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A microprocessor navigation systems using the Omega process is discussed. Several methods for correcting incoming sky waves are presented along with the hardware design which depends on a microcomputer. The control program is discussed, and block diagrams of the Omega processor and interface systems are presented.
The Power and Attitude Control Expert System (PACES) is an object oriented and rule based expert system which provides spacecraft engineers with assistance in isolating and correcting problems within the Power and Attitude Control Subsystems of the Tracking and Data Relay Satellites (TDRS). PACES is designed to act in a consultant role. It will not interface to telemetry data, thus preserving full operator control over spacecraft operations. The spacecraft engineer will input requested information. This information will include telemetry data, action being performed, problem characteristics, spectral characteristics, and judgments of spacecraft functioning. Questions are answered either by clicking on appropriate responses (for text), or entering numeric values. A context sensitive help facility allows access to additional information when the user has difficulty understanding a question or deciding on an answer. The major functionality of PACES is to act as a knowledge rich system which includes block diagrams, text, and graphics, linked using hypermedia techniques. This allows easy movement among pieces of the knowledge. Considerable documentation of the spacecraft Power and Attitude Control Subsystems is embedded within PACES. The development phase of TDRSS expert system technology is intended to provide NASA with the necessary expertise and capability to define requirements, evaluate proposals, and monitor the development progress of a highly competent expert system for NASA's Tracking and Data Relay Satellite Program.
A new flight simulation facility has been developed at NASA Lewis to allow integrated propulsion-control and flight-control algorithm development and evaluation in real time. As a preliminary check of the simulator facility and the correct integration of its components, the control design and physics models for an STOVL fighter aircraft model have been demonstrated, with their associated system integration and architecture, pilot vehicle interfaces, and display symbology. The results show that this fixed-based flight simulator can provide real-time feedback and display of both airframe and propulsion variables for validation of integrated systems and testing of control design methodologies and cockpit mechanizations.
The European Robotic Arm (ERA) is a contribution to the Russian Segment of the International Space Station Alpha. It will start operating on the Russian Segment during the assembly phase. ERA is designed and produced by a large industrial consortium spread over Europe with Fokker Space & Systems as prime contractor. In this paper, we will describe some of the overall design aspects and focus on the development of several mechanisms within ERA. The operation of ERA during the approach of its end effector towards the grapple interface and the grapple operation is discussed, with a focus on mechanisms. This includes the geometry of the end effector leading edge, which is carefully designed to provide the correct and complete tactile information to a torque-force sensor (TFS). The data from this TFS are used to steer the arm such that forces and moments are kept below 20 N and 20 N.m respectively during the grappling operation. Two hardware models of the end effector are built. The problems encountered are described as well as their solutions. The joints in the wrists and the elbow initially used a harmonic drive lubricated by MoS2. During development testing, this combination showed an insufficient lifetime in air to survive the acceptance test program. The switch-over to a system comprising planetary gearboxes with grease lubrication is described. From these development efforts, conclusions are drawn and recommendations are given for the design of complex space mechanisms.
Apparatus is provided which controls humidity in a gas. The apparatus employs a porous interface that is preferably a manifolded array of stainless steel tubes through whose porous surface water vapor can pass. One side of the porous interface is in contact with water and the opposing side is in contact with gas whose humidity is being controlled. Water vapor is emitted from the porous surface of the tubing into the gas when the gas is being humidified, and water vapor is removed from the gas through the porous surfaces when the gas is being dehumidified. The temperature of the porous interface relative to the gas temperature determines whether humidification or dehumidification is being carried out. The humidity in the gas is sensed and compared to the set point humidity. The water temperature, and consequently the porous interface temperature, are automatically controlled in response to changes in the gas humidity level above or below the set point. Any deviation from the set point humidity is thus corrected.
A computer program provides semiautomatic control of a moveable robot used to perform optical calibration of video-camera-based optoelectronic sensor systems that will be used to guide automated rendezvous maneuvers of spacecraft. The function of the robot is to move a target and hold it at specified positions. With the help of limit switches, the software first centers or finds the target. Then the target is moved to a starting position. Thereafter, with the help of an intuitive graphical user interface, an operator types in coordinates of specified positions, and the software responds by commanding the robot to move the target to the positions. The software has capabilities for correcting errors and for recording data from the guidance-sensor system being calibrated. The software can also command that the target be moved in a predetermined sequence of motions between specified positions and can be run in an advanced control mode in which, among other things, the target can be moved beyond the limits set by the limit switches.
The VIPER project has so far produced a formal specification of a 32 bit RISC microprocessor, an implementation of that chip in radiation-hard SOS technology, a partial proof of correctness of the implementation which is still being extended, and a large body of supporting software. The time has now come to consider what has been achieved and what directions should be pursued in the future. The most obvious lesson from the VIPER project was the time and effort needed to use formal methods properly. Most of the problems arose in the interfaces between different formalisms, e.g., between the (informal) English description and the HOL spec, between the block-level spec in HOL and the equivalent in ELLA needed by the low-level CAD tools. These interfaces need to be made rigorous or (better) eliminated. VIPER 1A (the latest chip) is designed to operate in pairs, to give protection against breakdowns in service as well as design faults. We have come to regard redundancy and formal design methods as complementary, the one to guard against normal component failures and the other to provide insurance against the risk of the common-cause failures which bedevil reliability predictions. Any future VIPER chips will certainly need improved performance to keep up with increasingly demanding applications. We have a prototype design (not yet specified formally) which includes 32 and 64 bit multiply, instruction pre-fetch, more efficient interface timing, and a new instruction to allow a quick response to peripheral requests. Work is under way to specify this device in MIRANDA, and then to refine the spec into a block-level design by top-down transformations. When the refinement is complete, a relatively simple proof checker should be able to demonstrate its correctness. This paper is presented in viewgraph form.
Reaction rate coefficients for electron-transfer processes at the electrode–electrolyte interface are commonly estimated by using the Butler–Volmer equation, but their values are inaccurate beyond a few tenths of volts of overpotential. The Marcus–Hush–Chidsey (MHC) formalism yields correct asymptotic behavior of the rate coefficients vs applied overpotential but has complex dependencies on the redox system’s intrinsic parameters, which can be difficult to model or measure. In this work, we bridge the two kinetics formalisms to estimate the reorganization energy, one of the important parameters for the MHC formalism, and investigate its dependence on other intrinsic parameters such as activation barriers, electronic coupling strength, and the density of states of the electrode surface. We examine the sensitivity of the reorganization energy to these parameters, establish some general relationships for accurately predicting rate coefficients using the MHC formalism over a wide range of applied overpotentials, and compare this approach to calculating MHC rate constants with other empirical approaches for the mechanisms of CO 2 reduction on different metal electrode surfaces.
The computer was programmed to handle data, perform limit checks, control normal operation, take corrective actions, and initiate shutdown for a fuel-cell system. The system was operated under computer control for periods up to 30 hr. The adequacy of the programming and interfacing techniques used was verified.
This paper presents a self-stabilizing distributed clock synchronization protocol in the absence of faults in the system. It is focused on the distributed clock synchronization of an arbitrary, non-partitioned digraph ranging from fully connected to 1-connected networks of nodes while allowing for differences in the network elements. This protocol does not rely on assumptions about the initial state of the system, other than the presence of at least one node, and no central clock or a centrally generated signal, pulse, or message is used. Nodes are anonymous, i.e., they do not have unique identities. There is no theoretical limit on the maximum number of participating nodes. The only constraint on the behavior of the node is that the interactions with other nodes are restricted to defined links and interfaces. This protocol deterministically converges within a time bound that is a linear function of the self-stabilization period. We present an outline of a deductive proof of the correctness of the protocol. A bounded model of the protocol was mechanically verified for a variety of topologies. Results of the mechanical proof of the correctness of the protocol are provided. The model checking results have verified the correctness of the protocol as they apply to the networks with unidirectional and bidirectional links. In addition, the results confirm the claims of determinism and linear convergence. As a result, we conjecture that the protocol solves the general case of this problem. We also present several variations of the protocol and discuss that this synchronization protocol is indeed an emergent system.
This paper addresses the technical aspects of the sample return system for the upcoming Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) asteroid sample return mission. The overall mission design and current implementation are presented as an overview to establish a context for the technical description of the reentry and landing segment of the mission.The prime objective of the OSIRIS-REx mission is to sample a primitive, carbonaceous asteroid and to return that sample to Earth in pristine condition for detailed laboratory analysis. Targeting the near-Earth asteroid Bennu, the mission launches in September 2016 with an Earth reentry date of September 24, 2023.OSIRIS-REx will thoroughly characterize asteroid Bennu providing knowledge of the nature of near-Earth asteroids that is fundamental to understanding planet formation and the origin of life. The return to Earth of pristine samples with known geologic context will enable precise analyses that cannot be duplicated by spacecraft-based instruments, revolutionizing our understanding of the early Solar System. Bennu is both the most accessible carbonaceous asteroid and one of the most potentially Earth-hazardous asteroids known. Study of Bennu addresses multiple NASA objectives to understand the origin of the Solar System and the origin of life and will provide a greater understanding of both the hazards and resources in near-Earth space, serving as a precursor to future human missions to asteroids.This paper focuses on the technical aspects of the Sample Return Capsule (SRC) design and concept of operations, including trajectory design and reentry retrieval. Highlights of the mission are included below.The OSIRIS-REx spacecraft provides the essential functions for an asteroid characterization and sample return mission: attitude control propulsion power thermal control telecommunications command and data handling structural support to ensure successful rendezvous with Bennu characterization of Bennus properties delivery of the sampler to the surface, and return of the spacecraft to the vicinity of the Earth sample collection, performed by the Touch-and-Go Sample Acquisition Mechanism (TAGSAM), to acquire a regolith sample from the surface Earth re-entry and SRC recovery. Following sample collection, OSIRIS-REx drifts away from Bennu until the Asteroid Departure Maneuver is commanded on March 4, 2021, sending OSIRIS-REx on a ballistic return cruise to Earth. No additional large deterministic maneuvers are required to return the SRC to Earth. During the cruise, tracking and trajectory correction maneuvers (TCMs) are performed as necessary to precisely target the entry corridor. As OSIRIS-REx approaches Earth, the reentry plans are reviewed starting about a year before arrival, and preparations begin. The spacecraft is targeted away from the Earth until 7 days before entry. The final two trajectory correction maneuvers bring the spacecraft on target toward the Utah Test and Training Range (UTTR), with sufficient time for contingency resolution. The SRC releases 4 hours prior to atmospheric entry interface and, using the Stardust capsule heritage design, employs a traditional drogue and main parachute descent system for a soft touchdown.
Conductivity modulation via ferroelectric polarization coupling with LaNiO 3 (LNO) is demonstrated at an epitaxial ferroelectric–LNO interface. Conductivity measurements, varying the thickness of the LNO channel, show that this phenomenon is confined to a few atomic layers at the interface. Combining in situ biasing and off-axis holography, we mapped out electrostatic potentials at the PbZr 0.2 Ti 0.8 O 3 (PZT)/LNO/SrTiO 3 (STO) heterostructure upon polarization switching. Using aberration-corrected STEM, the interfacial atomic structures were investigated for the two different PZT polarization states. Polarization in PZT induces a significant change in the in-plane O–Ni–O bond angles, with a 37° modulation in the topmost 1 or 2 LNO unit cells, driven by strain in the oxygen sublattice for the two opposite polarization directions in PZT. Both oxygen and cation sublattices exhibit strain responses exceeding 10% upon switching. This atomic-layer structural modulation highlights a mechanism for functional oxide heterostructure development, offering pathways for advancements in nonvolatile memory, sensors, and energy-efficient transistors.
Advancements in technology have allowed the miniaturization of systems used in aerospace vehicles. This technology is driven by the need for next-generation systems that provide reliable, responsive, and cost-effective range operations while providing increased capabilities such as simultaneous mission support, increased launch trajectories, improved launch, and landing opportunities, etc. Leveraging the newest technologies, the command and telemetry processor (CTP) concept provides for a compact, flexible, and integrated solution for flight command and telemetry systems and range systems. The CTP is a relatively small circuit board that serves as a processing platform for high dynamic, high vibration environments. The CTP can be reconfigured and reprogrammed, allowing it to be adapted for many different applications. The design is centered around a configurable field-programmable gate array (FPGA) device that contains numerous logic cells that can be used to implement traditional integrated circuits. The FPGA contains two PowerPC processors running the Vx-Works real-time operating system and are used to execute software programs specific to each application. The CTP was designed and developed specifically to provide telemetry functions; namely, the command processing, telemetry processing, and GPS metric tracking of a flight vehicle. However, it can be used as a general-purpose processor board to perform numerous functions implemented in either hardware or software using the FPGA s processors and/or logic cells. Functionally, the CTP was designed for range safety applications where it would ultimately become part of a vehicle s flight termination system. Consequently, the major functions of the CTP are to perform the forward link command processing, GPS metric tracking, return link telemetry data processing, error detection and correction, data encryption/ decryption, and initiate flight termination action commands. Also, the CTP had to be designed to survive and operate in a launch environment. Additionally, the CTP was designed to interface with the WFF (Wallops Flight Facility) custom-designed transceiver board which is used in the Low Cost TDRSS Transceiver (LCT2) also developed by WFF. The LCT2 s transceiver board demodulates commands received from the ground via the forward link and sends them to the CTP, where they are processed. The CTP inputs and processes data from the inertial measurement unit (IMU) and the GPS receiver board, generates status data, and then sends the data to the transceiver board where it is modulated and sent to the ground via the return link. Overall, the CTP has combined processing with the ability to interface to a GPS receiver, an IMU, and a pulse code modulation (PCM) communication link, while providing the capability to support common interfaces including Ethernet and serial interfaces boarding a relatively small-sized, lightweight package.
Development of complex air vehicle configurations is placing increasing demands on wind tunnel testing capabilities. A major area of concern is wall induced interference. Recent developments in wall interference technology provide a means for assessing and correcting for the wall induced interference using information contained in the distribution of flow variables measured at, or near, the wall. The restoration of the NASA-ARC 12-ft pressure wind tunnel (PWT) provides an opportunity to incorporate a measurement system with which wall interference assessment/correction (WIAC) technology can be applied. In this first phase of the development of a WIAC system for the PWT, the design criteria for the placement and the geometry of wall static pressure orifices were determined with a three step approach. First, the operational environment of the PWT was analyzed as to the requirements for the WIAC system. Second, appropriate wall interference theories were evaluated against the requirements determined from the operational environment. Third, the flow about representative models in the PWT was calculated and, specifically, the pressure signatures at the location of the test section wall were obtained. The number of discrete pressure measurements and their locations were determined by curve fitting the pressure distribution through the discrete measurements and evaluating the resulting error.
We present the extension of GR-Athena++ to general-relativistic magnetohydrodynamics (GRMHD) for applications to neutron star spacetimes. The new solver couples the constrained transport implementation of Athena++ to the Z4c formulation of the Einstein equations to simulate dynamical spacetimes with GRMHD using oct-tree adaptive mesh refinement. We consider benchmark problems for isolated and binary neutron star spacetimes demonstrating stable and convergent results at relatively low resolutions and without grid symmetries imposed. The code correctly captures magnetic field instabilities in nonrotating stars with total relative violation of the divergence-free constraint of 10 –16 . It handles evolutions with a microphysical equation of state and black hole formation in the gravitational collapse of a rapidly rotating star. For binaries, we demonstrate correctness of the evolution under the gravitational radiation reaction and show convergence of gravitational waveforms. We showcase the use of adaptive mesh refinement to resolve the Kelvin–Helmholtz instability at the collisional interface in a merger of magnetised binary neutron stars. GR-Athena++ shows strong scaling efficiencies above 80% in excess of 10 5 CPU cores and excellent weak scaling is shown up to ~5 × 10 5 CPU cores in a realistic production setup. GR-Athena++ allows for the robust simulation of GRMHD flows in strong and dynamical gravity with exa-scale computers.
The problem of tracking Alpha voltage variations in an electroencephalogram is discussed. This problem is important in encephalographic studies of sleep and effects of different stimuli on the brain. Very often the Alpha voltage is tracked by passing the EEG signal through a bandpass filter centered at the Alpha frequency, which hopefully will filter out unwanted noise from the Alpha activity. Some alternative digital techniques are suggested and their performance is compared with the standard technique. These digital techniques can be used in an environment where an electroencephalograph is interfaced with a small digital computer via an A/D convertor. They have the advantage that statistical statements about their variability can sometimes be made so that the effect sought can be assessed correctly in the presence of random fluctuations.
This is the final report of a Space Station Automation and Robotics Planning Study, which was a joint project of the Boeing Aerospace Company, Boeing Commercial Airplane Company, and Boeing Computer Services Company. The study is in support of the Advanced Technology Advisory Committee established by NASA in accordance with a mandate by the U.S. Congress. Boeing support complements that provided to the NASA Contractor study team by four aerospace contractors, the Stanford Research Institute (SRI), and the California Space Institute. This study identifies automation and robotics (A&R) technologies that can be advanced by requirements levied by the Space Station Program. The methodology used in the study is to establish functional requirements for the operator system interface (OSI), establish the technologies needed to meet these requirements, and to forecast the availability of these technologies. The OSI would perform path planning, tracking and control, object recognition, fault detection and correction, and plan modifications in connection with extravehicular (EV) robot operations.
On Earth, the C-13 content of organic compounds is depleted by roughly 13 to 23 permil from atmospheric carbon dioxide. This difference is largely due to isotope effects associated with the fixation of inorganic carbon by photosynthetic organisms. If life once existed on Mars, then it is reasonable to expect to observe a similar fractionation. Although the strongly oxidizing conditions on the surface of Mars make preservation of ancient organic material unlikely, carbon-isotope evidence for the existence of life on Mars may still be preserved. Carbon depleted in C-13 could be preserved either in organic compounds within buried sediments, or in carbonate minerals produced by the oxidation of organic material. A technique is introduced for rapid and precise measurement of the C-13 contents of individual organic compounds. A gas chromatograph is coupled to an isotope-ratio mass spectrometer through a combustion interface, enabling on-line isotopic analysis of isolated compounds. The isotope ratios are determined by integration of ion currents over the course of each chromatographic peak. Software incorporates automatic peak determination, corrections for background, and deconvolution of overlapped peaks. Overall performance of the instrument was evaluated by the analysis of a mixture of high purity n-alkanes of know isotopic composition. Isotopic values measured via IRM-GCMS averaged withing 0.55 permil of their conventionally measured values.