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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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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2021

Titan’s Global Radiant Energy Budget During the Cassini Epoch (2004-2017)

Radiant energies of planets and moons are of wide interest in the fields of geoscience and planetary science. Based on long-term multiinstrument observations from the Cassini spacecraft, we provide here the first observational study of Titan's global radiant energy budget and its seasonal variations. Our results show that Titan's radiant energy budget is not balanced over the Cassini era (2004–2017) with the absorbed solar energy (1.208 ± 0.008) × 10^(23) J larger than the emitted thermal energy (1.174 ± 0.005) × 10^(23) J. The energy imbalance is 2.9 ± 0.8% of the emitted thermal energy. Titan's global radiant energy budget is not balanced either at the timescales of Earth's years and Titan's seasons. In particular, the energy imbalance can be beyond 10% of the emitted thermal energy at the timescale of an Earth year. The energy imbalance revealed in this study has important impacts on Titan, which should be examined further by theories and models.

Ellen C. Creecy↗
NASA NTRS2024

PDC25 Epoch 1 Damage Risk Maps Content Key

These maps represent asteroid impact damage estimates modeled for the PDC25 Hypothetical Asteroid Impact Exercise, as part of the 9th AIAA Planetary Defense Conference (PDC2025). This exercise assesses a realistic but fictitious hypothetical scenario, not a real asteroid threat.

SMD↗
NASA NTRS1992

History of water on Mars - A biological perspective

A general scenario is developed for the history of liquid water on the surface of Mars, according to which the history of water on Mars can be divided into four epochs based on the fundamental temperature and pressure characteristics. In Epoch I, the mean annual temperature is assumed to have been above freezing and the pressure to have been above 1 atm; liquid water was widespread and life could have arisen and become abundant. In Epoch II, the mean annual temperature fell below freezing, but peak temperatures were above freezing; In Epoch II ice-covered lakes could have provided a habitat for life. In Epoch III, both the mean and the peak temperatures were below freezing, and only transient liquid water would be possible; under these conditions, microbial ecosystems living in endolithic rock 'greenhouses' could have continued to survive. Finally, in Epoch IV, the pressure dropped to near the triple point pressure of water; at this stage, life on the surface of Mars would have become extinct.

Mckay, Christopher P.↗
NASA NTRS2001

The FU Orionis Phenomenon and Solar Nebula Material

We summarize astronomical, meteoritic, and theoretical evidence relating to the FU Orionis phenomenon. This evidence suggests that at early times (the first few 10(exp 5) yr), the solar nebula experienced a hot phase characterized by high accretion rates (the "FU Ori epoch"), punctuated by episodic outbursts of enhanced mass flow through the inner part of the disk (less than or equal to 0.3 AU). Throughout this epoch, disk midplane temperatures exceeded 1000 K at 1 AU. Diminishing infall from the cloud core led to decreasing mass flux throughout the disk. When mass flow de creased below the value critical for outburst (5 x 10(exp -7) solar mass/yr, as suggested by thermal ionization instability models), outbursts ceased and the T Tauri epoch began. Outburst timescales are too long to explain calcium- and aluminum-rich inclusion (CAI) and chondrule formation. Volatility-dependent fractionation patterns seen in meteoritic materials suggest that solids formed beginning during a hot epoch when temperatures exceeded 1400 K, and the presence of volatiles in chondrites argues that this process continued until the nebula had cooled to below 400 K. The thermal ionization instability model for FU Ori outbursts is in quantitative agreement with astronomical observations. Its results imply that the terrestrial region of the nebula reached the hot end of this range only during a time when mass flow through the disk was high enough to trigger outbursts (i.e., the FU Ori epoch) and reached the cool end of this range only during the later T Tauri epoch. According to the models, heating of material in the terrestrial planet region during individual FU Ori outbursts would be limited to surface layers of the nebula, leaving midplane materials (which are at greater than or equal to 1000 K) largely unaffected. Alternative FU Ori models should be developed, particularly if compositional differences among chondrite clans are attributable to episodic heating.

Bell, K. R.↗
NASA NTRS1977

Expressions for the precession quantities based upon the IAU /1976/ system of astronomical constants

The structure of the expressions usually employed in calculating the effects of precession is examined, and a method is outlined for revising the expressions to account for changes in the fundamental astronomical constants. It is shown that the basic set of parameters, upon which depend the lengthy polynomials for computing the mean obliquity of data and the elements of the precession matrix, consists of the mean obliquity, the speed of general precession in longitude at a fixed epoch, and the system of planetary masses. Special attention is given to the motion of the ecliptic pole, formulations for a basic epoch as well as an arbitrary epoch, and ecliptic motion relative to the basic epoch. Numerical precession quantities at epoch J2000.0 (JED 2451545.0) are presented which result from the revision of astronomical constants adopted at the XVI General Assembly of the IAU.

Lieske, J. H.↗
NASA NTRS1998

Modeling the Variability of the BL Lacertae Object PKS 2155-304

The bright X-ray-selected BL Lacertae object PKS 2155-304 has been the target of two intense multi-wavelength campaigns in 1991 November and in 1994 May. Although the spectral energy distributions at both epochs were quite similar, the source exhibited two very distinct variability patterns that cannot be easily reconciled with homogeneous one-zone C7 jet models. During the first epoch the variability was almost achromatic in amplitude, with a time lag between X-rays and ultraviolet radiation (UV) of approximately three hours, while during the second epoch the variability amplitude increased as a function of wavelength with the EUV flare peaking approximately one day after the X-ray flare. We model the source using a time-dependent inhomogeneous accelerating jet model. We reproduce the general characteristics of the different variability signatures by assuming that plasma disturbances with different physical properties propagate downstream in an underlying jet characterized by the same set of physical parameters at both epochs. A time delay of approximately one day between the hardening of the UV spectral index and the UV flux present at both epochs is modeled with stochastic fluctuations in the particle acceleration manifested through small variations of the maximum energy of the injected electrons. We predict that similar time delays will be present in future observations even in the absence of strong variability event. We stress the importance of observations at neighboring frequencies as a diagnostic tool for the structure of the quiescent jet in blazars especially in the seemingly dull case in which strong variability is absent.

Georganopuolos, Markos↗
NASA NTRS2005

Salt Kinematics and InSAR

As part of a long-term attempt to learn how the climatic and tectonic signal interact to shape a steady state mountain monitored displacement of a markers in SE termination and also near the summit of a small viscous salt fountain extruding onto the Central plateau of Iran. The marker displacements relate to the first InSAR interferograms of salt extrusion (980913 to 990620) calculated Earth tides, winds, air pressures and temperatures. In the first documented staking exercise, hammered wooden stakes vertically through the surgical marl (c. 1 Ocm deep) onto the top of crystalline salt. These stakes installed in an irregular array elongate E-W along the c.50 m high cliff marking the effective SE terminus of the glacier at Qum Kuh(Centra1 Iran) ,just to the E of a NE trending river cliff about 40 m high. We merely measured the distances between pairs of stakes with known azimuth about 2 m apart to calculate sub horizontal strain in a small part of Qum Kuh. Stakes moved and micro strains for up to 46 pairs of stakes (p strain= ((lengthl-length2)/1engthl) x 10-1) was calculated for each seven stake epochs and plotted against their azimuth on simplified array maps. The data fit well the sine curves cxpected of the maximum and minimum strain ellipses. The first documented stakes located on the SE where the InSAR image show -1 1 to 0 mm pink to purple, 0 to lOmm purple to blue, and show high activity of salt in low activity area of the InSAR image (980913 to 990620).Short term micro strains of stake tie lines record anisotropic expansions due to heating and contraction due to cooling. All epochs changed between 7 to 1 17 days (990928 to000 1 16), showed 200 to 400 micro strain lengthening and shortening. The contraction and extension existed in each epoch, but the final strain was extension in E-W in Epoch land 6, contraction in E-W direction during epochs 2-3-4-5 and 7. The second pair of stakes hammered about 20 cm deep into the deep soils(more than 1 m) , near summit, where the colors change between 19 to 29mm in InSAR image(9809 13 to 990620). Additional information is included in the original abstract.

Aftabi, Pedarm↗
NASA NTRS1996

System and method for generating attitude determinations using GPS

A GPS attitude receiver for determining the attitude of a moving vehicle in conjunction with a first, a second, a third, and a fourth antenna mounted to the moving vehicle. Each of the antennas receives a plurality of GPS signals that each include a carrier component. For each of the carrier components of the received GPS signals there is an integer ambiguity associated with the first and fourth antennas, an integer ambiguity associated with second and fourth antennas, and an integer ambiguity associated with the third and fourth antennas. The GPS attitude receiver measures phase values for the carrier components of the GPS signals received from each of the antennas at a plurality of measurement epochs during an initialization period and at a measurement epoch after the initialization period. In response to the phase values measured at the measurement epochs during the initialization period, the GPS attitude receiver computes integer ambiguity resolution values representing resolution of the integer ambiguities. Then, in response to the computed integer ambiguity resolution values and the phase value measured at the measurement epoch after the initialization period, it computes values defining the attitude of the moving vehicle at the measurement epoch after the initialization period.

Cohen, Clark E.↗