Low Earth Orbit (leo)

Abstract: The power system is a vital subsystem in a spacecraft. As long as the spacecraft has power, it can perform its mission. Almost all other failures can be worked out by ground operations from ground stations but a power loss is very fatal for the spacecraft. In the early years of spaceflight, the power system was also the limiting factor in any mission duration. Many studies show that solar cell power (short-circuit current and open-circuit voltage) are degraded by space environment radiation. The power system is designed such that the end of life (EOL) power is adequate for the mission’s requirements. Beginning of life (BOL) power is set by the estimate of the radiation damage over the spacecraft’s lifetime. It is well known in the literature, the radiation damage to solar cells is caused by high-energy protons from solar flares and from trapped electrons in the Van Allen belt. The purpose of this paper is to investigate the power system design trades involved in the mission analysis of a low earth orbit (LEO) satellite at an altitude of 700 km. Based on the power requirements of the payload and the constant power requirements for the remainder of the spacecraft (platform subsystems), the solar arrays and batteries for the spacecraft will be sized.

Abstract. LEO-LEO infrared-laser occultation (LIO) is a new occultation technique between Low Earth Orbit (LEO) satellites, which applies signals in the short wave infrared spectral range (SWIR) within 2 µm to 2.5 µm. It is part of the LEO-LEO microwave and infrared-laser occultation (LMIO) method that enables to retrieve thermodynamic pro- files (pressure, temperature, humidity) and altitude levels from microwave signals and profiles of greenhouse gases and further variables such as line-of-sight wind speed from si- multaneously measured LIO signals. Due to the novelty of the LMIO method, detailed knowledge of atmospheric influ- ences on LIO signals and of their suitability for accurate trace species retrieval did not yet exist. Here we discuss these in- fluences, assessing effects from refraction, trace species ab- sorption, aerosol extinction and Rayleigh scattering in detail, and addressing clouds, turbulence, wind, scattered solar ra- diation and terrestrial thermal radiation as well. We show that the influence of refractive defocusing, foreign species absorption, aerosols and turbulence is observable, but can be rendered small to negligible by use of the differential trans- mission principle with a close frequency spacing of LIO ab- sorption and reference signals within 0.5 %. The influences of Rayleigh scattering and terrestrial thermal radiation are found negligible. Cloud-scattered solar radiation can be ob- servable under bright-day conditions, but this influence can be made negligible by a close time spacing (within 5 ms) of interleaved laser-pulse and background signals. Cloud ex- tinction loss generally blocks SWIR signals, except very thin or sub-visible cirrus clouds, which can be addressed by re- trieving a cloud layering profile and exploiting it in the trace species retrieval. Wind can have a small influence on the trace species absorption, which can be made negligible by using a simultaneously retrieved or a moderately accurate

Colonization of other planets is deemed realistic [1]. This would mitigate against Earth’s periodic global extinction events [2] and the next ice age; our nearest relative, Neanderthal, went extinct in the last ice age. Promisingly, the space-faring nations are planning long-duration expeditions beyond low Earth orbit (LEO) [3]. The economic cost is vast, estimated at sev- eral tens of billions of Euros [4], as technology must be developed to permit human presence on these missions (e.g. advanced life support and integrated sensing systems and superior radiation shielding). Accordingly, we currently know virtually nothing of the ( patho)phy- siologic adaptations associated with habitation beyond LEO and, therefore, little of the long-term prospects for other worldly habitation.

A satellite placed in space is constantly affected by the space environment, resulting in various impacts from tempo- rary faults to permanent failures depending on factors such as satellite orbit, solar and geomagnetic activities, satellite local time, and satellite construction material. Anomaly events commonly occur during periods of high geomag- netic activity that also trigger plasma variation in the low Earth orbit (LEO) environment. In this study, we diagnosed anomalies in LEO satellites using electron data from the Medium Energy Proton and Electron Detector onboard the National Oceanic and Atmospheric Administration (NOAA)-15 satellite. In addition, we analyzed the fluctuation of electron flux in association with geomagnetic disturbances 3 days before and after the anomaly day. We selected 20 LEO anomaly cases registered in the Satellite News Digest database for the years 2000–2008. Satellite local time, an important parameter for anomaly diagnosis, was determined using propagated two-line element data in the SGP4 simplified general perturbation model to calculate the longitude of the ascending node of the satellite through the position and velocity vectors. The results showed that the majority of LEO satellite anomalies are linked to low-energy electron fluxes of 30–100 keV and magnetic perturbations that had a higher correlation coefficient (~ 90%) on the day of the anomaly. The mean local time calculation for the anomaly day with respect to the nighttime migration of energetic electrons revealed that the majority of anomalies (65%) occurred on the night side of Earth during the dusk- to-dawn sector of magnetic local time.

growth of space debris population represents a collision threat for satellite and manned spacecraft in Earth orbit. Recent studies have concluded that regions within Low Earth Orbit (LEO) have already reached a critical den- sity of objects which will eventually lead to a cascading process known as the Kessler syndrome. 2 It is expected for the LEO debris population to increase by approxi- mately 30% in the next 200 years. 1, 3 The Inter-Agency Space Debris Coordination Committee has issued guide- lines to mitigate the growth of space debris. 4 However it

In this paper two strategies are proposed to de-orbit up to 10 non- cooperative objects per year from the region within 800 and 1400 km altitude in Low Earth Orbit (LEO). The underlying idea is to use a single servicing spacecraft to de-orbit several objects applying two different approaches. The first strategy is analogous to the Traveling Salesman Problem: the servicing spacecraft rendezvous with multiple objects in order to physically attach a de-orbiting kit that reduces the perigee of the orbit. The second strategy is analogous to the Vehicle Routing Problem: the servicing spacecraft ren- dezvous and docks with an object, spirals it down to a lower altitude orbit, undocks, and then spirals up to the next target.

Abstract—Conical log spiral antennas are famous for being appro- priate for tracking, telemetry and command (TT&C) applications in low earth orbit (LEO) satellites. In this work, a conical linear (Archimedean) spiral antenna is introduced and investigated for the same purpose. The electric field integral equation (EFIE) technique is applied to a triangular-patch surface model of the conical equiangular linear spiral antenna. This antenna is optimized to produce the radia- tion characteristics required for TT&C applications for LEO satellites. The input impedance, polarization and radiation patterns of this an- tenna are investigated over the operating band of frequencies. Some of the obtained results especially those concerning the input impedance, radiation pattern, polarization and bandwidth are verified experimen- tally. It is shown that the proposed antenna is quite appropriate for TT&C in LEO satellite applications.

With the aim of characterizing geomagnetic variabil- ity in the auroral zones during very quiet times and at low Earth orbit (LEO) altitude, Ritter and Lühr (2006) investigated on the one hand the behavior of residuals in the total field, representing the signals from the auroral electrojet, and on the other hand residuals in the field components perpendicular to the main magnetic field direction, representing signals from field-aligned cur- rents. Here, observations have been reduced by core field predictions and by a homogenous magnetospheric field model based on the Dst index. These authors derived a correlation of 0.5 and higher between perpendicular magnetic deflections (indicating field-aligned currents) and total field residuals (indicating the auroral electrojet) when analyzing both quiet and disturbed conditions and/ or sunlit polar regions, where enhanced conductivity in the E region is expected compared with the dark, quiet regions. Similar good correlations were derived between interplanetary magnetic field proxies and the total field residuals. However, for very quiet conditions and the dark polar hemisphere these correlations are consider- ably reduced, and variations in the solar wind could not be related to variations in the polar ionospheric currents. During geomagnetic quiet times, the authors also iden- tified stationary anomalies and attributed those to the lithospheric field, which was not accounted when build- ing the magnetic residuals. Recently, based on Swarm constellation residuals to the core, magnetospheric and lithospheric field, Lühr et al. (2015a, b) have derived scale lengths of polar field-aligned currents and found that small-scale currents persist for only about 10 s at a par- ticular location, while large-scale currents may persist up to 60 s.

Charged particles injected into dielectric material of artificial satellites may cause data flipping, command errors and charges in dielectric material prop- erties. In this work we report the results of an evaluation of rare earth alumi- nates as possible radiation shields for its application in Low Earth Orbit (LEO) satellite construction. With help of Geant4 software, we calculated the radia- tion dose that a target receives at a typical LEO (685 km) as a function of the shield thickness. The target used was a silicon plate, the shields used were hollow cubes of rare earth aluminate walls (YAlO 3 , LaAlO 3 , NdAlO 3 and

radar is a part of the larger Goldstone Deep Space Communications Complex, which is one of three sites that constitute the NASA Deep Space Network [22]. Nominally tasked with communicating with deep space missions, the radar has collected orbital debris data on an as available basis since 1993. Utilizing a 70-meter reflector antenna to transmit and a 34-meter reflector that listens for return signals off orbital debris, Goldstone operates in a fixed staring mode, not attempting to track any objects that pass through the radar beam. The Goldstone radar is capable of getting data for debris as small as 2 mm; this size range is still capable of inflicting significant damage to spacecraft through collisions, although it poses a much smaller risk for complete spacecraft loss compared to larger debris objects [22]. All of the observational data obtained from Goldstone is processed by Jet Propulsion Laboratory and delivered to the Orbital Debris Program Office at Johnson Space Center, where it can be utilized for better characterizing the debris environment in low-Earth orbit.

This paper presents a novel method of manipulating the spatial pattern of a frac- tionated micro-satellite constellation in Low Earth Orbit. The method developed allows satellites to manipulate the longitudinal position of their ground-tracks over the Earth’s surface, such that they pass over specified targets. This is achieved firstly by pairing satellites on the constellation to the targets on the Earth’s sur- face, and then by developing an artificial potential field controller to define the thrust commands which move the satellites into the appropriate orbital slots to converge upon their targets. The latter is achieved using Coupled Selection Equa- tions - a dynamical systems approach to combinatorial optimisation.

Knowledge of the Earth Atmospheric Remnants (AtR) composition at altitudes from 180 km to 240 km is of paramount importance for the development of air-breathing technology which is of interest here, mainly ad- dressing needs of Low Earth Orbits (LEO). Hall Effect Thruster (HET) and Radio-frequency Ionization Thruster (RIT) devices are expected to be used in this case. More generally, atmosphere composition is also important for satellite drag and re-entry studies.

satellites to appear to hover in a fixed position in the sky. Because it is such a narrow region and so highly prized for observation and communication, the problem of space debris is greatly exacerbated. Debris can stay in GEO for centuries at a time, whereas the lowest orbits in LEO can decay into the upper atmosphere in less than a decade. To prevent this coveted band from being overtaken by debris, the International Telecommunications Union set up strict debris mitigation guidelines in 1960. (Zoller, 2007). A key stipulation of this agreement requires prospective satellites to be registered to a specific location in GEO through the International Telecommunications Union. This registration entitles the satellite to be in its particular spot for a fixed period of time and only that time. Afterwards, it is required to vacate the spot for new use, usually by moving to a higher “graveyard” orbit that makes way for new satellites. Medium Earth Orbit (MEO) is the region between LEO and GEO which is not overly populated or of great concern for debris management. By contrast, most debris and active satellites currently in orbit are in LEO which has no universal orbital management system like GEO has under the International Telecommunications Union. The lack of regulations in LEO coupled with the sheer number of satellites and other pieces of space debris make it a policy arena that is worth

The satellite systems dedicated for global coverage are comprised of constellations of low Earth orbit (LEO) and geostationary Earth orbit (GEO) satellites [1]. The satel- lite’s launching process toward geostationary orbit be- cause of too large distance form the Earth, takes few steps. In the first step the satellite is injected into a low Earth circular orbit (LEO). In the second step, the satel- lite’s orbit is transformed from the low Earth orbit into an elliptical transfer orbit by maneuvers at perigee, in order to attain the apogee equal to geostationary (GEO) orbit’s radius. Finally, the satellite is placed from the elliptical transfer orbit to the final destination, as geosta- tionary orbit [2,3]. The geostationary orbit is unique faced with too close proximity of satellites in this orbit. To avoid mutual interferences and collision, a method of multi-satellites separation has to be applied [4].

Keywords: Low earth orbit satellite networks, all bloking probability, hand-os, deomposition algorithms.. Department of Computer Siene.[r]

DOI: 10.4236/ijaa.2018.84026 369 International Journal of Astronomy and Astrophysics relative to an Earth-fixed observer [3]. This principal characteristic of the GEO makes it suitable for communication and navigation satellites [4]. Meanwhile, it is essential of the frequency resources for construction of the communication and navigation satellites’ systems [5]. Hence, it is of significance to monitor the usage of the frequency resources of GEO satellites. Based on this background, problem A of CTOC9 has considered the orbit design and optimization mission for the low earth orbit (LEO) satellites in formation to observe the GEO satel- lites’ beams [6]. The J2 perturbation must be considered when propagating the orbits and maintaining the flying formation [7].

LEGISLATION The US Federal Communications Commission FCC has approved rules that would allow as many as six companies to share the radio spectrum for low-earth orbit LEO satellite servic[r]

Interaction between the solar wind and the Earth’s magnetosphere is associated with large-scale currents in the ionosphere at polar latitudes that flow along magnetic field lines (Birkeland currents) and horizontally. These current systems are tightly linked, but their global behaviors are rarely analyzed together. In this paper, we present estimates of the average global Birkeland currents and horizontal ionospheric currents from the same set of magnetic field measurements. The magnetic field measurements, from the low Earth orbiting Swarm and CHAMP satellites, are used to co-estimate poloidal and toroidal parts of the magnetic disturbance field, represented in magnetic apex coordi- nates. The use of apex coordinates reduces effects of longitudinal and hemispheric variations in the Earth’s main field. We present global currents from both hemispheres during different sunlight conditions. The results show that the Bir- keland currents vary with the conductivity, which depends most strongly on solar EUV emissions on the dayside and on particle precipitation at pre-midnight magnetic local times. In sunlight, the horizontal equivalent current flows in two cells, resembling an opposite ionospheric convection pattern, which implies that it is dominated by Hall currents. By combining the Birkeland current maps and the equivalent current, we are able to calculate the total horizontal current, without any assumptions about the conductivity. We show that the total horizontal current is close to zero in the polar cap when it is dark. That implies that the equivalent current, which is sensed by ground magnetometers, is largely canceled by the horizontal closure of the Birkeland currents.

In this paper, transfers from low Earth orbit (LEO) to so-called eight-shaped orbits at the collinear libration points in the circular restricted three-body problem are investigated. The potential of these orbits (both natural and sail displaced) for high-latitude observation and telecommunication has recently been established. The transfer is modelled by distinguishing between a near-Earth phase and an interplanetary phase. The near-Earth phase is first assumed to be executed with the Soyuz Fregat upper-stage, which brings the spacecraft from LEO to a highly elliptic orbit. From there, the interplanetary phase is initiated which uses low-thrust propulsion to inject the spacecraft into one of the eight-shaped orbit’s manifolds. Both solar electric propulsion (SEP), solar sailing and hybridised SEP and solar sailing are considered for this phase. The objective is to maximise the mass delivered to the eight-shaped orbit starting from a realistic Soyuz launch vehicle performance into LEO. Optimal trajectories are obtained by solving the optimal control problem in the interplanetary phase with a direct pseudospectral method. The results show that (over the full range of propulsion techniques) 1564 to 1603 kg can be injected into a natural eight-shaped orbit. Within this relatively small range, hybrid propulsion performs best in terms of mass delivered to the eight-shaped orbit, while SEP enables the fastest transfer times. With the interplanetary phase optimised, the upper-stage near-Earth phase is replaced by a multi-revolution low-thrust spiral. Locally optimal control laws for the SEP thruster and solar sail are derived to minimise the time of flight in the spiral. Both pure SEP and hybrid spiral show a significant reduction in the mass required in LEO to deliver the spacecraft to the eight-shaped orbits. While hybrid propulsion did not stand out for the use of an upper-stage near-Earth phase, it does for the use of a low-thrust spiral as it significantly reduces the spiral time with respect to the pure SEP case.

In order to verify the performance of deep neural network in satellite orbit prediction, the long short-term memory neural network prediction is carried out based on the actual data of X, Y and Z coordinates of the satellite's geocentric inertial coordinate system. The experimental object was the TacSat2 US scientific imaging satellite, launched in December 2006 with orbital height of 413KM × 424KM near-circular orbit, and the experiment was performed at UTC time from 12:00:00 on July 1,2007 to October 8, 2017 12:00:00 total of 100 days of data as a learning sample. The 100-day satellite orbital X, Y, Z values are calculated by STK (satellite Tool Kit) High Precision Orbital Predictor (HPOP) and the learning samples are sampled at 1-minute intervals for the next 20 days. The results of X-axis prediction are partially shown in Figure.3. The error analysis mainly records the maximum absolute error and training time according to the training times. As shown in Table 1.