30-11-2012, 05:29 PM
MINIATURE TT and C MODULE FOR SMALL SATELLITES IN LOW EARTH ORBITS
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INTRODUCTION
COM DEV EUROPE has developed a low-cost and lightweight S-Band TT&C transponder, for Low Earth
Orbit (LEO) missions. The design is based on Commercial Off-The-Shelf (COTS) components and targets
earth observation missions with short mission durations of 3-5 years. To enable the customer to access low cost
launch vehicles, the STC-MS01 has been designed free of any components that have US ITAR restrictions. The
TT&C transponder is based on a Software-Defined–Radio (SDR) architecture. This makes the unit very flexible
and easily adaptable to new mission requirements.
ARCHITECTURE
The TT&C transponder as a functional assembly consists of two physically separate modules, the electronics
module, commonly referred to as the TT&C transponder and the diplexer. The here-described diplexer is a
generic S-Band diplexer, which would be tailored to meet the specific mission needs. The TT&C transponder
consists of two sub-modules, the receiver and the transmitter. Both sub-modules are independently powered; the
nominal supply voltage is 28V±6V. The receiver hosts all functions that are shared between the receiver and
transmitter; shared functions are the clock generator, the RS422 interfaces, as well as the central FPGA. [02]
The receiver consists of a two stage super-heterodyne architecture, the first stage is implemented in electronics,
while the second stage is a logical implementation in firmware. A Low Noise Amplifier (LNA) with a noise
figure of better than 2dB forms the input stage of the receiver. The amplified signal than passes through the first
frequency converter stage, which is followed by the image reject and channel select filter. The channel select
filter is wide enough to support ranging up to a bandwidth of 800 kHz. The channel select filter is followed by
the IF-Amplifier chain, which consists of two functional blocks, a linear operating amplifier stage, followed by
a limiting amplifier stage. The amplified IF signal is then fed forward into a one-bit sampler that performs the
analog to digital conversion. The digital first-IF signal is finally further processed by firmware in the FPGA.
The transmitter architecture is based on a direct modulator. The firmware in the FPGA generates the I/Q signals,
which are fed into a dual Digital to Analog Converter (DAC). The DAC is followed by a signal reconstruct and
image reject filter. The filtered signal feeds the vector modulator, in which the modulated RF signal is
generated. The RF signal is then fed forward into the SSPA, which is designed around a GaN RF power
transistor. The power amplifier can generate signal levels up to +37dBm, or +33dBm depending on the applied
bias conditions. The SSPA efficiency reaches 49% in the +37dBm mode or 35% in 33dBm mode. Com Dev
Europe is currently formally qualifying the GaN transistor for space flight application within the framework of
an ESA program.
TEST APPROACH
COM DEV has a core competence in development of flexible test systems using its proprietary CodeOne®
Enterprise solution that has been developed over a number of years. This system allows automated testing
scripts to be rapidly developed using a simple excel front end with drivers for Agilent test equipment that
automatically records calibration status and configures output test data efficiently and rapidly. COM DEV
engages CodeOne® extensively throughout its internal product test operations with over 100 test systems or
stations that use it. COM DEV has significant experience with practical deliveries of Payload Test Systems
(PTS) and TR Module Tester into Canadian, US and European customers. The combination of CodeOne®
software, together with COTS Test Equipment, and custom-designed test equipment (custom interfaces and
signals), results in a highly flexible testing environment. The major benefits to the user are the consistency of
approach, in generating test procedures, making measurements and reporting the performance.
Using CodeOne® offers maintaining calibration and traceability throughout the entire production process, even
up to the launch pad. The test system (top-left picture) is offered as an option together with the TT&C
transponder. The GIOVE-A (bottom-right picture showing GIOVE-A in the clean room in Baikonur) mission is
the most prominent example where the integrated end-to-end test approach has been used from design, through
integration up to the launch pad.
PA and QUALIFICATION APPROACH
The STC-MS01 is targeting low-cost missions in Low Earth Orbits (LEO) with mission durations of up to three
years. COM DEV EUROPE follows the Microspace philosophy of Quality Assurance, although COM DEV
EUROPE implements a Product Assurance (PA) program to ensure that the project deliverable items meet the
requirements contained in the contractual documents. The Product Assurance Program emphasizes a
preventative approach, and ensures that documentary evidence of product quality is available in the form of
design documentation and inspection and test results.
COTS components are used for the fabrication of the STC-MS01. The components are purchased in large
batches from the same manufacturing lot. This guarantees that all units will have the same component reliability
figures. A database for all parts used with reference to application, mission and environment is maintained. The
operational success of each satellite is recorded. Any faults identified with the parts performance on mission are
also recorded. This database builds up an extensive heritage listing for all parts used.
Wherever possible Com Dev Europe uses automated PCB population in the production process. The PCB
population is performed by external partners, which have been vetted for the quality requirements of this
production process. For all work that is carried out internally COM DEV EUROPE makes use of its existing
operating policies and procedures (OPPE’s), which are available at COM DEV for review, as they are deemed
appropriate through OPP 4.1.101 ‘COM DEV Europe Group Quality Manual’. Assembled PCBs shall meet the
requirements of IPC-A-610 Class 3 High Performance Electronics