The LTP experiment

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The LTP experiment
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Free falling particles mark (co-moving)
coordinates
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Mass-energy
distort rulers (metric tensor)
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How accurately coordinate frame must be marked by
free-falling particles?
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How accurate must be free-fall of
particles? (lack of spurious relative
acceleration)
A major leap in the definition of inertial frames
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The LTP Concept Take the 5 Mo km out of one
LISA arm fit it into one Spacecraft and
demonstrate free-fall
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Interferometer
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Formally endorsed by Science Working Team
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Experiment Main Goals

• Demonstrate that total acceleration noise in
  realistic conditions is not larger than goals
• March toward LISA by
• Identify and subtract largest contributions to
  total noise
• Twickle parameter to minimize noise contributions
  that cannot be subtracted
• Account quantitatively for residual, non
  subtracted noise

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New Science reqs.
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old LISA reqs
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LISA PF reqs.
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LISA PF expected sensitivity
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Residual, non-subtracted, non-suppressed noise
must fit noise model
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Experiment Main Goals

• Measure coupling to S/C and verify model of
  largest sources

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On ground with torsion pendulum
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Experiment Main Goals

• Measure coupling to S/C and verify model of
  largest sources
• Demonstrate operation of high resolution optical
  metrology with free-falling end-mirrors

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Spurious forces add to space-time metric
distortion
But also essential do measure distance between
centers of mass Interferometer alignments are top
requirements
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Dynamics in the presence of imperfections
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Experiment Main Goals

• Measure coupling to S/C and verify model of
  largest sources
• Demonstrate operation of high resolution optical
  metrology with free-falling end-mirrors
• Verify feasibility of heavy test-mass precision
  release into free-fall
• Verify feasibility and induced disturbances of
  cosmic ray charge control

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A ultra sensitive gravimeter
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LTP and DRS, a simple scenario
LTP TM1
LTP TM2
DRS TM2
DRS TM1
DRS TM1 linear displacements, angular conjugated
in brackets
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high priority (laser output) data TM
Upload new setting TC
high priority (laser output) data TM
Upload new setting TC
Gross failure
Pre-processing
no
Data ok?
results ok?
yes
Continue processing
Continue sequence
Ground pre-processing
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Run
P1 P2 P3 .
Preparatory Phase
T1 T2 ..
Transition Phase
C1 C2 C3 .
Core Phase
Post measurement phase
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A typical preparatory element IFO acquisition
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Verification of strap-down interferometry
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LTP Design
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Thermal Design
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Include cables
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Redundancy a hot topic
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Tools tested for systematics
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An element of LISA interferometry
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Sapphire for electrodes
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Venting to space under trade-off
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AOM
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On ground torsion pendulum
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Testing Campaign with 40 mm TM concluded

• Final noise upper limit
• Radiometer effect
• Constant Stiffness Actuation
• Actuation noise

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Instrument limit reached at ? 1.510-13ms-2/vHz
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Temperature gradients
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Measurement of thermal gradient induced forces

• Coherent modulation of heaters on sensor
• Search for temperature gradient induced torques
  in excess of that expected for radiometric and
  radiation pressure effects

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The radiometer effect puzzle
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Force to voltage conversion 1 carrier frequency
per DOF ? DOF are independent
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Actuation with 200 Hz carrier
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Large gaps (4 mm, 96
Mass motion due to initial thermal drift
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No extra Argon leakage. Outgassing rate ? ? vs.
pumping speed to be optimized
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Pendulum Bench Facilities

• To be used in FM testing
• To be included in Class 10,000 Clean Room
  (currently 100,000)

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New facility under construction
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Thermometers for thermal gradient experiment
Space qualified. Under test
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Extracting the plunger from the adhesion well
A requirement for the actuator
A measurable contact property
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Testing quality of free fall
LISA PF