Page 1
Francis Everitt
Testing Einstein with Orbiting Gyroscopes
[+ some remarks on STEP]
Symposium on Geometry & the Universe
Stony Brook20-21 October 2005
Page 2
Roadmap for a Gravity Probe
GP-B & the drama of launch
Basic experiment concept
Near Zeroes & why we need them
On-orbit
Dither & aberration: 2 secrets of GP-B
Calibration/verification
Wider lessons, with some remarks on STEP
Page 3
Testing Einstein – NASA’s Contributions
Gravity Probe BTwo new effects with ultra-accurate gyroscopes
Laser Ranging: toreflectors on Moon (1968+)
The Gravity Probe Aclock experiment (1976)
Radar Time Delay: to Viking Lander on Mars (1976)to Cassini spacecraft
around Saturn (1999+)
Page 4
The Relativity Mission ConceptThe Relativity Mission Concept
"If at first the idea is not absurd, then there is no hope for it."
-- A. Einstein
( ) ( ) ⎥⎦⎤
⎢⎣⎡ −⋅+×= ωRωRvR 23232
323
RRcGI
RcGMΩ
• Basic formula:
• Oblateness correction: * Dan Wilkins (Physics), John Breakwell (Aero/Astro)
Leonard Schiff
Page 5
Launch: April 20, 2004 – 09:57:24
Page 6
Delta II Accuracy - 50%x
Boeing & Luck -- A Near Perfect Orbit
Orbit achieved ~100 mfrom the pole
Required Final Orbit Area
Delta II Nominal Accuracy
Page 7
Gyro I: Overview
• Electrical Suspension
• Gas Spin-up
• Magnetic Readout "Everything should be made as simple as possible, but not simpler."
-- A. Einstein
Page 8
Gyro II: Suspension Characteristics• Operates over 9 orders of magnitude of g levels• Range of motion within cavity (15,000 nm) for:
- science (centered in cavity)- spinup (offset to spin channel ~ 11,000 nm)- calibration (offset, 200 nm increments)
• Alignment (roll phased voltage variation)
• thickness of sheet of paper ~ 100,000 nm• diameter of atom ~ .1 to .5 nm Nanometer references
Forward GSS boards
Aft GSS
Analog ground-based version:John Nikirk, Dick Van Patten & John Gill (Aero/Astro)
Digital flight version:* Bill Bencze (EE) & joint Stanford-
Lockheed Martin team, including 3 Aero/Astro, 2 EE PhDs & 6 undergraduates (4 departments)
Page 9
Gyro III: The Spin-up Problem(s)
"Any fool can get the steam into the cylinders; it takes a clever man to get it out again afterwards." -- G. J. Churchward, ~ 1895
Differential Pumping Requirement
spin channel ~ 10 torr (sonic velocity)
electrode area < 10-3 torr
Torque Switching Requirement
Tr/Ts < Ω0 ts ~ 10-14
Ts, Tr - spin & residual cross-track torquests - spin time; Ω0 - drift requirement
* Dan Bracken (Physics)Don Baganoff (Aero/Astro)+ refinements by John Lipa, John
Turneaure & several students
Page 10
Gyro IV: London Moment Readout
Noise performanceDC trapped flux < 10-6 gaussAC shielding > 1012
Centering stability < 50 nm
Requirement
“SQUID” 1 marc-s in 5 hours
Jim Lockhart (* Physics & SFSU)Barry Muhlfelder (HEPL)
* Greg Gutt & * Ming Luo (EE) Bruce Clarke (HEPL)Terry McGinnis (Lockheed)
+ many more
Page 11
The GPThe GP--B Cryogenic PayloadB Cryogenic Payload
Payload in ground testing at Stanford, August 2002
* Peter Selzer (Physics) - porous plug for space* John McCuan (Math) - helium tidal studies
Two notable doctoral dissertations:
Page 12
The GP-B Flight Probe
Assembled probe at Lockheed prior to shipment to Stanford
Lockheed Martin Lead: Gary Reynolds
Page 13
"Design a precision apparatus as if it were made of jello – if it is stable then, it may just work."
-- H.A. Rowland, ~1900
Alignment, Bonding & Cryogenic Stability
Assembly & alignment: Doron Bardas (Physics), * Robert Brumley (EE!)
Silicate bonding: Jason Gwo (Berkeley Chemistry!)
Page 14
1 marcsec/yr = 3.2 × 10-11 deg/hr
Why go to space?
0.1 marcsecis the
width of a human hair
seen from 100 miles
Gyroscope drift≤ 0.05 marcsec/yr
Readout error effect≤ 0.08 marcsec/yr
Guide star proper motion uncertainty≤ 0.09 marcsec/yr
)
Six Crucial Near Zeros1) rotor inhomogeneities
2) "drag-free"
3) rotor asphericity
4) magnetic field
5) pressure
6) electric charge
Near Zeros & Why We Need Them
GP-B Co-PIs:
Brad ParkinsonDan DeBraJohn Turneaure
Page 15
GP-B rotor ~3 x 10-7
drift-rate for the drag-free GP-B< 0.01 marc-s/yr
Drift-rateTorqueMoment of Inertia
Ω = T / Iωs
T = M ƒ δrI = 2Mr2 /5
ƒ
δr
requirement Ω < Ω0 ~ 0.1 marc-s/yr
δrr ƒ < vs Ω0
25
vs = ωsr = 950 cm/s (80 Hz)
(1.54 x 10-17 rad/s)
On Earth (ƒ = g)
Standard satellite (ƒ ~ 10-8 g)
GP-B drag-free (ƒ ~ 10-12 gcross- track average)
< 5.8 x 10-18
< 5.8 x 10-10
< 5.8 X 10-6δrr
δrr
δrr δr
r
Drag-free eliminates mass-unbalance torque -- and key to understanding/quantification of other support torques
(ridiculous)
(unlikely)
(straightforward)
Mass-Unbalance, Drag-Free: 1st & 2nd Near Zeros
Page 16
STANFORDThorwald van HooydonkFrane MarceljaVictor Graham (visitor)
Self-aligning lapsUniform rotation-rate, pressure6 combinations of directions, reversed2 & 2 every 6 secondsContinuous-feed lapping compoundControlled pHInterested, skilled operators!
MSFCWilhelm AngeleJohn RasquinEd White
Asphericity: 3rd Near Zero -- Making
Page 17
Roundness Measurement to ~ 1 nm
Asphericity: 3rd Near Zero -- Measuring
* Grace Chang (A/A)
* Rebecca Eades (Math)
* Benjamin Lutch (undeclared)
* Dave Schleicher (Comp Sci)
* Dieter Schwarz (EE)
* Michael Bleckman (Hamburg)
* Christoph Willsch (Göttingen)
Students 1988 - 1992
Page 18
Ultra-low Magnetic Field: 4th Near Zero
flux = field x area
successive expansions stable field levels ~ 10-7 gauss
10-12 [ =120 dB! ] ac shielding through combination of cryoperm, lead bag, local superconducting shields & symmetry
Superconducting Lead Bag Technology
* Blas Cabrera (1976 Physics PhD)Dewar bag
Jim Lockhart (* Physics, SFSU),Mike Taber (* Physics, HEPL),Chuck Warren, Dave Murray
Magnetic material testing John Mester, Grace Brauer
Page 19
Mission Operations Center
Anomaly Room
On-Orbit: GP-B Mission Operations
Marcie Smith (NASA Ames)Kim Nevitt (NASA MSFC)Rob Nevitt (NavAstro)Brett Stroozas (NavAstro)Lewis Wooten (NASA MSFC)Ric Campo (Lockheed Martin)Jerry Aguinado (LM)
+ many more
Program Manager – Gaylord Green
Page 20
Initial Gyro Levitation and De-levitation using analog backup system
GP-B Gyro On-Orbit Initial Liftoff
0 2 4 6 8 10 12-40
-30
-20
-10
0
10
20
30
Time (sec)
Pos
( µm
)
Gyro2 Position Snapshot, VT=135835310.3
Initial suspension Suspension
release
Gyro “bouncing”
Rot
or P
ositi
on (µ
m)
Time (sec)
David Hipkins (HEPL)* Yoshimi Ohshima (A/A)Steve Larsen (LM)Colin Perry (LM)
+ many more!
Page 21
Suspension Performance On-Orbit
0 500 1000 1500 2000 2500 3000-6
-4
-2
0
2
4
G3
X p
os (n
m)
seconds
Rep. position profile in science mode (not drag free), GP-B Gyro3 (VT=142,391,500)
0 0.05 0.1 0.15 0.2 0.2510-12
10-11
10-10
10-9
10-8
Mag
(nm
)
Freq (Hz)
Single sided FFT, GP-B Gyro3 (VT=142,391,500)
Measurement noise –0.45 nm rms
Gyro position –non drag-free gravity gradient effects in Science Mission Mode
Noise floor
Page 22
Gyro Readout Performance On-Orbit I
SQUIDOutput
(V)
Zero to peak ~ 100 arc/sec
Bruce Clarke, Barry Muhlfelder + the team
Page 23
Mass Unbalance & : 1st Near Zero
Gyro # 1 @ 3 Hz
36-hour Polhode Period
0 20 40 60 80 100 120 140 160 1800
1
2
3
4
5
6
7
Elapsed Minutes since Vt = 147228407.1 s
Am
plitu
de (n
m)
Sample Polhode Period, Gyro 1
∆ II
< 2x10-6
Gyro # 1 @ 79.3858 Hz
Mass Unbalance (nm)
6.03.34.46.9On-orbit data
13.516.814.518.8Prelaunch estimate
4321Gyro #
∆II( (
Mac Keiser & Paul Shestople + the team
Page 24
Drag-Free: 2nd Near Zero
Demonstrated accelerometer (drag free) performance better than 10-11 g DC to 1 Hz
10-4
10-3
10-2
10-1
10010
-12
10-11
10-10
10-9
10-8
10-7
Drag-free control effort and residual gyroscope acceleration (2004/239-333)
Con
trol E
ffort
(g)
Frequency (Hz)
Gyro CE inertialSV CE inertial
Thruster Force
Residual gyro acceleration
Acc
el(g
)
Drag-free on
Drag-free offAcc
eler
atio
n (n
g)
Acc
eler
atio
n (g
)
Lockheed Martin Attitude/Translational Control Design Lead: Jon Kirschenbaum
Toward guide star Cross track
Page 25
* John Bull + * Jen Heng Chen (A/A)
Boil-off, Altitude & Thrust --A Subtle Combination
A very different control system– Continuous flow proportional thrusters– Reynolds' # ρvl/η ~ 10!! -- flowing like honey
Thrust calibration:
Lockheed Martin thrusters:
* Yusuf Jafry (A/A) with LM team
Jeff Vanden Beukel
He specific impulse vs.mass flow rate
Page 26
Ultra-low Pressure: 5th Near ZeroLow Temperature Bakeout (ground demonstration)
Gyro spindown periods on-orbit (years)
Gyro #1 ~ 50 15,800
Gyro #2 ~ 40 13,400
Gyro #3 ~ 40 7,000
Gyro #4 ~ 40 25,700
before bakeout after bakeout
pressure < 1.5 x 10-11 torr(+ minute eddy-current damping effects?)
The Cryopump
John Lipa, John Turneaure (Physics) + students; adsorption isotherms for He at low temperature,* Eric Cornell, (undergraduate honors thesis)
Page 27
Discharge of Gyro #1
Rotor Electric Charge: 6th Near Zero
Ti Steering Electrode
Typical charge rates ~ 0.1 mV/day
Saps Buchman, Dale Gill, Bruce Clarke (Physics, HEPL) + * Brian DiDonna & * Ted Quinn (Physics)
Page 28
Physical length 0.33 mFocal length 3.81 mAperture 0.14 mAt focal planeImage dia. 50 µm0.1 marc-s 0.18 nm
Some dimensions
Beam splitter assembly (detail)
Star Tracker I: ConceptDesign Lead: Don Davidson, Davidson Optronics, Inc. & OID
Page 29
Star Tracker II: Under Test
Artificial Star #3
Detector Package
John Lipa, Jason Gwo, Suwen Wang(Physics, HEPL), Bob Farley (Lockheed),John Goebel (NASA Ames)
Telescope development* Mo Badi (Ap Phys), * Dana Clark (ME),* Chris Cumbermack (Pre-med!), * Howard Shen (EE) + 6 othersArtificial Star #3* Ted Acworth, * Rob Bernier
Si Diode Detector
Page 30
Star Tracker III: Acquiring Star
Drive-in time ~ 110 s
RMS pointing ~ 90 marc-s
Page 31
IM Peg (HR 8703) Guide Star Identification
IM PegGuide Star
HR Peg(acquired)
NhS1(acquired)
Palomar Star Map
Preliminary HR 8703 Positions for Peak of Radio BrightnessSolar System Barycentric, J2000 Coordinate System
(Right Ascension - 22h53m) x 15 cos(Dec) (mas)3250032550326003265032700
Dec
linat
ion
- 16o 5
0' 2
8'' (
mas
)
250
300
350
400
450
500
550
16.9 Jan 97 18.9 Jan 97
30.0 Nov 97 21.9 Dec 9727.9 Dec 97 1.8 Mar 98
12.5 Jul 98 8.4 Aug 9817.3 Sept 98 13.8 Mar 99
15.6 May 99 19.3 Sept. 99
15.0 Dec 91
22.4 June 9313.2 Sept 93
24.3 July 94
10.0 Dec 99 15.6 May 00
7.3 Aug 00 6.1 Nov 007.1 Nov 00
29.5 June 0122.0 Dec 01
14.7 Apr 02
20.2 Oct 01
Very Large Array, Socorro, New Mexico
• Optical & radio binary star• Magnitude - 5.7 (variable)• Declination - 16.84 deg • Proper motion measured by
SAO using VLBI
Page 32
Ground-based & Space Observations of IM Peg
Through GP-B, IM Peg will be most completely characterized
star in the entire heavens!GP-B flight data (peaked toward red)
G. Henry's ground-based data (visible light)
John Goebel (NASA Ames)Suwen Wang (Stanford)Michael Ratner (SAO) Greg Henry (U of Tenn.)Jeff Kolodziejczak
(NASA Marshall Center)Svetlana Berdyugina
(ETH, Switzerland)
Page 33
gyro output
scale factors matched for accurate subtraction
Aberration (Bradley 1729) -- Nature's calibrating signal for gyro readout
telescope output
Dither -- Slow 30 marc-s oscillations injected into pointing system
Dither & Aberration: Two Secrets of GP-B
Continuous accurate calibration of GP-B experiment
Orbital motion varying apparent position of star (vorbit/c + special relativity correction)
Earth around Sun -- 20.4958 arc-s @ 1 year periodS/V around Earth -- 5.1856 arc-s @ 97.5 min period
Page 34
A. Initial orbit checkout (128 days)re-verification of all ground calibrations [scale factors, tempco’s etc.]
disturbance measurements on gyros at low spin speed
B. Science Phase (353 days)exploiting the built-in checks [Nature's helpful variations]
C. Post-experiment tests (46 days)refined calibrations through deliberate enhancement of disturbances, etc. […learning the lesson from Cavendish]
3 Phases of In-flight Verification
Mac Keiser, * Ed Fei (undeclared), Michael Heifetz, Jie Li, Yoshimi Ohshima (* A/A), * Michael Salomon (A/A), David Santiago (* Physics), Alex Silbergleit, * Sara Smoot (A/A), Vladimir Solomonik, Karl Stahl (* ME) + Bill Bencze, Peter Boretsky, Bruce Clarke, Dan DeBra, Barry Muhlfelder, Paul Shestople, John Turneaure, Suwen Wang, Paul Worden
Data Reduction Team:
Page 35
Wider Significance of the GP-B ExperiencePhysics-Aero/Astro collaboration from the start
'Near Zero' in space
Some technologies Drag-freePointingCryogenics
Integrated Science/Operations team
University/industry/NASA collaboration
Page 36
Satellite Test of the Equivalence Principle
Dz
time
Orbiting drop tower experiment
Dz
Dz
time
F = ma mass - the receptacle of inertiaF = GMm/r2 mass - the source of gravitation
Newton’s Mystery
* More time for separation to build* Periodic signal
Page 37
Space > 5 Orders of Magnitude Leap
10-18
10-16
10-14
10-12
10-10
10-8
10-6
10-4
10 -2
1700 1750 1800 1850 1900 1950 2000
Newton
Bessel
Dicke
Eötvös
Adelberger, et al.LLR
STEP
“Mission Success”
α effect (min.)
DPV runaway dilaton (max.)
.
1 TeV Little String Theory
~ 5 x 10-13
100
Microscope
Page 38
Research Center Partners Stanford University
University of Birmingham, UK
ESTEC
FCS Universität, Jena, Germany
Imperial College, London, UK
Institut des Hautes Études Scientifiques, Paris ONERA, Paris, France
PTB, Braunschweig, Germany
Rutherford Appleton Laboratory, UK
University of Strathclyde, UK
Universitá di Trento, Italy
ZARM, Universität Bremen, Germany
22”
STEP International Collaboration
Page 39
Some Elements of the STEP Mission
2-axis tilt platform
bearing under test
assembled flight instrument
magnetic bearing
differential SQUID readout SQUID assembly
Page 40
Test Mass Shape & Composition
Material Z N N + Zµ
− 1⎛⎝⎜ ⎞
⎠⎟103
Baryon Number
N −Zµ
Lepton Number
Z Z −1( )µ N + Z( )
13
Coulomb Parameter Be 4 5 -1.3518 0.11096 0.64013Si 14 14.1 0.8257 0.00387 2.1313Nb 41 52 1.0075 0.11840 3.8462Pt 78 117.116 0.18295 0.20051 5.3081
Dimensions give 6th order insensitivity
to gravity gradient disturbances from
spacecraft -- µm tolerances
Damour C&QG 13 A33 (1996)
Test masses as ‘different’ as possible
Page 41
Helium Tide Control
void sizes 100 to 1000 nm
confines He even in 1g
passed cryogenic shake test
250 mm
MEarth
ωorbitr
x
Rwe
ll
y
mA
mB
rθ
He
Silica Aerogel Constraint
Page 42
STEP: a Landmark in Fundamental PhysicsWhat Physics has done for Space?
© Alan Bean, courtesy Greenwich Workshop Inc . What Space can do for Physics?
Newton
Bessel
Dicke
Eötvös
Adelberger & LLR
STEP10–18
1700 1800 1900 2000
10–16
10–14
10–12
10–10
10–8
10–6
10–4
10–2
10 0
“I guess one of the reasons we got here today was because of a gentleman named Galileo….who made a rather significant discovery about falling objects in gravity fields.”
--David Scott
STEP (and probably only STEP) has the potential of discovering new forces in Nature that would tell us a lot about why the universe is as it is, and what its ultimate state will be.”
--Thibault Damour