Alternative Bi-Prop Regulator

Advanced Technology

Status

Ongoing
Status date

2014-11-24

Objectives

Nearly all current telecommunications platforms use mechanical pressure regulators (MPR) for Helium control in their chemical propulsion system. However, such MPRs have significant drawbacks inherent to their design: fixed set point, high internal leak rate and high minimum operating inlet pressure. An alternative method is electronic regulation. Such bang-bang regulators have been frequently used in Electric Propulsion systems for regulating low-flow, low-pressure Xenon applications. The objective of this work is to demonstrate that using electronic regulators can also be applied to high-flow and high-pressure pressurant gas applications, such as for large (420N) bipropellant thrusters typical of telecommunications platforms. The name given to the resulting product is HEPR: Helium Electronic Pressure Regulator.

Challenges

N/A

Benefits

The advantages of the Helium Electronic Pressure Regulator (HEPR) compared to MPRs are:

Adjustable pressure set points along the whole mission
Minimum required inlet pressure close to the outlet pressure
Flexibility in exchanging thruster type during AIT
Removal of pyrovalves thanks to the low internal leak rate
Three barriers between the pressurant and the propellant tanks
Possibility to passivate the Helium tank at the end of the mission

The initial study indicates significant improvements in the overall performance of a chemical propulsion system, with mass savings over 20 kg for geostationary satellites with HEPR compared with the ones with MPR.

Features

The concept behind the HEPR is a bang-bang regulator that consists of three solenoid valves in series and a cavity between the last two valves. At each given time, at least one control valve is in a closed position. High accuracy low pressure transducers are used to feedback the propellant tanks pressure to an electronic block. This pressure information is then used to toggle the valves based on the desired pressure set-point. The HEPR is able to regulate with an accuracy of ±0.1 bar a high pressure Helium flow of 0.5 g/s down to an outlet set-point to be chosen between 10 and 24 bar.

System Architecture

The HEPR architecture baseline is presented below. It has four parallel branches, of which two are redundant. Two branches are therefore being activated at the same time to deliver the correct Helium flow rate. The redundant branches (SV4-SV5-SV6 and SV10-SV11-SV12) would be activated in case of failure in one of the nominal one. The cavities are however shared between the nominal and the redundant branches.

The electronics part consists of four identical blocks, each block commanding the three valves on one branch.

Click for larger image

Image credit: Romain Delanoë, OHB Sweden AB

SV = Solenoid Valve

FDV = Fill and Drain Valve

CV = Cavity

HPT/LPT = High / Low Pressure Transducer

TP = Test Port

Several other types of architectures are possible depending on the valve used in the bang-bang regulation and on the expected functionality of the regulator.

Plan

Preliminary system level assessments are first conducted on the implementation of a HEPR in a chemical propulsion system and the performance impacts are quantified. A breadboard aimed at demonstrating the HEPR concept is then designed, assembled and tested. The initial estimates, design trade-offs and simulation results are eventually discussed and compared with regards to the outcome of the breadboard campaign.

Current status

The Final Review was successfully held on the 8^th of April 2014. All the actions are closed and the study is now finished.

A breadboard aimed at demonstrating the HEPR concept has been designed, assembled and tested. The initial estimates and design trade-offs have been validated through this breadboard campaign, showing promising results.