How to Simplify Data Logging in Space

Communications and imaging functions performed by satellite payload instruments have become increasingly more sophisticated. They are required to collect huge amounts of telemetry data to ensure safe and reliable satellite operations.

Telemetry is a multi-faceted function. In addition to monitoring the health of the satellite, it also detects faults, helps in isolating and recovering a satellite from the ground station in case something is amiss, and allows the satellite to control payload instrumentation loading autonomously. This in turn helps in the consumption of power and thermal dissipation, which are critical to avoid overloading and to preserve the life of the satellite.

Telemetry data logging has traditionally been accomplished using multiple circuit cards that are power-hungry and contain many discrete components.  The component count of these I/O cards and the area and power they consume can all be significantly reduced by leveraging the latest advances in radiation-hardened mixed-signal integrated circuits.

The direct benefits of reduced board space utilization is visible in applications such as the Ganymede Laser Altimeter (GALA), one of the scientific instruments being tested for use on board the European Space Agency (ESA) Jupiter Icy Moon Explorer (JUICE) mission scheduled to launch in 2022. This altimeter system will measure the distance of the spacecraft from the surface of Jupiter’s icy moons Ganymede, Europa and Calisto by calculating the time it takes a laser beam to travel to the surface, be reflected and return to the telescope within the instrument.  Laser altimeter system supplier Hensoldt Optronics chose the LX7730 telemetry controller to provide processing for instrument data including temperature, voltage, and supply currents.  Within its small footprint, the LX7730 is active in several closed loop controls, necessary for an accurate laser operation with low electromagnetic interference (EMI) levels.  Regular calibration procedures reduce temperature and lifetime dependent drifts and ensure the required accuracy of the acquired digitized values.

Limitations and Drawbacks of Discrete Solutions

Large circuit cards, commonly referred to as I/O cards, laden with discrete components such as analog multiplexers, analog to digital converters, current drivers and voltage references capture telemetry data. These components capture different data including voltage levels and current consumption, temperature, mechanical strain, pressure and magnetic field strength, all essential parameters for monitoring payload health. These I/O cards are typically very large, occupying 12 to 18 square inches of precious real estate inside each payload equipment. Digital channelizers are complex payloads used for communications applications, signal processing systems for imaging or radar applications, and are often chassis-based requiring multiple I/O cards for telemetry purposes. Telemetry I/O cards consume a lot of power and generate heat, which increases the bill-of-materials cost of the payload equipment significantly. Further, circuit cards designed around discrete devices are not flexible or configurable.

Reducing Component Count Increases Reliability

Recent advances in the technology of radiation-hardened mixed signal ICs have resulted in better integration minimizing component count and thus decreasing the area occupied by these I/O cards. Functions such as multiplexers, amplifiers, filters, ADCs and DACs that could be accomplished with small-scale integration and discrete components previously, can now be housed in one single IC.  Data pertaining to critical satellite parameters that are constantly monitored by sensors can now be read and processed due to this dramatic reduction in board space.  This integration results in the dual benefit to satellite manufacturers of increased reliability due to fewer components and reduced time and cost required for screening, testing and qualification of these numerous components since this is now accomplished in one effort with a single IC. Microsemi’s LX7730 Telemetry Controller is an example of this advancement. It integrates these functions into a compact 132-pin hermetic ceramic or a 208-pin plastic quad flat pack and is QML qualified for both class Q and class V flows that are often required for the most demanding space applications.     

Mixed Signal and Digital Companion ICs

An FPGA, such as the RTG4, can be used in each payload for telemetry processing purposes; firstly reading telemetry data from the mixed signal telemetry acquisition IC, secondly performing dual functions of processing and decision-making using data from the mixed signal device, and thirdly reporting health status in to the satellite’s central computer using the prevailing command bus protocol. FPGAs are commonly used to implement standard spacecraft control buses such as Mil Std 1553, SpaceWire, and CAN bus, as well as non-standard bus protocols which are proprietary to the satellite integrator.

Using a highly integrated IC and an FPGA, a complete telemetry gathering system can be implemented. This system can be demonstrated with Microsemi’s Six Sensor Demo that utilizes the company’s RTG4 FPGA connected via SPI to the LX7730 Telemetry Controller. The controller IC acquires data from a small network of sensors connected to it and displays the measured values on a laptop screen via a GUI. The FPGA sends the address, data and read/write bits of the SPI frame to the IC that returns the ADC data to the FPGA. Finally, the FPGA applies the necessary scaling to the ADC output and sends the scaled data to the GUI through a UART.

Size, Weight and Reliability

The latest solutions for telemetry gathering greatly simplify data logging tasks and free up the main processor for other tasks. At the same time, high levels of integration of the mixed signal functions dramatically reduce the overall size and weight of the telemetry logging subsystem while increasing reliability, thus addressing three critical requirements in today’s satellite systems.

Visit our Radiation-Hardened Mixed-Signal ICs page to view a video demonstration of telemetry data logging using our LX7730 Rad Hard Telemetry Controller with our RTG4 FPGA.  You can also link to more information like datasheets, radiation reports, conference papers, and development tool user guides for the on LX7730 and other rad hard mixed signal ICs.