X/Y Antenna Ground Terminals:
A Small Sat Cost Effective Approach
March 21, 2014
Advantages of X/Y Antenna Configuration
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
Advantages of X/Y Antenna Configuration
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.
Advantages of
X/Y Antenna
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
Advantages of X/Y Antenna Configuration
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 descends1.
“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
Advantages of X/Y Antenna Configuration
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.
Cost
Advantages
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
Advantages of X/Y Antenna Configuration
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
Advantages of X/Y Antenna Configuration
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.
1.
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-BetweenFailures (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
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 www.TrackMySat.com
or email us at [email protected].
www.telecomsys.com/
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