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Astrophysics, Instrumentation and Methods for Astrophysics, astro-ph.IM
Abstract:
The Space Technology 7 Disturbance Reduction System (ST7-DRS) is a NASA
technology demonstration payload that operated from January 2016 through July
of 2017 on the European Space Agency's LISA Pathfinder spacecraft. The joint
goal of the NASA and ESA missions was to validate key technologies for a future
space-based gravitational wave observatory targeting the source-rich milliHertz
band. The two primary components of ST7-DRS are a micropropulsion system based
on colloidal micro-Newton thrusters (CMNTs) and a control system that
simultaneously controls the attitude and position of the spacecraft and the two
free-flying test masses (TMs). This paper presents our main experimental
results and summarizes the overall the performance of the CMNTs and control
laws. We find that the CMNT performance to be consistent with pre-flight
predictions, with a measured system thrust noise on the order of
$100\,\textrm{nN}/\sqrt{\textrm{Hz}}$ in the $1\,\textrm{mHz}\leq f \leq
30\,\textrm{mHz}$ band. The control system maintained the TM-spacecraft
separation with an RMS error of less than 2$\,$nm and a noise spectral density
of less than $3\,\textrm{nm}/\sqrt{\textrm{Hz}}$ in the same band. Thruster
calibration measurements yield thrust values consistent with the performance
model and ground-based thrust-stand measurements, to within a few percent. We
also report a differential acceleration noise between the two test masses with
a spectral density of roughly $3\,\textrm{fm}/\textrm{s}^2/\sqrt{\textrm{Hz}}$
in the $1\,\textrm{mHz}\leq f \leq 30\,\textrm{mHz}$ band, slightly less than
twice as large as the best performance reported with the baseline LISA
Pathfinder configuration and below the current requirements for the Laser
Interferometer Space Antenna (LISA) mission.
