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Formation Flying and Position Determination for a Space-Based Interferometer in GEO Graveyard Orbit
Spacecraft formations enable a variety of mission concepts, from gravity reconstruction to extrasolar planet detection to heliophysics observatories. In particular, space-based radio interferometers can detect signals in frequency ranges that are absorbed by Earth’s ionosphere or atmosphere. Furthermore, such formation missions are now feasible under constrained cost caps due to the growing availability of SmallSat components with spaceflight heritage that are compatible the CubeSat formfactor. Accordingly, we analyze a mission concept operating multiple SmallSats in a passive cluster to establish a space-based interferometer. The goal of this array is to reconstruct radio emissions associated with Coronal Mass Ejections (CMEs) from the Sun, giving us insight into the particle acceleration occurring during these events. This low-cost mission concept presents a number of unique challenges in regards to mission design and navigation, particularly the configuration of the spacecraft to optimize science return and the reconstruction of precise spacecraft-spacecraft separation values. After providing a brief overview of the mission concept, this paper presents several key features of the mission design and orbit determination strategy that enable this potential heliophysics mission.
Holographic determination of the position of spacecraft
Spacecraft position determination by holographic approach involving single star formation
Method for Determining Artillery Position
A method is described for determining the position of artillery in which a circle of four closely spaced microphones is located at two measurement sites for acoustic radio direction finding of muzzle blasts. A method for determining the position of artillery using this procedure is discussed.
Method for determining artillery position
A method is disclosed for determining the position of cannon from measurement sites whose distance from each other lies in the same order of magnitude as the distance between the cannons -- that distance being in the kilometer range -- with the help of the travel time evaluation of muzzle blasts received at the measurement sites. There are at least two measurement sites, consisting of a cruciform of four microphones each positioned so that one axis is oriented to an arbitrarily chosen reference direction with the microphones spaced closely together. In this arrangement of diametrically opposed microphones, the respective travel times are determined and placed in a relationship whose arctangent is a radio bearing to the reference direction in which radio bearings are determined with consideration of their position and their opposing distance from the cannon position.
Autonomous reconfigurable GPS/INS navigation and pointing system for rendezvous and docking
The briefing describes work using the Global Positioning System to determine position of spacecraft and the development of computer tools to utilize these position determinations to enable autonomous rendezvous. Using GPS data in conjunction with Inertial Navigation Systems (INS) provides the capability for absolute spacecraft navigation, navigation of one spacecraft relative to another, and attitude determination. Some results presented are based on limited observations, though simulation results are documented. A GPS/INS navigation flight experiment could provide a platform for evaluating approaches for autonomous operation and reconfigurability of the navigation and attitude determination subsystem for future space vehicles. Current emphasis is on the development and demonstration of an Onboard Mission Manager (OMM) and a Multi-Mode Navigation Kalman filter. Sensor data will be handed over to the OMM, which will determine the appropriate response and generate commands for the Kalman filter to use to reconfigure itself. Global Positioning System measurements and INS data will be processed in the integrated navigation filter and used to compute errors in position, velocity, and attitude. Inertial Navigation Systems instrument errors (biases, scale factors, etc.) also can be estimated. The OMM then will use a knowledge base to determine appropriate system response. The GPS is good for missions that have attitude pointing accuracy requirements within the 100 to 200 arcsecond range.
Location of Lunakhod 2 from laser ranging observations
Results of laser ranging attempts on Lunakhod 2 are presented. Laser ranging can only be accomplished at night, so only the straight-line distance between the end points of a daytime traverse can be determined. Uncertainties of positional determination are strongly dependent on the length of the tracking arc. The data, obtained in the first two lunar nights, are too sparse to yield reliable positional determinations. The results clearly illustrate the critical importance of a high-quality lunar ephemeris for the interpretation of sparse data.
Determination of radio-frame position for Earth and Jupiter from Ulysses encounter tracking
Radio metric tracking data acquired from the Ulysses spacecraft about its encounter with Jupiter in February 1992 allow an accurate measurement of some components of the orbital elements describing the positions of the Earth and Jupiter with respect to extragalactic radio sources. Range and Doppler data acquired from the Earth while the spacecraft is far from any planet provide an estimate of the spacecraft trajectory relative to the orbit of the Earth. Doppler data near Jupiter provide an accurate position determination of the spacecraft with respect to Jupiter. Very Long Baseline Interferometry observations of the spacecraft with respect to the distant radio sources provide a direct measure of the spacecraft position in the radio reference frame. Combining these measurements provides a means to estimate the locations of the Earth and Jupiter in the radio reference frame. One of the three Euler angles describing the orientation of the Earth's orbit in the radio frame has been determined to an accuracy of 50 nanoradians; the result agrees with other recent determinations of this orientation. The position of Jupiter at the time of Ulysses encounter has been determined to 15 nanoradians in ecliptic latitude and longitude.
Apparatus and method for determining the position of a radiant energy source
The position of a terrestrial RF source is determined from a geostationary, synchronous satellite by scanning the beam of a narrow beam width antenna in first and second orthogonal directions over a region including the source. The peak level of energy transduced by the antenna in each of the scanning directions is detected and correlated with the scanning position of the beam by feeding the output of a detector responsive to the transduced signal to an indicator of an X-Y recorder. The X and Y axes of the recorder are scanned in synchronism with the beam being respectively scanned in the first and second directions to form X and Y traces on which are indicated the detected peak position in each of the scanning directions. The source position is determined from an intersection of lines drawn parallel to the X and Y axes and including the detected peak position of each trace.
Determination of Radio-Frame Position for Earth and Jupiter from Ulysses Encounter Tracking
Radio metric tracking data acquired from the Ulysses spacecraft about its encounter with Jupiter in February 1992 allow an accurate measurement of some components of the orbital elements describing the positions of the Earth and Jupiter with respect to extragalactic radio sources. Range and Doppler data acquired from the Earth while the spacecraft is far from any planet provide an estimate of the spacecraft trajectory relative to the orbit of the Earth. Doppler data near Jupiter provide an accurate position determination of the spacecraft with respect to Jupiter. Very Long Baseline Interferometry observations of the spacecraft with respect to the distant radio sources provide a direct measure of the spacecraft position in the radio reference frame. Combining these measurements provides a means to estimate the locations of the Earth and Jupiter in the radio reference frame.
Determination of positive anode sheath in anodic carbon arc for synthesis of nanomaterials
In the atmospheric pressure anodic carbon arc, ablation of the anode serves as a feedstock of carbon for production of nanomaterials. It is known that the ablation of the graphite anode in this arc can have two distinctive modes with low and high ablation rates. The transition between these modes is governed by the power deposition at the arc attachment to the anode and depends on the gap between the anode and the cathode electrodes. Probe measurements combined with optical emission spectroscopy are used to analyze the voltage drop between the arc electrodes. These measurements corroborated previous predictions of a positive anode sheath (i.e. electron attracting sheath) in this arc, which appears in both low and high ablation modes. However, the positive anode sheath was determined to be ~3–8 V, significantly larger than ~0.5 V predicted by previous models. Thus, there are apparently other physical mechanisms not considered by these models that force the anode sheath to be electron attracting in both ablation regimes. Another key result is a relatively low electron temperature (~0.6 eV) obtained from OES using a collisional radiative model. This result partially explains a higher arc voltage (~20 V) required to sustain the arc current of 50–70 A than predicted by existing simulations of this discharge.
High-Order Mesh r-Adaptivity with Tangential Relaxation and Guaranteed Mesh Validity
High-order meshes are crucial for achieving optimal convergence rates in curvilinear domains, preserving symmetry, and aligning with key flow features in moving mesh simulations [1], but their quality is challenging to control. In prior work, we have developed techniques based on Target-Matrix Optimization Paradigm (TMOP) to adapt a given high-order mesh to the geometry and solution of the partial differential equation (PDE) [2, 3]. Here, we extend this framework to address two key gaps in the literature for highorder mesh 𝑟-adaptivity. First, we introduce tangential relaxation on curved surfaces using solely the discrete mesh representation, eliminating the need for access to underlying geometry (e.g., CAD model). Second, we ensure a continuously positive Jacobian determinant throughout the domain. This determinant positivity is essential for using the high-order mesh resulting from 𝑟-adaptivity with arbitrary quadrature schemes in simulations. The proposed approach is demonstrated to be robust using a variety of numerical experiments.
Determination of surface state energy positions by surface photovoltage spectrometry- CdS
Surface state energy positions determination in high-energy gap semiconductors by photovoltage spectral distribution
Determination of Position of Jupiter From Very-Long Baseline Interferometry Observations of Ulysses
Very-long baseline interferometry (VLBI) observations of the Ulysses spacecraft near its encounter with Jupiter on 1992 February 8 were made to determine the angular position of Jupiter with respect to well known extragalactic radio sources. Spacecraft range and Doppler data were used to determine the position of the spacecraft with respect to Jupiter. Thirty-one VLBI observations of the spacecraft were made within 30 days of Ulysses closest approach to Jupiter, using the California-Spain and California-Australia baselines of NASA's Deep Space Network. When combined, these data determine the position of Jupiter at the time of encounter with an accuracy of 0.003 min in right ascension and 0.005 sec in declination. In addition, the Earth-Jupiter distance was determined with 20 m accuracy.
ATS simultaneous and turnaround ranging experiments
This report explains the data reduction and spacecraft position determination used in conjunction with two ATS experiments - Trilateration and Turnaround Ranging - and describes in detail a multilateration program that is used for part of the data reduction process. The process described is for the determination of the inertial position of the satellite, and for formating input for related programs. In the trilateration procedure, a geometric determination of satellite position is made from near simultaneous range measurements made by three different tracking stations. Turnaround ranging involves two stations; one, the master station, transmits the signal to the satellite and the satellite retransmits the signal to the slave station which turns the signal around to the satellite which in turn retransmits the signal to the master station. The results of the satellite position computations using the multilateration program are compared to results of other position determination programs used at Goddard. All programs give nearly the same results which indicates that because of its simplicity and computational speed the trilateration technique is useful in obtaining spacecraft positions for near synchronous satellites.
Method for Determining Artillery Position
A method is described for determinig artillery positions. Two groups of four closely spaced microphones are placed at known positions, and radio bearings are determined by projectile flight time differences of muzzle blasts. The advantages of the method are discussed.
A Study into the Method of Precise Orbit Determination of a HEO Orbiter by GPS and Accelerometer
In the present day, orbit determination by Global Positioning System (GPS) is not unusual. Especially for low-cost small satellites, position determination by an on-board GPS receiver provides a cheap, reliable and precise method. However, the original purpose of GPS is for ground users, so the transmissions from all of the GPS satellites are directed toward the Earth s surface. Hence there are some restrictions for users above the GPS constellation to detect those signals. On the other hand, a desire for precise orbit determination for users in orbits higher than GPS constellation exists. For example, the next Japanese Very Long Baseline Interferometry (VLBI) mission "ASTRO-G" is trying to determine its orbit in an accuracy of a few centimeters at apogee. The use of GPS is essential for such ultra accurate orbit determination. This study aims to construct a method for precise orbit determination for such high orbit users, especially in High Elliptical Orbits (HEOs). There are several approaches for this objective. In this study, a hybrid method with GPS and an accelerometer is chosen. Basically, while the position cannot be determined by an on-board GPS receiver or other Range and Range Rate (RARR) method, all we can do to estimate the user satellite s position is to propagate the orbit along with the force model, which is not perfectly correct. However if it has an accelerometer (ACC), the coefficients of the air drag and the solar radiation pressure applied to the user satellite can be updated and then the propagation along with the "updated" force model can improve the fitting accuracy of the user satellite s orbit. In this study, it is assumed to use an accelerometer available in the present market. The effects by a bias error of an accelerometer will also be discussed in this paper.
Method of Controlling Steering of a Ground Vehicle
A method of controlling steering of a vehicle through setting wheel angles of a plurality of modular electronic corner assemblies (eModules) is provided. The method includes receiving a driving mode selected from a mode selection menu. A position of a steering input device is determined in a master controller. A velocity of the vehicle is determined, in the master controller, when the determined position of the steering input device is near center. A drive mode request corresponding to the selected driving mode to the plurality of steering controllers is transmitted to the master controller. A required steering angle of each of the plurality of eModules is determined, in the master controller, as a function of the determined position of the steering input device, the determined velocity of the vehicle, and the selected first driving mode. The eModules are set to the respective determined steering angles.