The project objective is to design, build and test an engineering model of a Xenon Flow Control Module, using MEMS based flow control elements. A key element to achieve both high performance and controllability of an EP system is the propellant feed system to the thruster, containing a key element in the flow controller. A typical EP thruster on-board a telecom satellite consumes a few grams per second of Xenon, and the precision and accuracy at which the Xenon flow rate can be controlled has an impact on the performance of the thruster. In the same fashion, the degree of controllability of the Xenon also enhances the controllability of the thruster which in turn provides performance and flexibility in control of the satellite.
A flow range between 0.5 to 25 mg/s with a control accuracy within the flow range less than 5% are a key challenge within this project. The flow rate requirement and accuracy shall apply throughout the wide operational temperature span, ranging from -30°C to +90°C.
The device is manufactured using MEMS technology, thus it is heavily miniaturized. Within a 40-mm diameter and 20-mm height cylinder the functionalities: flow controlling, flow rate measurement, pressure sensing, and temperature sensing are hosted. The total system mass is less than 100 g, and maximum power consumption below 5W.
Following functionalities are hosted together in a single MEMS-chip:
- Flow control valve
- Flow sensing device
- Pressure sensing device
- Temperature sensing device
The valve is able to control the flow within 1 to 18 mg/s GXe, using only a few Watt of power. The flow sensing device measure the current mass flow rate to enable closed loop control. The flow sensing device resolve at least 0.25 mg/s flow rate changes. In order to meet the required flow rate read-out accuracy, both temperature and gas pressure are monitored. Full performance, in terms of mass flow accuracy and response time is achieved at housing temperature ~60°C, thus external heaters is required.
The key component in the FCM is the proportional flow control valve. Closely integrated with the valve are also a mass flow sensor, pressure sensor and temperature sensor, as well as the associated electronics needed to close the control loop.
End of project would result in an EM-level FCM. However, the complexity of this device requires first short loop manufacturing and tests to establish the design of the critical components within the module. When sufficient data was achieved regarding component design, a BBM was to be manufactured. The project is finalised with manufacturing and test of an EM model.
End of project has resulted in an EM-level FCM using MEMS technology to achieve flow controlling, flow rate measurement, pressure sensing, and temperature sensing. The XeFCM is capable to regulate very small flow rate changes. Changes around 50µg/s have been demonstrated. The valve is able to control the flow within 1 to 18 mg/s GXe, using only a few Watts of power. The XeFCM has the ability to compensate for varying inlet pressure variations. The small volumes inside the XeFCM makes it rather sensitive to the variations, but the small (dead) volumes are beneficial to the control loop. Oscillations around 250µg/s where measured, using both slow and rapid pressure variations. The XeFCM has been demonstrated functional at the maximum and minimum operational temperatures.