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NASA NTRS2009

Cooperative Three-Robot System for Traversing Steep Slopes

Teamed Robots for Exploration and Science in Steep Areas (TRESSA) is a system of three autonomous mobile robots that cooperate with each other to enable scientific exploration of steep terrain (slope angles up to 90 ). Originally intended for use in exploring steep slopes on Mars that are not accessible to lone wheeled robots (Mars Exploration Rovers), TRESSA and systems like TRESSA could also be used on Earth for performing rescues on steep slopes and for exploring steep slopes that are too remote or too dangerous to be explored by humans. TRESSA is modeled on safe human climbing of steep slopes, two key features of which are teamwork and safety tethers. Two of the autonomous robots, denoted Anchorbots, remain at the top of a slope; the third robot, denoted the Cliffbot, traverses the slope. The Cliffbot drives over the cliff edge supported by tethers, which are payed out from the Anchorbots (see figure). The Anchorbots autonomously control the tension in the tethers to counter the gravitational force on the Cliffbot. The tethers are payed out and reeled in as needed, keeping the body of the Cliffbot oriented approximately parallel to the local terrain surface and preventing wheel slip by controlling the speed of descent or ascent, thereby enabling the Cliffbot to drive freely up, down, or across the slope. Due to the interactive nature of the three-robot system, the robots must be very tightly coupled. To provide for this tight coupling, the TRESSA software architecture is built on a combination of (1) the multi-robot layered behavior-coordination architecture reported in "An Architecture for Controlling Multiple Robots" (NPO-30345), NASA Tech Briefs, Vol. 28, No. 10 (October 2004), page 65, and (2) the real-time control architecture reported in "Robot Electronics Architecture" (NPO-41784), NASA Tech Briefs, Vol. 32, No. 1 (January 2008), page 28. The combination architecture makes it possible to keep the three robots synchronized and coordinated, to use data from all three robots for decision- making at each step, and to control the physical connections among the robots. In addition, TRESSA (as in prior systems that have utilized this architecture) , incorporates a capability for deterministic response to unanticipated situations from yet another architecture reported in Control Architecture for Robotic Agent Command and Sensing (NPO-43635), NASA Tech Briefs, Vol. 32, No. 10 (October 2008), page 40. Tether tension control is a major consideration in the design and operation of TRESSA. Tension is measured by force sensors connected to each tether at the Cliffbot. The direction of the tension (both azimuth and elevation) is also measured. The tension controller combines a controller to counter gravitational force and an optional velocity controller that anticipates the motion of the Cliffbot. The gravity controller estimates the slope angle from the inclination of the tethers. This angle and the weight of the Cliffbot determine the total tension needed to counteract the weight of the Cliffbot. The total needed tension is broken into components for each Anchorbot. The difference between this needed tension and the tension measured at the Cliffbot constitutes an error signal that is provided to the gravity controller. The velocity controller computes the tether speed needed to produce the desired motion of the Cliffbot. Another major consideration in the design and operation of TRESSA is detection of faults. Each robot in the TRESSA system monitors its own performance and the performance of its teammates in order to detect any system faults and prevent unsafe conditions. At startup, communication links are tested and if any robot is not communicating, the system refuses to execute any motion commands. Prior to motion, the Anchorbots attempt to set tensions in the tethers at optimal levels for counteracting the weight of the Cliffbot; if either Anchorbot fails to reach its optimal tension level within a specified time, it sends message to the other robots and the commanded motion is not executed. If any mechanical error (e.g., stalling of a motor) is detected, the affected robot sends a message triggering stoppage of the current motion. Lastly, messages are passed among the robots at each time step (10 Hz) to share sensor information during operations. If messages from any robot cease for more than an allowable time interval, the other robots detect the communication loss and initiate stoppage.

Stroupe, Ashley↗

DOE OSTI2021

Parsec-scale Properties of Steep- and Flat-spectrum Extragalactic Radio Sources from a VLBA Survey of a Complete North Polar Cap Sample

We observed with the Very Long Baseline Array (VLBA) at 2.3 and 8.6 GHz a complete flux-density-limited sample of 482 radio sources with decl. > +75° brighter than 200 mJy at 1.4 GHz drawn from the NVSS catalog. A total of 34% of the sources show parsec-scale emission above the flux density detection limit of 30 mJy; their accurate positions and parsec-scale structure parameters are determined. Among all the sources detected at least at the shortest VLBA baselines, the majority, or 72%, have a steep single-dish spectrum. The fraction of the sources with a detectable parsec-scale structure is above 95% among the flat-spectrum objects and close to 25% among the steep-spectrum objects. We identified 82 compact steep-spectrum source candidates, which make up 17% of the sample; most of them are reported for the first time. The compactness and the brightness temperature of the sources in our sample show a positive correlation with single-dish and VLBA spectral indices. All the sources with a significant 8 GHz variability were detected by the VLBA snapshot observations, which independently confirmed their compactness. We demonstrated that 54% of the sources detected by the VLBA at 2.3 GHz in our sample have a steep VLBA spectrum. The compact radio emission of these sources is likely dominated by optically thin jets or mini-lobes, not by an opaque jet core. These results show that future VLBI surveys aimed at searching for new sources with parsec-scale structure should include not only flat-spectrum sources but also steep-spectrum ones in order to reach an acceptable level of completeness.

47 OTHER INSTRUMENTATION↗

NASA NTRS2021

Parsec-scale Properties of Steep- and Flat-spectrum Extragalactic Radio Sources from a VLBA Survey of a Complete North Polar Cap Sample

A V Popkov↗

DOE OSTI2020

Ultra‐Steep Slope Impact Ionization Transistors Based on Graphene/InAs Heterostructures

With the continued scaling of transistors, there is a growing trend for developing steep slope transistors with subthreshold swing (SS) below Boltzmann limitation ( k T/ q ). To this end, impact ionization metal oxide semiconductor (I‐MOS) transistors are attractive for a unique combination of high ON‐state current density, small hysteresis, and ultra‐steep SS slope. However, the performance of I‐MOS is generally limited by the relatively thick depletion region and large operation voltage required for the activation of impact ionization (typically >5 V). Herein, a high‐performance I‐MOS is constructed by van der Waals integrating single‐crystal InAs film with graphene. Due to the low bandgap of InAs as well as the semi‐metallic nature of graphene, the InAs/graphene I‐MOS demonstrates a low operation voltage of 1.5 V, high ON‐state current of 230 μA μm −1 , steep SS <0.6 mV dec −1 , and large ON–OFF ratio >10 6 at temperature below 200 K. Furthermore, a negative transconductance and steep current oscillation is observed in the subthreshold regime, and a device working mechanism is proposed for this novel phenomenon. This study not only pushes the performance limit of I‐MOS but also defines a general pathway to van der Waals heterostructures between conventional III–V compound semiconductors and novel 2D materials for unconventional device functions.

Liu, Yuan↗

NASA NTRS2007

Robot Would Climb Steep Terrain

This brief describes the steep terrain access robot (STAR) -- a walking robot that has been proposed for exploring steep terrain on remote planets. The STAR would be able to climb up or down on slopes as steep as vertical, and even beyond vertical to overhangs. Its system of walking mechanisms and controls would be to react forces and maintain stability. To enable the STAR to anchor itself in the terrain on steep slopes to maintain stability and react forces, it would be necessary to equip the tips of the walking legs with new ultrasonic/ sonic drill corers (USDCs) and to develop sensors and control algorithms to enable robust utilization of the USDCs.

Kennedy, Brett↗

NASA NTRS2012

A Peculiar Class of Debris Disks from Herschel/DUNES: A Steep Fall Off in the Far Infrared

Context. The existence of debris disks around old main sequence stars is usually explained by continuous replenishment of small dust grains through collisions from a reservoir of larger objects. Aims. We present photometric data of debris disks around HIP 103389 (HD199260), HIP 100350 (HN Peg, HD206860), and HIP 114948 (HD 219482), obtained in the context of our Herschel Open TIme Key Program DUNES (DUst around NEarby Stars). Methods. We used Herschel/PACS to detect the thermal emission of the three debris disks with a 30 sigma sensitivity of a few mJy at l00 micron and 160 micron. In addition, we obtained Herschel/PACS photometric data at 70 micron for HIP 103389. These observations are complemented by a large variety of optical to far-infrared photometric data. Two different approaches are applied to reduce the Herschel data to investigate the impact of data reduction on the photometry. We fit analytical models to the available spectral energy distribution (SED) data using the fitting method of simulated therma1 annealing as well as a classical grid search method. Results. The SEDs of the three disks potentially exhibit an unusually steep decrease at wavelengths >= 70 micron. We investigate the significance of the peculiar shape of these SEDs and the impact on models of the disks provided it is real. Using grain compositions that have been applied successfully for modeling of many other debris disks, our modeling reveals that such a steep decrease of the SEDs in the long wavelength regime is inconsistent with a power-law exponent of the grain size distribution -3.5 expected from a standard equilibrium collisional cascade. In contrast, a steep grain size distribution or, alternatively an upper grain size in the range of few tens of micrometers are implied. This suggests that a very distinct range of grain sizes would dominate the thermal. emission of such disks. However, we demonstrate that the understanding of the data of faint sources obtained with Herschel is still incomplete and that the significance of our results depends on the version of the data reduction pipeline used. Conclusions. A new mechanism to produce the dust in the presented debris disks, deviations from the conditions required for a standard equilibrium collisional cascade (grain size exponent of -3.5), and/or significantly different dust properties would be necessary to explain the potentially steep SED shape of the three debris disks presented.

Ertel, S.↗

DOE OSTI2021

Research on the Influence Mechanism of the High‐Steep Slope on the Deformation Characteristics of Bridge Substructure

With the development of the Chinese railway, the high‐steep slope is irreversible to be faced; especially under severe conditions such as heavy rainfall and earthquake, this kind of slope is prone to geological disasters, which seriously affects the safety and stability of the bridge substructure. Aiming to this, long‐term monitorization and numerical analysis were carried out in this research, and the influence mechanism of the high‐steep slopes on the stress and deformation characteristics of the bridge structure was studied. The research results show that under the effect of rainfall and earthquake, the original stress balance in the high‐steep slope is broken, and the possibility of landslide thrust increases; under the comprehensive impact of residual landslide thrust, traction force at slope foot, vertical gravity of bridge slab and vehicle, and the bridge cap will deform. Besides, the deformation of the bridge pier exceeds the allowable lateral displacement of the top of the bridge pier, reaching 111.7%∼112.4% of the limit, which seriously affects the stability of the bridge structure and the safety of the railway service. Therefore, by increasing the support strength of the slope foot and the diameter of the bridge pile foundation, the traction force of the slope foot can be reduced, and the sliding resistance of the bridge pile foundation can be improved so as the safety of the bridge structure can be promoted.

Zhang, Yufang (ORCID:0000000348912060)↗

NASA NTRS1986

The stratigraphy of the Steep Rock Group, N.W. Ontario, with evidence of a major unconformity

The Steep Rock Group is exposed 6 km north of Atikokan, 200 km west of Thunder Bay. It is situated on the southern margin of the Wabigoon Belt of the Archaean Superior Province, N. W. Ontario. Reinvestigation of the geology of the Group has shown that the Group lies unconformably on the Tonalite Complex to the east. This unconformity has been previously suspected, from regional and ine mapping but no conclusive outcrop evidence for its existence has as yet been published. The strike of the group, comprised of Basal Conglomerate, Carbonate Member, Ore Zone and Ashrock is generally north-northwest dipping steeply to the southwest. Of the 7 contacts between the Steep Rock Group and the Tonalite Complex, 3 expose the unconformity (The Headland, S. Roberts Pit, Trueman Point), and 4 are faulted. These three outcrops demonstrate unequivocally that the Steep Rock group was laid down unconformably on the underlying Tonalite Complex, which is circa 3 Ga old.

Wilks, M. E.↗

NASA NTRS1988

An X-ray and radio study of steep-spectrum radio soruces. I - Four fields from the Clark Lake Observatory 26 MHz survey

A multifrequency study of fields containing steep-spectrum radio sources is presented. New spectral and spatial data are used to determine the locations and optical identifications of steep-spectrum sources which previously had either poor positions or questionable correspondence to known sources. X-ray images from the Einstein Observatory provide estimates of the extent, temperature, density, and thermal pressure of hot gas associated with galaxies and clusters of galaxies. From the equations relating synchrotron emission to inverse Compton scattering of 3 K background photons, lower limits to the average magnetic field strength in the source are derived. For the resolved radio sources of known distance, the minimum nonthermal pressure and the corresponding magnetic field strength are also calculated. For the four fields discussed in this paper, it is found that three out of five steep-spectrum sources are embedded in a cluster atmosphere and two are unidentified. Except for unresolved radio structures associated with cores of galaxies, the estimated thermal pressure is sufficient to confine the radio sources.

Harris, D. E.↗

NASA NTRS2016

New Approaches to Inferences for Steep-Sided Domes on Venus

New mathematical approaches for the relaxation and emplacement of viscous lava domes are presented and applied to steep-sided domes on Venus. A similarity solution approach is applied to the governing equation for fluid flow in a cylindrical geometry for two distinct scenarios. In the first scenario, dome relaxation is explored assuming a constant volume of fluid (i.e. lava) has been rapidly emplaced onto the surface. Cooling of lava is represented by a time-variable viscosity and singularities inherent in previous models for dome relaxation have been eliminated. At the onset of relaxation, bulk dynamic viscosities lie in the range between 10(exp 10) - 10(exp 16) Pa s, consistent with basaltic-andesite to rhyolitic compositions. Plausible relaxation times range from 5 to 5000 years, depending on initial lava viscosity. The first scenario, however, is only valid during the final stages of dome relaxation and does not consider the time taken for lava to be extruded onto the surface. In the second scenario, emplacement and growth of a steep-sided dome is considered when the volume of lava on the surface increases over time (i.e. time-variable volume approach). The volumetric flow rate may depend on an arbitrary power of the dome thickness, thus embracing Newtonian as well as other rheologies for describing terrestrial and planetary mass flows. The approach can be used to distinguish between basic flow rate models for fluid emplacement. The formalism results in radial expansion of a dome proportional to t(sup 1/2), consistent with the diffusive nature of the governing equation. The flow at the front is shown to thicken as the front advances for a constant rate of lava supply. Emplacement times are intimately correlated with the bulk rheology. Comparison of the theoretical profiles with the shape of a typical dome on Venus indicates that a Newtonian bulk rheology is most appropriate, consistent with prior studies. However, results here suggest a bulk dynamic viscosity of 10(exp 12) - 10(exp 13) Pa s and emplacement times of approximately 2-16 years. Both scenarios investigated give emplacement times significantly less than prior estimates and compositions consistent with basaltic andesite.

steep-sided domes↗

DOE OSTI2026

Effects of slope steepness and cross-slope wind speed on fire spreading behavior for various vegetation

Wildland fire behavior is significantly influenced by environmental factors such as slope steepness, wind speed, and fuel type. Understanding these interactions is critical for improving predictive models and fire management. This study explores how slope steepness and cross-slope wind speed influence fire spread dynamics in various fuel bed types. Simulations are conducted using a physics-based wildland fire model, HIGRAD/FIRETEC, across six slope angles (0–50 %), four cross-slope wind speeds (4–10 m s –1 ), and three fuel bed types (grass, shrubland, and forest). Representative cases are additionally compared with FARSITE fireline evolution. Fire behavior is categorized into distinct propagation types based on spread characteristics and analyzed. The fire propagation angle, which indicates deviation from the wind direction, generally increases with steeper slopes and decreases with stronger cross-slope winds. Secondary upslope propagation is observed in shrubland under moderate slopes, while secondary downwind propagation occurs in all fuel beds at higher wind speeds. These findings highlight fire spread characteristics that differ from predictions by traditional models like Rothermel’s. By capturing complex propagation patterns and dynamics, this study demonstrates the value of a physics-based, atmosphere-fire coupled model for accurate wildland fire prediction. Incorporating secondary propagations and the influence of fuel bed complexities into predictive models can improve the accuracy of fire spread forecasts, enabling more effective fire management and risk mitigation efforts.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2023

Young but fading radio sources: searching for remnants among compact steep-spectrum radio sources

The incidence of young but fading radio sources provides important information on the life cycle of radio emission in radio-loud active galactic nuclei. Despite its importance for constraining the models of radio source evolution, there are no systematic studies of remnants in complete samples of young radio sources. We report results of the study of 18 compact steep-spectrum (CSS) radio sources, selected from the statistically complete B3-VLA (Very Large Array) CSS sample, characterized by a steep optically thin spectrum (α ≥ 1.0) and no core detection in earlier studies. Our deep multifrequency VLA, pc-scale Very Long Baseline Array, and enhanced Multi Element Remotely Linked Interferometer Network (e-MERLIN) observations allowed us to locate the core component in 10 objects. In three CSS sources, there is no clear evidence of present-time active regions, suggesting that they are likely in a remnant phase. Among sources with core detection, we find three objects that have no clear active regions (hotspots) at the edges of the radio structure, suggesting that the radio emission may have just restarted. Our results support a power-law distribution of the source ages, although the poor statistics prevents us from setting solid constraints on the percentage of remnants and restarted sources in subpopulations of radio sources.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2025

Discovery of a z ∼ 0.8 ultra steep spectrum radio halo in the MeerKAT-South Pole Telescope Survey

Radio haloes are diffuse synchrotron sources that trace the turbulent intracluster medium (ICM) of galaxy clusters. However, their origin remains unknown. Two main formation models have been proposed: the hadronic model, in which relativistic electrons are continuously injected by cosmic-ray protons; and the leptonic turbulent re-acceleration model, where cluster mergers re-energize electrons in situ. A key discriminant between the two models would be the existence of ultra-steep spectrum radio haloes (USSRHs), which can only be produced through turbulent re-acceleration. Here, we report the discovery of an USSRH in the galaxy cluster SPT-CLJ2337–5942 at redshift $z = 0.78$ in the MeerKAT-South Pole Telescope 100 deg$^2$ UHF (0.58–1.09 GHz) survey. This discovery is noteworthy for two primary reasons: it is the highest redshift USSRH system to date; and the close correspondence of the radio emission with the thermal ICM as traced by Chandra X-ray observations, further supporting the leptonic re-acceleration model. The halo is underluminous for its mass, consistent with a minor merger origin, which produces steep-spectrum, lower luminosity haloes. This result demonstrates the power of wide-field, high-fidelity, low-frequency ($\lesssim 1$ GHz) surveys like the MeerKAT-SPT 100 deg$^2$ programme to probe the origin and evolution of radio haloes over cosmic time, ahead of the Square Kilometre Array.

X-rays: galaxies↗

NASA NTRS1977

Noise data for a twin-engine commercial jet aircraft flying conventional, steep, and two-segment approaches

Center-line noise measurements of a twin-engine commercial jet aircraft were made during steep landing approach profiles, and during two-segment approach profiles for comparison with similar measurements made during conventional approaches. The steep and two-segment approaches showed significant noise reductions when compared with the -3 deg base line. The measured noise data were also used to develop a method for estimating the noise under the test aircraft at thrust and altitude conditions typical of current landing procedures and of landing procedures under development for the Advanced Air Traffic Control System.

Hastings, E. C., Jr.↗

NASA NTRS1982

Flight dynamics of rotorcraft in steep high-g turns

An analyticl procedure developed to permit a systematic examination of rotorcraft flight dynamics in steep high-g turns is presented. The procedure is used in a numerical investigation of a tilt-rotor aircraft and three single-rotor helicopters that have different types of main rotor systems. The results indicate (1) that strong coupling in longitudinal and lateral-directional motions exists for these rotorcraft in high-g turns; (2) that for single-rotor helicopters, the direction of turn has a significant influence on flight dynamics; and (3) that a stability and control augmentation system that is designed on the basis of standard small-disturbance equations of motion from steady straight and level flight and that otherwise performs satisfactorily in operations near 1 g, becomes significantly degraded in steep turning flight.

Chen, R. T. N.↗

NASA NTRS1983

Terminal area automatic navigation, guidance and control research using the Microwave Landing System (MLS). Part 5: Design and development of a Digital Integrated Automatic Landing System (DIALS) for steep final approach using modern control techniques

The design and development of a 3-D Digital Integrated Automatic Landing System (DIALS) for the Terminal Configured Vehicle (TCV) Research Aircraft, a B-737-100 is described. The system was designed using sampled data Linear Quadratic Gaussian (LOG) methods, resulting in a direct digital design with a modern control structure which consists of a Kalman filter followed by a control gain matrix, all operating at 10 Hz. DIALS uses Microwave Landing System (MLS) position, body-mounted accelerometers, as well as on-board sensors usually available on commercial aircraft, but does not use inertial platforms. The phases of the final approach considered are the localizer and glideslope capture which may be performed simultaneously, localizer and steep glideslope track or hold, crab/decrab and flare to touchdown. DIALS captures, tracks and flares from steep glideslopes ranging from 2.5 deg to 5.5 deg, selected prior to glideslope capture. Digital Integrated Automatic Landing System is the first modern control design automatic landing system successfully flight tested. The results of an initial nonlinear simulation are presented here.

Halyo, N.↗

NASA NTRS1991

An X-ray and radio study of steep-spectrum radio sources. II - Four fields from a 22 MHz polar cap survey

Four fields containing radio sources with spectral indices greater than unity at low frequencies have been observed over a wide range of radio wavelengths and at X-ray wavelengths. For most of the steep-spectrum sources no optical identifications have been found to the detection limit of the Palomar Schmidt prints, even with the positional precision of about 1 arcsec from VLA maps. This implies that the associated galaxies or clusters lie at a great distance. X-ray emission was not detected from any of the steep-spectrum radio sources. In one case, an extended source appears to be a radio halo in an uncataloged cluster of galaxies at a redshift of 0.125, and it is suggested that this object is a promising candidate for the detection of inverse Compton X-rays, since it is not a high-luminosity source of thermal X-rays.

Dewdney, P. E.↗

NASA NTRS1994

Mg II absorption in a sample of 56 steep-spectrum quasars

We present an analysis of the statistical properties of Mg II absorbers found in the spectra of 56 intrinsically faint, steep-spectrum radio quasars. We observe for the first time a significant excess of associated Mg II absorbers over the number expected from cosmologically distributed absorbers. This result is in contrast to previous Mg II surveys in which the QSOs were optically selected. This distinction is similar to the result for associated C IV absorbers, in which intrinsically faint, steep-spectrum quasars show excess associated absorption and intrinsically bright QSOs (both radio-loud and radio-quiet) do not show an excess. From our spectra a statistically complete list of absorption lines is derived, and we find 29 Mg II absorbers, 18 of which have not been previously reported. We also determine several characteristics of the quasar emission lines in our spectra. The Mg II absorber distribution as a function of redshift and equivalent width is calculated both for our sample alone and from our sample combined with spectra from other surveys. For the redshift distribution n(z) = n(1 + z)(exp gamma), we obtain, using the combined sample, the values gamma = 1.11 +/- 0.46 for W(min) = 0.6 A and gamma = 2.47 +/- 0.68 for W(min) = 1.0 A. We find that the distribution fo strong absorbers is inconsistent with no evolution at a confindence level between 2.2 and 2.9 sigma, depending on the deceleration parameter q(sub 0). The deviation from no evolution is similar to what had been previously reported.

Aldcroft, Thomas L.↗