CA2266153A1

CA2266153A1 - Multi-media satellite

Info

Publication number: CA2266153A1
Application number: CA002266153A
Authority: CA
Inventors: Ryan Granlund; James Wight
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-03-18
Filing date: 1999-03-18
Publication date: 2000-09-18

Abstract

A satellite for use in a multi-media constellation network comprising a satellite body, photovoltaic solar planes affixed to the body and adapted to receive sunlight and provide electric power to the satellite, the body being provided with microwave transmitter and receiver means including rotating drums containing microwave, antennae and reflectors for reflecting transmitted and received signals to provide a movable footprint for the satellite adapted for illuminating a fixed earth cell for an extended period of time, inter-satellite optical links adapted to transmit and receive control signals and data among satellites, a telemetry tracking and control system for communication with ground control stations to control the orbital position and orientation of the satellite, electrical batteries for storing electrical energy to provide power to the optical control systems, and an ion thruster for satellite propulsion and a three axis attitude control system, whereby the satellite operates in its assigned orbital plane, and transmits and receives data from earth fixed cells and communicates with adjacent satellites using inter-satellite optical links.

Description

FIELD OF THE INVENTION:
The present invention relates to a multi-media satellite constellation network and in particular to a satellite for use in such network.
BACKGROUND TO THE INVENTION:
Satellites for use in constellation networks are required to receive and transmit data in up and down links from earth fixed cells, while the satellite is in a low earth orbit and transiting the cell. Unique properties are required in the satellite to accommodate communication with the earth cells as well as communication links with other satellites, referred to as "inter-satellite links" (ISL).
As disclosed in the above companion application, a multi-media satellite constellation network comprises four hundred and fifty satellites orbiting in fifteen planes, all of which planes are equally spaced about the equator and pass through both the north and south poles. The satellites are orbiting with thirty satellites equally spaced from each other in each of the fifteen planes. Each satellite is provided with solar energy for operation of all electronic and optical equipment, and an ion engine for positioning of the satellite.
The earth cell system utilized consists of fixed locations on the earth and communication of data and other signals is achieved from the earth cell to the satellite and from the satellite to the earth cell using uplink/downlink technology.
Communication between satellites is also required in this constellation, so that data intended for users of the constellation remote from the location of an originating earth cell is transmitted from one satellite to the next, until a satellite located over the intended recipient earth cell can transmit the data to the recipient. While the term "data" is used, it should be understood that this can include a variety of data feeds from cellular telephones to ISDN, B-ISDN and other mass data transfer configurations.
With a constellation of several hundred low earth orbit satellites, it is possible to provide real-time, point-to-point or point-to-multi-point communications for high-speed data, video audio or voice, anywhere over the earth's surface. The low satellite altitudes ensure that propagation delays are small so that video conferencing and other forms of real-time communications can be comfortably undertaken. The satellites will typically receive and transmit through many small, contiguous spot beams. Each spot beam will illuminate a relatively restricted region of the earth's surface and provide multiple access by a large number of transmitting stations within the spot beam, the concept being very similar to a cellular telephone system. Because of the very high speed of the satellites, an array of spot beams, fixed with respect to the satellite, would move rapidly over the earth's surface and require frequent switching or "hand-off" between spot beams.
The time between spot beam hand-offs would be just a few seconds and would provide difficult to implement on-board the satellites and could result in frequency communication losses.
To overcome this problem, a cell structure fixed to the earth's surface is the preferred approach.
The earth fixed cell structure requires that each spot beam track its allocated cell position while the satellite is in motion. That is, spot beams fixed to the earth require that the spot beams move with respect to the spacecraft. At least two methods have been proposed to steer the spot beams appropriately, one is based on electronically steered phased array antennas and the other is based on mechanically steering

2 each individual spot beam with two-axis gimbals for each spot beam antenna. The phased arrays, as identified in the Teledesic patents, are very complex and costly. Alternatively, the large number of gimbals needed for the mechanically steered systems will lead to severe reliability as well as cost considerations. The subject of the present disclosure is an alternative innovative means for tracking fixed ground cells.
The specifications for such a constellation are as follows:
Constellation Specifications 450 Satellites plus 15 spares 15 Planes Fixed altitude for every plane of 900km Inclination: 90 degrees (Polar) Orbital Period: 103 minutes Lifetime: 10 years In accordance with the present invention, a satellite for use in a multi-media satellite constellation comprises a bus, or body, to which are attached solar panels for conversion for sunlight into electrical energy, an ion engine or thruster for positioning, an optical inter-satellite link tower projected beneath the body, rotary drums containing radio frequency beam transmitters and receivers, for projecting spot beams, reflectors reflecting said spot beams to and from earth cells, an electro-optic payload for processing electrical and optical incoming and outgoing signals, both to said optical inter-satellite link system and to said transmitting and receiving antennae, and a battery supply for storing said electrical energy from said solar panels, whereby said satellite

3 communicates with earth cells and with other satellites while orbiting the earth.
BRTEF DESCRIPTION OF THE DRAWINGS:
Figure 1 is a perspective view of the satellite from a position slightly above the satellite, Figure 2 is a perspective view of the satellite from a position below the satellite, Figure 3 is a close-up view of the satellite body, or bus, from above, Figure 4 is a corresponding view of the satellite body from below, Figure 5 is a rear view of the satellite body, Figure 6 is a top view of the satellite body with the top removed, Figure 7 is a top view of the satellite body with the top and payload removed, Figure 8 is a diagrammatic illustration of the satellite footprint, Figure 9 is an elevation of the satellite with the panels extended, Figure 10 is a plan view of the satellite of Figure 9, Figure 11 is a bottom view of the figure not showing the solar panels, Figure 12 is a front view of the satellite with the panels removed, Figure 13 is a respective view of the lower portion of the satellite body, and Figure 14 is a right side view of the satellite body.
j~FTATTED DESCRIPTION OF THE INVENTION:
Figure 1 is a perspective view of the overall configuration of the satellite including solar panels 10, and

4 body or bus 11 with optical tower 12 protruding from the lower portion of the bus 11.
In Figure 2, the solar panels are as before. The bus 11 is shown with the optical tower 12 extended and illustrating the positioning of the drums and reflectors, which will be shown in detail on Figures 4, 5, 11 and 13.
Figure 3 is a close-up view of the body 11 on which the solar panels 10 are connected, and showing the optical inter-satellite link tower 12 extended below the bus 11.
Figure 4 is a close-up of the bus 11, solar panels 10, inter-satellite optical link tower 12, drums 13 and 14 and reflectors 15, 16 and 17. A fourth reflector, not shown in this figure, is positioned complementary to reflector 16 on the opposite side of the center channel 18.
Figure 5 illustrates the rear view of the satellite bus 11 illustrating the thruster ports 19 mounted adjacent the bottom panel 18 and showing the inter-satellite optical link tower 12, drums 13 and 14 and reflectors 15, 16, 17 and 20.
Figure 6 is a view of the satellite bus 10 showing the xenon ion propulsion system thrusters 21 and 22, the xenon fuel tank 23, the nickel hydride batteries 4, the GYROWHEELtm three axis attitude control system 25 and the main payload 26.
In Figure 7 the main payload has been removed and the remaining components consisting of drums 13 and 14 with radiators 27, 28, 29 and 30 shown from above.
The microwave transmission system consists of the drums 14, the radiators 27, 28, 29 and 30 and the reflectors 15, 16, 17 and 19. The radiation and complementary reception of the microwave antenna system provides a square footprint having the dimension of each side of 1,424 km and is comprised of 64 spot beams, the dimension of each spot beam being 200x200 km. The object of the drums 13 and 14 and the reflectors 15, 16, 17 and 20 is to provide a satellite footprint which remains focused on an earth cell as the satellite moves along its orbit over the earth cell. The manner in which this is effected is disclosed in the copending application referred to above.
Figure 9 is an elevation view of the satellite with the solar panels 10 extended from the bus 11 and with the dimensions of the satellite illustrated thereon.
Figure 10 is a plan view of the satellite of the present invention. The dimensions on these drawings are in meters.
Figure 11 is a bottom view of the satellite body 11 clearly showing the inter-satellite optical link tower 12, the rollers 13, 14 and reflectors 15, 16, 17 and 20.
Figure 12 is a front view showing the relative location of the bus or body, the lower channel 18, the front roller 13, and the reflectors 15 and 17.
Figure 13 is perspective view of the satellite body from below showing the drums 13 and 14, thereflectors 15 and 16, the inter-satellite optical link tower 12 in retracted position and the lower channel 18.
Figure 14 is a side view of the satellite body illustrated in Figure 13 showing the drums 13 and 14, the body 11 and the channel 18. One of the thruster ports 19 is also illustrated in this view.
As previously discussed, the function of the satellite is to act as an up and down link between earth cells operating at frequencies in the 20 and 30 gigahertz range, and to communicate among the satellites of the constellation utilizing the inter-satellite optical link, transmit data and control signals among the satellites of the constellations.
The payload contained within the satellite performs a number of functions. There are microwave transmitting horns in each of the rollers to which signals and power are supplied through a slip-ring mechanism, there is a telemetry tracking and control system which controls operation of the satellite to maintain its position in orbit, or to remove the satellite when it requires replacement. This equipment operates in conjunction with the GYROWHEELtm which provides three axis attitude control for the satellite.
There is electrical to optical conversion equipment required for transmitting optical signals on the inter-satellite optical links, and there are microwave receivers and transmitters irradiating to earth cells.
The drum and reflector systems onboard of the satellite cause the footprint of the satellite to remain focused on the fixed earth cell for a much longer period than the time that the satellite is over the earth fixed cell. Typically the satellite footprint would remain on the cell for only a few seconds. By utilizing the drum and the reflector system as disclosed in the companion application, communication can be maintained between the satellite and the zarth fixed cell for a period of approximately 12 minutes.
A person understanding the above-described invention may now conceive of alternative designs, using the principles described herein. All such designs which fall within the scope of the claims appended hereto are considered to be part of the present invention.

Claims

We claim:

1. A satellite for use in a multi-media constellation network comprising a satellite body, photovoltaic solar planes affixed to said body and adapted to receive sunlight and provide electric power to said satellite, said body being provided with microwave transmitter and receiver means including rotating drums containing microwave, antennae and reflectors for reflecting transmitted and received signals to provide a movable footprint for the satellite adapted for illuminating a fixed earth cell for an extended period of time, inter-satellite optical links adapted to transmit and receive control signals and data among satellites, a telemetry tracking and control system for communication with ground control stations to control the orbital position and orientation of the satellite, electrical batteries for storing electrical energy to provide power to the optical control systems, and an ion thruster for satellite propulsion and a three axis attitude control system, whereby said satellite operates in its assigned orbital plane, and transmits and receives data from earth fixed cells and communicates with adjacent satellites using inter-satellite optical links.

2. A satellite as defined in claim 1 wherein said inter-satellite optical link is mounted in a tower, which on deployment of said satellite extends below the satellite and provides communication between the satellite and adjacent satellites by optical signals.

3. A satellite as defined in claim 1 wherein said photovoltaic panels are adapted to be folded into position atop the satellite body, and the inter-satellite optical link tower is adapted to be telescoped within the satellite body for launch purposes.

4. A method of satellite communication between earth cells comprising:
providing a plurality of satellites arranged in orbital planes, spaced equally about the earth, said orbital planes passing through the poles, providing uplink means in each earth cell for communication with said satellites, providing means on each satellite for receiving signals from earth cells and transmitting signals to earth cells, and further means for transmitting signals and data between satellites comprising an inter-satellite optical link.