Archive for the ‘Satellite Ground Station’ Category

ILM Antenna being installed.

The Improved Limited Motion (ILM) Antenna installation started with site location and preparations.  Due to wind loading, weight requirements and stress analysis these antennas must be secured to a solid base. In this case the antenna was being installed on the roof of a new 2 floor addition to the facility. Extensive engineering and analysis was done during the design of this addition to insure that the antenna could be added safely.

Four pads were prepared for the installation to secure the antenna structures to the roof. The mounting bolts were secured in high strength concrete based on the antenna manufactures specification and the structural analysis.

ILM Antenna location for installation

When the antenna arrived, the install team unpacked and inventoried the shipment, placing the components in the defined assembly area. The assembly started by placing the hub on a stable fixture. The back frame that holds the dish panels in place was assembled. Each support strut and mounting bracket had to be aligned and torqued down in place to ensure the stability of the completed surface. The panels were installed and aligned with openings left to accommodate access and simplify attachment of the completed dish structure to the pedestal.

A crane was used to lifted the pedestal of the antenna into position on the roof  where it was aligned and secured. With the pedestal securely in place the crane lifted the dish and it was guided into place.

After verifying the alignment of the panels, the support structure and sub-reflector assembly could be installed. Final panels were then installed in place to complete the dish.

The antenna control interface, motors, RF equipment, cabling and waveguide were installed. Mechanical and communications testing followed to commission the antenna for service.

The completed antenna shown in this final picture.  Exterior panels were added to inclose the support structure of the antenna. This was part of a de-icing system that used propane heaters to warm the dish surface and feed assembly preventing snow or ice from  accumulation during the winter season.  As with all antennas of this type lightning rods were installed and grounded to protect against damage from lightning strikes.

TT&C Ground Station

Back in 1980 after leaving the Army, I was hired to work for SBS as a Satellite Controller and ground station technician at their Satellite Control Center (SCC).  The Clarksburg Telemetry, Tracking and Command (TT&C) ground station in Maryland was nearing completion and was under acceptance testing in preparation for the first launch of a SBS satellite. Over 14 years of operation the station facilities grew to include added functionality, Carrier System Monitor (CSM) area, Central Reference Station (CRS),  Video Support Center (VSC) for uplink monitoring and assistance and finely a Launch Control Facility. The station power was supported by an uninterpretable power system including 500 KW diesel and turbine generators,  battery backup and an automated transfer system to switch from commercial power to the backup systems. Office space was available for management, the engineering staff and a facilities engineer who maintain the heating, air conditioning and humidity control systems.  Each shift was staffed to support 24 hour operations of all of these functional areas and also maintain or repair the equipment.

SBS TT&C ground station early 80's

This picture shows the 3 NEC 7.8 meter Ku-Band limited motion antennas we used for control of the SBS satellites. Also shown is a mobile ground station parked between 2 of the fixed antennas that we used for video demonstrations and remote onsite testing. The NEC antennas moved in the X and Y axises using jack screws driven by electric motors.  Once the antenna was pointed at the satellite it was capable of tracking using a modified program track system. The antenna drive speed was 0.01 degree per second, and the range of movement was limited to a section of the satellite ark assigned to the SBS satellites for on orbit operations. These antennas were linear polarized and the feed assembly  could be rotated for horizontal or vertical polarization. Electric heating elements were imbedded in the individual panels of the dish and are used to prevent accumulation of snow or ice on the dish surface. During on station operations of the satellites, data is collected and process as telemetry, time stamped X & Y angle data measurements are taken to process tracking and used in orbit determination,  range tones are transmitted and received , and commands are sent to the satellite.

The SCC section of the Operations area shows the racks to the left that held the HP 1000 E series mainframe computers used for satellite and ground systems  command,  control, and data processing. The baseband processing, voice communications network and time translation  equipment was located in the center. With the modems and interfaces to dedicated data and voice lines to the right.  Status changes and alarm conditions were sent to the event status printers located next to the two computer control terminals.

SBS SCC computers and Baseband racks

(This was state of the art in high tech at the time).  This room had raised floors to allow cabling and airflow to cool the racks of equipment. The three cabinets to the right in the picture are an EdPac system used to control humidity and maintain the rack temperature between 65 and 68 degrees to optimize equipment performance and eliminate the potential of static shocks. For fire protection the room was designed with a halon system that would seal the room, release the halon into the room to extinguish the fire and then evacuate any smoke and/or halon gas from the room in less than 2 minutes.

Satellite control and monitoring was preformed at this console that accommodated 2 flight controllers and a operations engineer. The monitors on top of the console provided a visual status of the RF equipment for each antenna, the transmit and receive path configurations, the IF equipment used in the paths in addition to computer status alarms.

The right half of the console was setup for commanding operations and the left side to allowed other satellites to be monitored simultaneously. Satellite simulators were used for launch preparation and to provide training of new engineers and controllers without interference with ongoing operations.

Pre-command checks

The 4 racks seen in the background of this picture contain the NEC RF equipment. Frequency conversion was accomplished using up and down converters that had a shared synthesizer to simplified link frequency selection. Each link had an attenuator to set it’s operating  level and provide an adjustment to raise or lower the output as needed. The transmit rack housed the IPA and HPA’s used to achieve the required transmit output power levels needed to meet the required link margins.

In the next picture the racks to the left support IF conversion and Antenna control equipment. The IF section has FM and Phase modulators for the transmit side and receivers with demodulators on the receive side.  IF input and output switch matrix hardware allowed computer or manual configuration of the up and down links at the 70MHz level.  The antenna control panels used by the operations team to manually point the antenna, change polarization from Horizontal to Vertical with minor angle adjustments, select program, modified program or step tracking, in addition to operations of the de-icing system. SCC expanded to full capacity

The Carrier System Monitor (CSM) equipment was initially installed by COMSAT General Corp.

CSM initial installation nearing completion

This system was used to monitor the traffic over the full 500 MHz frequency bandwidth of the satellite.  It contained all test equipment required to analyzed each link and track transmitted power, frequency, bandwidth, type of modulation and data error rates for each user on the satellite. We preformed acceptance testing on each of the 3 systems.

The fully operational system was optimized so one person could operate all 3 systems, monitoring 3 satellites at the same time. The CSM provided the capability to monitor traffic 24 hours a day and also supported network activation and customer network support.  These activities included daily carrier/traffic analysis, printouts used in network monitoring, status reporting, trending and to support information requested by the customer billing office.

CSM in full operations

The racks in the back to the left in the picture above (not completely shown) is the Video Support Center area.  As SBS started to lease out more space on the satellite for full time and occasional use video transmission services, 4 racks of video support equipment were added. Color-bar generators were used to provide test patterns along with all video test equipment needed to test the quality of the video up and down links.  As the satellite links started to be encrypted VideoCypher units were also installed and maintained as part of our support.

As an upgrade RF equipment installation started on the third antenna after the second satellite was launched.

Installation of LM-3 RF racks.

The Central Reference Station was installed to provide timing for networks. Using a ultra-stable timing source, the system would transmit a TDMA carrier into each of the 10 channels of the satellite providing a common reference. This would allow a more dynamic and flexible network configuration so any station could transmit on only one channel while receiving on more than one channel using this reference signal.

Additional RF racks being completed for the CRS

In preparation for our third satellite additional RF equipment and a fourth antenna was installed for backup.

Four operational LM Antennas

In the mid 80′s an addition was built to expand the SCC to support up to 6 satellites and preform Launch and checkout operations. This added 2 floors with a new SCC on the first floor, the Mission Control Center (MCC) launch operations facility on the second floor and 2 Improved Limited Motion (ILM’s) Azimuth – Elevation tracking Antennas made by TIW.

Expantion of building completed.

The new SCC had areas supporting control, new HP A900 computers and processing equipment, data analysis, and offices for the Operations manager and engineers.

New Satellite Control console

The new console used new HP 100 terminals equipped with touchscreen technology. Security monitors and remote control cameras were installed to view the equipment and the facility grounds.

The computer system controlled graphics generators connected to a video switch for easy switching of telemetry displays, security cameras, graphs, and video feeds. New Cisco switches and roughers were installed along with dial back modems for network configuration and remote access.

The offices had access to monitors and the video switch to monitor data and operations.

The Mission directors console in the MCC had monitors that were connected to a video switch used to select displays of satellite telemetry, plots, launch site video feeds, or signal strength test equipment. The voice network could access any of 8 channels ranging from remote tracking stations to the launch site in addition to telephone lines and operations networks. There were corded handsets and headsets available for each work area.

The engineering support consoles, had the same features for each subsystem engineer.

For support of additional backup power requirements a new 500 KW turbine generator  was added during the expansion.

This TT&C station was used by SBS, and in 1985 became part of MCI.  By 1990 this facility was sold to COMSAT.  COMSAT moved their control center to Clarksburg and integrated both operations to control 8 satellites form this site. Eventually COMSAT converted the station into a Tele-port as the satellites reached the end of their operational life and now it is owned and operated by Lockheed .

Dish Antenna Basics

Parabolic Dish Antennas are used in satellite communications to transmit, receive or both transmit and receive signals. Feed assemblies are designed and installed in the center of the main dish to radiate transmit signals or collect receive signals. Polarization of the signals are also considered when selecting a feed assembly and the typical types are Horizontal (H), Vertical (V), Right hand Circular (RCP) or Left hand Circular (LCP) polarizations. These antennas have a gain that is based on the diameter of the main dish and the frequencies used.  An acceptable course approximation of the antenna gain is 1 dB per foot.

When used for receive, the antenna operates by reflecting the receive signals from a main dish to a sub reflector that focuses the signal and reflects it onto a feed assembly. The output signals from the feed assembly is connected to the receive amplifier.

When used for transmit, the output from the transmit amplifier is connected to the transmit feed.  The transmit signal is radiated from the feed assembly that is focused on the sub-reflector. Transmitted signals are then reflected from the sub reflector to the main dish  and radiated from the main dish to the satellite it is pointed at.

Curvature of the dish and distance from the main dish to the sub-reflector are selected based on the frequency of the signals to be received or transmitted.  The diameter is selected for the gain required from the antenna. In the direct TV receive only application the antenna is mounted in a fixed position. Antenna drive systems are used to allow repositioning of the antenna and can range from a limited motion control system using an X and Y coordinate system to a full motion antenna drive using an azimuth and elevation coordinate system.

Types of Satellite Ground Stations

The purpose of a Satellite Ground Station is to provide a facility to support the necessary links from the ground to the satellite. These facilities serve many purposes and applications.

The transmit and receive frequency bands used are defined by the FCC and other international regulatory administrations or commissions and are licensed to the owner of the satellite along with the bandwidth and it’s orbital location.  The owners company will administer frequency assignments and bandwidth for all the traffic over the satellite. Each ground station is also licensed to transmit at specific frequencies, modulation type and power levels.  Receive only applications do not require a license.

There are smaller applications that only require an antenna, receive hardware, and/or limited transmit, and an interface for data, video or voice. These fall into a category that is referred to as earth terminals, Hubs and VSAT terminals. These systems connect one location to a network through the satellite and are not normally spoken of as ground stations they are considered terminals. Uses of this type include receive only systems where the information is transmitted from a central location and received at multiple locations Satellite TV falls into this area. Transmit only terminals have been used to collect information and transmit it a central location for processing such as seismic detectors, flow rate monitors and buoys to mention a few. Two way communications are also supported by these terminals for transfer of data, voice and video for training systems, teleconferencing with remote locations, transfer of data and billing information, and voice systems.  Similar types of all of these systems have also been installed in airplanes, trains, ships and trucks to suite their application needs as well.

Ground stations are normally larger facilities and are dedicated to providing links to the satellite or multiple satellites. Communications centers provide the interface to a wide variety of sources, cable, fiber optic, microwave, cellular, video, data, voice and other satellites. Communications Hubs, Tele-ports and customer premise terminals fall into this classification. These facilities transmit and receive large volumes of traffic and have redundant equipment to minimize outages due to equipment failures. To minimize the chances of equipment failure and extend the operational life of the hardware, it is installed in rooms that are both temperature and humidity controlled. Commercial power outages can cause significant loss of revenue so they normally install uninterrupted power systems (battery backup) called UPS and generators for use when commercial power is not available.

Telemetry Tracking and Command stations specialize in the control of the satellite and processing of it’s data. Often these stations have one antenna for each satellite it operates and a spare antenna with fast full motion control so it can be used to quickly access any satellite being controlled. These stations are typically collocated with or directly connected to Satellite Control Centers, Network Control Centers, and Broadcast Centers.

Ground Station Basics

Ground stations provide the interface to a wide variety of sources, cable, fiber optic, microwave, cellular, video, data, voice and other satellites. Simplified the station is broken down into it’s basic communications interface, baseband, Intermediate Frequency (IF) and Radio Frequency functional sections. I will address the basic breakdown of a ground station from a top level approach to the process used to provide links to and from a satellite or satellites.

For this example we will transmit a Ku-Band  Frequency Modulated carrier with a 46 MHz bandwidth at 14 GHz as the assigned frequency being transmitted at 100 watts of power. The corresponding receive signal will be 12 GHz at the same bandwidth of 46 MHz.

First you start with a building or small shelter. The equipment is installed to connect to the source to be transmitted, and the received information to it’s destination, this is the communications interface.  This is where the connections to data lines, cable connections, direct connections to a LAN, fiber optic connections,  and video feeds are made.

The data in it’s raw form is called a baseband signal, circuit, or line.  Single voice lines can be converted to multi-channel circuits, groups or trunks with baseband equipment and is referenced as multiplexing. Multiplexing can be preformed on voice, data and video signals using specific hardware for the type employed, Time Division Multiplexing (TDM) is one example.  In turn the receive signals will require de-multiplexing. The source may arrive as a multiplexed signal and not require this processing. Signal levels are set or adjusted at the baseband stage to meet the input requirements of the next section.

The baseband signals are then passed to the Intermediate Frequency (IF) equipment where the raw (baseband signal) is modulated onto a carrier frequency. Types of modulation used are based on the signals used, common types are FM, PM, TDMA, BPSK, and QPSK. For the purpose of discussion we are using a 70 MHz carrier and Frequency Modulate (FM) it with the data. Through the modulation process the 70 MHZ carrier will deviate +/- from the center frequency and simply put the measured result is the bandwidth of the carrier, it is set or adjusted in the modulator.  The output of the modulator in this case is then called a 70MHz carrier and is adjusted to a 46 MHz bandwidth at the proper input level to be applied to the next stage.

Following IF conversion the carrier is passed to the Radio Frequency (RF) equipment. At the RF stage the carrier frequency is converted from a 70 MHz carrier to the selected transmit frequency 14 GHz carrier using an up converter. The resulting output is a carrier at 14 GHz at the same bandwidth set in the IF stage. The carrier is then passed to an intermediate amplifier to control the output level of the carrier by setting the drive level for the input to the high power amplifier stage to achieve the 100 watts output. High power amplifiers are the transmitter and are connected to the transmit port of the antenna.

The satellite receives the antennas transmitted carrier from the ground, translates the frequency to the down-link frequency to prevent interference between the transmit and receive frequencies and sends it back to the ground.

The antenna now receives the carrier from the satellite at the receive frequency of 12 GHz. Low Noise Amplifiers (LNA) are used to compensate for transmission losses to the ground. The output from the LNA is sent to a down-converter to convert the 12 GHz carrier back to a FM modulated 70 MHz IF carrier and adjusted to the input level for the receiver.

Back at the IF receive stage the 70 MHz carrier is removed in the receiver by the corresponding demodulator to produce the baseband signals or data. These baseband receive signals are either de-multiplexed or passed directly back to the communications interface.  Where the connections to data lines, cable connections, direct connections to a LAN, fiber optic connections,  and video feeds are made.

To minimize the chances of equipment failure and extend the operational life of the hardware, it can be installed in rooms that are both temperature and humidity controlled. Commercial power outages can cause significant loss of revenue. To prevent or minimize power outages  uninterrupted power systems (battery backup) called UPS and generators are installed for use when commercial power is not available.

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INFORMATION

Shining light on satellites and how they operate. Drawing from over 30 years of knowledge and experience in all phases of the life of a satellite from concept, to operations, and through end of life. You will find short topics intended to give you an understanding of how they work, the general concepts, and principals used along with information on ground systems. There is also a section dedicated to topics that can be used as basic concept training along with links to animations and 3D models I have created.