SEARCH · Search NASA
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
We present single event effects (SEE) evaluation of the Everspin Technologies 1Gb non-volatile ST-DDR4 spin-transfer torque MRAM.
Explore the source record for details and available documents.
Computerized prediction analyses of radial spin acceleration effects on solid propellant rocket motor ballistics and heat transfer
This document reports on the accomplishments of the Innovative Partnerships Program during the two years of 2009 and 2010. The mission of the Innovative Partnerships Program is to provide leveraged technology alternatives for mission directorates, programs, and projects through joint partnerships with industry, academia, government agencies, and national laboratories. As outlined in this accomplishments summary, the IPP at NASA's Kennedy Space Center achieves this mission via two interdependent goals: (1) Infusion: Bringing external technologies and expertise into Kennedy to benefit NASA missions, programs, and projects (2) Technology Transfer: Spinning out space program technologies to increase the benefits for the nation's economy and humanity
Transient spin-up and spin-down flows inside of spacecraft fuel tanks need to be analyzed in order to properly design spacecraft control systems. Knowledge of the characteristics of angular momentum transfer to and from the fuel is used to size the de-spin mechanism that places the spacecraft in a controllable in-orbit state. In previous studies, several analytical models of the spin-up process were developed. However, none have accurately predicted all of the flow dynamics. Several studies have also been conducted using Navier-Stokes based methods. These approaches have been much more successful at simulating the dynamic processes in a cylindrical container, but have not addressed the issue of momentum transfer. In the current study, the spin-up and spin-down of a fuel tank filled with gaseous xenon has been investigated using a three-dimensional unsteady Navier-Stokes code. Primary interests have been concentrated on the spin-up/spin-down time constants and the initial torque imparted on the system. Additional focus was given to the relationship between the dominant flow dynamics and the trends in momentum transfer. Through the simulation of both a cylindrical and a spherical tank, it was revealed that the transfer of angular momentum is nonlinear at early times and tends toward a linear pattern at later times. Further investigation suggests that the nonlinear spin up is controlled by the turbulent transport of momentum, while the linear phase is controlled by a Coriolis driven (Ekman) flow along the outer wall. These results indicate that the spinup and spin-down processes occur more quickly in tanks with curved surfaces than those with defined top, bottom, and side walls. The results also provide insights for the design of spacecraft de-spin mechanisms.
Forced convective heat transfer from isothermal and nonisothermal uniformly spinning bodies of revolution obtained by similar flow analysis
Forced convective heat transfer from isothermal and nonisothermal uniformly spinning bodies of revolution obtained by similar flow analysis
The local rate of mass transfer to the bottom endwall of a large aspect ratio cylinder was measured during spin-up/spin-down. The local mass transfer rate was a strong function radial position along the endwall. At the center during spin-up from rest, the maximum enhancement in mass transfer occurred after the Ekman time scale and before the viscous time scale. At the center during spin-down to rest, a stagnation vortex formed, causing the mass transfer rate to decay and then increase back to the original value of the order of the viscous time scale. Away from the center a much more complicated pattern was observed, but spin-up and spin-down were similar. Two peaks in mass transfer rate occurred for an Ekman number over 0.0074. Alternating spin-up and spin-down with a short period caused the center of the endwall to experience a nearly sinusoidal variation in mass transfer with the frequency equal to the forcing frequency. Near the edge the frequency was twice the forcing frequency.
The Cosmic Background Explorer (COBE) spacecraft will be launched by the Shuttle from Vandenberg AFB into a 300 km altitude, 99 deg inclination, 6 a.m. or 6 p.m. ascending node orbit. After release from the Remote Manipulator System (RMS) arm, an on-board monopropellant hydrazine propulsion system will raise the orbit altitude to 900 km. The spacecraft continuously spins during transfer orbit operations with the spin axis nominally horizontal and in or near the orbit plane. The blowdown propulsion system consists of twelve 5 lb thrusters (3 'spin', 3 'despin', and 6 'axial') with the latter providing initially 30 lb of force parallel to the spin axis for orbit raising. The spin/despin jets provide a constant roll rate during the transfer orbit phase of the mission and the axials control pitch and yaw. The axial thrusters are pulsed on for attitude control during coast periods and are normally on- and off-modulated for control during orbit raising. Attitude sensors employed in the control loops include an array of two-axis digital sun sensors and three planar earth scanners for position measurements, as well as six gyroscopes for rate information. System redundancy is achieved by means of unique three-axes-in-a-plane geometry. This triaxial concept results in a fail-safe operational system with no performance degradation for many different component failure modes.
An orbiting tethered satellite can propel itself by reaction against the gravitational gradient, with expenditure of energy but with no use of on-board reaction mass. Energy can be added to the orbit by pumping the tether length in the same way as pumping a swing. Examples of tether propulsion in orbit without use of reaction mass are discussed, including: (1) using tether extension to reposition a satellite in orbit without fuel expenditure by extending a mass on the end of a tether; (2) using a tether for eccentricity pumping to add energy to the orbit for boosting an orbital transfer; and (3) length modulation of a spinning tether to transfer angular momentum between the orbit and tether spin, thus allowing changes in orbital angular momentum.
Examples of tether propulsion in orbit without the use of reaction mass are discussed. These include (1) using tether extension to reposition a satellite in orbit without fuel expenditure by extending a mass on the end of the tether; (2) using a tether for eccentricity pumping to add energy to the orbit for boosting and orbital transfer; and (3) length modulation of a spinning tether to transfer angular momentum between the orbit and tether spin, thus allowing changes in orbital angular momentum.
The evolution of a rotating massive cloud, starting at interstellar densities, continuing through a series of intermediate fragmentation stages, and ending with stellar multiple systems with components near the main sequence, is outlined. The scenario is based on results of two- and three-dimensional numerical hydrodynamical calculations of collapsing clouds. Transfer of spin angular momentum primarily into orbital motion is assumed to occur at each fragmentation stage. Expected initial conditions in the cloud lead to final fragments which have in many cases the masses and angular momenta appropriate to observed main-sequence systems. Other points of comparison with observations are briefly noted.
The semimajor axis of the Lageos orbit is decreasing secularly at the rate of -1.1 mm/day due to an unknown force. Nine possible mechanisms are investigated. Five of the mechanisms, resonance with the Earth's gravitational field, gravitational radiation, the Poynting-Robertson effect, transfer of spin angular momentum to the orbital angular momentum, and drag from near Earth dust are ruled out because they are too small to require unacceptable assumptions to account for the observed rate. Three other mechanisms, the Yarkovsky effect, the Schach effect, and terrestrial radiation pressure could possibly give the proper order of magnitude for the decay rate, but the characteristic signatures of these perturbations do not agree with the observed secular decrease. Atmospheric drag from a combination of charged and neutral particles is the most likely cause for the orbital decay. This mechanism explains at least 71 percent of the observed rate of decrease of the semimajor axis.
The use of spinning tethers to transfer payloads from low earth orbit (LEO) to geosynchronous earth orbit (GEO) has previously been considered for payload masses up to 4000 kg (4 MT). The construction of the solar power station requires a transfer of 22,568 MT per year from LEO to GEO. This is envisioned to be carried out in payload units of 20 MT or 40 MT, which implies a frequency of 1188 or 594 flights per year, respectively. We could say from the outset that the use of spinning tethers for such large payloads at such high launch frequencies does not appear promising. This is inherent in the principles of spinning tether transfer, which we will briefly sketch below. Somewhat different scenarios are possible, but the basic physics remains the same. We consider only a single stage from LEO to GTO tether system, since the complexity involved in phasing the launches, docking, and spinups for a two-stage system for so many payloads rules out a two-stage system, in our opinion. The payload must first be launched to LEO, where it docks with the tether launch platform and is connected to the tether. The tether (tens of kilometers long) is then deployed with the payload upward. In order to give the payload the velocity necessary to launch it into a geosynchronous transfer orbit (GTO), i.e., to impart the required Av, the tethered system must be spun up about the center of mass of the tether-platform-payload system. The two end masses (platform and payload) are driven to rotate about the center of mass of the tethered system. Both the final rotational velocity and the phasing of the tether spin have to be controlled so that payload is in the vertically up position at the perigee of the LEO and with the velocity required to achieve the GTO when it is released at that point. Upon release, the payload then goes into GTO, where it again requires an acceleration to reach GEO (circularization of the orbit). The platform goes into a lower orbit, from which it must be raised in order to be at the proper LEO for docking with another payload. For this scheme to make sense at all, the platform must be envisioned as having a solar powered electrical thrust system to regain LEO and to spin up the tethered system. Similarly, solar powered electrical propulsion would be used to circularize the orbit to GEO.
This PowerPoint presentation defines technology transfer and discusses spin-out/off pros/cons involving whether to include a project within NASA or to contract outside NASA. The author discusses what would making the technology transfer happen by suggesting to evaluate NASA technologies/needs and find partners with ability to do business with NASA. The presentation concludes with recent Goddard successes.
During some part or all of each mission, about half of all scientific and commercial spacecraft will spin. For example, commercial spacecraft are made to spin during the transfer maneuver from low Earth orbit to the mission orbit to obtain gyroscopic stiffness. Many spacecraft spin continuously in orbit for the same reason. Other reasons for spinning include controlling the location of liquid propellants within their tanks and distributing solar heat loads. Although spinning has many benefits, it also creates problems because of the unavoidable wobble motion that accompanies spinning. Wobbling makes the spacecraft's flexible components oscillate. The energy dissipated by the internal friction of these components causes the wobbling amplitude to increase continually until, at some point, the attitude control thrusters must be fired to bring the spacecraft's amplitude back to an acceptable level.
The TELSTAR 4 communication satellites being manufactured by Martin Marietta Astro Space (Astro Space) for AT&T are three axis stabilized spacecraft scheduled to be launched on expendable vehicles such as the Atlas or Ariane rockets. Typically, these spacecraft consist of a box that holds the electronics and supports the antenna reflectors and the solar array wings. The wings and reflectors are folded against the sides of the box during launch and the spacecraft is spun for attitude control in that phase; they are then deployed after achieving the final orbit. The launch phase and transfer orbits required to achieve the final geosynchronous orbit typically take 4 to 5 days during which time the power required for command, telemetry, attitude control, heaters, etc., is provided by two 50 AH nickel hydrogen batteries augmented by the exposed outboard solar panels. In the past, this situation has presented no problem since there was a considerable excess of power available from the array. In the case of large high powered spacecraft such as TELSTAR 4, however, the design power levels in transfer orbit approach the time-averaged power available from the exposed surface area of the solar arrays, resulting in a very tight power margin. To compound the difficulty, the array output of the spinning spacecraft in transfer orbit is shaped like a full wave rectified sine function and provides very low charging rates to the batteries during portions of the rotation. In view of the typically low charging efficiency of alkaline nickel batteries at low rates, it was decided to measure the efficiency during a simulation of the TELSTAR 4 conditions at the expected power levels and temperatures on three nickel hydrogen cells of similar design. The unique feature of nickel hydrogen cells that makes the continuous measurement of efficiency possible is that hydrogen is one of the active materials and thus, cell pressure is a direct measure of the state of charge or available capacity. The pressure is measured with a calibrated strain gage mounted on the outside of the pressurized cell.
Hall effect, resistivity, spin resonance and thermoelectric properties of poly/N-vinyl carbazole/-iodine complex, demonstrating charge transfer state existence in system