LISA Pathfinder: Mission Status · 2011-12-20 · LISA Pathfinder LPF Development Approach LPF is a...
Transcript of LISA Pathfinder: Mission Status · 2011-12-20 · LISA Pathfinder LPF Development Approach LPF is a...
LISA Pathfinder: Mission Status
Paul McNamaraLISA Pathfinder Project Scientist
LISA Pathfinder
Introduction
LISA Pathfinder (LPF) is a technology validation mission for NGO1
– LPF was approved by ESA to demonstrate the concept of low frequency gravitational wave detection in space
LISA Pathfinder will test in flight:– Inertial sensors (a.k.a. Gravitational Reference Sensor)– Interferometry between free floating test masses– Drag Free and Attitude Control System (DFACS)– Micro-Newton propulsion technologyThe basic idea of LISA Pathfinder is to squeeze one arm of the NGO constellation from 1 million km to a few tens of cm!– Fully tests NGO local interferometry
1 When approved by the Science Programme Committee, LISA Pathfinder was a dedicated technology validation mission for the LISA mission. In the mean time, LISA has been reformulated and renamed NGO
LISA Pathfinder
Mission Concept
LISA Pathfinder
Mission Concept
LISA Pathfinder
Mission Concept
LISA Pathfinder
Mission Concept
LISA Pathfinder
Mission Concept
LISA Pathfinder
LISA Pathfinder consists of:– Spacecraft
• Provided by ESA– Industrial Prime Contractor: Astrium UK
• s/c also includes the drag free control software (DFACS) and micro-Newton thrusters
– Payloads• The LISA Technology Package (LTP)
– Provided by European member states and ESA– Consists of inertial sensors, and interferometric readout
• The Disturbance Reduction System (DRS)– Provided by NASA– Consists of processor running drag-free
control software and micro-Newtonthrusters
LTP Core Assembly
LPF
LISA Pathfinder
LISA Pathfinder
DFACS Principle
LISA Pathfinder
x1 interferometer
LISA Pathfinder
x1 Drag Free
LISA Pathfinder
x2-x1 Interferometer
LISA Pathfinder
X2 low frequency control
LISA Pathfinder
DFACS
LISA Pathfinder
LPF Development Approach
LPF is a Pathfinder for spaceborne gravitational wave detectors– System design is for NGORelaxation of performance requirements is only allowed to make testing conditions achievable. It shall not affect the design.Implications:– When one subsystem reaches a given level of readiness for LISA
Pathfinder (CDR, QR, FAR, etc) it reaches the same level of readiness for NGO too.
– All the development risks up to that stage are consequently retired also for NGO
– Risk of unforeseen system level problems (estimated to be low) is finally retired by the flight.
LISA Pathfinder
NGO basic design items
Free flying test mass subject to very low parasitic forces:– Drag free control of spacecraft (non-contacting spacecraft)– Low noise microthruster to implement drag-free– Large gaps, heavy masses with caging mechanism– High stability electrical actuation on cross degrees of freedom– Non contacting discharging of test-masses– High thermo-mechanical stability of S/C– Gravitational field cancellation
Precision interferometric, local ranging of test-mass and spacecraft:– pm resolution ranging, sub-mrad alignments– High stability monolithic optical assemblies
Precision 1 million km spacecraft to spacecraft precision ranging:– High stability telescopes– High accuracy phase-meter– High accuracy frequency stabilization– Constellation acquisition– Precision attitude control of S/C
LISA Pathfinder
Items that can only be validated in flight
Free flying test mass subject to very low parasitic forces:– Drag free control of spacecraft (non-contacting spacecraft)– Low noise microthruster to implement drag-free– Large gaps, heavy masses with caging mechanism– High stability electrical actuation on cross degrees of freedom– Non contacting discharging of test-masses– High thermo-mechanical stability of S/C– Gravitational field cancellation
Precision interferometric, local ranging of test-mass and spacecraft:– pm resolution ranging, sub-mrad alignments– High stability monolithic optical assemblies
Precision 1 million km spacecraft to spacecraft precision ranging:– High stability telescopes– High accuracy phase-meter– High accuracy frequency stabilization– Constellation acquisition– Precision attitude control of S/C
LISA Pathfinder
Free flying test mass subject to very low parasitic forces:– Drag free control of spacecraft (non-contacting spacecraft)– Low noise microthruster to implement drag-free– Large gaps, heavy masses with caging mechanism– High stability electrical actuation on cross degrees of freedom– Non contacting discharging of test-masses– High thermo-mechanical stability of S/C– Gravitational field cancellation
Precision interferometric, local ranging of test-mass and spacecraft:– pm resolution ranging, sub-mrad alignments– High stability monolithic optical assemblies
Precision 1 million km spacecraft to spacecraft precision ranging:– High stability telescopes– High accuracy phase-meter– High accuracy frequency stabilization– Constellation acquisition– Precision attitude control of S/C
Items benefiting from in-flight validation
LISA Pathfinder
Free flying test mass subject to very low parasitic forces:– Drag free control of spacecraft (non-contacting spacecraft)– Low noise microthruster to implement drag-free– Large gaps, heavy masses with caging mechanism– High stability electrical actuation on cross degrees of freedom– Non contacting discharging of test-masses– High thermo-mechanical stability of S/C– Gravitational field cancellation
Precision interferometric, local ranging of test-mass and spacecraft:– pm resolution ranging, sub-mrad alignments– High stability monolithic optical assemblies
Precision 1 million km spacecraft to spacecraft precision ranging:– High stability telescopes– High accuracy phase-meter– High accuracy frequency stabilization– Constellation acquisition– Precision attitude control of S/C
NGO Design Items Validated By LISA Pathfinder
LISA Pathfinder
LTP Salient Features
LISA Technology Package (LTP) is the European instrument payload of LPF
Two Au:Pt test masses housed in separate vacuum enclosuresRelative position of test masses read-out by:– Heterodyne laser interferometry on
sensitive axis– Capacitive sensing on all axesFour interferometers on ultra-low expansion optical bench– x1, x2-x1, Frequency noise, reference
interferometer
LISA Pathfinder
LTP Status
All electronic units have been delivered and integrated to the spacecraft– Laser, laser modulator, phasemeter, payload computer, UV lamp unit,
ISS front-end electronics, diagnostics
Reference Laser Unit Phasemeter
Payload Computer ISS Front-End Electronics LPF during AIT at Astrium UK
LISA Pathfinder
LTP Status
Most of the components of the LTP Core Assembly are ready, however subsequent integration has been delayed.– Optical bench– Inertial sensor
• Test Masses• Vacuum enclosure• Grabbing, positioning and release
mechanism
Optical Bench Test Mass Grabbing, positioning and Release Mechanism (GPRM)
Uncoated Au:Pt Test Mass
LISA Pathfinder
LTP Status
Delays in the integration, and delivery, of the LTP Core Assembly are due to problems with the test mass launch lock– Original (hydraulic) launch lock
failed during testing– A new design has now been
selected, and flight units are being manufactured
• New design is a much simpler, single-shot mechanism utilising a paraffin actuator
• Delivery of FMs is scheduled for September 2012
ESA Presentation | 30/NOV/2011 | Slide 10
ESA UNCLASSIFIED – For Official Use
LISA Pathfinder
TOQM
In-lieu of the LCA, a Thermal-Optical Qualification Model (TOQM) was created to allow the environmental testing of the spacecraft to proceed– Consists of a flight optical bench, with flight mounting struts, and
thermal mass dummies of the inertial sensors
LISA Pathfinder
LPF Spacecraft Bus
All units of the spacecraft bus have been delivered and integrated– Only units not yet integrated are the micro-thrusters (which are
mounted on the outside on the spacecraft)System environmental tests are now complete
Following closed-loop tests in January, spacecraft will be put into storage awaiting the delivery of the LCA
LISA Pathfinder
System Test Campaigns
Sine Vibration Transfer Orbit Thermal Test
EMC On-Station Thermal Test
LISA Pathfinder
OSTT Sequence
0 2 4 6 8 10 12 14 16 18 20 22
Time (Days)
Max. Hot
Min. Cold
Amb. TP0
TP1
TP3
TP21
TP4 TP5 TP7 & 8
Pum
p D
own
TB H
ot L
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scie
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Tran
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IST03 Cold
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TB C
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PFM
SC
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Test Completion
TP9
TP13
TP11TP2
TP17&18
Re-
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SCM
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TP20
TP16 TP14 TP12
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TOQ
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TP15
TOQ
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peci
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0 2 4 6 8 10 12 14 16 18 20 22
Time (Days)
TOQM Testing TB Test Phases TV/IST Test Phases Noise Characterisation Testing Initial/ Final SFTs @ Ambient
Max. Hot
Min. Cold
Amb.
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Tes
t Seq
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Dia
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Pre
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TOQ
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Per
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Cha
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M H
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LTP
SC
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Re-
Pres
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Test CompletionOM
S F
acili
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oise
C
hara
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isat
ion
LISA Pathfinder
Fit to OSTT Performance
LISA Pathfinder
Micro-thrusters
LPF will carry two sets of micro-thrusters– The NASA supplied Colloidal Thrusters– European supplied thrustersThe baseline thruster for LPF is the Cs Field Emission Electric Propulsion (FEEP) thrusterDue to delays in the qualification schedule of the FEEPs, the project has recently instigated a review of the use alternative thrusters for LPF– Cold Gas thrusters (the GAIA thruster)– Micro Radio-frequency Ionisation Thrusters (µ-RIT)
LISA Pathfinder
Micro-Thrusters
Review Board Conclusions (May 2011):– Continue FEEP development, culminating in two tests demonstrating the LPF
lifetime (600Ns) by June 2012– Industry to study the cold gas thrusters, with PDR to be held in October 2011– Industry to study micro-RIT thrusters with SRR in September 2011, and PDR
by the end of the year
As of now:– Cold Gas PDR was successful
• Major issue is the schedule for the delivery of the thruster units
• Board recommended to start the procurement of the long-lead items before the decision is made on the flight thruster technology
– Micro-RIT• SRR has been held• Development of the technology will
continue up to PDR level
Measured thrust noise of GAIA thrusters
LISA Pathfinder
Micro-Thrusters
Review Board requested that the FEEP tests continue into next year– Culminating in two thruster assembly endurance tests, both of which
must demonstrate the full LPF total impulse requirements.After thorough investigation, the FEEP thruster head has been redesigned to limit caesium leakage from the emitter slit– Achieved in part by narrowing the slit width from 1.3µm to 0.7µm
Ongoing thruster unit validation test is demonstrating that the new design of thruster is working perfectly!!
Downselect on which thruster to take to flight will be made in June 2012.
LISA Pathfinder
Micro-Thrusters
NB: As of today, total impulse now at ~300Ns (~900hours). Equivalent to ~50% of LPF total impulse requirement
LISA Pathfinder
LPF Performance The LISA Pathfinder Mission 7
1 10 1000.1
Frequency [mHz]
1
10
100
SpectralDensity
� fms−2/√
Hz
�
TotalDirect Forces
OMSAngular
ElectrostaticActuation
Thrusters
OMSSensing
Star
Tracker
Figure 1. The differential acceleration noise budget arising from the requirementson the individual groups of noise sources. The grey areas are out of the measurementband for LPF but are interesting for LISA.
construction of the flight hardware has begun and are, as such, necessarily conservative.
Once the hardware is built and tested in realistic settings, we get more reliable estimates
of the performance of individual subsystems. In addition, a detailed understanding of
the differences in the environment under which the subsystems are tested compared to
the environment expected in orbit could lead to further improvements. As well as the
testing and analysis of flight hardware, studies of the system as a whole can lead to data
analysis methods and system identification techniques (see, for example, [10, 11])which
will allow the system to be optimised in orbit, resulting in reductions of the coupling
of some noise sources to differential force on the test-masses. Some examples of these
improvements are given below.
3.1.1. Measured performance of the electrostatic actuators The electrostatic actuation
is used to control the position of TM2 to ensure that it tracks the free-falling TM1. When
estimating the differential acceleration of the two test-masses, this commanded actuation
is removed (see [12]). As such, any fluctuations in the applied actuation force which
are not present in the commanded actuation will not be removed and will be a direct
contributor to the estimated differential acceleration. These fluctuations ultimately
arise in fluctuations of the dc voltages applied to produce a dc force that counteracts
any gravitational imbalance within the SC. The flight models of the electronics which
produce the dc voltages have now undergone direct measurement and have shown that
the fluctuations are at the level of 3 − 8 ppm/√Hz at 1mHz. Together with detailed
modelling of the expected gravitational imbalances (estimated to be around 0.65 nm s−2),
this performance lead to a lower estimate for the expected force noise fluctuations.
Further discussion of this can be found in [13]. Panel (a) of figure 2 shows (in red) the
The LISA Pathfinder Mission 11
1 10 1000.1
Frequency [mHz]
1
10
100
SpectralDensity
� fms−2/√
Hz
�
TotalDirect ForcesElectrostaticActuation
Thrusters
OMSSensing
StarTracker
Requirements
Figure 3. The differential acceleration noise budget arising from the best-case orexpected performance of the individual subsystems. The grey areas are out of themeasurement band for LPF but are interesting for LISA.
improves upon the LISA Goal in the LPF measurement band, and is only about a
factor of 3 away at the lower end of the LISA band.
1 10 1000.1
Frequency [mHz]
1
10
100
SpectralDensity
� fms−2/√
Hz
� 1000
LPF Mission RequirementsLISA Mission RequirementsLPF Performance (Subsystem Requirements)LPF Performance (Best Estimate)LPF Performance (Free-Flight)
Figure 4. A comparison of different performance estimates for the LPF Mission. Weshow the performance expected if all systems perform as per their requirements, thecurrent best estimate performance, and the estimated performance for the free-flightexperiment. Also shown are the overall mission requirements for LPF and LISA.
Extensive performance noise model has been developed by both the PI and industryThe main goal of LPF is to validate this noise modelModel is updated as ground test results become availableCurrent Best Estimate of LPF is now approaching the NGO requirements!
Requirements noise projection
Current Best Estimate
LISA Pathfinder
In Summary
All environmental tests completeThe caging mechanism launch lock drives the critical pathResults from OSTT (TOQM) demonstrate performance better than requirementsCold Gas thrusters are a viable alternative to the FEEPs.The project will enter hibernation at the beginning of next year– Hibernation is scheduled to last
~15months
Launch is scheduled for June 2014.
LabenCarlo Gavazzi SpaceALTAARCSContravesKaiser ThredeNTESCISYSSpacebelSRONTechnologicaTESATZARMJPLNASA GoddardBUSEK
Thank youESA ESTECESA ESACESA ESOCEADS Astrium UKEADS Astrium GmbHUniversity of TrentoAlbert Einstein InstituteUniversity of GlasgowUniversity of BirminghamImperial College LondonETH ZurichInstitut d-Estudis Espacials de CatalunyaUniversidad Politecnica de Barcelona APC ParisIFR Stuttgart