustion.

Olson, Sandra L.↗
NASA NTRS2012

NASA's Next Solar Sail: Lessons Learned from NanoSail - D2

NanoSail-D2 unfurled January 17th, 2011 and commenced a nine month Low Earth Orbit path to reentry to evaluate a sail's capacity to deploy in space and deorbit satellites. The orbit was strongly affected by variables including but not limited to: initial attitude, orbit lighting, solar radiation pressure, aerodynamic drag, gravity, and Center of Pressure offsets. The effects of these variables were evaluated through a 3-DOF rigid body simulation. The sail experienced stability in orbits which were continuously lit, i.e. did not orbit behind Earth. Probable drag area experienced by the sail for the mission is also estimated from orbital data and compared to the attitude simulation results. Analysis focuses on sail behavior in full lighting conditions to establish the limits of the sails stability in full lighting. Solar radiation pressure, aerodynamic drag, and gravity torque effects are described. Lastly, a reasonable upper bound on the variation of the Center of Pressure from the geometric center of the sail plane is established. Each of these results contributes to the design requirements for future solar sails.

Katan, Chelsea↗
NASA NTRS1988

Optimization of slender wings for center-of-pressure shift due to change in Mach number

It is observed that the center of pressure on a wing shifts as the Mach number is changed. Such shifts are in general undesirable and are sometimes compensated for by actively shifting the center of gravity of the aircraft or by using active stability controls. To avoid this complication, it is desirable to design the wings of a high speed aircraft so as to minimize the extent of the center-of-pressure shifts. This, together with a desire to minimize the center-of-pressure shifts in missile control surfaces, provides the motivation for this project. There are many design parameters which affect center-of-pressure shifts, but it is expected that the largest effects are due to the wing planform. Thus, for the sake of simplicity, this study is confined to an investigation of thin, flat, (i.e., no camber or twist), relatively slender, pointed wings flying at a small angle of attack. Once the dependence of the center of pressure on planform and Mach number is understood, we can expect to investigate the sensitivity of the center-of-pressure shifts to various other parameters.

Andersen, Carl M.↗
NASA NTRS1992

Pitch Control Margin at High Angle of Attack - Quantitative Requirements (Flight Test Correlation With Simulation Predictions)

Aircraft designs that employ relaxed static stability (RSS) have the following problem: reduced pitching moments associated with RSS at high angle of attack (AOA) require a minimum pitch recovery moment or margin to guarantee a safe return from high AOA maneuvers at the most aft center of gravity (CG) encountered during a mission. Recent incidents and mishaps on Class IV aircraft have demonstrated a need for establishing quantitative longitudinal high AOA pitch control margin design guidelines for future aircraft. The Naval Air Warfare Center - Aircraft Division (NA WC-AD) is currently supporting an effort in conjunction with NASA Langley Research Center (NASA LaRC) to quantify such requirements. NASA LaRC has conducted a series of extensive simulation evaluations to define these design guidelines. The purpose of flight tests were to validate the overall research test methodology by comparing pilot comments, pilot ratings, and aircraft response characteristics gathered during inflight recoveries from high AOA conditions to those gathered during the fixed-base simulation sessions. Tests were completed on an F/A-18A in six flights for a total of 9.8 flight hours using an AOA and CG buildup sequence. Flight test results have validated the simulation studies in that pilot rating of high AOA nose-down recoveries were based on the short-term response interval in the forms of pitch acceleration and rate. In addition, flight test has demonstrated that high AOA pitch control margin can be evaluated using a stabilized pushover method.

Flight Testing↗
NASA NTRS1996

Subsonic Aerodynamic Characteristics of a Circular Body Earth-to-Orbit Vehicle

A test of a generic reusable earth-to-orbit transport was conducted in the 7- by 10-Foot high-speed tunnel at the Langley Research Center at Mach number 0.3. The model had a body with a circular cross section and a thick clipped delta wing as the major lifting surface. For directional control, three different vertical fin arrangements were investigated: a conventional aft-mounted center vertical fin, wingtip fins, and a nose-mounted vertical fin. The configuration was longitudinally stable about the estimated center-of-gravity position of 0.72 body length and had sufficient pitch-control authority for stable trim over a wide range of angle of attack, regardless of fin arrangement. The maximum trimmed lift/drag ratio for the aft center-fin configuration was less than 5, whereas the other configurations had values of above 6. The aft center-fin configuration was directionally stable for all angles of attack tested. The wingtip and nose fins were not intended to produce directional stability but to be active controllers for artificial stabilization. Small rolling-moment values resulted from yaw control of the nose fin. Large adverse rolling-moment increments resulted from tip-fin controller deflection above 13 deg angle of attack. Flow visualization indicated that the adverse rolling-moment increments were probably caused by the influence of the deflected tip-fin controller on wing flow separation.

Lepsch, Roger A., Jr.↗
NASA NTRS2008

Effects of Varying Surface Inclines and Suit Pressure: Implications on Space Suit Design

Suited human performance studies in reduced gravity environments to date include limited observations from Apollo Lunar surface Extravehicular Activities (EVA) and from previous studies conducted in partial gravity simulation environments. The Constellation Program EVA Systems Project office has initiated tests to develop design requirements for the next generation Lunar EVA suit. Theses studies were conducted in the Space Vehicle Mock-Up Facility (SVMF) at Johnson Space Center from which the results provided recommendations for suit weight, mass, center of gravity, pressure, and suit kinematic constraints that optimize human performance in partial gravity environments.

Clowers, Kurt↗
NASA NTRS1993

Experimental performance of a ventral nozzle with pitch and yaw vectoring capability for SSTOVL aircraft

Aircraft with supersonic, short takeoff and vertical landing capability have been proposed to replace some of the current high-performance aircraft. Several of these configurations use a ventral nozzle in the lower fuselage, aft of the center of gravity, for lift or pitch control. Internal vanes canted at 20 deg were added to a swivel-type ventral nozzle and tested at tailpipe to ambient pressure ratios up to 5.0 on the Powered Lift Facility at NASA Lewis Research Center. The addition of sets of four or seven vanes decreased the discharge coefficient of the nozzle by at least 6 percent and did not effect the thrust coefficient. Side force produced by the nozzle with vanes was 14 percent or more of the vertical force. In addition, this side force caused only a smalll loss in vertical force in comparison to the nozzle without vanes. The net thrust force was 8 deg from the vertical for four vanes and 10.5 deg for seven.

Esker, Barbara S.↗
NASA NTRS1984

Propellant transfer: Tethered depot

Spacebasing of orbital transfer vehicles at a space station requires a depot that safely and efficiently stores and transfers the resupply propellants. In order to transfer propellants, a method effectively acquire only liquid and vent only gas must exist. A method that produces a low gravity to settle propellants would bypass these weaknesses, while allowing ground-like operations. This low gravity can be passively produced using gravity gradient techniques. A satellite with a large length to diameter ratio, such as a depot attached to a space station with a tether, stabilizes along on Earth radial because of an outward acceleration proportional to the distance from the satellite's center of gravity. Analysis indicates that liquid can be setteled with relatively short tether lengths. The feasibility, design requirements, and operational limitations of a tethered refueling depot were investigated with special emphasis on slosh control.

Kroll, K.↗
NASA NTRS2011

NEEMO 14: Evaluation of Human Performance for Rover, Cargo Lander, Crew Lander, and Exploration Tasks in Simulated Partial Gravity

The ultimate success of future human space exploration missions is dependent on the ability to perform extravehicular activity (EVA) tasks effectively, efficiently, and safely, whether those tasks represent a nominal mode of operation or a contingency capability. To optimize EVA systems for the best human performance, it is critical to study the effects of varying key factors such as suit center of gravity (CG), suit mass, and gravity level. During the 2-week NASA Extreme Environment Mission Operations (NEEMO) 14 mission, four crewmembers performed a series of EVA tasks under different simulated EVA suit configurations and used full-scale mockups of a Space Exploration Vehicle (SEV) rover and lander. NEEMO is an underwater spaceflight analog that allows a true mission-like operational environment and uses buoyancy effects and added weight to simulate different gravity levels. Quantitative and qualitative data collected during NEEMO 14, as well as from spacesuit tests in parabolic flight and with overhead suspension, are being used to directly inform ongoing hardware and operations concept development of the SEV, exploration EVA systems, and future EVA suits. OBJECTIVE: To compare human performance across different weight and CG configurations. METHODS: Four subjects were weighed out to simulate reduced gravity and wore either a specially designed rig to allow adjustment of CG or a PLSS mockup. Subjects completed tasks including level ambulation, incline/decline ambulation, standing from the kneeling and prone position, picking up objects, shoveling, ladder climbing, incapacitated crewmember handling, and small and large payload transfer. Subjective compensation, exertion, task acceptability, and duration data as well as photo and video were collected. RESULTS: There appear to be interactions between CG, weight, and task. CGs nearest the subject s natural CG are the most predictable in terms of acceptable performance across tasks. Future research should focus on understanding the interactions between CG, mass, and subject differences.

Chappell, Steven P.↗
NASA NTRS2001

Changes in root cap pH are required for the gravity response of the Arabidopsis root

Although the columella cells of the root cap have been identified as the site of gravity perception, the cellular events that mediate gravity signaling remain poorly understood. To determine if cytoplasmic and/or wall pH mediates the initial stages of root gravitropism, we combined a novel cell wall pH sensor (a cellulose binding domain peptide-Oregon green conjugate) and a cytoplasmic pH sensor (plants expressing pH-sensitive green fluorescent protein) to monitor pH dynamics throughout the graviresponding Arabidopsis root. The root cap apoplast acidified from pH 5.5 to 4.5 within 2 min of gravistimulation. Concomitantly, cytoplasmic pH increased in columella cells from 7.2 to 7.6 but was unchanged elsewhere in the root. These changes in cap pH preceded detectable tropic growth or growth-related pH changes in the elongation zone cell wall by 10 min. Altering the gravity-related columella cytoplasmic pH shift with caged protons delayed the gravitropic response. Together, these results suggest that alterations in root cap pH likely are involved in the initial events that mediate root gravity perception or signal transduction.

NASA Discipline Plant Biology↗
NASA NTRS1997

Artificial gravity for human missions

The author examines the merits and problems associated with full-time rotation and intermittent G stimulation as weightlessness countermeasures during prolonged space flight.

NASA Discipline Neuroscience↗
NASA NTRS1989

Airplane-Acceleration Display For Low-Gravity Research

Bar-graph display facilitates precise control of trajectories. Overall display system includes accelerometer block, power-supply-and-interface box, thrust-axis display, and pitch-and-lateral-axes display. Accelerometer block includes three servoaccelerometers orthogonally mounted on adjustable triaxial base allowing fine alignment of accelerometers with respect to airplane. Accelerometer block and power-supply-and-interface box located near center of gravity of airplane in lugguage area. LED bar-graph displays take up less panel space and easier to align with axes represented. No moving parts and not subject to parallax. With help of display, pilot adheres to predetermined fraction of g, with minimal lateral acceleration.

Millis, Marc G.↗
NASA NTRS1975

Measurement of the inertial properties of the Helios F-1 spacecraft

A gravity pendulum method of measuring lateral moments of inertia of large structures with an error of less than 1% is outlined. The method is based on the fact that in a physical pendulum with a knife-edge support the distance from the axis of rotation to the system center of gravity determines the minimal period of oscillation and is equal to the system centroidal radius of gyration. The method is applied to results of a test procedure in which the Helios F-1 spacecraft was placed in a roll fixture with crossed flexure pivots as elastic constraints and system oscillation measurements were made with each of a set of added moment-of-inertia increments. Equations of motion are derived with allowance for the effect of the finite pivot radius and an error analysis is carried out to find the criterion for maximum accuracy in determining the square of the centroidal radius of gyration. The test procedure allows all measurements to be made with the specimen in upright position.

Gayman, W. H.↗