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1 April 19, 2023Paik-1

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


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.


Spherical Outer Test Mass

SMART test mass pairs(Example)

STEP test mass pair

0

0

BB

ACCBBA

aa

aaaaaa

A spherical shell approximates a point mass more closely.

Smaller moments for 3

Closure conditions satisfied:


Suspension and Alignment

Meander-pattern suspension coil for STEP

AuxiliarySuspension Tube

MainSuspension

TubeSuspensionCurrent Loop 2

SuspensionCurrent Loop 1

DifferentialCurrent Loop

Outer Test MassSensing Coil

Inner Test MassSensing Coil

TantalumNiobiumCoil-form

Suspension and alignment by current along a single tube

Axisalignment 10-5 rad

CMRR 108

with error compensation

Centering by currents on 4 auxiliary tubes


Accelerometer Orientation

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

x

yz


Technology Heritage

SGG for 1-m 1/r2 law test Diff linear accelerometer CMRR 107

41013 g Hz1/2 noise Best resolution (104) of

1/r2 law at 1 m

SGG for airborne gravity Diff angular acc. CMRR = 109

SGG for submillimeter 1/r2 law test

Differential linear accelerometer

Search for extra dimensions to 20 m

Superconducting Gravity Gradiometer (SGG)

Wire-based S/C technology

7 April 19, 2023

Levitation on a Single Tube

• This critical technology has been demonstrated. Test setup

• Measured frequency squared versus current squared:

Sliding mode Vertical mode

Screening current

Wire

S/C tube

8

P.I.: Ho Jung PaikJPL Contact: Inseob Hahn

January 11, 2008

SMEX-ISS Concept Gate Review

SMART (Standard Model And Relativity Test)

9 April 19, 2023

SMART: H.J. Paik, University of Maryland

• Science objectives: To test EP to 1017 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. MarylandCo-I: M.V. Moody, U. MarylandJPL Project Scientist: TB

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

• Exp. module: JEM-EF, Site #9 preferred.

• Goal minimum 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.

10 April 19, 2023

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).

11 April 19, 2023

Instrument• The current state of instrument development:

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.

EP EP Accelerometer/ EP EPTi-Pt Pt-Nb Gradiometer Nb-Ti Nb-Nb

L xa1

x

Ixa

xa xx

xa2L xb1L xb2L

L xa1

x

¯ x̄a2Lx̄b1L x̄b2L

¯

xbI

xaI¯ x̄bI

Detection circuit

12 April 19, 2023

Science Traceability: Baseline Investigation

Science Objectives

Science Meas. Requirements

Instrument Functional Requirements

Mission Functional Requirements (top-level)

Test EP to one part in 1017

Resolve aD to 1017 g at 10–2 Hz

T 2 K, T 10–5 K Hz–1/2

aD 10–13 m s–2 Hz–1/2

CMRR = 108

(by error compensation)

Vibration isolation > 0.1 Hz

Dewar rolled at 10–2 Hz

a 10–5 m s–2 Hz–1/2

10–6 rad s–2 Hz–1/2

3 month science operation

10-3 10-2 10-1 100

Frequency (Hz)

10-7

10-6

10-5

10-4

10-3

Line

ar A

ccel

erat

ion

(m s

-2 H

z-1/2

)

10-3 10-2 10-1 100

Frequency (Hz)

10-8

10-7

10-6

10-5

10-4

Ang

ular

Acc

eler

atio

n (r

ad s

-2 H

z-1/2

)Airborne SGG with CMRR = 109

ISS vibration noise spectra

13 April 19, 2023

Mission Design

• Level of microgravity required: 10–5 g.

• 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.

Payload Interface Unit (ISS/JEM-EF

Interface)

RadiatorGrapple Fixture

Launch Lock & Rotation

System

HTV Carrier Interface

Electronics

Site #9

x

14 April 19, 2023

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.

Yr #1 Yr #2 Yr #3 Yr #4

Start PDR CDR EOMSIR Launch

Ph A/B Ph C Ph D Ph E Ph F

SRR

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