# 27 July 2006

White Paper

**Needed Changes in Ground Antennas and Commercial Availability for
Continued Ground Reception of NOAA GOES 10 Imager and Sounder Satellite
Data for the Remaining Days of its Operational Life with a Growing North
South Satellite Inclination**

**Technical Study by the Communications Subdivision of The Aerospace
Corporation of El Segundo California, USA**

**Donald Olsen**

**Lou Sacks**

**In Collaboration with NOAA-NESDIS Engineering**

**Roger Heymann**

**Introduction**

The Aerospace corporations Communication's Subdivision was asked by the
National Oceanic and Atmospheric Administration's (NOAA's) National
Environmental Satellite Service (NESDIS) engineering staff in late May
2006 to work with it in evaluating the change in ground antenna
requirements for GOES 10. Replacement of the existing ground antennas at
each user's site(s) will be required for users to continue to have
quality reception of GOES 10 imager and sounder "GVAR" data.

This brief note identifies the major issues forcing a change to the
rigid fixed satellite antennas used in the normal properly operating
GOES satellites, defines the characteristics of the needed antenna
system, and identifies two commercial companies in the U.S. that offer
very high quality relatively low cost equipment appropriate for GOES 10
data reception in the years ahead. Each of the appropriate antenna
systems from these two companies is identified to cost less then
\$10,000 U.S. dollars with shipping, insurance for shipping, and
construction of ground steel reinforced concrete pad being at additional
cost.

The Communications Subdivision has a long history of collaborating on
technology studies and research for NOAA-NESDIS engineering on satellite
communications issues; particularly for the emerging GOES-R satellite
series.

The given situation here involves NOAA moving the GOES 10 satellite from
its present location today at 135^0^ W longitude in support of NOAA
operation to 60^0^ W longitude to dedicate its operations to serving
only Latin America's nations. NOAA expects the GOES 10 satellite to be
in place at 60^0^ W longitude in the spring of 2007 to begin providing
its data to Latin American nations supporting operational weather
forecasting.

The dedication of GOES 10 use by NOAA for full time sensor scanning over
Latin America is among the initial steps being taken as NOAA and Latin
American nations initiate and build a new program of Earth science
collaboration titled "Earth Observation Partnership of the Americas"
(EOPA)

The operational problem forcing a change in antenna systems to the
ground receiving systems is that GOES 10 has a growing north-south
inclination problem with respect to its orbital location on the equator.

**Problem**

GOES 10 in its present geostationary orbit provides weather data at
L-band throughout the GOES Earth view. Its existing orbit location
however does not provide optimum coverage to the Central American and
South American countries. To enable these countries to better receive
the GOES 10 data, NOAA has committed to moving the GOES 10 satellite to
a new 60 degree longitude location that is more directly above the Latin
American countries; and dedicate the imager and sounder operations to
scanning Latin America. The contours for the ground terminal elevation
angles for the new GOES 10 location are shown in Figure 1 when crossing
the equator. The north-south motion will cause the set of coverage
contours to move up and down in latitude a degree for degree of GOES-10
north south motion of its nadir point from the equator.

The forces on GOES 10 from its motion and the Earth's gravity force
would be in perfect balance in geo orbit if they were the only forces
acting on the satellite. But they are not; the moon and sun pull as well
but to a much smaller degree resulting in east/west and north/south
inclination of the satellite. During a geo-satellite's lifetime (such as
GOES 10), the fuel onboard the satellite is used to fire the satellite's
small thruster engines to make small changes in the satellites east/west
and north/south positions to counter these various forces. These
thruster firings keep the satellite inclination to a small fraction of a
degree. If the inclination is small compared to the beamwidth of the
ground terminal antennas --- as is the case for the 3.5 -- 4 meter GOES
10 ground terminals --- those terminals can track the satellite using
fixed pointed antennas.

The major concern is that the GOES 10 satellite is now approaching the
end of its station keeping propellant. It is a very normal operating
procedure near the end of geostationary satellite's availability of on
board fuel (GOES 10 situation) for owner/operators such as NOAA-NESDIS
to stop making corrections for its north/south motions; but to continue
making the east/west motion corrections. This is so, because making the
north/south thruster firings to correct for the north south motion
requires too much fuel. The reduced station keeping will cause the GOES
10 satellite inclination to increase at a rate of between 0.6 and 0.9
degrees per year. At the end of five years the daily inclination could
approach 6 degrees. As a result, the Latin American countries using
fixed pointed ground terminals will be unable to track the GOES 10
satellite during its daily inclination swing.

Figure 1 - New GOES 10 Location

![](media/image1.wmf){width="6.377083333333333in" height="4.78125in"}

As the GOES 10 satellite moves in and out of the region in which the
antenna can receive imager and sounder GVAR data, nations in Latin
America will not get data for that time period. This problem can be
solved by replacing the ground terminals with antennas having dual axis
motion capability that will enable them to track the GOES 10 satellite
for the maximum inclination of 6 degrees. This White Paper addresses the
issues involved in replacing the Latin America fixed pointed ground
terminals with dual motion tracking ones.

**Solution Using Ground Terminal with Dual Axis Motion**

This GOES 10 data reception and antenna problem can be solved by
replacing each Latin American fixed and rigid ground antenna with one
having north/south and east/west dual axis motion. Table 1 shows some
Latin America ground locations and their corresponding longitudes,
latitudes and altitudes. The last two columns in the table show the
required azimuth and elevation motion (over a 24 hour time period) for a
dual axis ground terminal tracking of the GOES 10 satellite at the new
60 degree W location assuming a 6 degree inclination. The ground
locations in Table 1 are illustrative only and may not represent the
location of the existing or planned GOES 10 ground terminals. The
elevation vs. azimuth plots for the ground locations shown in Table 1
are included in Appendix A.

Table 1- Ground Location Parameters

+-------------------+---------+-------+---------+----------+---------+
| Ground Location   | Lo      | Lat   | A       | Azimuth  | El      |
|                   | ngitude | itude | ltitude | Angle    | evation |
|                   |         |       |         |          | Angle   |
|                   | (Deg W) | (Deg) | (       | (        |         |
|                   |         |       | Meters) | Degrees) | (D      |
|                   |         |       |         |          | egrees) |
+-------------------+---------+-------+---------+----------+---------+
| Yucatan           | 90      | 20    | 10      | 111-128  | 44-53   |
+-------------------+---------+-------+---------+----------+---------+
| Ecuador           | 80      | -5    | 10      | 61-93    | 63-67   |
+-------------------+---------+-------+---------+----------+---------+
| Rio de Janeiro    | 45      | -23.5 | 10      | 318-332  | 52-64   |
+-------------------+---------+-------+---------+----------+---------+
| Buenos Aires      | 60      | -35   | 10      | -0.4-0.3 | 43-56   |
+-------------------+---------+-------+---------+----------+---------+
| Santiago          | 72      | -35   | 200     | 18-24    | 41-54   |
+-------------------+---------+-------+---------+----------+---------+
| Cape Horn         | 70      | -55   | 0       | 11-13    | 20-33   |
+-------------------+---------+-------+---------+----------+---------+
| Recife, Brazil    | 35      | -8    | 10      | 273-298  | 56-61   |
+-------------------+---------+-------+---------+----------+---------+
| Manaus, Brazil    | 60      | -3    | 10      | -215-10  | 80-90   |
+-------------------+---------+-------+---------+----------+---------+
| Boa Vista, Brazil | 60.7    | 2.8   | 10      | 10-175   | 80-89   |
+-------------------+---------+-------+---------+----------+---------+
| Paramaribo,       | 55.3    | 5.5   | 10      | 202-277  | 75-85   |
| Suriname          |         |       |         |          |         |
+-------------------+---------+-------+---------+----------+---------+

Many manufacturers provide ground station antennas that are capable of
high speed tracking, i.e., of low orbiting satellites (LEO); however
these antennas can be very expensive. The goal of this White Paper is to
identify low cost (less than \$20K) antenna systems that would be
suitable for tracking the slow moving (6 degree inclination) GOES 10
from Latin America. Two commercial providers have been identified:

1\) Patriot Antenna Systems.

Patriot Antenna Systems may be the largest manufacturer and supplier of
satellite receive antennas in the world. Patriot Antenna systems has a
3.8 meter antenna, that has dual axis motion and is motorized and
operational in the K- and X-band Radio frequency spectrum. Although GOES
broadcasts data in the L band, L-band antenna feeds are commercially
available from manufacturers such as from Seavey Engineering Associates,
Inc. Patriot says they are very flexible in being able to make such a
system available to install an L-band feed. The L band feed for GOES 10
should operate in the 1675-1695 MHz portion of the Radio Frequency
spectrum.

The Patriot dual axis motorized antenna is integrated with a Research
Concepts, Inc (RCI) RCI 2000C model electronic antenna controller and
satellite tracker. This is a cost effective system design and will
easily meet the GOES 10 inclination need as soon as the L-band antenna
feed issue is addressed.

The contact at Patriot Antenna Systems is:

Edward Stuart

517-629-5990

www.sepatriot.com

The distributor contact for Patriot Antenna Systems is:

Richard Lowery

Eastern Communications

757-547-1969

2\) America Antenna Inc.

America Antenna Inc. will have a new dual axis product line out this
fall that uses a 4.0 meter antenna. It has dual axis motorized antenna
motion that also uses Research Concepts Inc (RCI) 2000C model electronic
antenna controller and satellite tracker. The 4.0 meter antenna operates
in L-, X- and K-band. Again, it must be noted, the L band feed for the
dual axis antenna needs to operate in the 1675-1695MHz portion of the
Radio Frequency spectrum.

The contact at American Antenna Inc. is:

Chuck Forsythe

812 877-4001

www.americanantenna.com

Research Concepts Inc. makes the Research Concepts Inc (RCI) 2000C model
electronic antenna controller and satellite tracker that is used by both
Patriot Antenna Systems and American Antenna Inc. Research concepts is a
small US high tech company with a staff of less then 10 people that
specializes in electronics, mathematics, and analyses associated with
tracking inclined satellites. A link on their web site
<http://www.researchconcepts.com/Files/track_wp.pdf> has an excellent
tutorial on satellite tracking.

The contact at Research Concepts Inc. is:

Mike McKinsky

913-422-0210

[www.researchconcepts.com](http://www.researchconcepts.com/)

**Costs**

Both American Antenna Inc. and Patriot Antenna Systems claim that the
total cost for their motorized dual axis antennas with the RC 2000C
controller is under \$10,000.

A heavy steel reinforced concrete pad may be needed (maybe 5" by 5" by
4-5" deep) at additional cost if the existing ground terminal antenna
does not have one. There will also be shipping and insurance costs to
Latin American nations for the antenna and associated hardware.

**Other Factors**

All GOES satellite GVAR ground reception systems need an antenna within
the range of 3.5 meters to 4.0 meters. This was true in the past, and is
true for GOES 10 in the future. Patriot Antenna Systems and American
Antenna Inc. propose to offer antennas that are 3.8 meters and 4.0
meters respectively. This is excellent. Some South American nations
asked if GOES can be received from their existing small diameter 1.8
meter tracking antennas. The answer is no. Figure 2 shows the user
antenna G/T vs. elevation angle for a relatively low LNA noise figure of
0.64 dB (46K). For user elevation angles exceeding 27 degrees (see outer
limit of useful Sounder measurement contour shown in Figure 1) a 3.3
meter dish would be required to meet the NOAA G/T spec of 15.2dB/K.

Figure 2 -- G/T vs. Elevation Angle

![](media/image2.wmf){width="5.622222222222222in" height="4.21875in"}

Antenna polarization is another factor to be defined. NOAA GOES
satellites use a linear north south polarization. This is one of the
factors to define when ordering a new GOES 10 antenna system (dual axis
tracking).

Because some of the GOES 10 user terminals are at high elevation angles
to the satellite there was some concern about the "keyhole effect". This
occurs when the satellite of interest passes directly overhead (90
degree user elevation angle). Since in many elevation-over-azimuth
gimbal designs the elevation angle motion is limited to 90 degrees the
azimuth mount would have to rapidly rotate by 180 degrees to accommodate
the elevation motion. Although this may be a concern for low earth orbit
(LEO) satellites it will not affect the GOES 10 terminals because of the
target dynamics (very slow satellite movement relative to the antenna
beamwidth). Furthermore, no ground locations were identified where the
user elevation angle corresponds to the 90 degree zenith pass where the
keyhole effect would occur.

Future efforts will be devoted to getting more accurate cost estimates
and to identifying other companies that may supply tracking antennas
with similar technical and cost characteristics to the two commercial
antenna providers mentioned in this report.

**Acknowledgements**

Dr. Chia-Chun Chao of The Aerospace Corporation's Astrodynamics
Department provided the antenna azimuth and elevation motion values
shown in Table 1 and in the plots given in Appendix A.

NOAA-NESDIS acknowledges as well the engineering inputs of Mr. Peter
Woolner, Senior Principal Engineer in satellite communications, of
Mitretek Systems, Inc.

**Appendix A**

**Predicted Ground Antenna Motion for Tracking GOES Spacecraft at 60
degree W with 6 degree Inclination**

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