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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.

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NASA NTRS1994

SCL: An off-the-shelf system for spacecraft control

In this age of shrinking military, civil, and commercial space budgets, an off-the-shelf solution is needed to provide a multimission approach to spacecraft control. A standard operational interface which can be applied to multiple spacecraft allows a common approach to ground and space operations. A trend for many space programs has been to reduce operational staff by applying autonomy to the spacecraft and to the ground stations. The Spacecraft Command Language (SCL) system developed by Interface and Control Systems, Inc. (ICS) provides an off-the-shelf solution for spacecraft operations. The SCL system is designed to provide a hyper-scripting interface which remains standard from program to program. The spacecraft and ground station hardware specifics are isolated to provide the maximum amount of portability from system to system. Uplink and downlink interfaces are also isolated to allow the system to perform independent of the communications protocols chosen. The SCL system can be used for both the ground stations and the spacecraft, or as a value added package for existing ground station environments. The SCL system provides an expanded stored commanding capability as well as a rule-based expert system on-board. The expert system allows reactive control on-board the spacecraft for functions such as electrical power systems (EPS), thermal control, etc. which have traditionally been performed on the ground. The SCL rule and scripting capability share a common syntax allowing control of scripts from rules and rules from scripts. Rather than telemeter over sampled data to the ground, the SCL system maintains a database on-board which is available for interrogation by the scripts and rules. The SCL knowledge base is constructed on the ground and uploaded to the spacecraft. The SCL system follows an open-systems approach allowing other tasks to communicate with SCL on the ground and in space. The SCL system was used on the Clementine program (launched January 25, 1994) and is required to have bidirectional communications with the guidance, navigation, and control (GNC) algorithms which were written as another task. Sequencing of the spacecraft maneuvers are handled by SCL, but the low-level thruster pulse commands are handled by the GNC software. Attitude information is reported back as telemetry, allowing the SCL expert system to inference on the changing data. The Clementine SCL flight software was largely reused from another Naval Center for Space Technology (NCST) satellite program. This paper details the SCL architecture and how an off-the-shelf solution makes sense for multimission spacecraft programs. The Clementine mission will be used as a case study in the application of the SCL to a 'fast track' program. The benefits of such a system in a 'better, cheaper, faster' climate will be discussed.

Buckley, Brian↗

NASA NTRS2014

X-Ray Observations of VY Scl-Type Nova-Like Binaries in the High and Low State

Four VY Scl-type nova-like systems were observed in X-rays during both the low- and the high-optical states. We examined Chandra, ROSAT, Swift and Suzaku archival observations of BZ Cam, MV Lyr, TT Ari and V794 Aql. The X-ray flux of BZ Cam is higher during the low state, but there is no supersoft X-ray source (SSS) as hypothesized in previous articles. No SSS was detected in the low state of the any of the other systems, with the X-ray flux decreasing by a factor between 2 and 50. The best fit to the Swift X-ray spectra is obtained with a multicomponent model of plasma in collisional ionization equilibrium. The high-state high-resolution spectra of TT Ari taken with Chandra Advanced CCD Imaging Spectrometer (ACIS-S) and the Chandra High Energy Transmission Grating (HETG) shows a rich emission line spectrum, with prominent lines of Mg, Si, Ne and S. The complexity of this spectrum seems to have origin in more than one region, or more than one single physical mechanism. While several emission lines are consistent with a cooling flow in an accretion stream, there is at least an additional component. We discuss the origin of this component, which is probably arising in a wind from the system. We also examine the possibility that the VY Scl systems may be intermediate polars, and that while the boundary layer of the accretion disc emits only in the extreme ultraviolet, part of the X-ray flux may be due to magnetically driven accretion.

accretion↗

NASA NTRS2001

X-Ray Spectra of VY Scl Stars Are Not Blackbodies

Using ASCA data, we find, contrary to other researchers using ROSAT data, that the X, ray spectra of the VY Scl stars TT Ari and KR Aur are poorly fit by an absorbed blackbody model but are well fit by an absorbed thermal plasma model. The different conclusions about the nature of the X-ray spectrum of KR Aur may be due to differences in the accretion rate, since this star was in a high optical state during the ROSAT observation, but in an intermediate optical state during the ASCA observation. TT Ari, on the other hand, was in a high optical state during both observations, so directly contradicts the hypothesis that the X-ray spectra of VY Sol stars in their high optical states are blackbodies. Instead, based on theoretical expectations and the ASCA, Chandra, and XMM spectra of other nonmagnetic cataclysmic variables, we believe that the X-ray spectra of VY Sol stars in their low and high optical states are due to hot thermal plasma in the boundary layer between the accretion disk and the surface of the white dwarf, and appeal to the acquisition of Chandra and XMM grating spectra to test this prediction.

Mauche, C. W.↗

NASA NTRS2008

Use of Spacecraft Command Language for Advanced Command and Control Applications

The purpose of this work is to evaluate the use of SCL in building and monitoring command and control applications in order to determine its fitness for space operations. Approximately 24,325 lines of PCG2 code was converted to SCL yielding a 90% reduction in the number of lines of code as many of the functions and scripts utilized in SCL could be ported and reused. Automated standalone testing, simulating the actual production environment, was performed in order to generalize and gauge the relative time it takes for SCL to update and write a given display. The use of SCL rules, functions, and scripts allowed the creation of several test cases permitting the detection of the amount of time it takes update a given set of measurements given the change in a globally existing CUI or CUI. It took the SCL system an average 926.09 ticks to update the entire display of 323 measurements.

Mims, Tikiela L.↗

NASA NTRS2008

Automatic Testcase Generation for Flight Software

The TacSat3 project is applying Integrated Systems Health Management (ISHM) technologies to an Air Force spacecraft for operational evaluation in space. The experiment will demonstrate the effectiveness and cost of ISHM and vehicle systems management (VSM) technologies through onboard operation for extended periods. We present two approaches to automatic testcase generation for ISHM: 1) A blackbox approach that views the system as a blackbox, and uses a grammar-based specification of the system's inputs to automatically generate *all* inputs that satisfy the specifications (up to prespecified limits); these inputs are then used to exercise the system. 2) A whitebox approach that performs analysis and testcase generation directly on a representation of the internal behaviour of the system under test. The enabling technologies for both these approaches are model checking and symbolic execution, as implemented in the Ames' Java PathFinder (JPF) tool suite. Model checking is an automated technique for software verification. Unlike simulation and testing which check only some of the system executions and therefore may miss errors, model checking exhaustively explores all possible executions. Symbolic execution evaluates programs with symbolic rather than concrete values and represents variable values as symbolic expressions. We are applying the blackbox approach to generating input scripts for the Spacecraft Command Language (SCL) from Interface and Control Systems. SCL is an embedded interpreter for controlling spacecraft systems. TacSat3 will be using SCL as the controller for its ISHM systems. We translated the SCL grammar into a program that outputs scripts conforming to the grammars. Running JPF on this program generates all legal input scripts up to a prespecified size. Script generation can also be targeted to specific parts of the grammar of interest to the developers. These scripts are then fed to the SCL Executive. ICS's in-house coverage tools will be run to measure code coverage. Because the scripts exercise all parts of the grammar, we expect them to provide high code coverage. This blackbox approach is suitable for systems for which we do not have access to the source code. We are applying whitebox test generation to the Spacecraft Health INference Engine (SHINE) that is part of the ISHM system. In TacSat3, SHINE will execute an on-board knowledge base for fault detection and diagnosis. SHINE converts its knowledge base into optimized C code which runs onboard TacSat3. SHINE can translate its rules into an intermediate representation (Java) suitable for analysis with JPF. JPF will analyze SHINE's Java output using symbolic execution, producing testcases that can provide either complete or directed coverage of the code. Automatically generated test suites can provide full code coverage and be quickly regenerated when code changes. Because our tools analyze executable code, they fully cover the delivered code, not just models of the code. This approach also provides a way to generate tests that exercise specific sections of code under specific preconditions. This capability gives us more focused testing of specific sections of code.

Bushnell, David Henry↗

NASA NTRS1988

Numerical simulation of tropical cumulus clouds and their interaction with the subcloud layer

A two-dimensional numerical model, with an emphasis on turbulent processes in the boundary layer and in clouds, was developed for simulating an ensemble of cumulus clouds. The model was used to investigate the response of tropical cumulus clouds to imposed large-scale vertical advection by performing two simulations which were identical except that one was with upward large-scale vertical velocity (the 'disturbed' case) and the other was without any advection (the 'undisturbed' case). The results showed that deep cumulus clouds formed in the disturbed case, while only shallow clouds formed in the undisturbed case. The subcloud layer (SCL) in the disturbed case was strongly affected by cumulus circulations and rain evaporation, with both cumulus updrafts and downdrafts being important contributors to the SCL sensible and latent heat fluxes. Cumulus-scale circulation in the disturbed SCL determined where new clouds formed by creating convergence zones and moisture anomalies.

Krueger, Steven K.↗

NASA NTRS1991

NASA Goddard Space Flight Center Robotic Processing System Program Automation Systems, volume 2

Topics related to robot operated materials processing in space (RoMPS) are presented in view graph form. Some of the areas covered include: (1) mission requirements; (2) automation management system; (3) Space Transportation System (STS) Hitchhicker Payload; (4) Spacecraft Command Language (SCL) scripts; (5) SCL software components; (6) RoMPS EasyLab Command & Variable summary for rack stations and annealer module; (7) support electronics assembly; (8) SCL uplink packet definition; (9) SC-4 EasyLab System Memory Map; (10) Servo Axis Control Logic Suppliers; and (11) annealing oven control subsystem.

Dobbs, M. E.↗

NASA NTRS1992

Distributed expert systems for ground and space applications

Presented here is the Spacecraft Command Language (SCL) concept of the unification of ground and space operations using a distributed approach. SCL is a hybrid software environment borrowing from expert system technology, fifth generation language development, and multitasking operating system environments. Examples of potential uses for the system and current distributed applications of SCL are given.

Buckley, Brian↗

NASA NTRS1992

Spacecraft attitude control using a smart control system

Traditionally, spacecraft attitude control has been implemented using control loops written in native code for a space hardened processor. The Naval Research Lab has taken this approach during the development of the Attitude Control Electronics (ACE) package. After the system was developed and delivered, NRL decided to explore alternate technologies to accomplish this same task more efficiently. The approach taken by NRL was to implement the ACE control loops using systems technologies. The purpose of this effort was to: (1) research capabilities required of an expert system in processing a classic closed-loop control algorithm; (2) research the development environment required to design and test an embedded expert systems environment; (3) research the complexity of design and development of expert systems versus a conventional approach; and (4) test the resulting systems against the flight acceptance test software for both response and accuracy. Two expert systems were selected to implement the control loops. Criteria used for the selection of the expert systems included that they had to run in both embedded systems and ground based environments. Using two different expert systems allowed a comparison of the real-time capabilities, inferencing capabilities, and the ground-based development environment. The two expert systems chosen for the evaluation were Spacecraft Command Language (SCL), and NEXTPERT Object. SCL is a smart control system produced for the NRL by Interface and Control Systems (ICS). SCL was developed to be used for real-time command, control, and monitoring of a new generation of spacecraft. NEXPERT Object is a commercially available product developed by Neuron Data. Results of the effort were evaluated using the ACE test bed. The ACE test bed had been developed and used to test the original flight hardware and software using simulators and flight-like interfaces. The test bed was used for testing the expert systems in a 'near-flight' environment. The technical approach, the system architecture, the development environments, knowledge base development, and results of this effort are detailed.

Buckley, Brian↗

NASA NTRS1992

ROMPS critical design review. Volume 1: Hardware

Topics concerning the Robot-Operated Material Processing in Space (ROMPS) Program are presented in viewgraph form and include the following: a systems overview; servocontrol and servomechanisms; testbed and simulation results; system V controller; robot module; furnace module; SCL experiment supervisor; SCL script sample processing control; SCL experiment supervisor fault handling; block diagrams; hitchhiker interfaces; battery systems; watchdog timers; mechanical/thermal systems; and fault conditions and recovery.

Dobbs, M. E.↗

NASA NTRS1972

Ultraviolet observations of weak-helium stars

Ultraviolet filter photometry aboard OAO-2 has been carried out for the weak helium stars 3 Cen A, 3 Sco, HD 144334, HD 21699, HD 144844, alpha Scl, HR 8535, HR 8770 and HD 144661. The flux distribution is compared with that of B3 to B8 main sequence and giant stars in terms of color-color diagrams. When allowance is made for line blocking shortward of 2800 A that most of the weak helium stars have normal fluxes in good agreement with their ground-based colors. The star alpha Scl is a light and spectrum variable. The strengthening of Ti II and Sr II lines around 2400 A appears to redistribute flux longward of the Balmer discontinuity. The flux distribution indicates an effective temperature about 1500 K higher than previously determined.

Bernacca, P. L.↗

NASA NTRS2003

Citizen Explorer: An Earth Observer With New Small Satellite Technology - 1

Citizen Explorer-I (CX-I), designed and built by students at Colorado Space Grant Consortium in Boulder to provide global ozone monitoring, employs a unique mission architecture and several innovative technologies during its mission. The mission design allows K-12 schools around the world to be involved as ground stations available to receive science data and telemetry from CX-I. Another important technology allows the spacecraft to be less reliant on ground operators. Spacecraft Command Language (SCL) allows mission designers to set constraints on the satellite operations. The satellite then automatically adheres to the constraints when the satellite is out of contact with Mission Operations. In addition to SCL, a low level of artificial intelligence will be supplied to the spacecraft through the use of the Automated Scheduling and Planning ENvironment (ASPEN). ASPEN is used to maintain a spacecraft schedule in order to achieve the objectives a mission operator would normally have to complete. Within the communications system of CX-I, internet of CX-I, internet protocols are the main method for communicating with the satellite. As internet protocols have not been widely used in satellite communication, CX-I provides an opportunity to study the effectiveness of using internet protocols over radio links. The Attitude Determination and Control System (ADCS) on CX-I uses a gravity gradient boom as a means of orienting the satellite's science instruments toward nadir. The boom design is unique because it is constructed of tape measure material. These new technologies' effectiveness will be tested for use on future small satellite projects within the space satellite industry.

Allen, Zachary↗

NASA NTRS1981

Lanning 10 and 33 - The X-ray, UV, and optical fluxes

UV spectra from IUE, optical spectroscopy, broad band photometry, and upper limits on the X-ray flux from Einstein are used to specify the characteristics of Lanning 10 and 33. Data on Lanning 33 are consistent with a 22,000 K Be star at a distance of 5 to 7 kpc, and Lanning 10 appears to include a F5-G0 star plus a hot component greater than 35,000 K at a distance of 0.9 to 1.3 kpc. The optical eclipsed fluxes are subtracted from the uneclipsed, and the observed fluxed distribution of the eclipsed light does not follow a simple power law, but is closer to a 12,000 K + or - 1000 K blackbody. Lanning 10 is placed in the category of VY Scl variables.

Szkody, P.↗

NASA NTRS1985

TT Arietis - The low state

A comprehensive photometric and spectroscopic study of the low state of the novalike variable TT Ari has been made with observations spanning the UV to IR spectral regions. The roughly 5 mag drop in the system's luminosity from the high state indicates that the mass-transfer rate decreased by more than two orders of magnitude. The drastic reduction in the luminosity of the accretion disk between the high and low states enabled the white dwarf component to be directly observed for the first time. The broad absorption profiles at various lines and the UV energy distribution are best fitted by a hot white dwarf. A lower limit of 200 pc for the distance to TT Ari is derived, and the behavior of TT Ari is compared to that of another novalike variable, MV Lyr. The long-term photometric behavior of TT Ari makes it a typical member of the VY Scl subclass of novalike variables.

Shafter, A. W.↗

NASA NTRS1986

IUE observations of magnetically controlled stellar winds in the helium peculiar stars

Dramatic periodic variations in the C IV resonance lines of magnetic helium-weak sn stars HD 5737 = alpha Scl, HD 21699 = HR 1063, and HD 79158 = 36 Lyn are discussed. In all three cases, the 1548,50 doublet is the only non-negligibly variable UV spectral feature. The line profiles are consistent with outflow in a jet-like structure. In HD 21699 this outflow arises from one of the magnetic polar regions. Observations of two additional He-wk sn stars do not reveal strong C IV absorption, implying that the UV characteristics of these stars are less uniform than the optical phenomenology.

Shore, Steven N.↗

NASA NTRS1987

The sn stars - Magnetically controlled stellar winds among the helium-weak stars

The paper reports observations of magnetically controlled stellar mass outflows in three helium-weak sn stars: HD 21699 = HR 1063; HD 5737 = Alpha Scl; and HD 79158 = 36 Lyn. IUE observations show that the C IV resonance doublet is variable on the rotational timescale but that there are no other strong-spectrum variations in the UV. Magnetic fields, which reverse sign on the rotational timescale, are present in all three stars. This phenomenology is interpreted in terms of jetlike mass loss above the magnetic poles, and these objects are discussed in the context of a general survey of the C IV and Si IV profiles of other more typical helium-weak stars.

Shore, Steven N.↗

NASA NTRS1992

ROMPS critical design review data package

The design elements of the Robot-Operated Material Processing in Space (ROMPS) system are described in outline and graphical form. The following subsystems/topics are addressed: servo system, testbed and simulation results, System V Controller, robot module, furnace module, SCL experiment supervisor and script sample processing control, battery system, watchdog timers, mechanical/thermal considerations, and fault conditions and recovery.

Dobbs, M. E.↗

NASA NTRS1995

Effects of temperature, frequency, flux density, and excitation waveform on the core loss and dynamic B-H loops of supermalloy

The availability of experimental data which characterize the performance of soft magnetic materials for the combined conditions of temperature and frequency over a wide flux density range for different types of excitation is almost nonexistent. An experimental investigation of an 80-20 Ni-Fe alloy (Supermalloy) was conducted over the temperature (T) range of 23 to 300 C, frequency (f) range of 1 to 50 kHz, and maximum flux densities (B(sub M)) from 0.1 T up to 0.7 T for both sine and square wave voltage excitation. The investigation focused on the effects of (B(sub M)), f, T, and excitation waveform on the specific core loss (SCL) and dynamic B-H loops. The results show that the ratio (R) of sine to square wave excitation specific core loss was always greater than unity for a given f and T and identical values of B(sub M). The values of R ranged from 1.07 to 1.34. The classical theory of core loss separation into a hysteresis and eddy current loss component was used to theoretically determine the lower and upper bounds on R, against which the experimental R-values were compared. The experimental R-values were also used to make a comparison of the core loss of a sine and square wave voltage driven transformer.

Schwarze, Gene E.↗