star: space-time asymmetry research testing lorentz ... · c v v c c v v c c instr cmb mm instr kt...

1 COSPAR2012 Mysore July 20

Shally Saraf for the Stanford STAR team

July 20, 2012

STAR: Space-Time Asymmetry Research

Testing Lorentz invariance in Low-earth orbit


STAR Concept

Science

1) Lorentz Invariance Violations

2) Velocity boost c dependence

“Kennedy-Thorndike Experiment”

3) >100x state of the art

Technology

1) “Capable” small satellite bus

180 kg, 185 W, secondary payload

2) Advanced frequency standards

3) Precision thermal control

Education

1) Graduate & Undergraduate

2) 3-5 year projects

3) Student led tasks

Science & Technology

on Small Satellites

Education driven

International collaborations

Lipa, et. al. “Prospects for an advanced Kennedy-Thorndike

experiment in low Earth orbit” arXiv:1203.3914v1[gr-qc]


STAR Collaboration

Collaborating Institutions

Main Contributions ALL

Science and EP&O

Ames Research Center

PM, SE, I&T, and SM&A

KACST

Spacecraft and Launch

Stanford University

PI and Instruments to TRL 4

German Space Agency et al

Instruments, Flight Clock

JILA

Instruments to TRL 4

Industrial Partner

Flight Instrument

Germany

German Aerospace Center (DLR)

ZARM & Bremen University

Humboldt University, Berlin

University of Konstanz

Kingdom of Saudi Arabia

King Abdulaziz City for Science

and Technology (KACST)

United States

NASA Ames Research Center (ARC)

Stanford University

Joint Institute for Laboratory

Astrophysics (JILA)

University of California-Davis

Industrial partner


STAR “Quad Chart”

SCIENCE What is the nature of space-time?

Is space isotropic?

Is the speed of light isotropic?

If not, what is its direction and

location dependency?

3×10-18 to 10-17

Mission design Circular sun-synchronous 650 km

circular orbit

180 kg,150 W

Launch 2015-2016

2-year lifetime

Class D Mission

Payload

Optical cavities ×4

0.1 K enclosure

I2 clocks ×2

Laser-based

comparator

BATC is payload consultant

Management

NASA Ames: PM, SE, SMA,

Mission Operations

Stanford: Science and Payload

KACST: Spacecraft and Launch

DLR: Payload Design & I2 Clock

ALL: Science & EPO


STAR Technology

Optical cavities

Molecular clocks

Hz10 15ff

Advanced frequency standards

Thermal shields

Control algorithms

Optical thermometry

12

9

10

10

shieldOutershieldInner

shieldOutershieldInner

FF

TT

nano Kelvin thermal control


Why Measure c Invariance?

Colladay and Kostelecky (1997)

“The natural scale for a fundamental theory including gravity is

governed by the Planck mass MP, which is about 17 orders of

magnitude greater than the electroweak scale mW associated

with the standard model. This suggests that observable

experimental signals from a fundamental theory might be

expected to be suppressed by some power of the ratio:

The STAR sensitivity could close that gap

1710~ P

W

M

mr


Measuring LIV

HOW DOES ONE MEASURE CHANGES IN c?

KT coefficient

(function vINSTR) rod clock

(1) By comparing the length of a rod (measured by

light beam) to the rate of a ticking clock

(2) By comparing the length of two rods ‘perpendicular’

to one another (both measured with a light beam)

MM coefficient

(function INSTR)

rod 2 rod 1


Kostelecky, 2002


Kinematic Approach to LIV

Is the CMB a preferred frame?

22

2sin

c

vvC

c

vvC

c

c CMBINSTRKT

CMBINSTRINSTRMM

Michelson

Morley

Coefficient

Kennedy

Thorndike

Coefficient

vINSTR, vCMB = velocity of instrument, preferred frame

INSTR = angle of light beam (instrument) to the PF

in Special Relativity CMM=CKT=0

RMS approach:

-Robertson (1949)

-Mansouri &

-Sexl (1977)


A velocity-dependent LIV would cause a c/c variation at the orbital rate

Measuring KT

= 90º

= 270º

= 180º

= 0º

vCMB, velocity of

preferred frame

vINSTR, velocity of

orbiting instrument

17

210

2 KTCMBINSTR C

c

vv

KT Coefficient

0º 90º 180º 360º 270º

c/c


Why KT in Space?

Kennedy-Thorndike signal enhancement

Signal modulated at satellite orbital variation ~1.5 hr

Signal modulated at orbital velocity differences 7 km/s

Diurnal Earth rotation signal <0.30 km/s @ 24 hr

Yearly Earth orbital motion signal at 30 km/s @ 8766 hr

Disturbance reduction Microgravity

Seismic quietness

Relaxed stress due to self weight

Far away from time dependent gravity gradient noises

KT Improvement in Space:

Faster signal modulation 4 (16)

Higher velocity modulation 20 to 30

Other considerations ~ 1 to 3

Net Overall Advantage 100


History of KT measurements

KT History

R.J. Kennedy E.M. Thorndike

KT

co

effic

ien

t

10-1

10-9

10-7

10-5

10-3

10-11

STAR 1

1920 1940 1960 1980 2000 2020

Year


STAR schedule, cost and status

Schedule

Three-year development

Two-year operations

Cost

Payload: ~ $ 50M

Total Mission: ~ $140M

Concept first proposed as a MOO 2008 SMEX

Second proposal submitted in 2011.

Review pointed out some weaknesses

Science, TRL levels

Current efforts:

Bring instrument to TRL 5

Using internal resources

Contributions from partners

Mitigate weaknesses of 2011 proposal


STAR Conceptual Diagram


clock based on atomic transition

clock based on length standard

beat measurement

with

varying laboratory velocity

Modern Kennedy-Thorndike tests


STAR Optical Setup & Noise Budget

Error Source KT MM

Optical Cavity – thermal expansion

(0.1microK temp. stability, 10–9 CTE)

1×10-16 1×10-16

Optical Cavity – mirror thermal noise

(loss < 10–6)

7×10–16 7×10–16

Optical Cavity – residual gas pressure 4.2×10–19 4.2×10–19

Optical Cavity – shot noise (locking) 1.7×10–18 1.7×10–18

Optical Cavity – satellite spin rate stability

(Δω/ω < 0.025)

1×10–17 1×10–17

Optical Cavity – satellite pointing

knowledge (0.5 deg)

1×10–17 1×10–17

Total Molecular Clock 5×10–16 N/A

Frequency Shifter (comparator) 2×10–16 2×10–16

Total Error at measurement frequency

with 2 clocks

6×10–16 2×10–15

Total Random Error after 2 year

integration time (Δc/c)

7×10–18 3×10–18

MARGIN 30% 70%


Optical cavity

Key optical cavity parameters:

L/L < 10-17 at orbit and harmonics

with 2 years of data

L/L < 10-17 at twice spin period

with 2 years of data

Derived requirements:

Expansion coefficient: < 10-9 per K

Operating temperature: within 1 mK

of expansion null (~ 15°C nom)

External strain attenuation: > 1012

Stiffness: L/L < 10-9 per g, 3-axis

Implied material: ULE glass Thermo- Mechanical

isolators

Support structure

Optical couplers

ULE cavity block

(4 cavities@ 45 deg)

18 COSPAR2012 Mysore July 20 Vortrag > Autor > Dokumentname > Datum

Iodine Reference


Next steps:

set up of a compact Iodine standard

multi-pass cell

baseplate made of Zerodur (for space-

qualification and pointing stability)

Using s.q. AI-Technology

(HTWG Konstanz / EADS Astrium)

Atomic reference


Thermal noise floor of cavities

State of the art: Iodine vs. cavity

Orbital period

STAR


Thermal enclosure

Main Requirements:

Thermal stability

Stress attenuation

Launch and space compatible

Multi-can structure

Thermal performance:

Cavity L/L < 10-17 (2 yr data) at:

- orbital period and harmonics

- twice spin period

Derived requirements (2 yr average):

Thermal stability of 10-8 K at orbit

Thermal gradient ~ 10-9 K/cm at orbit

Maintain cavities temperature to 1 mK


Thermal modeling of enclosure


Strain attenuation model - FEA

Estimated strain attenuation: > 103 per can

Extrapolating to entire enclosure: > 1015

Exceeds requirement by x1000


Fundamental frequencies

The first mode of the assembly was found to be 77 Hz

First lateral mode: 77.6 Hz First axial mode: 93.9 Hz


Optical Coupling System

Control

Electronics

Length

Reference

Laser, Optical Bench

Absolute Reference

Laser, Optical Bench

Absolute Reference

Optical Fiber

Function Box

Thermally Stabilized

Fiber Conduit


STAR mission characteristics

ESPA compatible secondary payload on an EELV launch

Circular sun-synchronous ~ 650 km orbit

Launch 2015-2016

2-year mission lifetime


Optical cavity work at Stanford

1064nm

1550nm

300 mm Iodine cell


Vibration –insensitive optical cavities

STRAIN DISTRIBUTION

• Zero relative displacement at the ends of the optics axis

• Static Load applied at the points marked on the perimeter


• 1110 line R(56)32-0 is interesting

• Lock laser to the a10 HFS

• Sub-doppler detection

• Modulation Transfer Spectroscopy

(MTS)

• Natural Linewidth ~ 400KHz

• Broadened line < 1MHz

• Investigate narrower lines at ~516nm

Iodine MTS setup at Stanford


Iodine setup at Stanford


Lorentz Symmetry & Lorentz Violations

STAR: Search for a Lorentz violation at the level of 3×10-18 to 10-17

A factor of 100 to 300 better than ground experiments

Both orientation & velocity dependent violations

LORENTZ SYMMETRY & LORENTZ VIOLATIONS

Time dilation: equal clocks tick at different rates

Length contraction: equal rods have different lengths

Lorentz violations would exist outside of a universal preferred

reference frame, the only frame in which c is truly isotropic


Questions?

Other possibilities for violations: • Birefringence of pulsed light

• Cosmic rays

• Spectroscopy of anti-matter

• Gamma ray dispersion

• Neutrino oscillations

• Spin dependent effects……

Kostelecky, Scientific American, 2002

star: space-time asymmetry research testing lorentz ... · c v v c c v v c c instr cmb mm instr kt...

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