Keisoku Giken Uses NI LabVIEW FPGA and LabVIEW Real-Time to Create Artificial Satellite Attitude Control Device Evaluation Models

Building an RWA for JAXA

NEC Aerospace Systems, Ltd., as part of the development of an attitude control device for JAXA, required a reaction wheel RWA assembly for development and evaluation. The RWA is composed of four wheel rotor modules that revolve in response to torque voltage input from the attitude control device. The system generates a pulse train corresponding to the number of revolutions and returns it to the attitude control device to close the control loop. The simulator should reproduce this complex system with a high degree of speed and accuracy and should have high functionality (for example, it should be simple to make experimental changes) while also being economical.

Because the client required extremely high speed and accuracy, (1) we created a simulator based on a PXI-8176 embedded real-time controller and a PXI-7831R reconfigurable I/O module, using a LabVIEW Real-Time Module and LabVIEW FPGA Module. We received the rotor physics model and implementation plan from the client.

Because an FPGA cannot perform floating-point calculations, we used a LabVIEW Real-Time Module to carry out complex physics-modeling calculations and a LabVIEW FPGA Module for the pulse train calculations and generation. Using this technique, we performed high-speed parallel execution required for this complex simulation.

Experiencing Ease Using LabVIEW

The programmer in charge had no VHDL experience for FPGA programming, but because LabVIEW FPGA Module programming is similar to the programming in a LabVIEW environment, this did not present an obstacle. By using an FPGA emulator for algorithm verification in the initial stages, we executed the extremely fast verification and modification cycles without wasting compile time. As a result, we achieved a significant reduction in development time.

We logged all time-series data by connecting a host computer to the embedded controller running the LabVIEW Real-Time Module program. On project completion, we verified the system in the presence of the client.

Concerning absolute accuracy, the system reflected the FPGA clock accuracy (10 ppm). For this reason, in some cases, the accuracy exceeded the requirements. We initially compensated for this by building in logic to compensate for FPGA clock errors, but in the end, we solved the problem completely by using an NI PXI-6608 timing I/O module, with a precision of 75 ppb, as the standard FPGA clock.

Regarding jitter, the system produced excellent results, with an actual observed p-p value of approximately 30 ns and a standard deviation of 8 ns (with the FPGA operating at a frequency of 80 MHz).

Delivering Accuracy, Flexibility, and Durability with NI Products

The fact that we produced a system to the required specifications within a comparatively short development period and at low cost was due in part to the NI PXI, LabVIEW FPGA Module, and LabVIEW Real-Time Module systems and NI development environments. Using these NI products, we produced operationally accurate and flexible software and deterministic, durable hardware simultaneously.

Our client was very satisfied with the system we supplied. The system was, of course, low in development costs, but it also benefited from simple and economic operation. There was no need to include the system in an expensive flight model, which would require specialist-technician operation and could suffer damage in the event of malfunction. Furthermore, the system provided a dramatic improvement in evaluation accuracy compared to previous simulation environments.

When using this system, we discovered problems that had been previously obscured by evaluation, which meant we could achieve new success in the field of evaluating attitude control devices.

For more information, contact:

Toshihiro Kanda

Keisoku Giken Co., Ltd.

Web: http://www.kgc.co.jp