Thermal experiments in LISA Pathfinder: preparing for operations Ferran Gibert 5th IGWM, Barcelona, May 13th 2015
LISA Pathfinder overview ESA mission with NASA collaboration to fly this year (!!!) Technology demonstrator to show LISA-like experiment feasibility: Test free-fall performance of onboard Inertial Sensors Test low-frequency pico-meter resolution interferometry Test micro-newton control of the spacecraft Characterize environment noise sources...
LISA Pathfinder overview ESA mission with NASA collaboration to fly this year (!!!) Technology demonstrator to show LISA-like experiment feasibility: Test free-fall performance of on board Inertial Sensors Test low-frequency pico-meter resolution interferometers TOP REQUIREMENT: Test micro-newton control performance (DFACS) 2 [ ( )] ω/2 π 1/ 2 14 S (ω) 3 10 1 + Δ a, LPF Characterize environment noise sources 3 mhz between 1-30mHz [m/ s2 / ( Hz)]
LTP temperature noise sources Actually, temperature noise sources also at other parts: Temperature gradients around the test masses Thermo-optical distortion of optical parts Thermoelastic distortion of the LTP structure
LTP temperature noise sources Actually, temperature noise sources also at other parts: Thermoelastic distortion of the LTP structure Temperature gradients around the test masses STRUT HEATING THERMAL EXPERIMENT ELECTRODE HOUSING (EH) THERMAL EXPERIMENT Thermo-optical distortion of optical parts OPTICAL WINDOW (OW) THERMAL EXPERIMENT
Thermal Diagnostics Subsystem LTP equipped with a dedicated Thermal Diagnostics subsystem to characterize the three kinds of temperature noise sources: 24 thermistors & 14 heaters Electrode housing thermal items Optical Window Optical Bench
EH Thermal Experiment Temperature gradients induce forces on the test masses through three mechanisms: Radiation pressure F RP =k RP T 3 Δ T Radiometer effect F RM =k RM p ΔT T Asymmetric outgassing F OG =k OG ΘOG e T ΘOG T 2 Aims: 1. Determine the coupling between temperature gradient on the X and IFO disturbance. 2. Disentangle the contribution of each thermal effect to estimate pressure in the cavity. Input signal: 1mHz temperature gradient signal induced by alternating H1 and H2 (500s pulses of ~10mW) Repeat the pattern with different modulation amplitudes and absolute temperatures ΔT
EH Thermal Experiment Data analysis through a demodulation process of ΔT and Fx Force on X estimated from motion measurements. Δ T x= ( T 3 +T 4 ) ( T 1 +T 2 ) 2 α= Fx ΔTx Thermal effects modelled and integrated to a global spacecraft simulator
EH Thermal Experiment Simulation conclusions: Thermal coefficients obtained for each absolute temperature Scenario dominated by outgassing effect. Small absolute temperature range (+2K), not allowing to estimate of RM effect contribution Still, we can set upper limits to each thermal effect Transfer function analysis on noise segments
EH Thermal Experiment On-ground tests by means of torsional pendulums Use of a EH-TM replica in a 4-mass torsion pendulum facility at the University of Trento Thermal effects characterized by externally changing T and P Thermal model validation tool Possibility of reproducing the full EH experiment PRELIMINAR DATA! Special thanks to: R. Dolesi, A. Cavalleri, C.D. Hoyle and the UNITN LISA group.
Struts Thermal Experiment Thermoelastic distortion assessed by applying series of pulses (~2W) individually to each heater in the struts. Extensive test during On Station Thermal Test after LTP core integration to spacecraft (Munich, 2011): Negligible heat flux into the optical bench Visible consequences to all the interferometer channels and many control loops.
Struts Thermal Experiment Distortion observed associated to Optical Bench torsion around Y due to vertical component of the force produced by thermal expansion of the heated strut. Gibert et al, CQG 32 (2015) Coupling of 1nm/K measured, a factor ~30 below sensitivity limit at 1mHz:
Data analysis pipelines Operations: specific data analysis pipeline for each experiment End-to-end scripts with all the analysis steps ready Use of LTPDA Toolbox, a dedicated MATLAB toolbox that provides a common language for the whole LPF DA community Tested in data analysis simulation campaigns Involving all the Data Analysis team Organized in daily teams: Main team: 1 investigator, 1 scribe and 2 DA External support team Similar scheme to be used during operations in ESOC
Summary Thermal diagnostics items already integrated to the satellite. Thermal coupling from temperature gradient in the EH easily determined. The identification of the contributions of the different thermal effects in the Electrode Housing remains uncertain due to the maximum available temperature range. Further work needed here. Thermoelastic distortion mechanism characterized through ground tests. Data analysis pipelines being developed and validated in simulation campaigns.
That's it... and that's close! Questions...?