content long 23-October-2017 06:07:37

Engineering

Drag-Free Propulsion System

The main objective of the LISA Pathfinder Drag-Free Propulsion System (DFPS), commanded by the Drag-Free and Attitude Control System (DFACS), is to counteract the disturbance forces and torques applied on the spacecraft in order to maintain the free-floating conditions on the master test mass.

In order to counteract the continuously changing disturbance forces, the thrusters must be able to deliver a continuously modulated thrust between minimum and maximum force (in the range 1 μN to 100 μN) with a response time better than the control system's command frequency (10 Hz). Effectively, the thrusters are used as ultra-precise proportional actuators continuously fired throughout the mission.

The propulsion system of the LISA Technology Package consists of micronewton thrusters installed on three of the panels of the science module; these are cold-gas (nitrogen) thrusters, based on those originally developed for ESA's Gaia mission.

In addition to its function during the drag-free operating mode (science mode), the DFPS also carries out all attitude and orbit control functions of the LISA Pathfinder spacecraft once the Propulsion Module, required for the transfer to L1, is jettisoned.

As well as the European cold-gas-based DFPS, LISA Pathfinder carries the US Colloidal Propulsion System. This system will perform drag-free operations for limited periods of time. Each thruster delivers a continuously modulated force of between 5 μN and 30 μN. There are a total of eight thrusters grouped in two clusters of four.


Last Update: 11 January 2016

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