SEARCH · Search NASA

Results for “fixed orbits”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13

All sources NASA NTRS DOE OSTI

DOE OSTI2024

Inscribing geodesic circles on the face of the superstratum

Abstract We use families of circular null geodesics as probes of a family of microstate geometries, known as (1,0, n) superstrata. These geometries carry a left-moving momentum wave and the behavior of some of the geodesic probes is very sensitive to this background wave. The left-moving geodesics behave like BPS particles and so can be placed in circular orbits anywhere in the geometry and actually “float” at fixed radius and angle in the three-dimensional “capped BTZ” geometry. The right-moving geodesics behave like non-BPS particles. We show that they provide a simple geometric characterization of the black-hole bound: when the momentum charge of the geometry is below this bound, such geodesics can be placed anywhere, but exceeding the bound, even by a small amount, means these geodesics are restricted to the deep interior of the geometry. We also show that for left-moving string probes, the tidal forces remain comparable with those of global AdS 3 . Nevertheless, for some of these probes, the “bumps” in the geometry induce an oscillatory mass term and we discuss how this can lead to chaotic scrambling of the state of the string.

Physics↗

DOE OSTI2026

Magnus force induced magnetic diode effect in skyrmion systems

We show that skyrmions can exhibit a “magnetic diode effect,” where there is a nonreciprocal response in the transport when the magnetic field is reversed. This effect can be achieved for skyrmions moving in channels with a sawtooth potential on one side and a reversed sawtooth potential on the other side. We consider the cases of both spin-transfer torque (STT) and spin–orbit torque (SOT). When the magnetic field is held fixed, the velocity response of the skyrmion is the same for current applied in either direction for both torques, so there is no current diode effect. When the magnetic field is reversed, under STT driving the velocity of the skyrmion reverses and its absolute value changes. Under SOT driving, the velocity remains in the same direction but drops to a much lower value, resulting in negative differential conductivity. For a fixed current, we find a nonreciprocal skyrmion velocity as a function of the applied field’s sign, in analogy to the velocity–current curves observed in the usual diode effect. The nonreciprocity is generated by the Magnus force, which causes skyrmions to interact preferentially with one side of the channel. Since the channel sides have opposite asymmetry, a positive magnetic field can cause the skyrmion to interact with the “hard” asymmetry side of the channel, while a negative magnetic field causes the skyrmion to interact with the “easy” asymmetry side. This geometry could be used to create new kinds of magnetic-field-induced diode effects that can be harnessed in new types of skyrmion-based devices.

36 MATERIALS SCIENCE↗

NASA NTRS1975

Geometrical procedures for the analysis of spacecraft attitude and bias determinability

Geometrical procedures are presented for predicting the determinability of spacecraft attitude and bias parameters. An analysis is presented on three common attitude measurements: sun angle, nadir angle, and sun-to-earth mid-scan rotation angle. First, the geometry of these measurements is considered for an arbitrary fixed location of the spacecraft; then the effect of orbital motion is analyzed. The results are summarized in a set of simple geometrical rules. The application of these rules to the Synchronous Meteorological Satellite-2 (SMS-2) is discussed. As a result of this geometrical analysis, modifications were made to the SMS-2 bias determination schedule which substantially enhanced the determinability of attitude sensor biases.

Wertz, J. R.↗

NASA NTRS1992

Orbit determination by solving for gravity parameters with multiple arc data

The orbit of a satellite that repeats in the earth fixed coordinates is determined by combining GPS tracking data from multiple arcs. The satellite dynamics are modeled with the epoch state and a set of parameters, called the bin parameters, that account for the effect of the local gravitational field on the satellite current state. The epoch state is specific to each arc, and the bin parameters are common to all repeat arcs. The estimation algorithm is based on the Square Root Information Filter. It involves partitioning of the measurement matrix and use of the Householder transformation to combine multiple arc data and solve for the epoch states and the bin parameters. The bin parameters can then be converted into the earth's gravitational field with a modest amount of computation.

Wu, Jiun-Tsong↗

NASA NTRS1992

Crustal deformation measurements in central Japan determined by a Global Positioning System fixed-point network

Results are presented from temporally dense measurements of crustal deformation associated with the convergence of the Eurasian (EUR), Pacific, North American, and Philippine Sea (PHS) plates, carried out in April 1988 by a 10-station GPS fixed-point network established in central Japan. Using regional orbit relaxation methods, the analysis of the first 17-month data revealed significant horizontal deformation across the Suruga trough. Namely, it was found that a site in the northern tip of PHS plate moved nearly westward with a velocity of 28 +/-5 mm per year, and a site at the southeastern tip of EUR plate moved south-southwestward with a velocity of 18 +/-5 mm per year. A significant vertical uplift with a velocity of 20 mm/yr was detected at a site inland of the Tokai district located in the Akaishi uplift zone and at a site on the Hatsushima Island in Sagami Bay.

Shimada, Seiichi↗

NASA NTRS1993

Nominal trajectories for the aeroassisted flight experiment

The problem of generating good nominal trajectories is considered with particular reference to an AFE type spacecraft flying with constant angle of attack and variable angle of bank. A simulated GEO-to-LEO aeroassisted orbital transfer is considered. It is shown that, for fixed control, the AFE trajectory exhibits strong intrinsic instability in the longitudinal motion and near neutrality in the lateral motion, while stability can be artificially induced via feedback control, the effectiveness of a feedback control scheme depends on control margin availability. The AFE nominal trajectory must be chosen as a compromise between good performance and good control margin.

Miele, A.↗

NASA NTRS1993

Atomic oxygen interaction at defect sights in protective coatings on polymers flown on LDEF

Although the Long Duration Exposure Facility (LDEF) has exposed materials with a fixed orientation relative to the ambient low-Earth-orbital environment, arrival of atomic oxygen is angularly distributed as a result of the atomic oxygen's high temperature Maxwellian velocity distribution and the LDEF's orbital inclination. Thus, atomic oxygen entering defects in protective coatings on polymeric surfaces can cause wider undercut cavities than the size of the defect in the protective coating. Because only a small fraction of atomic oxygen reacts upon first impact with most polymeric materials, secondary reactions with lower energy thermally accommodated atomic oxygen can occur. The secondary reactions of scattered and/or thermally accommodated atomic oxygen also contribute to widening the undercut cavity beneath the protective coating defect. As the undercut cavity enlarges, exposing more polymer, the probability of atomic oxygen reacting with underlying polymeric material increases because of multiple opportunities for reaction. Thus, the effective atomic oxygen erosion yield for atoms entering defects increases above that of the unprotected material. Based on the results of analytical modeling and computational modeling, aluminized Kapton multilayer insulation exposed to atomic oxygen on row 9 lost the entire externally exposed layer of polyimide Kapton, yet based on the results of this investigation, the bottom surface aluminum film must have remained in place, but crazed. Atomic oxygen undercutting at defect sites in protective coatings on graphite epoxy composites indicates that between 40 to 100 percent of the atomic oxygen thermally accommodates upon impact, and that the reaction probability of thermally accommodated atomic oxygen may range from 7.7 x 10(exp -6) to 2.1 x 10(exp -3), depending upon the degree of thermal accommodation upon each impact.

Banks, Bruce A.↗

NASA NTRS1993

Rapid oscillations in cataclysmic variables. 11: X-ray pulses in YY Draconis

ROSAT observations of the cataclysmic variable YY Draconis reveal pulses with a period of 264.6 + or - 1.2 s, confirming the presence of a rapidly rotating, magnetic white dwarf. Comparison with the periods seen in ultraviolet and blue light indicates that the 275-s ultraviolet signals arises from the reprocessing of X-ray pulsations in structures fixed in the binary reference frame. Only harmonics and orbital sidebands of the white dwarf spin frequency are observed, not the spin frequency itself.

Patterson, Joseph↗

NASA NTRS1999

Effects of Solar Array Shadowing on the Power Capability of the Interim Control Module

The Interim Control Module (ICM) is being built by the US Naval Research Laboratory (NRL) for NASA as a propulsion module for the International Space Station (ISS). Originally developed as a spinning spacecraft used to move payloads to their final orbit, for ISS, the ICM will be in a fixed orientation and location for long periods resulting in substantial solar panel shadowing. This paper describes the methods used to determine the incident energy incident energy on the ICM solar panels and the power capability of the electric power system (EPS). Applying this methodology has resulted in analyses and assessments used to identify ICM early design changes/options, placement and orientations that enable successful operation of the EPS under a wide variety of anticipated conditions.

Fincannon, James↗

NASA NTRS2001

Induced compression wood formation in Douglas fir (Pseudotsuga menziesii) in microgravity

In the microgravity environment of the Space Shuttle Columbia (Life and Microgravity Mission STS-78), were grown 1-year-old Douglas fir and loblolly pine plants in a NASA plant growth facility. Several plants were harnessed (at 45 degrees ) to establish if compression wood biosynthesis, involving altered cellulose and lignin deposition and cell wall structure would occur under those conditions of induced mechanical stress. Selected plants were harnessed at day 2 in orbit, with stem sections of specific plants harvested and fixed for subsequent microscopic analyses on days 8, 10 and 15. At the end of the total space mission period (17 days), the remaining healthy harnessed plants and their vertical (upright) controls were harvested and fixed on earth. All harnessed (at 45 degrees ) plant specimens, whether grown at 1 g or in microgravity, formed compression wood. Moreover, not only the cambial cells but also the developing tracheid cells underwent significant morphological changes. This indicated that the developing tracheids from the primary cell wall expansion stage to the fully lignified maturation stage are involved in the perception and transduction of the stimuli stipulating the need for alteration of cell wall architecture. It is thus apparent that, even in a microgravity environment, woody plants can make appropriate corrections to compensate for stress gradients introduced by mechanical bending, thereby enabling compression wood to be formed. The evolutionary implications of these findings are discussed in terms of "variability" in cell wall biosynthesis.

manned↗

NASA NTRS1991

Berthing simulator for space station and orbiter

The development of a real-time man-in-the-loop berthing simulator is in progress at NASA Lyndon B. Johnson Space Center (JSC) to conduct a parametric study and to measure forces during contact conditions of the actual docking mechanisms for the Space Station Freedom and the orbiter. In berthing, the docking ports of the Space Station and the orbiter are brought together using the orbiter robotic arm to control the relative motion of the vehicles. The berthing simulator consists of a dynamics docking test system (DDTS), computer system, simulator software, and workstations. In the DDTS, the Space Station, and the orbiter docking mechanisms are mounted on a six-degree-of-freedom (6 DOF) table and a fixed platform above the table. Six load cells are used on the fixed platform to measure forces during contact conditions of the docking mechanisms. Two Encore Concept 32/9780 computers are used to simulate the orbiter robotic arm and to operate the berthing simulator. A systematic procedure for a real-time dynamic initialization is being developed to synchronize the Space Station docking port trajectory with the 6 DOF table movement. The berthing test can be conducted manually or automatically and can be extended for any two orbiting vehicles using a simulated robotic arm. The real-time operation of the berthing simulator is briefly described.

Veerasamy, Sam↗

NASA NTRS2016

Determination of Ceres Physical Parameters Using Radiometric and Optical Data

The Dawn spacecraft was launched on September 27th, 2007. Its mission is to rendezvous with and observe the two largest bodies in the main asteroid belt, Vesta and Ceres. It has completed over a year’s worth of direct observations of Vesta from early 2011 through late 2012. In the spring of 2015, the Dawn spacecraft entered orbit around the asteroid Ceres for the start of what is expected to be more than a year of science operations. The science data collected from this encounter consist of infrared (IR) images and spectra, visible images through a number of color filters, gamma ray detections and measurements of the Ceres gravity field. These data will be collected during several science phases: an Approach phase (1500000-4860 km from Ceres), a Survey orbit (4860 km radius), a High Altitude Mapping Orbit (HAMO) (1940 km radius) and a Low Altitude Mapping Orbit (LAMO) (855 km radius). The Approach phase included three Rotational Characterization (RC) opportunities. Designing each science orbit and successfully transferring into that orbit requires a sufficiently accurate estimate of Ceres physical parameters (body fixed frame, GM and harmonics). This paper focuses on work performed to estimate Ceres physical parameters using Deep Space Network (DSN) radiometric tracking data and optical measurements derived from science camera imagery. This paper describes planning for the data acquisition, as well as processing techniques and methodology. The trajectories predicted by the gravity field estimations are also compared with the actual as-flown trajectories. Observations of the gravity at high altitudes are found to be sufficient to design precision orbits at lower altitudes. Follow-up analysis after successfully reaching LAMO is included, as is a discussion of lessons learned.

Kennedy, Brian M.↗

NASA NTRS2017

An Alternative Approach to Human Servicing of Crewed Earth Orbiting Spacecraft

As crewed spacecraft have grown larger and more complex, they have come to rely on spacewalks, or Extravehicular Activities (EVA), for mission success and crew safety. Typically, these spacecraft maintain all of the hardware and trained personnel needed to perform an EVA on-board at all times. Maintaining this capability requires volume and up-mass for storage of EVA hardware, crew time for ground and on-orbit training, and on-orbit maintenance of EVA hardware. This paper proposes an alternative methodology, utilizing launch on-need hardware and crew to provide EVA capability for space stations in Earth orbit after assembly complete, in the same way that one would call a repairman to fix something at their home. This approach would reduce ground training requirements, save Intravehicular Activity (IVA) crew time in the form of EVA hardware maintenance and on-orbit training, and lead to more efficient EVAs because they would be performed by specialists with detailed knowledge and training stemming from their direct involvement in the development of the EVA. The on-orbit crew would then be available to focus on the immediate response to the failure as well as the day-to-day operations of the spacecraft and payloads. This paper will look at how current unplanned EVAs are conducted, including the time required for preparation, and offer alternatives for future spacecraft. As this methodology relies on the on-time and on-need launch of spacecraft, any space station that utilized this approach would need a robust transportation system including more than one launch vehicle capable of carrying crew. In addition, the fault tolerance of the space station would be an important consideration in how much time was available for EVA preparation after the failure. Each future program would have to weigh the risk of on-time launch against the increase in available crew time for the main objective of the spacecraft.

Mularski, John R.↗

NASA NTRS1996

On the Antenna Pattern of Orbitting Interferometer

We consider the response of an interferometer moving with respect to a fixed reference frame, and derive a simple expression for the beam-pattern factors and the polarization-averaged antenna power pattern...Then, we consider a class of motions where the detector's plane is constrained to move on the surface of a cone of constant aperture; at the same time, the two arms are rotating around a vertical axis...In addition, we consider the case of an Earth-based interferometer...Finally, we discuss LISA's response to circularly polarized sinusoidal waves, coming from a few known binary systems in our Galaxy.

interferometer interferometry antenna motions LISA↗

NASA NTRS1961

A Study of the Positions and Velocities of a Space Station and a Ferry Vehicle During Rendezvous and Return

A study is made of the families of non-thrusting ascent trajectories of a ferry vehicle during rendezvous with an orbiting body, referred to as a space station. It is shown that these trajectories may also be interpreted as descent trajectories of the ferry from the station to the earth. The rendezvous trajectories start at the end of the boost period (assumed to be 60 miles) and terminate at the station. The equations of motion are derived and results are shown for two typical orbits of the station: a 300-mile circular orbit and a 100-to-500-mile elliptical orbit. Trajectories are described in terms of a rotating coordinate system fixed in the station and launch conditions are tabulated in terms of non-rotating inertial coordinates. Boundaries are given in terms of launch (at time of booster burnout) and rendezvous conditions for the example cases. The considerations used to calculate these boundaries and the significance of some of the trends are discussed.

TRAJECTORY↗

NASA NTRS1983

Space Station Attitude Control System Concept and Requirements

There is currently no single Space Station configuration which is accepted as a baseline. However, the latest approach is toward symmetry in both geometry and mass distribution. This minimizes aerodynamic and gravity gradient torques. Solar arrays and radiators drive the configuration strongly. One axis of the solar arrays needs to be perpendicular to the orbit plane, and the geometric and principal axis should remain common along this axis to minimize secular torques. The need for both inertial and earth-fixed modes drives the structure of the Station toward a disk-like shape in the orbital plane.

Nicaise, P. D.↗

NASA NTRS1975

Quantization and symmetry in periodic coverage patterns with applications to earth observation

Analytical approaches based on an idealized physical model and concepts from number theory show that in periodic coverage patterns, uniquely defined by their revolution numbers R (orbital) and N (rotational), the subnodal points are earth-fixed, and they divide the equator into R equal segments of length s. The ascending subsatellite trace crosses each point once (only) each period. The descending subnodal points coincide with the ascending points if the integers N and R have like parity, and bisect the intervals between them if opposite. The interval between consecutive unidirectional crossings is Ns. Symmetries extend the equatorial results to all parallels of latitude. Complete periodic patterns of traces exhibit an overall symmetry, with trace intersections confined to discrete coordinate values which are quantized in longitude (basic s-unit) and symmetric in latitude.

King, J. C.↗

NASA NTRS1978

Imaging of X-ray aurorae from Spacelab

The Atmospheric X-ray Emission Telescope (AXET) is designed to image and measure the spatial, temporal, and spectral distributions of X-ray aurorae produced in the upper atmosphere by precipitating energetic electrons. The bremsstrahlung-produced X radiation penetrates to stratospheric depths where it can modify ozone, conductivity, and other critical atmospheric parameters. Remote sensing of this radiation from topside will provide vital data on solar-terrestrial relationships and mechanisms that could help trigger tropospheric response to solar activity. The X rays also provide direct information concerning the dynamics of radiation-belt processes within the magnetosphere. AXET is designed to detect sources up to 50 keV and to image them below 25 keV by means of directionally sensitive proportional counters with passive collimators. It will be mounted in the Space Shuttle on a single fixed platform designed to optimize viewing conditions for the anticipated orbits and aspects of early Spacelab missions.

Goldberg, R. A.↗