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NASA NTRS2011

The Kepler Light Curves of V1504 Cygni and V344 Lyrae: A Study of the Outburst Properties

We examine the Kepler light curves of V1504 Cyg and V344 Lyr, encompassing approximately 460 d at 1 min cadence. During this span each system exhibited approximately 40 outbursts, including four superoutbursts. We find that, in both systems, the normal outbursts lying between two superoutbursts increase in duration by a factor approximately 1.2 - 1.7, and then reset to a small value after the following superoutburst. In V344 Lyr the trend of quiescent intervals between normal outbursts is to increase to a local maximum about half way through the supercycle the interval from one superoutburst to the next - and then to decrease back to a small value by the time of the next superoutburst, whereas for V1504 Cyg the quiescent intervals are relatively constant during the supercycle. Both of these trends are inconsistent with the Osaki's thermal-tidal model, which robustly predicts a secular increase in the quiescent intervals between normal outbursts during a supercycle. Also, most of the normal outbursts have an asymmetric, fast-rise/slower-decline shape, which would be consistent with outbursts triggered at large radii. The exponential rate of decay of the plateau phase of the superoutbursts is 8 d mag(sup -1) for approximately 1504 Cyg and 12 d mag(sup -1) for V344 Lyr. This time scale gives a direct measure of the VISCOUS time scale III the outer accretion disk given the expectation that the entire disk is in the hot, viscous state during superoutburst. The resulting constraint on the Shakura-Sunyaev parameter, alpha(sub hot) approximately equal to 0.1, is consistent with the value inferred from the fast dwarf nova decays. By looking at the slow decay rate for superoutbursts, which occur in systems below the period gap, in combination with the slow decay rate in one long outburst above the period gap (in U Gem), we infer a steep dependence of the decay rate on orbital period for long outbursts. We argue that this relation implies a steep dependence of alpha(sub cold) on orbital period, which may be consistent with recent findings of Patterson, and is consistent with tidal torquing as being the dominant angular momentum transport mechanism in quiescent disks in interacting binary systems.

Cannizzo, John K.↗

NASA NTRS1980

On the secular decrease in the semimajor axis of Lageos orbit

The semimajor axis of the Lageos orbit is decreasing secularly at the rate of -1.1 mm/day due to an unknown force. Nine possible mechanisms are investigated. Five of the mechanisms, resonance with the Earth's gravitational field, gravitational radiation, the Poynting-Robertson effect, transfer of spin angular momentum to the orbital angular momentum, and drag from near Earth dust are ruled out because they are too small to require unacceptable assumptions to account for the observed rate. Three other mechanisms, the Yarkovsky effect, the Schach effect, and terrestrial radiation pressure could possibly give the proper order of magnitude for the decay rate, but the characteristic signatures of these perturbations do not agree with the observed secular decrease. Atmospheric drag from a combination of charged and neutral particles is the most likely cause for the orbital decay. This mechanism explains at least 71 percent of the observed rate of decrease of the semimajor axis.

Rubincam, D. P.↗

NASA NTRS1974

Pioneer Mars 1979 mission options

Two mission concepts utilizing modified Pioneer Venus hardware are presented as relatively low-cost alternatives for scientific exploration of Mars in 1979. Mission A would perform in situ aeronomy measurements in the Martian ionosphere and include several remote sensing instruments capable of geological surface mapping at low altitudes. The initial high eccentricity orbit would be allowed to decay in an adaptive mode. Mission B would sequentially deploy (from an orbiter bus), four, nondestructing surface penetrometers carrying instrumentation to investigate soil density, composition and chemistry, subsurface water, and perhaps seismology. Mission B is more expensive than mission A, since it requires more extensive hardware modifications and systems development.

Niehoff, J. C.↗

NASA NTRS1991

Review of ESOC re-entry prediction results of Salyut-7/Kosmos-1686

An overview of activities at ESA/ESOC during the followup of the Salyut-7/Kosmos-1686 decay, and of related cooperations with space agencies, research institutes, and national bodies within the ESA Member States, within the U.S. and within the USSR, is presented. A postflight analysis indicated areas for improvement in the forecast procedures, especially during the last day of the orbital lifetime. Corresponding revised decay predictions are presented for Salyut-7/Kosmos-1686, and the improved procedures are verified by an analysis of the reentries of Kosmos-1402A and Kosmos-1402C.

Klinkrad, H.↗

NASA NTRS1990

Relationship of radar cross section to the geometric size of orbital debris

An accurate determination of the sizes of orbiting debris objects is essential to predicting collision rates, atmospheric decay rates, and fragmentation laws for orbiting objects. The radar cross section (RCS) is the most common means of estimating the size of orbiting objects. However, the RCS is prone to error due to Mie scattering, compositional effects, geometrical effects, tumbling, and other dependencies. Optical measurement methods are theoretically much more accurate, but necessitate estimates of the object's albedo. This paper examines the relationship of RCS and optical cross section to physical size and albedo, and presents rules useful for quantizing the physical size of space objects.

Badhwar, Gautam D.↗

NASA NTRS1977

Atmospheric braking to circularize an elliptical Venus orbit

The use of atmospheric drag to circularize an elliptical spacecraft orbit at Venus is analyzed parametrically for the Venus Orbital Imaging Radar Mission (VOIR) in 1983. Navigation, maneuver, and guidance requirements are discussed for the decay of a 24-hr orbit to a close circular orbit in about 30-60 days. A prototype 'Aerobrake' is described which is approximately 5 m in diameter and 25 kg in mass and which replaces a chemical retroengine of about 1300 kg in mass (delta V = 2.5 km/s) by a 700 kg in-orbit mass. The aerobrake, a light deployable Inconel sheet, shields the spacecraft from the flow and radiates the aerodynamic heating.

Mcronald, A. D.↗

NASA NTRS2006

Design and "As Flown" Radiation Environments for Materials in Low Earth Orbit

A conservative design approach was adopted by the International Space Station Program for specifying total ionizing radiation dose requirements for use in selecting and qualifying materials for construction of the International Space Station. The total ionizing dose design environment included in SSP 30512 Space Station Ionizing Radiation Design Environment is based on trapped proton and electron fluence derived from the solar maximum versions of the AE-8 and AP-8 models, respectively, specified for a circular orbit at 500 km altitude and 51.7 degree inclination. Since launch, the range of altitudes utilized for Space Station operations vary from a minimum of approximately 330 km to a maximum of approximately 405 km with a mean operational altitude less than 400 km. The design environment, therefore, overestimates the radiation environment because the particle flux in the South Atlantic Anomaly is the primary contributor to radiation dose in low Earth orbit and flux within the Anomaly is altitude dependent. In addition, a 2X multiplier is often applied to the design environment to cover effects from the contributions of galactic cosmic rays, solar energetic particle events, geomagnetic storms, and uncertainties in the trapped radiation models which are not explicitly included in the design environment. Application of this environment may give radiation dose overestimates on the order of 1OX to 30X for materials exposed to the space environment, suggesting that materials originally qualified for ten year exposures on orbit may be used for longer periods without replacement. In this paper we evaluate the "as flown" radiation environments derived from historical records of the ISS flight trajectory since launch and compare the results with the SSP 30512 design environment to document the magnitude of the radiation dose overestimate provided by the design environment. "As flown" environments are obtained from application of the AE-8/AP-8 trapped particle models along the ISS flight trajectory including variations in altitude due to decay of the vehicle orbit and periodic reboosts to higher altitudes. In addition, an estimate of the AE-8 model to predict low Earth orbit electron flux (because the radiation dose for thin materials is dominated by the electron component of the radiation environment) is presented based on comparisons of the AE-8 model to measurements of electron integral flux at approximately 850 km from the Medium Energy Proton and Electron Detector on board the NOAA Polar Operational Environmental Satellite.

Minow, Joseph↗

NASA NTRS1985

The long term behaviour of Earth orbits and the implications for debris control

GEO orbits with inclinations which remain less than 45 degrees are very stable. Although the inclination of the orbital plane may vary as much as 15 degrees over a period of about 50 years, the orbit altitude will always remain within a few hundred kilometers of geosynchronous altitude, GEO orbits with inclinations greater than 45 degrees exhibit remarkable instabilities ir the eccentricity due to gravitational resonance. Over a period of a century the eccentricity can reach such a large value that reentry is a possibility. The combined effects of the Sun, Moon, and oblate Earth play a significant role in determining the lifetime of a GEO transfer orbit. Depending on the initial orientation of the orbital plane with respect to the Sun and Moon, lifetimes may vary from under 6 months to over several hundred years. Transfer orbits with inclinations over 45 degrees show strong instabilities in the perigee altitude resulting in generally short lifetimes of less than a few years. All transfer orbits can be designed to decay within one year if the initial perigee altitude is less than 231 km. However, there are restrictions on orbit plane placement and time of year of launch.

Mueller, A. C.↗

NASA NTRS1986

Towards a theory for Neptune's arc rings

It is proposed that the incomplete rings of Neptune consist of a number of short arcs centered on the corotation resonances of a single satellite. The satellite must have a radius of the order of 100 km or more and move on an inclined orbit. Corotation resonances are located at potential maxima. Thus, mechanical energy dissipated by interparticle collisions must be continually replenished to prevent the arcs from spreading. It is shown that each corotation resonance is associated with a nearby Lindblad resonance, which excites the ring particles' orbital eccentricity, thus supplying the energy required to maintain the arc. The ultimate energy reservoir is the satellite's orbital energy. Therefore, interaction with the arcs damps the satellite's orbital inclination. The self-gravity of the arcs limits their contraction and enforces a relation between arc length and mass. The estimated arc masses are so small, of the order of 10 to the 16th g, that the satellite's orbital inclination suffers negligible decay over the age of the solar system. The inferred surface mass densities are comparable to those found in the major rings of Saturn and Uranus.

Goldreich, P.↗

NASA NTRS1993

Satellite situation report, volume 33, number 4

The Satellite Situation Report is a listing of those satellites (objects) currently in orbit and those which have previously orbited the Earth. Some objects are too small or too far from the Earth's surface to be detected; therefore, the Satellite Situation Report does not include all manmade objects orbiting the Earth. Generally, satellites are classified as follows: (1) Payloads may contain one or more functioning or nonfunctioning experiments. Usually only the owners of the satellites know if the experiments are functioning, and there is no one source which indicates the operational status of all payloads and/or experiments. Payloads are normally the first listed in the Satellite Situation Report, i.e., 1982 087A, unless there are multiple payloads for the launch. In which case, the first objects cataloged are usually all payloads, unless a subsequent payload is later identified after objects other than payloads have been cataloged. (2) Platforms are used to support a payload while it is being placed into orbit. A platform may remain in orbit long after its purpose is served, usually longer than rocket bodies. It is usually the first object identified in the Satellite Situation Report listing after the payload(s), i.e., 1982 087B (when a platform is not used, the first object after the payload(s) is usually the rocket body). (3) Rocket bodies are used to place the payload and platform (if one is used) into orbit. Some launches may have more than one rocket body because of the payload weight or the type of orbit or experiment. Most rocket bodies decay within a short time after the payload (and platform) have achieved orbit. Rocket bodies are usually the third object listed in the Satellite Situation Report after the payload(s), i.e., 1982 087C. (4) Debris in orbit occurs when parts (nose cone shrouds, lens or hatch covers) are separated from the payload, when rocket bodies or payloads disintegrate or explode, or when objects are placed into free space from manned orbiting spacecraft during operations. Debris is detected by its size and distance from the Earth. Debris objects are the last objects after payload(s), platform, and rocket body(s) listed in the Satellite Situation Report, i.e., 1982 087D, 1982 087E, 1982 087F.

Source record↗

NASA NTRS2001

Vorticity Transport and Wave Emission in the Protoplanetary Nebula

Higher order numerical algorithms (4th order in time, 3rd order in space) are applied to the Euler/Energy equations and are used to examine vorticity transport and wave motion in a non-self gravitating, initially isentropic Keplerian disk. In this talk we will examine the response of the nebula to an isolated vortex with a circulation about equal to the rotation rate of Jupiter. The vortex is located on the 4 AU circle and the nebula is simulated from 1 to 24 AU. We show that the vortex emits pressure-supported density and Rossby-type wave packets before it decays within a few orbits. The acoustic density waves evolve into weak (non entropy preserving) shock waves that propagate over the entire disk. The Rossby waves remain in the vicinity of the initial vortex disturbance, but are rapidly damped. Temporal frequencies and spatial wavenumbers are derived using the simulation data and compared with analytical dispersion relations from the linearized Euler/Energy equations.

Davis, S. S.↗

NASA NTRS2002

Vorticity Transport and Wave Emission In A Protoplanetary Disk

Higher order numerical algorithms (4th order in time, 3rd order in space) are applied to the Euler equations and are used to examine vorticity transport and wave motion in a non-self gravitating, initially isentropic Keplerian disk. In this talk we will examine the response of the disk to an isolated vortex with a circulation about equal to the rotation rate of Jupiter. The vortex is located on the 4 AU circle and the nebula is simulated from 1 to 24 AU. We show that the vortex emits pressure-supported density and Rossby-type wave packets before it decays within a few orbits. The acoustic density waves evolve into weak (non entropy preserving) shock waves that propagate over the entire disk. The Rossby waves remain in the vicinity of the initial vortex disturbance, but are rapidly damped. Temporal frequencies and spatial wavenumbers are derived from the nonlinear simulation data and correlated with analytical dispersion relations from the linearized Euler and energy equations.

Davis, S. S.↗

NASA NTRS1995

Harmonic oscillators and resonance series generated by a periodic unstable classical orbit

The presence of an unstable periodic classical orbit allows one to introduce the decay time as a purely classical magnitude: inverse of the Lyapunov index which characterizes the orbit instability. The Uncertainty Relation gives the corresponding resonance width which is proportional to the Planck constant. The more elaborate analysis is based on the parabolic equation method where the problem is effectively reduced to the multidimensional harmonic oscillator with the time-dependent frequency. The resonances form series in the complex energy plane which is equidistant in the direction perpendicular to the real axis. The applications of the general approach to various problems in atomic physics are briefly exposed.

Kazansky, A. K.↗

NASA NTRS2004

Charge Storage, Conductivity and Charge Profiles of Insulators as Related to Spacecraft Charging

Dissipation of charges built up near the surface of insulators due to space environment interaction is central to understanding spacecraft charging. Conductivity of insulating materials is key to determine how accumulated charge will distribute across the spacecraft and how rapidly charge imbalance will dissipate. To understand these processes requires knowledge of how charge is deposited within the insulator, the mechanisms for charge trapping and charge transport within the insulator, and how the profile of trapped charge affects the transport and emission of charges from insulators. One must consider generation of mobile electrons and holes, their trapping, thermal de-trapping, mobility and recombination. Conductivity is more appropriately measured for spacecraft charging applications as the "decay" of charge deposited on the surface of an insulator, rather than by flow of current across two electrodes around the sample. We have found that conductivity determined from charge storage decay methods is 102 to 104 smaller than values obtained from classical ASTM and IEC methods for a variety of thin film insulating samples. For typical spacecraft charging conditions, classical conductivity predicts decay times on the order of minutes to hours (less than typical orbit periods); however, the higher charge storage conductivities predict decay times on the order of weeks to months leading to accumulation of charge with subsequent orbits. We found experimental evidence that penetration profiles of radiation and light are exceedingly important, and that internal electric fields due to charge profiles and high-field conduction by trapped electrons must be considered for space applications. We have also studied whether the decay constants depend on incident voltage and flux or on internal charge distributions and electric fields; light-activated discharge of surface charge to distinguish among differing charge trapping centers; and radiation-induced conductivity. Our experiments also show that "Malter" electron emission occurs for hours after turning off the electron beam. This Malter emission similar to emission due to negative electron affinity in semiconductors is a result of the prior radiation or optical excitations of valence electrons and their slow drift among traps towards the surface where they are subsequently emitted. This work is supported through funding from the NASA Space Environments and Effects Program.

Dennison, J. R.↗

NASA NTRS1993

Dwarf novae

Dwarf novae are defined on grounds of their semi-regular brightness variations of some two to five magnitudes on time scales of typically 10 to 100 days. Historically several different classification schemes have been used. Today, dwarf novae are divided into three sub-classes: the U Geminorum stars, the SU Ursae Majoris stars, and the Z Camelopardalis stars. Outbursts of dwarf novae occur at semi-periodic intervals of time, typically every 10 to 100 days; amplitudes range from typically 2 to 5 mag. Within certain limits values are characteristic for each object. Relations between the outburst amplitude, or the total energy released during outburst, and the recurrence time have been found, as well as relations between the orbital period and the outburst decay time, the absolute magnitude during outburst maximum, and the widths of long and short outbursts, respectively. Some dwarf novae are known to have suspended their normal outburst activity altogether for a while. They later resumed it without having undergone any observable changes. The optical colors of dwarf novae all are quite similar during outburst, considerably bluer than during the quiescent state. During the outburst cycle, characteristic loops in the two color diagram are performed. At a time resolution on the order of minutes, strictly periodic photometric changes due to orbital motion become visible in the light curves of dwarf novae. These are characteristic for each system. Remarkably little is known about orbital variations during the course of an outburst. On time-scales of minutes and seconds, further more or less periodic types of variability are seen in dwarf novae. Appreciable flux is emitted by dwarf novae at all wavelengths from the X-rays to the longest IR wavelengths, and in some cases even in the radio. Most dwarf novae exhibit strong emission line spectra in the optical and UV during quiescence, although some have only very weak emissions in the optical and/or weak absorptions at UV wavelengths.

Ladous, Constanze↗

NASA NTRS1983

Linearized transfer between inclined circular orbits using low-thrust blow down propulsion system

Noncoplanar transfers between neighboring circular orbits are presented for spacecraft using their own low-thrust blow down propulsion system. It is assumed that the out-of-plane angle between the decaying thrust vector and the current orbit plane remains constant for each extended burn. Switching conditions are derived for the cutoff and relight of the propulsion system in order to carry out a given transfer with inclination change. Furthermore the location where the thrust acceleration is initially applied with respect to the line of nodes of the two orbits is uniquely determined. Finally an analytic derivation of the linearized coplanar motion for stationkeeping and terminal rendezvous studies is also presented and a scheme for deriving the second order correction shown.

Kechichian, J. A.↗

NASA NTRS1979

A semi-analytic theory for the motion of a close-earth artificial satellite with drag

A semi-analytic method is used to estimate the decay history/lifetime and to generate orbital ephemeris for close-earth satellites perturbed by the atmospheric drag and earth oblateness due to the spherical harmonics J2, J3, and J4. The theory maintains efficiency through the application of the theory of a method of averaging and employs sufficient numerical emphasis to include a rather sophisticated atmospheric density model. The averaged drag effects with respect to mean anomaly are evaluated by a Gauss-Legendre quadrature while the averaged variational equations of motion are integrated numerically with automatic step size and error control.

Liu, J. J. F.↗

NASA NTRS2019

Seasonal- and Beta-Angle-Dependent Latitude Bias Variations in Natural Decays

Prior work has demonstrated pronounced statistical clustering of natural decays of medium-to-high-inclination orbital objects peaking approximately 30 degrees in Argument of Latitude ahead of nodal crossings. This effect is caused by the physical bulge in the Earth and the overlying atmosphere, that cyclically modifies effective altitude (and therefore density) faster than the trajectory's decay itself. While prior work has averaged seasonal and RAAN effects over all non-uniform atmosphere possibilities to support long-term characterization of the clustering of final entries in generating a pre-mission Expectation of Casualty, the current study characterizes seasonal and beta angle effects as potential influences on the near-term statistical risks of specific tactical decay scenarios, relative to the average. Such effects on the density profile along an orbit may be important considerations in any scenario where small orbital adjustments are used to optimize the timing and location of final entry trajectories. I.E., two identical spacecraft entering in different seasons and/or beta angles may have different minimum-risk scenarios for identical control capabilities and space weather conditions. Further, the early heating history of shallow trajectories is explored, examining the influence of dramatically different density profiles over the final orbit as the spacecraft either skims over or dives into the atmosphere.

Bacon, John B.↗