gravity probe b reaches the science...
TRANSCRIPT
![Page 1: Gravity Probe B Reaches the Science Phaseirfu.cea.fr/Phocea/file.php?file=Seminaires/841/t841_1.pdf · (a) final 60 - 80 Hz spins (b) ATC tuning (c) ‘coarse’ gyro alignment l](https://reader033.vdocuments.site/reader033/viewer/2022060608/605fb461a13c3c466b1e42c4/html5/thumbnails/1.jpg)
Page 1
Gravity Probe BReaches the
Science Phase
27 September 2004
R. Torii
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The Relativity Mission ConceptThe Relativity Mission Concept
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Main GP-B Systems
Gyroscope Telescope Science Instrument
Cryogenic Probe Payload Space Vehicle
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• Two modes: A) Displacement, turn off active force control of rotor position “flying spacecraft around rotor” and B) Accelerometer, fire thrusters based on commanded forces on rotor
• Electrostatic system used to control position of gyroscope rotors provides sensor for both modes
• Proportional thrusters offer better control over on-off thrusters
• Gas supply for thrusters provided by boil off of liquid helium cryogen
GP-B Proportional ThrustersGP-B Proportional Thruster Schematic
Drag-Free Implementation
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GP-B Launch: April 20, 2004 -- 09:57:24
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Delta II Accuracy - 50%x
The Actual Orbit - Delta II
Orbit Achieved ~100 meters
From the pole
Required Final Orbit Area
Delta II Nominal Accuracy
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GP-B Launch: April 20, 2004 -- 09:57:24
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GP-B Set-up Highlights
l Weeks 1 - 4(a) SQUID set-up (b) telescope set-up (c) gyro suspension (d) low-T bakeout e)
first drag-free
l Weeks 5 - 8(a) ‘flux-flush’ (b) 0.3 Hz spin (c) lock on guide star (d) charge control
l Weeks 9 - 12(a) increase S/V roll rate (b) reboot flight computer (c) 3 Hz spins
l Weeks 13 - 16(a) final 60 - 80 Hz spins (b) ATC tuning (c) ‘coarse’ gyro alignment
l Weeks 17 - 19(a) final 77.5 s period roll (b) ATC tuning (c) fine (~ 5 arc-s) gyro alignment
GP-B Launch: 20 April 2004 – 09:57:24
Entered Science Phase: 27 August 2004 – 12:00:00
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On-Orbit GP-B Technology Demonstrations
Electrostatic Positioning System –– 0.45 nm rms position noise
Gyroscopes –– Spin-down < 1 µHz/hourCharging < 0.3 pC/day
Charge Control System –– < 5 pC controlGSS Charge Measurement < 1 pC rmsUV Charge Discharge Rate > 0.3 pC/min
SQUID Readout –– < 3x10-5 Φ0/√Hz at 0.5 rpmBeats requirement, all SQUIDS
Magnetics –– AC attenuation ~ 1012
dc trapped flux ~ 1 µG
Telescope System –– < 34 marcsec/√Hz readout noise
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Technologies Demonstrated On-Orbit by GP-B
Orbit Accuracy –– Inclination error < 0.00007 deg, (< 100m)orbit average to star < 0.004 deg
Proportional Helium Thruster –– 1 – 10 mN/thruster
Drag Free Control –– < 10 nm vehicle positionmean cross-track average < 10-11 g
GPS System –– > 95% lock ratio at all roll ratesTime transfer accuracy < 3 µsec UTC to vehicle timeNavigation accuracy < 7 m rms, < 0.7 cm/s
Superfluid Flight Dewar (2400 l ) –– Lifetime ~ 15 months, Porous plug Dynamic flow range 2-18 mg/s
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Gyro #4 Analog Backup Levitation and De-levitation
GP-B Gyroscope Suspension
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Position Measurement Performance
0 500 1000 1500 2000 2500 3000-6
-4
-2
0
2
4
G3 X
pos (
nm
)
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
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Gravity Gradient Measured by GyroscopesGyro #3, #4 Suspension Control Effort (2+ orbits)
Raw gravity gradient resolution < 10-9 g
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Discharge of Gyro #1
GP-B Charge Management
Discharge of Science Gyros Demonstrated
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Superconducting SQUID Readout
•
A spinning superconductor develops a
magnetic “pointer” aligned with its spin axis
“SQUID” – ultra sensitive low noise magnetometer
reads angle to 1 milliarc second in 5 hours
Output of SQUID low-pass filter for caged gyros over 22 hours
)(GssLe
mcB ωωωωωωωω 71014.1
2 −−−−××××−−−−====−−−−====
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SQUID Readout Noise Beats Spec(PSD (PSD ΦΦΦΦΦΦΦΦ00//√√Hz vs Hz)Hz vs Hz)
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Polhode Motion
Gyro # 1
Spin Speed – 3 Hz
July 4 - 7, 2004
36-hour Polhode Period
Fpolhode = ∆ I/I cos(θ)Fspin
=> ∆ I/I < 2x10–6
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Gyro #4 London Moment Readout Data
SQUIDOutput
(V)
Zero to peak ~ 100 arc/sec
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Drag-Free Performance
Drag-free on
Drag-free off
Twice orbital term reduced by > 100
Suppression of Z axis gravity gradient acceleration
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GP-B Telescope Pointing
Telescope Detector Signals Telescope Detector Signals Telescope Detector Signals Telescope Detector Signals
from IM Peg Divided by Rooftop Prismfrom IM Peg Divided by Rooftop Prismfrom IM Peg Divided by Rooftop Prismfrom IM Peg Divided by Rooftop Prism
-2
0
2
4
6
8
10
12
14
0 100 200 300 400 500 600
Sample SequenceSample SequenceSample SequenceSample Sequence
ST_SciSlopePX_B ST_SciSlopeMX_B
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Acquiring Guide Star
Drive in time ~ 110 s
RMS pointing ~ 80 marc-s
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HR 8703 (IM PEG) Guide Star Identification
IM Peg
Guide 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
De
clin
atio
n -
16
o 5
0' 2
8''
(ma
s)
250
300
350
400
450
500
550
16.9 Jan 9718.9 Jan 97
30.0 Nov 97 21.9 Dec 9727.9 Dec 97 1.8 Mar 98
12.5 Jul 98 8.4 Aug 98
17.3 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 00
7.1 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 bySAO using VLBI
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The Science Mission
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STEP
27 September 2004
R. Torii
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Satellite Test of the Equivalence Principle
Dz
time
Orbiting drop tower experiment
Dz
Dz
time
F = ma mass - the receptacle of inertia
F = GMm/r2 mass - the source of gravitationNewton’s Mystery {
* More time for separation to build
* Periodic signal{
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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”
αeffect (min.)
{
DPV runaway dilaton (max.)
.
1 TeV Little String Theory
~ 5 x 10-13
100
Microscope
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Can Gravity Be Made to Fit?
• Unification in physics – through fields (Maxwell), geometry (Einstein),
symmetries and new particles (electroweak theory)….and
now (?) supersymmetry and strings
• The problems of gravity – quantization; 10-42;
cosmological constant
Λ
(10-120!); equivalence
• Partial steps toward Grand Unification– Strings/supersymmetry in early Universe scalar-tensor theory, not Einstein’s
– Damour - Polyakov: small
Λlong range equivalence-violating dilaton
• EP violations inherent in all known GU theories
– Runaway dilaton theories
– 1 TeV Little String Theory (Antoniadis, Dimopoulos, Giveon)
STEP’s 5 orders of magnitude take physics into new theoretical territory
Gravity
Strong Nuclear Force
Weak Nuclear Force
ElectroMagnetism
⇒
⇒
(Witten)
(Damour, Piazza, Veneziano) { {η >> 10-18
up to 10-14η
~ 10-15
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Differential Accelerometer Science Instrument
Payload Space Vehicle
Significant technology advances
from SCR/RDR 1999 to SMEX 2002
DA Package
Dewar
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Requirement Satisfied by analysis using measured performance of
GPB SQUID and coil Key Technology Development
Ø (1972 –) Concept proven. Acceleration
sensitivity requirement met. (H.
Paik, P. Worden, S. Vitale)
Ø (1999) Coil inductance L(x) design verified.
Ø (2000) Flight coil designed, (2001) built.
Ø Manufacturing
Ø (2004) GPB SQUID readout performance
verified in polar orbit (SAA passes).
Ø Plan to develop with Strathclyde/Jena
Ø Cryogenic electronics development
Ø Verify flight SQUID position sensitivity
mass mass
SQUID
pancake coil
Magnetic
Model
Modular design
allows coil form to be processed
independently
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Meets requirement on aligned mass motion
while preserving acceleration sensitivity Key Technology Development
Ø (1986) Concept proven (P. Worden). Bearing
performance limited by
Ø Manufacturing
Ø Trapped magnetic flux creep
Ø (1998) Distance between bearing and test masses REDUCED by factor of 10
Ø (2001) Manufactured niobium thin film
bearing meeting requirements
Ø (2001) Attached superconducting cables
Defines axis of
measurement
Aligns motion
of test masses
100 µm
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Requirement Each test mass surrounded by
thirteen capacitance electrodes
Key Technology Development
Ø (2000) Capacitance electrode baseline
configuration by Stanford/ONERA
Ø (2001) Manufactured thin film electrodes
isolated by channels
Ø (2004) GPB UV charge control verified in
polar orbit (SAA passes)
Ø Plan to develop with Imperial College better electrostatic model and hardware
Ø Overlay magnetic coils with gold
Ø Develop dielectric to isolate gold coating
Ø Finite element model
Electric Model
FFTCAP (MIT)
MESH:
13 Plates + Mass
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Requirement Met by optimal test
mass shape and positioning capabilityKey Technology Development
Ø Test Mass Fabrication
Ø (1993 -) Test mass design and verification by
Strathclyde.
Ø (2002) Test mass density homogeneity verification
by Birmingham.
Ø (2002) Test mass manufacturing capability by PTB
and Axsys, Inc.
Ø Test Mass Positioning Capability
Ø (2002) Capacitive position sensor by ONERA.
Ø Verify flight magnetic bearing radial force.
Ø Alignment of capacitance sensors to bearing.
Ø Axial positioning using SQUID pickup coil.
Ø Cryogenic electronics development.
FiberSuspension
x, y, z, θz
z
+ 2 axis tilt
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STEP Technology Development
Plan 27 month plan enables
prototype Payload testingTechnology Development Goals
Ø Demonstrate maturity of STEP enabling technologies
Ø Define STEP Payload verification method
Ø Organize STEP error analysis to support Payload verification
0
1 2 3 4 5 6 7 8 9 10 11 12 13 1 4 15 16 1 7 18 19 20 21 22 2 3 2 4 25 26 27 28 29 30 31 32
0
30 00
60 00
90 00
120 00
150 00
180 00
210 00
240 00
1 2 3 4 5 6 7 8 9 10 11 1 2 13 1 4 15 16 17 18 19 20 2 1 22 2 3 2 4 25 2 6 27 28 29 30 31 32
m o n th s
cu
mu
lati
ve
fu
nd
ing
($
K)
Aerogel Manufacture Spec.
Inner Accelerometer Full Accelerometer: DA
Instrument Spec.
Dewar/Probe Spec. Dewar Build
Probe/DAP Build
Payload I&T
Large Scale Aerogel Test
Electronics Development
$3M $13M
Payload Systems Eng.
Spacecraft Systems Eng.
PDR27 Month Technology Development
Phase B
Incremental Prototyping
Engineering Hardware