X/Y Antenna Ground Terminals: A Small Sat Cost Effective Approach

Transcription

1 X/Y Antenna Ground Terminals: A Small Sat Cost Effective Approach March 21, 2014

2 Introduction With the insurgence of the small satellite market the demand for cost effective ground terminals has never been greater. The advancement in the small satellite technologies along with their ability to be launched in mass on hosted payloads or from the Space Station has greatly opened up this area to many companies and investors. Many of these small satellite manufacturers are start-up companies and must first rely on demonstration flights to gain technical momentum and future investments. Typically, during the demonstration phase of their development they will need to rely on contracted ground station services for data reception of their low-earth orbit (LEO) or medium-earth orbit (MEO) satellite technical demonstration flights. In the beginning this is an economical approach over owning and operating their dedicated ground terminals, until the constellation starts to grow. Some of the proposed and existing constellations could exceed 200 spacecraft. Tracking a large constellation would require ground terminals to perform 50 to 100 passes or more per day. This would become a costly expense if each of these passes were to be performed by a ground terminal contracted service provider. Some of these small satellite constellations require continued downlink communications as they orbit the earth in order to receive real time earth imagery. This continued continuity would require a worldwide network of ground terminals, which could result in a costly venture. With the advancements made in both hardware and software ground terminal technologies, the cost to own dedicated ground terminals has been greatly reduced. With the advancements made in both hardware and software ground terminal technologies, the cost to own dedicated ground terminals has been greatly reduced. This reduction in costs now makes it possible for small satellite start-up companies and universities with limited funds to procure their own dedicated ground terminals. One of the most efficient cost effective antenna configurations in support of LEO and MEO missions has proven to be the X/Y antenna configuration. There are many advantages to the use of this configuration over other pedestal geometries which are outlined in this white paper. Page 1

3 Introduction With the insurgence of the small satellite market the demand for cost effective ground terminals has never been greater. The advancement in the small satellite technologies along with their ability to be launched in mass on hosted payloads or from the Space Station has greatly opened up this area to many companies and investors. Many of these small satellite manufacturers are start-up companies and must first rely on demonstration flights to gain technical momentum and future investments. Typically, during the demonstration phase of their development they will need to rely on contracted ground station services for data reception of their low-earth orbit (LEO) or medium-earth orbit (MEO) satellite technical demonstration flights. In the beginning this is an economical approach over owning and operating their dedicated ground terminals, until the constellation starts to grow. Some of the proposed Advantages of and existing constellations could exceed 200 spacecraft. Tracking a large constellation would require ground terminals to perform 50 to 100 passes or more per day. This would become a costly expense if each of these passes were to be performed by a ground terminal contracted service provider. Some X/Y of these small satellite Antenna constellations require continued downlink communications as they orbit the earth in order to receive real time earth imagery. This continued continuity would require a worldwide network of ground terminals, which could result in a costly venture. Configuration With the advancements made in both hardware and software ground terminal technologies, the cost to own dedicated ground terminals has been greatly reduced. This reduction in costs now makes it possible for small satellite startup companies and universities with limited funds to procure their own dedicated ground terminals. One of the most efficient cost effective antenna configurations in support of LEO and MEO missions has proven to be the X/Y antenna configuration. There are many advantages to the use of this configuration over other pedestal geometries which are outlined in this white paper. Page 2

4 One of the biggest advantages of an X/Y configuration is its ability to eliminate the keyhole (loss of data reception) as the satellite approaches Zenith. Only the fastest and most expense elevation/azimuth pedestals can overcome this problem and provide continues uninterrupted LEO/MEO tracking. For example, a LEO pass with a 780 km orbit utilizing an elevation/azimuth pedestal with a max velocity of 6 degrees per second would start to loss reception at 85 degrees elevation and would remain off track for about 25 seconds as it ran full speed to catch-up to the satellite as it descends 1. One of the biggest advantages of an X/Y configuration is its ability to eliminate the keyhole (loss of data reception) as the satellite approaches Zenith. This would result in 25 seconds of lost data during a period where the signalto-noise ratio would be at its best. The cost to obtain a higher performance elevation/azimuth system capable of out running the keyhole becomes a cost challenge for most small satellite operators, especially if multiple antennas are required to support the mission. Some other cost draw backs resulting in this high dynamic operation is the increased wear and tear on the system. This may require in the long term increase maintenance to be performed, such as more frequent motor and gear box changes. Another cost factor sometimes over looked is the amount of electricity required for a high dynamic track. Most LEO and MEO stations are placed in remote locations where facility power is limited and or expensive. The elevation/azimuth-tilt pedestals, also known as a 3-axis pedestal is another configuration used for LEO tracking. This design eliminates the keyhole by titling back on its 3rd axis on those satellite passes that approach Zenith. This decreasing the elevation angle and allow ample time for the azimuth axis to rotate and stay on target. Some of disadvantages of this configuration is that there are more moving parts and these units can be more difficult to manufacturer, this increasing the cost to procure. We should point out there is sometimes debate whether or not a X/Y configuration has its own keyhole. This keyhole is not at Zenith, but at the East (90 degrees) and West (270 degrees) at an elevation of less than 2 degrees. Most X/Y pedestals can out run this keyhole, but in reality at this low angle there is no practical reason to track any spacecraft because the data quality would be very poor. This makes the keyhole debate regarding an X/Y antenna configuration used for tracking LEO or MEO spacecraft a moot point. 1 Selecting a Pedestal for Tracking LEO Satellites at Ka Band, by Keith Willey University of Technology, Sydney (UTS), Cooperative Research Centre for Satellite Systems Sydney, Australia, published in Microwave Journal, April 1, 2000 Page 3

5 Introduction With the insurgence of the small satellite market the demand for cost effective ground terminals has never been greater. The advancement in the small satellite technologies along with their ability to be launched in mass on hosted payloads or from the Space Cost Station has greatly opened up this area to many companies and investors. Many of these small satellite manufacturers are start-up companies and must first rely on demonstration flights to gain technical momentum and future investments. Typically, during the demonstration phase of their development Advantages they will need to rely on contracted ground station services for data reception of their low-earth orbit (LEO) or medium-earth orbit (MEO) satellite technical demonstration flights. In the beginning this is economical approach over owning and operating their dedicated ground terminals, until the constellation starts to grow. Some of the proposed and existing constellations could exceed 200 spacecraft. Tracking a large constellation would require ground terminals to perform 50 to 100 passes or more per day. This would become a costly expense if each of these passes were to be performed by a ground terminal contracted service provider. Some of these small satellite constellations require continued downlink communications as they orbit the earth in order to receive real time earth imagery. This continued continuity would require a worldwide network of ground terminals, which could result in a costly venture. With the advancements made in both hardware and software ground terminal technologies, the cost to own dedicated ground terminals has been greatly reduced. This reduction in costs now makes it possible for small satellite startup companies and universities with limited funds to procure their own dedicated ground terminals. One of the most efficient cost effective antenna configurations in support of LEO and MEO missions has proven to be the X/Y antenna configuration. There are many advantages to the use of this configuration over other pedestal geometries which are outlined in this white paper. Page 4

6 X/Y Pedestal Cost Savings Advantage The X/Y configuration basically has two orthogonal axes. The best way to describe this is to imagine to rolling pins stacked on each other, with the upper roller rotated 90 degree from the lower roller. The upper roller would be the X-Axis and the lower the Y-Axis as shown in Figure 1. This configuration has several advantages related to cost and operation. 1. The keyhole is eliminated because the upper axis just simply rotates as the satellite approach Zenith. This allows the antenna to move at a very low velocity of less than 1 degree per second during any antenna pass. This low velocity (low mechanical dynamic) and elimination of the keyhole has several cost advantages. a. Lower power consumption, this could provide a significant savings over a long period of time especially if the station is performing multiple tracks throughout a day. b. Less wear and tear on the components equate to maintenance cost savings. Motors should last 2 to 4 years depending on the number of passes the terminal is performing each day. Typically these are small low speed brushless motors and are not too expensive to procure. Figure 2 shows the velocity difference between an Elevation/Azimuth positioner and X/Y positioner on a LEO pass with an 800 Km orbit (1). This shows how fast the velocity must increases as it approaches 90 degrees elevation. The lower dynamic of the X/Y antenna also allows the system to point more accurately during a pass. This is an important factor especially when tracking Ka-band. Figure 1 Figure 2 Page 5

7 1. c. With the elimination of the keyhole more data becomes available during those high signal-to-noise ratio portions of the track. If a satellite operation relies on the sale imagery data, this ensures they will have the highest quality data product available throughout the satellite pass. 2. The X/Y configuration is less costly to manufacture over other pedestal configurations. a. The upper and lower axes use basically the same parts. With technology advancements in robotics, these same proven commercial technologies are being utilized in these new antenna pedestal designs. b. The use of less-parts than other types of positioners and the use proven commercial components increase the Mean-Time-Between- Failures (MTBF). Since the upper and lower axis use the same parts, less spare parts would need to be obtained. c. The X/Y housing and related castings are less costly to produce because the upper and lower units are cast in a single housing. In Figure 3, the example shows a technology now available in the X/Y configuration and the similarity the upper and lower house share. d. The X/Y movement eliminates cable wrap. This eliminates the need for costly slip rings or rotary joints. You can see in Figure 3 the use of energy chains. These provide a resting place for the cables to be secured as the system rotates left, right and up and down. Figure 3 Page 6

8 Conclusion Each of the antenna configurations has their place in aerospace. The Elevation/Azimuth is the best configuration for tracking along the horizon which is often performed when working on ranges in the development of aircraft and missile technologies. The 3-axis system has the ability to cross between range applications and satellite tracking applications but comes at a cost. The X/Y configuration is truly the one positioner technology designed specifically for LEO and MEO satellite tracking applications. It can be produced at a lower cost, has less moving parts and has proven itself to be very reliable because it operates at a very low dynamic regardless of the satellite position. This makes the system more obtainable by organizations such as small satellite operators and universities by providing an opportunity to purchase a cost effective ground terminal of their own. TCS Space & Component Technology has developed a cost effective X/Y antenna pedestal technology that specializes in precision satellite tracking. These systems are specifically designed for the Low and Medium satellite tracking in support of Earth Observation, Remote Sensing, and TT&C applications. With our state of the art manufacturing techniques, we offer the most efficient product delivery schedule in the industry. Advanced Transmit (TX) and Receive (RX) feed technologies through Ka-band are available. The system does not require a radome for operation, but if required TCS can provide a low cost solution. For more information visit or us at TrackMySat@telecomsys.com TeleCommunication Systems, Inc. (TCS). All rights reserved. Enabling Convergent Technologies is a registered trademark of TCS. All other trademarks are the property of their respective companies. Information subject to change without notice. NASDAQ: TSYS