Geostationary Arc Research Articles

Interference into radio broadcast satellite uplinks

Radio frequency interference into satellite transmission channels is a matter of concern. There have been many studies of this subject by the ITU (International Telecommunications Union) particularly to mobile user receivers in the satellite radio broadcasting services by IMT (International Mobile Telecommunications) transmitters, since such receivers have high sensitivities (e.g., downlink channel system noise temperatures of under 100 deg. Kelvin) and provide Satellite Digital Audio Radio Service (SDARS) quality using relatively low satellite signal levels on the ground. Recently, proposals have been made by future low orbit satellite constellations, IMT and terrestrial interconnection systems to share radio frequency bands used by the transmission uplinks to radio broadcasting satellites. The broadcasting satellite uplink transmission channel at 7 GHz has typical system noise temperatures of 900 deg. Kelvin followed by very high electronic and antenna amplification. The overall system transmission design is generally set so the satellite broadcast uplink C/N does not appreciably degrade the downlink C/N, since the downlink simultaneously serves than 35 million mobile users with satellite radio service in North America. This paper describes the effect of potential interference into a satellite radio broadcast service from in-band and adjacent band transmissions and from associated intermodulation products by sharing uplink frequency spectrum transmitters. The analysis shows that such sharing services should be carefully arranged in the radio frequencies utilized and limited in flux densities impinging the geostationary orbital arc so harmful interference to radio broadcast satellite services does not occur.

Observations in the thermal IR and visible of a retired satellite in the graveyard orbit, and comparisons to active satellites in GEO

There exists a population of defunct satellites in the geo-stationary arc that potentially pose a hazard to current and future operational satellites. These drifting, non-station-kept objects have a variety of ages and sizes, and many are trapped in libration orbits around the Earth׳s two gravitational potential wells (the non-spherical nature of the Earth gives rise to two geo-potential wells or “stable points” that affect objects in geostationary and geosynchronous orbits), whereas others were boosted to higher altitudes into so-called “graveyard” orbits.We have observed several of the approximately 49 objects in libration orbits about the Western stable point (R. Choc, T. Flohrer, and B. Bastida, “Classification of Geosynchronous Objects,” Issue 13, ESA/ESOC, February 2011), as well as objects in graveyard orbits. We have carried out an observational campaign utilizing The Aerospace Corporation׳s 3–13µm Broadband Array Spectrograph System (BASS), as well as with several optical sensors to collect data on a representative sample of these objects at a variety of solar phase angles. Here we report on recent BASS observations of a retired satellite in the “graveyard” orbit, and compare them with data we had collected over six years ago, while the satellite was still active. Data are also presented on similar satellites that are still active. We describe our methods, the data collected, our results, and our future plans.

Decommissioning of the Inmarsat 2F3 satellite

The current paper describes the detailed operational planning process required for the decommissioning of the Inmarsat 2F3 satellite. The background to events which lead to the decision to decommission this satellite is presented and descriptions of the methods used to monitor the onboard propellant reserves are included in order to explain their role in determining the date of service termination. Orbital and operational factors are elaborated and then folded into a baseline plan for executing a sequence of orbit raising manoeuvres that would be necessary to increase the satellite altitude above the busy geostationary arc. Subsystem passivation activities to be performed on arrival at the final graveyard orbit are discussed and the paper concludes with the story of what actually happened with the first ever Inmarsat satellite decommissioning.

Modelling of the optical observations of a geosynchronous fragmentation event

A study of the evolution and optical detectability of a fragmentation debris cloud in geosynchronous orbit has been carried out. The 1998 NASA breakup model has been used to generate orbit data for 95 fragments larger than 10 cm size from a 1000 kg satellite. The orbital evolution of these fragments is studied using a precision numerical propagator, employing a high-fidelity force model. Although the fragments rapidly disperse throughout the geostationary arc, they remain localised in right ascension of ascending node and inclination, and are driven along a narrow inertial corridor by luni-solar perturbations. The ESA PROOF software is used to study the detectability of the fragments using a 1- and 0.5-m telescope design. The 1-m telescope can detect 82% of the fragments (down to 13 cm in size) whilst the 0.5-m telescope can detect 39% of the fragments (down to 30 cm size). Due to the large along-track spread of the fragments, a time limit of 1-month post-breakup can be established for a space surveillance system to catalogue the breakup fragments. After this time the angular separation is such that the fragments disperse into the background population, and are no longer distinguishable as originating from a common breakup event.

Design of multibeam parabolic torus reflector antennas

Design formulas, principles, and procedures for a multibeam parabolic torus reflector antenna (PTRA) are presented. A six-beam PTRA with 15° geostationary arc coverage for satellite communication is described. Experimental and theoretical radiation patterns are given. Six identical beams are obtained with low sidelobe and low cross-polarization levels. A comparison between the calculated and measured patterns of the central beam shows good agreement. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 27: 343–347, 2000.

Advanced Reflector Antennas for Geostationary Spacecraft

With satellite communications on a continuous rise the geostationary arc and orbital slots as well as the frequency spectrum available becomes increasingly crowed. This directly influences the design of the spacecraft antennas as gain and isolation requirements are tightened to be compatible with this environment. Typically, two distinctly different antenna designs emerge depending on the requirements. For more regional type coverages with one shaped beam and with polarisation isolation requirements the shaped reflector antenna is often chosen. The multifeed reflector antennas fulfil the needs of multibeam antennas with stringent isolation requirements between beams that are spatially isolation. State-of-the-art designs continue to be provident by Dornier Satellitensysteme GmbH. For the shaped reflector antenna past and several on-going programmes at Dornier Satellitensysteme employ this type of design among them the INSAT-2E shaped reflector antennas which were delivered to ISRO in early 1997. For the multifeed antenna the most recent example is the highly complex INTELSAT-VIII antenna subsystem featuring 88 feed elements and high spatial and polarisation isolation requirements. Presently four antenna subsystems of this kind are in orbit and the multifeed antennas for the INTELSAT IX programs are under manufacture at Dornier Satellitensysteme GmbH. The design of the INSAT-2E shaped reflector antennas and the INTELSAT-VIII multifeed reflector antenna is described in this paper.

Consideration of Practical Visibility of Geostationary Augmentation Satellites from Aircraft

The visibility of geostationary augmentation and GPS satellites from typical aircraft engaged in banked turning maneuvers is considered. First, the optical visibility from the GPS antenna location to the geostationary orbital arc is analyzed. It is shown that if two geostationary satellites at substantially different azimuths are available, they are blocked at different times during the aircraft turn, so that at no time during the maneuver is the aircraft without at least one geostationary's signal. Test flight data provided by Boeing for GPS satellites are then used to indicate that actual signal reception often continues well below the pessimistic optical mask. These considerations, as well as the operational fact that large banking angles do not occur in the final approach phase where integrity and continuity are most important, suggest that geostationary augmentation will remain effective at much higher latitudes than has been indicated in previous references.

Ku‐ vs. C‐band and digital vs. analogue television transmission in a tropical climate

AbstractThis paper analyses the Ku‐band versus C‐band transmission for digital and/or analogue TV, keeping in mind Ku‐band attenuation in the tropical climate as a function of earth‐station antenna elevation angle. The analysis is done for the case that adjacent satellites illuminate the same converage area and that interfering signals are of same e.i.r.p. and spectral make‐up. It is shown that a multiplex of compressed digital carriers requires smaller receiving antennas than a single analogue TV carrier. It turns out that because of low power requirements of the compressed digital carrier and/or for high e.i.r.p. values, the earth‐station antenna diameter is interference limited. Below the interference limit the aperture can only be reduced by applying an elliptical area to provide for a narrower beamwidth along the geostationary arc.

Scan limitations of shaped dual-offset reflector antennas for multiple satellite access

The performance of offset Cassegrain antennas, shaped to provide wide scan angles, is outlined for use in earth stations which are capable of accessing several satellites simultaneously. The effect on the beam efficiency of scanning over a rectangular-shaped coverage region located about the geostationary arc is described. Limitations on scan performance are discussed as is the effect of satellite tracking by feed movement.

A satellite system synthesis model for orbital arc allotment optimization

A mixer-integer programming formulation is presented of a satellite system synthesis problem, or geostationary-orbital-planning synthesis problem, which is referred to as the arc allotment problem (AAP). Each satellite administration is to be allotted a weighted-length segment of the geostationary orbital arc within which its satellites may be positioned at any longitude. The objective function maximizes the length of the unweighted arc segment allotted to every administration, subject to single-entry cochannel interference restrictions and constraints imposed by the visible arc for each administration. Useful relationships between special cases of AAP and another satellite synthesis problem are established. Solutions to two example problems are presented. >

The Evolution of the Geostationary Platfom Concept

The paper will review the conceptual development over the last decade of the use of very large spacecraft, i.e., "platforms," in geostationary orbit. Geostationary platforms were originally conceived as an efficient means of increasing the capacity at a point in the geostationary orbital arc. This geostationary platform was seen as a solution to the predicted crowding of the orbital arc since it could provide the functions of many individual satellites of conventional design. Also, geostationary platforms have been suggested for mounting very large antennas as will be required for mobile communications, or high power sources as will be required for broadcast services to small terminals. More recently these "large satellite" platforms were also envisioned as including earth observation and other science payloads. The advent of the Space Station which can provide a staging base for platform assembly and test in space at low earth orbit (LEO), prior to launch to geostationary earth orbit (GEO), will introduce a new dimension to practical platform design. This dimension has reintroduced the geostationary platform concept as a potential communications and science spacecraft of the post-IOC-Space Station family. This paper describes the evolution of concepts for geostationary platforms over the last decade based on both communications and science user scenarios developed worldwide.

Halt the New Satellite Give away

Abstract. The geostationary arc is an orbit in space in which a satellite, 22,300 miles up, moving at the speed at which the earth revolves, can continue to hover over a continent on earth, monitoring weather and military activities, rebroadcasting entertainment and information programs, newspaper and magazine printing plates and particularly communications. In the latter use it replaces surface microwave relay transmitters every 30 miles (which replaced the much more expensive long landlines), at an estimated savings of more than half a billion dollars annually for this use alone. Because the orbit cannot accommodate all the applicants for slots within it, the Federal Government should grant, for an adequate fee, three year licenses, raising the fee on renewal to absorb the annual economic rent.