Efficient Computation of Optimal Low Thrust Perturbed Orbit Transfers
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Taheri, Ehsan↗
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Exploration of Spatial Chaotic Orbits Using Isolating Neighborhoods
Isolating blocks and isolating neighborhoods have previously been used to compute periodic and quasiperiodic orbits around the collinear libration points in the circular restricted three-body problem. Isolating neighborhoods may be used to further explore the boundary between the Lissajous and quasihalo orbits at en- ergies where the halo orbits have bifurcated from the Lyapunov orbits. A method to compute trajectories that are forward and backward asymptotic to the libration point invariant set using very small velocity corrections is developed here. The method is then used to compute representative trajectories within this region and characterize their behavior.
Lo, Martin W.↗
A new method for satellite orbit determination using an operational worldwide transponder network
The method utilizes computer programs developed for the forthcoming ATS-F/NIMBUS-F tracking and data relay experiment where the basic tracking measurements are multiple path round-trip propagation times and rates. This method of orbit computation has recently been successfully evaluated by tracking a geostationary satellite (ATS-3) using an existing VHF (150 MHz) network of automatic transponders. A master station sequentially interrogates each transponder via the ATS-3. The master site is located at Schenectady, N. Y. and four automatic transponders were located at Shannon, Reykajavik, Buenos Aires, and Seattle respectively. Data at hourly intervals were collected during a 24 hour period on April 18-19, 1973. After correcting this data for known systematic errors it was provided as input to an orbit determination program where all satellite motions during signal propagation are rigorously accounted for. The resulting estimated ATS-3 orbit yielded observational residuals on the order of 100 meters. By using more than one satellite the present scheme is further capable of accurately locating several stationary or mobile terminals as part of the overall orbital solution.
Lynn, J. J.↗
Selection of a model of Earth's albedo radiation, practical calculation of its effect on the trajectory of a satellite
Theoretical models of Earth's albedo radiation was proposed. By comparing disturbing accelerations computed from a model to those measured in flight with the CACTUS Accelerometer, modified according to the results. Computation of the satellite orbit perturbations from a model is very long because for each position of this satellite the fluxes coming from each elementary surface of the terrestrial portion visible from the satellite must be summed. The speed of computation is increased ten times without significant loss of accuracy thanks to a stocking of some intermediate results. Now it is possible to confront the orbit perturbations computed from the selected model with the measurements of these perturbations found with satellite as LAGEOS.
Walch, J. J.↗
Minimum-fuel, power-limited transfers between coplanar elliptical orbits
Two techniques of computing coplanar, minimum-fuel, power-limited transfers are presented, based on approximate solutions obtained by the averaging method. For the first technique, the average solution provides estimates of the initial adjoint variables, and the second provides approximations of the optimal controls in feedback form. The accuracy of the techniques for computing coplanar, minimum-fuel, power-limited transfers is evaluated for a number of initial and final orbits.
Mease, Kenneth D.↗
New error calibration tests for gravity models using subset solutions and independent data - Applied to GEM-T3
A new method has been developed to provide a direct test of the error calibrations of gravity models based on actual satellite observations. The basic approach projects the error estimates of the gravity model parameters onto satellite observations, and the results of these projections are then compared with data residual computed from the orbital fits. To allow specific testing of the gravity error calibrations, subset solutions are computed based on the data set and data weighting of the gravity model. The approach is demonstrated using GEM-T3 to show that the gravity error estimates are well calibrated and that reliable predictions of orbit accuracies can be achieved for independent orbits.
Lerch, F. J.↗
Nonconservative force model parameter estimation strategy for TOPEX/Poseidon precision orbit determination
The TOPEX/Poseidon spacecraft was launched on August 10, 1992 to study the Earth's oceans. To achieve maximum benefit from the altimetric data it is to collect, mission requirements dictate that TOPEX/Poseidon's orbit must be computed at an unprecedented level of accuracy. To reach our pre-launch radial orbit accuracy goals, the mismodeling of the radiative nonconservative forces of solar radiation, Earth albedo an infrared re-radiation, and spacecraft thermal imbalances cannot produce in combination more than a 6 cm rms error over a 10 day period. Similarly, the 10-day drag modeling error cannot exceed 3 cm rms. In order to satisfy these requirements, a 'box-wing' representation of the satellite has been developed in which, the satellite is modelled as the combination of flat plates arranged in the shape of a box and a connected solar array. The radiative/thermal nonconservative forces acting on each of the eight surfaces are computed independently, yielding vector accelerations which are summed to compute the total aggregate effect on the satellite center-of-mass. Select parameters associated with the flat plates are adjusted to obtain a better representation of the satellite acceleration history. This study analyzes the estimation of these parameters from simulated TOPEX/Poseidon laser data in the presence of both nonconservative and gravity model errors. A 'best choice' of estimated parameters is derived and the ability to meet mission requirements with the 'box-wing' model evaluated.
Luthcke, S. B.↗
Mars rover technology development requirements
The technology development requirements for various Mars rover range capabilities are discussed, focusing on local navigation of the rover. The capabilities of two methods are compared. In one method, operators on the earth view stereo pictures sent by the rover and determine short traverse paths which the rover follows. The other method achieves more autonomous capability by using computer vision from orbital imagery with approximate long routes commanded from earth. The locomotion, navigation, ground operations, computation, power, thermal control, communications, sample acquisition, and analysis and preservation requirements are examined.
Bedard, Roger↗
Approach and landing simulator for Space Shuttle Orbiter touchdown conditions
This study describes a computer simulation that provides an accurate calculation of the touchdown conditions. The program is small enough to operate on a personal computer. The program simulates the Orbiter trajectory from an altitude of 10,000 ft to the earth's surface. It assumes the Orbiter files close to its reference altitude profile, with negligible crosswind effects. Flight data have proven both assumption to be valid. By incorporating these assumptions with the Shuttle guidance logic, a quick approximation can be made of the touchdown speed and downrange distance to an accuracy within 400 ft of the mainframe prediction.
Walyus, Keith D.↗
A Monte Carlo error analysis program for near-Mars, finite-burn, orbital transfer maneuvers
A computer program was developed which performs an error analysis of a minimum-fuel, finite-thrust, transfer maneuver between two Keplerian orbits in the vicinity of Mars. The method of analysis is the Monte Carlo approach where each off-nominal initial orbit is targeted to the desired final orbit. The errors in the initial orbit are described by two covariance matrices of state deviations and tracking errors. The function of the program is to relate these errors to the resulting errors in the final orbit. The equations of motion for the transfer trajectory are those of a spacecraft maneuvering with constant thrust and mass-flow rate in the neighborhood of a single body. The thrust vector is allowed to rotate in a plane with a constant pitch rate. The transfer trajectory is characterized by six control parameters and the final orbit is defined, or partially defined, by the desired target parameters. The program is applicable to the deboost maneuver (hyperbola to ellipse), orbital trim maneuver (ellipse to ellipse), fly-by maneuver (hyperbola to hyperbola), escape maneuvers (ellipse to hyperbola), and deorbit maneuver.
Green, R. N.↗
A distributed computing approach to mission operations support
Computing mission operation support includes orbit determination, attitude processing, maneuver computation, resource scheduling, etc. The large-scale third-generation distributed computer network discussed is capable of fulfilling these dynamic requirements. It is shown that distribution of resources and control leads to increased reliability, and exhibits potential for incremental growth. Through functional specialization, a distributed system may be tuned to very specific operational requirements. Fundamental to the approach is the notion of process-to-process communication, which is effected through a high-bandwidth communications network. Both resource-sharing and load-sharing may be realized in the system.
Larsen, R. L.↗
Voyager Encounter Highlights
The following are presented: computer animation of trajectories for both Voyagers 1 and 2; view of Jupiter during one orbit of Ganymede; computer animation of Voyager 2's encounter with Jupiter and its satellites; time lapse of the planet's rotation and its satellites; stroboscopic sequence of selected frames; cloud motion; Jupiter's Great Red Spot (4/25 - 5/24, 1979) through a violet filter; and the Great Red Spot through a blue filter by Voyager 1. The dynamics of Jupiter's clouds are shown - the whole planet is shown first, then two closer looks are repeated several times. Also included are pans of stills of Jupiter's satellites and a computer simulation tour of Saturn system from POV just behind Voyager, made of 116 images of Saturn through a green filter and of 516 images taken by Voyager 1 (9/12 - 9/14, 1980). Frames are enhanced to show the motion of features in Saturn's rings. Pans of stills of Saturn's satellites are shown. There is computer animation of the planet's system, rings, and Sigma Sagittari. Images on January 14, 1986 are through an orange filter. Uranus's satellites are shown as is computer animation of an August 1989 encounter.
Source record↗
Calculation of nonequilibrium radiation in the flight regimes of aeroassisted orbital transfer vehicles
A computer code has been developed that calculates radiative properties of nonequilibrium air in the low-density regimes expected during the flight of aeroassisted, orbital transfer vehicles. From the given nonequilibrium thermodynamic state variables, the code calculates number densities of internal states and the accompanying emission and absorption characteristics. In addition, the code calculates the number density of the hypothetical gas in radiative equilibrium that produces the same radiation emission as the given nonequilibrium gas. Sample results are shown to demonstrate how the code predicts the nonlinear variation of radiation with density at low densities.
Park, C.↗
Calculation of Nonequilibrium Radiation in the Flight Regimes of Aeroassisted Orbital Transfer Vehicles
A computer code has been developed that calculates radiative properties of nonequilibrium air in the low-density regimes expected during the flight of aeroassisted, orbital transfer vehicles. From the given nonequilibrium thermodynamic state variables, the code calculates number densities of internal states and the accompanying emission and absorption characteristics. In addition, the code calculates the number density of the hypothetical gas in radiative equilibrium that produces the same radiation emission as the given nonequilibrium gas. Sample results are shown to demonstrate how the code predicts the non-linear variation of radiation with density at low densities.
Park, Chul↗
Differential transformation for satellite injection.
This paper provides an analytical method for computing the required orbital inclination change when the nominal orbital node rate is slightly modified to meet satellite mission requirements. A first-order theory retaining up to J sub 2 terms of the earth-oblateness perturbation has been found adequate to generate a four-decimal digit accuracy for required orbital changes. A numerical example of an actual ITOS series prelaunch analysis has been given to illustrate computational steps.
Sugai, I.↗
Generating Animated Displays of Spacecraft Orbits
Tool for Interactive Plotting, Sonification, and 3D Orbit Display (TIPSOD) is a computer program for generating interactive, animated, four-dimensional (space and time) displays of spacecraft orbits. TIPSOD utilizes the programming interface of the Satellite Situation Center Web (SSCWeb) services to communicate with the SSC logic and database by use of the open protocols of the Internet. TIPSOD is implemented in Java 3D and effects an extension of the preexisting SSCWeb two-dimensional static graphical displays of orbits. Orbits can be displayed in any or all of the following seven reference systems: true-of-date (an inertial system), J2000 (another inertial system), geographic, geomagnetic, geocentric solar ecliptic, geocentric solar magnetospheric, and solar magnetic. In addition to orbits, TIPSOD computes and displays Sibeck's magnetopause and Fairfield's bow-shock surfaces. TIPSOD can be used by the scientific community as a means of projection or interpretation. It also has potential as an educational tool.
Candey, Robert M.↗
Control of an artificial infrared environment to simulate complex, time varying orbital conditions
A computer-controlled infrared simulation system has recently been developed for thermal vacuum ground testing of spacecraft in the Space Environment Simulation Laboratory of the NASA Manned Spacecraft Center. The system can simultaneously follow as many as 30 separate time-varying intensity profiles for irradiation of different areas of a test spacecraft, producing an environment that more closely resembles the changing conditions experienced by an orbiting spacecraft. A description of the hardware is included, but emphasis is placed upon computer techniques that have been developed to maximize the capabilities of the control system within the constraints imposed by a limited computer capability. Among the topics discussed are open-loop control, closed-loop control, manual alteration of profiles, compensation for slow response of the radiation source, and compensation for interacting control zones. Examples of typical results obtained using the control system are also presented.
Dewey, R. L.↗
Computational Study of a McDonnell Douglas Single-Stage-to-Orbit Vehicle Concept for Aerodynamic Analysis
This paper presents the results of a computational flow analysis of the McDonnell Douglas single-stage-to-orbit vehicle concept designated as the 24U. This study was made to determine the aerodynamic characteristics of the vehicle with and without body flaps over an angle of attack range of 20-40 deg. Computations were made at a flight Mach number of 20 at 200,000 ft. altitude with equilibrium air, and a Mach number of 6 with CF4 gas. The software package FELISA (Finite Element Langley imperial College Sawansea Ames) was used for all the computations. The FELISA software consists of unstructured surface and volume grid generators, and inviscid flow solvers with (1) perfect gas option for subsonic, transonic, and low supersonic speeds, and (2) perfect gas, equilibrium air, and CF4 options for hypersonic speeds. The hypersonic flow solvers with equilibrium air and CF4 options were used in the present studies. Results are compared with other computational results and hypersonic CF4 tunnel test data.
Prabhu, Ramadas K.↗