File Name: communication and navigation system .zip
To realize the system of LEO-augmented GNSS, three methods to integrate communication and navigation signal for LEO communication system with the least influence on the communication performance are analyzed.
Ambient ionospheric scintillations are caused by naturally occurring irregularities and lead to the degradation of satellite communications signals and of the GPS navigation signals primarily in the UHF and L-band range. Scintillations are responsible for decreased satellite-to-ground message throughput and for delayed signal acquisition. The objective is also to detect conditions that could lead to scintillation in particular regions and thus provide outage forecasts hours before its onset for affected communication frequencies and potential GPS signal degradation.
The mission includes three critical elements:. Figure 1 : Schematic of the formation in latitude variation of ionization density in the equatorial F region, known as the equatorial anomaly or the Appleton anomaly image credit: AFRL. Legend to Figure 1 : The diagram illustrates that during daytime the eastward dynamo electric field from the E region maps along the magnetic field to F-region heights above the magnetic equator.
The minisatellite was built, tested and integrated by Spectrum Astro Inc. ADCS Attitude Determination and Control Subsystem utilizes 2 star trackers, 2 inertial measurement units, 3 torque rods, 2 momentum wheels, and a three-axis magnetometer. The orbit average power consumption is W for the bus and 64 W for the payload in "survey mode" and W for the bus and 63 W for the payload in the "forecast or operational mode.
A near-equatorial launch site is needed to achieve the near-equatorial orbit. The mission data will be made available to the scientific community. AFRL program office at Hanscom Air Force Base, Bedford, MA is responsible for the instrument payload, payload integration and test, model development, data center operations, and data product generation and distribution.
In this mode, the requirement for real-time data is lifted and a full complement of instruments will collect data to be used in the development of specification and forecast models. During this period also referred to as "operational mode" , key instruments will be operated on a more limited duty cycle. The data from the instruments will be transmitted in real-time to the Data Center where it will be processed to provide global ionospheric scintillation specification and forecasts for the use of the US Air Force.
The data collected by the satellite will be available for the use of the scientific community during all phases of the mission. This layer lies some 60 to km above the Earth's surface, where it interacts and co-mingles with the neutral particles of the tenuous upper atmosphere.
The upper atmosphere and ionosphere change constantly in response to forces from above and below, including explosions on the sun, intense upper atmosphere winds, and dynamic electric field changes. In addition to interfering with satellite orbits, such changes can produce turbulence in the ionosphere that cause what's known as scintillations, which interfere with radio wave navigation and communication systems, especially at low latitudes near the equator.
Such regions have rarely been studied directly for extended periods of time, because orbits in this denser region of the atmosphere are not sustainable long-term without on board propulsion. The observations revealed the presence of strong shears in the horizontal ionosphere motions at the base of the ionosphere, places where charged particles flow by each other in opposite directions.
Such shears and undulations — spotted throughout the nighttime, equatorial ionosphere — are believed to be the source of large-scale instabilities that ultimately drive the detrimental scintillations. Any changes to the guidelines will be handled through the budget formulation process. These combined with the continuing downward progression of CINDI with altitude confirm that there will be more extensive NWM data collection and analysis during this proposal period.
Additional data and operations are clearly required to accomplish the proposed science objectives. CINDI will continue to be the only mission providing coincident information on the dynamic state of the ionosphere and thermosphere as the solar cycle declines. This makes it an important data set for achieving system science of the effect of the Sun and magnetosphere on the Earth atmosphere.
The CINDI team also showed significant thermospheric density responses to variable solar flux and magnetic activity. They provide perspectives on how the geospace system responds to variable solar and geomagnetic forcing as well as the impacts of the lower atmosphere on the thermosphere-ionosphere. CINDI represents an important component of the HSO Heliophysics System Observatory , enabling the inclusion of the connected ionosphere and thermosphere system in a coherent study of the geospace environment.
All indicators suggest that satellite and instrument performance will continue to be excellent until the satellite reentry, which is anticipated to occur sometime in Originally scheduled to collect data for two years, the satellite has continued to provide crucial observations for five years running.
CINDI, a NASA instrument in the Explorer Program, has had the opportunity to watch as the sun has increased in activity, and with its direct measurements of how neutral and charged particles interact, the instruments continue to help improve predictions of just when disturbances in the ionosphere will be at their worst. One of the early observations by CINDI was of the top of the ionosphere layer, which is dominated by hydrogen ions near dawn.
The middle layer of the area is dominated by oxygen ions. Figure 5: Schematic view of GPS radio waves travelling through a disturbed layer of Earth's electrically charged atmosphere, the ionosphere, they can be disrupted image credit: NASA. This comes as a surprise, since current models of Schumann resonances predict these waves should be caged at a lower altitude, between the ground and a layer of Earth's atmosphere called the ionosphere.
The key points are: The researchers didn't expect to observe these resonances in space, but it turns out that energy is leaking out and this opens up many other possibilities to study our planet from above. The waves created by lightning do not look like the up and down waves of the ocean, but they still oscillate with regions of greater energy and lesser energy. These waves remain trapped inside an atmospheric ceiling created by the lower edge of the "ionosphere" — a part of the atmosphere filled with charged particles, which begins about km up into the sky.
In this case, the sweet spot for resonance requires the wave to be as long or twice, three times as long, etc as the circumference of Earth. As this wave flows around Earth, it hits itself again at the perfect spot such that the crests and troughs are aligned. Voila, waves acting in resonance with each other to pump up the original signal. Figure 6: Waves created by lightning flashes — here shown in blue, green, and red — circle around Earth, creating something called Schumann resonance.
These waves can be used to study the nature of the atmosphere they travel through image credit: NASA, Fernando Simoes. Schumann resonances had been predicted in ; they were first measured reliably in the early s.
Since then, scientists have discovered that variations in the resonances correspond to changes in the seasons, solar activity, activity in Earth's magnetic environment, in water aerosols in the atmosphere, and other Earth-bound phenomena.
While models suggest that the resonances should be trapped under the ionosphere, it is not unheard of that energy can leak through. And the team was rewarded. Detection of these Schumann resonances in space requires, at the very least, an adjustment of the basic models to incorporate a "leaky" boundary at the bottom of the ionosphere.
But detecting Schumann resonance from above also provides a tool to better understand the Earth-ionosphere cavity that surrounds Earth. A few of these findings are listed below: Tidal structures have been observed in ion density, ionospheric irregularities, electric fields and neutral density.
Plasma irregularities were often embedded within them. Their frequencies strongly depended on longitude and season. The absence of equatorial plasma bubbles just after sunset was consistent with the E- field measurements: the pre-reversal enhancements in the E-field were almost never seen during this solar minimum.
Similar effects observed in DMSP data confirmed that irregularities were present in the dawn side of the orbit rather than in the dusk side. During the first months of CINDI operations the transition between the ionosphere and space was found to be at about km altitude during the nighttime, barely rising above km during the day. These altitudes were extraordinarily low compared with the more typical values of km during the nighttime and km during the day.
The overall objective is to determine when ionospheric structures will appear, over what spatial extent they will exist, and how severe the effects of such structures will become. The challenge is to effectively integrate these proven sensors into scintillation forecasts and nowcasts. The VEFI objective is to provide in-situ measurements of:. In addition, the VEFI experiment includes a magnetometer sensor, a lightning detector design and testing provided by the University of Washington , and a fixed-bias Langmuir probe which serves as the trigger input for the burst memory.
The objective is to investigate the role of ion-neutral interactions in the generation of small and large-scale electric fields in the Earth's upper atmosphere. Ion-neutral interactions are a key process in controlling the dynamics of all planetary atmospheres and their understanding is important to describing the electrodynamic connections between the sun and the upper atmosphere. Also in-situ measurement of small spatial scale 1 km , low altitude neutral wind vector in meridional and vertical directions.
The CORISS objective is remote sensing of the electron density vertical profile at various bearings relative to track where rising and setting GPS satellites are visible.
S4: The nominal sampling time is 0. The objective of DIDM is to measure the Earth's electric field parallel to the magnetic field in-situ measurements of the ion distribution and its moments within the ionosphere. DIDM measures magnitude and direction of the incoming ion flux. The electric field is derived from the relationship between electric field, measured ion drift velocity and measured magnetic field strength.
DIDM utilizes miniaturized state-of-the-art detector components and on-board digital signal processing. The instrument consists of two side-by-side ion detectors [MCP Microchannel Plate type] arranged within one unit of 2.
Both detectors can measure the normal and perpendicular velocity components of incident ions. Those ions with energies higher than a certain threshold potential are electrostatically focused onto charge multiplying microchannel plates MCPs and high-resolution wedge and strip charge detecting anodes. The images created by these impacting ions on the anode are digitally processed on-board to reconstruct the full 3-D ion velocity vector.
The CERTO objective is to determine ionospheric electron density by using a three-frequency beacon; cooperative ionospheric observations with fixed ground receivers.
CERTO provides a global ionospheric map to aid the prediction of radio-wave scattering. This knowledge will improve navigation accuracy and communications capacity for military and commercial systems. This device provides auxiliary data needed to interpret the ion drift measurements. Ground segment:. The stations are all located within 20 degrees of the Earth's magnetic equator. The SCINDA tool is part of a process that results in simple tri-color maps of disturbances over the equator and the corresponding areas of likely communication outages.
Such maps help scientists to better understand how scintillation structures develop, and enable operators to determine practical strategies for maintaining reliable communications. Jeong, K. Ray, J. Retterer, B. Basu, W. Burke, F. Rich, K. Groves, C. Huang, L. Gentile, D. Decker, W.
Borer, C. Cooke, J. Cooke, G.
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NASA Communications and Navigation Infrastructure Requirements. TA6. hybrid optical and RF communication systems should reduce mass.
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