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Test of the Equivalence Principle on ISS. Ho Jung Paik, Krishna Venkateswara, M. Vol Moody Department of Physics, University of Maryland Collaborators: Inseob Hahn, Talso Chui, and Konstantin Penanen Jet Propulsion Laboratory NASA ISS Workshop on Fundamental Physics

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slide1

Test of the Equivalence Principle

on ISS

Ho Jung Paik, Krishna Venkateswara, M. Vol Moody

Department of Physics, University of Maryland

Collaborators:

Inseob Hahn, Talso Chui, and Konstantin Penanen

Jet Propulsion Laboratory

NASA ISS Workshop on Fundamental Physics

October 13-15, 2010, Dana Point, CA

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scientific value of ep tests
Scientific Value of EP Tests

In string theory, the 10-D tensor gravitational field G has two partners: scalar field  (dilaton) and antisymmetric tensor field B. They are coupled to the other fields in ways generally violating the EP.

Many scalar and pseudo-scalar partners of the graviton may survive as massless particles in the four-dimensional low energy world (dilatons, axions, moduli fields, etc.).

The observed accelerating expansion of the universe is consistent with a cosmological constant , which is 120 orders of magnitude smaller than the quantum corrections to the vacuum-energy density.

It is important to test the founding principles of GR, such as the EP, to the highest possible precision because the failure to quantize gravity and the  problem may be partly due to incompleteness of GR.

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spherical outer test mass
Spherical Outer Test Mass
  • A spherical shell approximates a point mass more closely.

 Smaller moments for  3

  • Closure conditions satisfied:

SMART test mass pairs

(Example)

STEP test mass pair

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suspension and alignment
Suspension and Alignment
  • Suspension and alignment by current along asingle tube

 Axis alignment 10-5 rad

 CMRR 108

with error compensation

  • Centering by currents on 4 auxiliary tubes

Meander-pattern suspension coil for STEP

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accelerometer orientation
Accelerometer Orientation

x

z

y

Orientations of the EP test masses with respect to the spacecraft spin axis (z)

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technology heritage
Technology Heritage
  • Superconducting Gravity Gradiometer (SGG)
  • Wire-based S/C technology
  • SGG for airborne gravity
  • Diff angular acc.
  • CMRR = 109
  • SGG for 1-m 1/r2 law test
  • Diff linear accelerometer
  • CMRR  107
  • 41013g Hz1/2 noise
  • Best resolution (104) of 1/r2 law at 1 m
  • SGG for submillimeter 1/r2 law test
  • Differential linear accelerometer
  • Search for extra dimensions to 20 m

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levitation on a single tube
Levitation on a Single Tube
  • This critical technology has been demonstrated. Test setup
  • Measured frequency squared versus current squared:

Sliding mode Vertical mode

Screeningcurrent

Wire

S/C tube

p i ho jung paik jpl contact inseob hahn january 11 2008

P.I.: Ho Jung PaikJPL Contact: Inseob HahnJanuary 11, 2008

SMEX-ISS Concept Gate Review

SMART

(Standard Model And Relativity Test)

smart h j paik university of maryland
SMART: H.J. Paik, University of Maryland
  • Exp. module: JEM-EF, Site #9 preferred.
  • Goalminimum temperature: 2 K.
  • Science cold instrument mass: 10 kg.
  • Instrument power consumption:100 W.
  • Pointing:Rotation at 0.01 Hz about the ISS pitch (or roll) axis is required.
  • Science objectives: To test EP to 1017 at range  104 km. Most quantum gravity theories involve EP-violating forces. SMART tests GR and other theories beyond Einstein, and searches for new interactions and particles beyond the Standard Model.
  • Science team members:

PI: Ho Jung Paik, U. Maryland

Co-I: M.V. Moody, U. Maryland

JPL Project Scientist: TB

  • JPL roles:Project management/ system engineering, support science instrument team, flight engineering, I&T, ATLO, CTM
slide10

Science Objectives

  • Science goals and objectives:

To test EP and search for new interactions and particles beyond the Standard Model.

  • Relationship to the astronomy program objectives in NASA science plan:

SMART supports NASA’s strategic goal:“Discover the origin, structure, evolution, and destiny of the universe.”

  • Relationship to other investigations:

SMART will improve by 102 over Microscope mission, a factor of 10 short of STEP.

  • Justification for space:

In orbit, Earth’s gravity is fully modulated,gaining 103 in signal,and accelerometers can achieve higher sensitivity (by 102-103).

instrument
Instrument
  • The current state of instrumentdevelopment:

SMART uses superconducting differential accelerometers, which are very similar to SGG, fully developed at UM.

  • Diagrams of the instrument:
    • Mass and power:The instrument weighs 10 kg, and requires 100 W.
    • Limits to the sensitivity:ISS dynamic and gravity noise will be dominant.
    • Heritage:GP-B, which utilizes similar technologies, has flown.

ISLES was supported by Microgravity Program (MP) in 2002-06.

      • Under NSF support, a ground ISL experiment is being performed.

Detection circuit

EP EP Accelerometer/ EP EP

Ti-PtPt-Nb Gradiometer Nb-TiNb-Nb

science traceability baseline investigation
Science Traceability: Baseline Investigation

Airborne SGG

with CMRR = 109

ISS vibration noise spectra

mission d esign
Mission Design
  • Level of microgravity required: 10–5g.
  • Temperature required: 2 K with stability to better than 0.1 K.
  • Servicing required after installation:None.
  • Uplink and downlink bandwidth required:<< 0.01 Mbps, 0.2 Mbps (ref: LTMPF PIA).
  • ISS payload accommodation location required:

The dewar needs to be rolled about the pitch or roll axis at ~10–2 Hz.

Site #9 of JEM-EF is a natural site that allows this rotation.

However, SMART can be accommodated at any other sites, as long as it is rotatable.

  • Mission time:Minimum 3-month space operation.

Launch Lock & Rotation

System

Grapple Fixture

Radiator

Electronics

x

Payload Interface Unit (ISS/JEM-EF Interface)

HTV Carrier Interface

Site #9

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Management: Top-Level Schedule

  • Science instrument
    • 1.5 year for Phase A/B
    • 0.5 year between CDR and Del to system I&T
    • 0.5 year system I&T at JPL
    • 4 month ATLO
    • 4 month operation in space
    • 6 month data analysis
  • JEM-EF site #9 availability is a big assumption.
    • But we can occupy another site with more engineering and less science.

Launch

EOM

Start

PDR

SRR

CDR

SIR

Ph F

PhC

PhD

PhE

Ph A/B

Yr #4

Yr #1

Yr #2

Yr #3