Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Low Earth Orbit”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Investigation of Teflon FEP embrittlement on spacecraft in low earth orbit

Teflon(TM) fluorinated ethylene-propylene (FEP) is used on the exterior of spacecraft surfaces in the low earth orbit environment for thermal control. Silverized or aluminized Teflon(TM) FEP used in the Long Duration Exposure Facility (LDEF) and the Hubble Space Telescope (HST) provided evidence of the low earth orbit environments. Samples from the LDEF and HST were evaluated for solar induced embrittlement and for synergistic effects of solar degradation and atomic oxygen.

deGroh, Kim K.↗
NASA NTRS2004

Low-earth-orbit Satellite Internet Protocol Communications Concept and Design

This report presents a design concept for a low-Earth-orbit end-to-end Internet-Protocol- (IP-) based mission. The goal is to maintain an up-to-date communications infrastructure that makes communications seamless with the protocols used in terrestrial computing. It is based on the premise that the use of IPs will permit greater interoperability while also reducing costs and providing users the ability to retrieve data directly from the satellite. However, implementing an IP-based solution also has a number of challenges, since wireless communications have different characteristics than wired communications. This report outlines the design of a low-Earth-orbit end-to-end IP-based mission; the ideas and concepts of Space Internet architectures and networks are beyond the scope of this document. The findings of this report show that an IP-based mission is plausible and would provide benefits to the user community, but the outstanding issues must be resolved before a design can be implemented.

Slywezak, Richard A.↗
NASA NTRS1993

Viscoelastic characterization of thin-film polymers exposed to low Earth orbit

The materials made available through the Long Duration Exposure Facility (LDEF) satellite provide a set of specimens that can be well characterized and have a known exposure history with reference to atomic oxygen and ultraviolet radiation exposure. Mechanical characteristics measured from control samples and exposed samples provide a data base for predicting the behavior of polymers in low earth orbit. Samples of 1.0 mil thick low density polyethylene were exposed to the low earth orbit environment for a period of six years. These materials were not directly exposed to ram atomic oxygen and offer a unique opportunity for measuring the effect of atomic oxygen and UV radiation on mechanical properties with little concern to the effect of erosion. The viscoelastic characteristics of these materials were measured and compared to the viscoelastic characteristics of control samples. To aid in differentiating the effects of changes in crystallinity resulting from thermal cycling, from the effects of changes in chemical structure resulting from atomic oxygen/UV attack to the polymer, a second set of control specimens, annealed to increase crystallinity, were measured as well. The resulting characterization of these materials will offer insight into the impact of atomic oxygen/UV on the mechanical properties of polymeric materials. The viscoelastic properties measured for the control, annealed, and exposed specimens were the storage and loss modulus as a function of frequency and temperature. From these datum is calculated the viscoelastic master curve derived using the principle of time/temperature superposition. Using the master curve, the relaxation modulus is calculated using the method of Ninomiya and Ferry. The viscoelastic master curve and the stress relaxation modulus provide a direct measure of the changes in the chemical or morphological structure. In addition, the effect of these changes on long-term and short-term mechanical properties is known directly. It should be noted that the dependence on directionality for the polymer films was considered since these films were manufactured by a blown-film process.

Letton, Alan↗
NASA NTRS1989

Low earth orbital atomic oxygen simulation for materials durability evaluation

The erosion yields of numerous materials have been evaluated in low earth orbital space tests. There appears to be three classes of materials: materials of high erosion yield which include most of the hydrocarbon organic materials; materials which either do not react with atomic oxygen or form self-protecting oxides which allow the underlying material to appear durable to atomic oxygen, and materials with low but nonnegligeable erosion yields, such as fluoropolymers. A NASA atomic oxygen effects test program has been established to utilize collective data from a multitude of simulation facilities to promote an understanding of mechanism and erosion yield dependencies. Atomic oxygen protective coatings for Kapton polymide solar array blankets, fiberglass-epoxy composite mast structures, and solar dynamic power system concentrator surfaces have been identified and evaluated under atomic oxygen exposure in RF plasma asher laboratory tests. The control of defect density in protective coatings appears to be the key to the assurance of long-term protection of oxidizable materials in low earth orbit.

Banks, Bruce A.↗
NASA NTRS2017

Radiation Information for Designing and Interpreting Biological Experiments Onboard Missions Beyond Low Earth Orbit

There is growing interest in flying biological experiments beyond low-Earth orbit (LEO) to measure biological responses potentially relevant to those expected during a human mission to Mars. Such experiments could be payloads onboard precursor missions, including unmanned private-public partnerships, as well as small low-cost spacecraft (satellites) designed specifically for biosentinel type missions. Designing such experiments requires knowledge of the radiation environment and its interactions with both the spacecraft and the experimental payload. Information is provided here that is useful for designing such experiments.

radiation↗
NASA NTRS1986

Large manned systems/environment interactions in Low Earth Orbit (LEO)

With the advent of the NASA Space Transportation System, regular flights of a large manned spacecraft, the Space Shuttle Orbiter, became a reality. From the earliest mission containing space science instruments as a payload on the third flight of the Orbiter (STS-3), it became apparent that the disturbance caused by the interaction of this orbiting system with the low Earth orbit (LEO) environment resulted in adverse conditions for the performance of scientific observations of the Orbiter natural environment and for certain high sensitivity optical observations. The interaction of the Space Shuttle Orbiter system can be divided into two parts, the structure-environment interaction, and the outgas cloud-environment interaction. These interaction are briefly discussed.

Raitt, W. J.↗
NASA NTRS1984

A low Earth orbit molecular beam space simulation facility

A brief synopsis of the low Earth orbit (LEO) satellite environment is presented including neutral and ionic species. Two ground based atomic and molecular beam instruments are described which are capable of simulating the interaction of spacecraft surfaces with the LEO environment and detecting the results of these interactions. The first detects mass spectrometrically low level fluxes of reactively and nonreactively surface scattered species as a function of scattering angle and velocity while the second ultrahigh velocity (UHV) molecular beam, laser induced fluorescence apparatus is capable of measuring chemiluminescence produced by either gas phase or gas-surface interactions. A number of proposed experiments are described.

Cross, J. B.↗
NASA NTRS1994

A facility to produce an energetic, ground state atomic oxygen beam for the simulation of the Low-Earth Orbit environment

Because of the continuing commitment to activity in low-Earth orbit (LEO), a facility is under development to produce energetic atmospheric species, particularly atomic oxygen, with energies ranging from 5 to 80 eV. This relatively high flux facility incorporates an ion engine to produce the corresponding specie ion which is charge exchanged to produce a neutral atomic beam. Ion fluxes of around 10(exp 15) sec(exp -1) with energies of 20-70 eV have been achieved. A geometrically augmented inertially tethered charge exchanger (GAITCE) was designed to provide a large column depth of charge exchange gas while reducing the gas load to the low pressure portion of the atomic beam facility. This is accomplished using opposed containment jets which act as collisional barriers to the escape of the dense gas region formed between the jets. Leak rate gains to the pumping system on the order of 10 were achieved for moderate jet mass flows. This system provides an attractive means for the charge exchange of atomic ions with a variety of gases to produce energetic atomic beams.

Ketsdever, Andrew D.↗
NASA NTRS1976

Charged particle radiation environment for the Spacelab and other missions in low earth orbit, revision A

The physical charged particle dose to be encountered in low earth orbit Spacelab missions is estimated for orbits of inclinations from e8.5 to 90 deg and altitudes from 200 to 800 km. The dose encountered is strongly altitude dependent, with a weaker dependence on inclination. Doses range from 0.007 rads/day at 28.5 deg and 200 km to 1.57 rads/day at 28.5 deg and 800 km behind a 5.0 g/sq cm shield. Geomagnetically trapped protons were the primary source of damage over most of the range of altitudes and inclinations, with galactic cosmic rays making a significant contribution at the lowest altitudes.

Watts, J. W., Jr.↗
NASA NTRS1984

Failure Analysis of Nickel-hydrogen Cell Subjected to Simulated Low Earth Orbit Cycling

A nickel-hydrogen cell completed 10,080 simulated low earth orbit charge/discharge cycles at depths-of-discharge ranging from 50 to 80 percent prior to failure. The cell is of the Air Force design, rated at 50 ampere-hours, 8.9 cm (3.5 inches) in diameter. Upon disassembly, the end of the polysulfone core supporting the electrode stack was found to have fractured. This allowed the electrode stack to expand. A massive short was found at the inner diameter of the electrodes centered roughly at plate set 34 to 37 from the positive end of the electrode stack. The damaged area extended through approximately one third of the electrode stack, with the effect becoming progressively less with distance from plate set 34 to 37. Measured thicknesses of the positive plates were significantly greater than the initial specification values. The postulated cause of failure is that positive plate growth caused fracture of the shoulder from the end of the polysulfone core on which the electrodes are mounted. The electrode stack relieved and pressure points were created at the area near the inner diameter of the plates at the tab attachment. A short occurred at a pressure point between opposing plates and propagated to other electrode sets due to thermal and mechanical stresses caused by the short.

Mueller, V. C.↗
NASA NTRS1985

Computer subroutines for estimation of human exposure to radiation in low Earth orbit

Computer subroutines to calculate human exposure to trapped radiations in low Earth orbit (LEO) on the basis of a simple approximation of the human geometry by spherical shell shields of varying thickness are presented and detailed. The subroutines calculate the dose to critical body organs and the fraction of exposure limit reached as a function of altitude of orbit, degree of inclination, shield thickness, and days in mission. Exposure rates are compared with current exposure limits.

Cucinotta, F. A.↗
NASA NTRS1989

Approximate angular distribution and spectra for geomagnetically trapped protons in low-earth orbit

The highly anisotropic nature of the radiation in the low-earth orbit has been ignored for most spacecraft shielding calculations made to date because the standard environmental models describe the omnidirectional flux only, because the varying attitude of the spacecraft in the environment is assumed to average out the effect and because of the added complexity of the calculation. The Space Station is planned to be stabilized with respect to the velocity vector and local vertical. Thus it will pass through the South Atlantic Anomaly where most of the radiation flux is encountered in much the same attitude on each pass. Any calculation including a complex shielding geometry should thus consider the angular distributuon of the incident radiation. An approximate trapped proton angular distribution is presented which includes both the 'pan caked' distribution relative to the magnetic field direction and the east-west effect which is energy dependent. This distribution is then used with a planar shielding geometry to obtain an estimate of the effect of the anisotropy on radiation dose rates in spacecraft.

Watts, J. W.↗
NASA NTRS1995

Low Earth Orbit satellite traffic simulator

This paper describes a significant tool for Low Earth Orbit (LEO) capacity analysis, needed to support marketing, economic, and design analysis, known as a Satellite Traffic Simulator (STS). LEO satellites typically use multiple beams to help achieve the desired communication capacity, but the traffic demand in these beams in usually not uniform. Simulations of dynamic, average, and peak expected demand per beam is a very critical part of the marketing, economic, and design analysis necessary to field a viable LEO system. An STS is described in this paper which can simulate voice, data and FAX traffic carried by LEO satellite beams and Earth Station Gateways. It is applicable world-wide for any LEO satellite constellations operating over any regions. For aeronautical applications to LEO satellites. the anticipates aeronautical traffic (Erlangs for each hour of the day to be simulated) is prepared for geographically defined 'area targets' (each major operational region for the respective aircraft), and used as input to the STS. The STS was designed by Constellations Communications Inc. (CCI) and E-Systems for usage in Brazil in accordance with an ESCA/INPE Statement Of Work, and developed by Analytical Graphics Inc. (AGI) to execute on top of its Satellite Tool Kit (STK) commercial software. The STS simulates constellations of LEO satellite orbits, with input of traffic intensity (Erlangs) for each hour of the day generated from area targets (such as Brazilian States). accumulated in custom LEO satellite beams, and then accumulated in Earth Station Gateways. The STS is a very general simulator which can accommodate: many forms of orbital element and Walker Constellation input; simple beams or any user defined custom beams; and any location of Gateways. The paper describes some of these features, including Manual Mode dynamic graphical display of communication links, to illustrate which Gateway links are accessible and which links are not, at each 'step' of the satellite orbit. In the two Performance Modes, either Channel capacity or Grade Of Service (GOS) for objects (Satellite beams, Gateways, and an entire satellite) are computed respectively by standard traffic table capacity lookup and blocking probability equations. GOS can be input, with number of channels calculated, or number of channels can be input, with GOS calculated. Also described are some of the STS Test Procedure approach and results. AGI plans to make the STS features available through their normal commercial STK products. E-Systems is a co-developer, tester, and user of the STS. The Test Procedure for the STS was prepared by E-Systems, as an independent tester for CCI, to support the CCI delivery of the STS to ESCA, for their customer INPE.

Hoelzel, John↗
NASA NTRS2000

Issues and Effects of Atomic Oxygen Interactions With Silicone Contamination on Spacecraft in Low Earth Orbit

The continued presence and use of silicones on spacecraft in low Earth orbit (LEO) has been found to cause the deposition of contaminant films on surfaces which are also exposed to atomic oxygen. The composition and optical properties of the resulting SiO(x)- based (where x is near 2) contaminant films may be dependent upon the relative rates of arrival of atomic oxygen, silicone contaminant and hydrocarbons. This paper presents results of in-space silicone contamination tests, ground laboratory simulation tests and analytical modeling to identify controlling processes that affect contaminant characteristics.

Banks, Bruce↗
NASA NTRS2002

Issues and Consequences of Atomic Oxygen Undercutting of Protected Polymers in Low Earth Orbit

Hydrocarbon based polymers that are exposed to atomic oxygen in low Earth orbit are slowly oxidized which results in recession of their surface. Atomic oxygen protective coatings have been developed which are both durable to atomic oxygen and effective in protecting underlying polymers. However, scratches, pin window defects, polymer surface roughness and protective coating layer configuration can result in erosion and potential failure of protected thin polymer films even though the coatings are themselves atomic oxygen durable. This paper will present issues that cause protective coatings to become ineffective in some cases yet effective in others due to the details of their specific application. Observed in-space examples of failed and successfully protected materials using identical protective thin films will be discussed and analyzed. Proposed approaches to prevent the failures that have been observed will also be presented.

Banks, Bruce A.↗
NASA NTRS2006

The Disposal of Spacecraft and Launch Vehicle Stages in Low Earth Orbit

As a result of the increasing number of debris in low Earth orbit (LEO), numerous national and international orbital debris mitigation guidelines recommend the removal of spacecraft and launch vehicle stages from LEO within 25 years after mission termination. The primary purpose of this action is to enhance space safety by significantly limiting the potential of future accidental collisions resulting in the creation of large numbers of new orbital debris. Likewise, the passivation of these objects, i.e., the removal of residual stored energies, while they remain in orbit is important to prevent the generation of debris via self-induced explosions. Characteristics and trends in the growth of the derelict spacecraft and launch vehicle stage populations in LEO are examined. Depending upon the final operational altitude of the vehicle, achieving the goal of orbital lifetime reduction can influence the design and deployment philosophy of a new space system. Some spacecraft and launch vehicle stages have combined their end-of-mission passivation operations with maneuvers to vacate long-lived orbital regimes. Perhaps the most dramatic demonstration of this type occurred in 2006 when a U.S. Delta IV second stage executed an unprecedented controlled-reentry maneuver from a circular orbit at an altitude near 850 km. For space systems in orbital regimes near the upper regions of LEO (i.e., between 1400 km and 2000 km altitude), maneuvers to place the vehicle above LEO might be more attractive than attempting to ensure an atmospheric reentry within 25 years, and at least one space system operator has selected this option. In some cases, careful consideration of natural orbital perturbations can also lead to reduced orbital lifetimes, although new launch constraints might need to be imposed.

Johnson, Nicholas L.↗
NASA NTRS2023

Commercial Low-Earth Orbit Destination (CLD) Capabilities of Interest and Resource Needs

The Commercial Low Earth Orbit (LEO) Development Program team has been working with NASA and the International Space Station (ISS) National Lab (NL) stakeholders to identify capabilities of interest to both conduct research/technology demonstrations and estimate the resources that will be needed from Commercial LEO Destinations (CLDs). Through a series of one-on-one and working group meetings with users/stakeholders, hardware items of interest to the user community were identified and converted into capabilities (e.g., centrifugation, microscope, pressure chamber, etc.). In parallel, resources needed to operate the research equipment (e.g., crew time, number of experiments, volume, etc.) were estimated in order for the CLD providers to better understand NASA’s potential future service requirements. The capabilities and the resources included in this White Paper do not represent NASA requirements. Instead, they constitute a preliminary set of potential capability and resource needs collated to guide CLD providers in appropriately sizing and outfitting their CLD designs. NASA is requesting feedback from industry on how these capabilities and resources align with their own needs as well as those of their non-NASA customers. Information on how the capabilities/resources impact the CLD designs is also requested. After assessing industry’s feedback to this white paper, NASA plans to issue a preliminary set of requirements for review.

International Space Station↗