Gravity Probe B, launched 20 April 2004, is a space experiment testing two fundamental predictions of Einstein's theory of general relativity (GR), the geodetic and frame-dragging effects, by means ...of cryogenic gyroscopes in Earth orbit. Data collection started 28 August 2004 and ended 14 August 2005. Analysis of the data from all four gyroscopes results in a geodetic drift rate of -6601.8±18.3 mas/yr and a frame-dragging drift rate of -37.2±7.2 mas/yr, to be compared with the GR predictions of -6606.1 mas/yr and -39.2 mas/yr, respectively ("mas" is milliarcsecond; 1 mas=4.848×10(-9) rad).
Gravity Probe B cryogenic payload Everitt, C W F; Parmley, R; Taber, M ...
Classical and quantum gravity,
11/2015, Letnik:
32, Številka:
22
Journal Article
Recenzirano
Odprti dostop
This paper gives a detailed account of the Gravity Probe B cryogenic payload comprised of a unique Dewar and Probe. The design, fabrication, assembly, and ground and on-orbit performance will be ...discussed, culminating in a 17 month 9 day on-orbit liquid helium lifetime.
A spaceflight electrostatic suspension system was developed for the Gravity Probe B (GP-B) Relativity Mission's cryogenic electrostatic vacuum gyroscopes which serve as an indicator of the local ...inertial frame about Earth. The Gyroscope Suspension System (GSS) regulates the translational position of the gyroscope rotors within their housings, while (1) minimizing classical electrostatic torques on the gyroscope to preserve the instrument's sensitivity to effects of General Relativity, (2) handling the effects of external forces on the space vehicle, (3) providing a means of precisely aligning the spin axis of the gyroscopes after spin-up, and (4) acting as an accelerometer as part of the spacecraft's drag-free control system. The flight design was tested using an innovative, precision gyroscope simulator Testbed that could faithfully mimic the behavior of a physical gyroscope under all operational conditions, from ground test to science data collection. Four GSS systems were built, tested, and operated successfully aboard the GP-B spacecraft from launch in 2004 to the end of the mission in 2008.
The results of the Gravity Probe B relativity science mission published in Everitt et al (2011 Phys. Rev. Lett. 106 221101) required a rather sophisticated analysis of experimental data due to ...several unexpected complications discovered on-orbit. We give a detailed description of the Gravity Probe B data reduction. In the first paper (Silbergleit et al Class. Quantum Grav. 22 224018) we derived the measurement models, i.e., mathematical expressions for all the signals to analyze. In the third paper (Conklin et al Class. Quantum Grav. 22 224020) we explain the estimation algorithms and their program implementation, and discuss the experiment results obtained through data reduction. This paper deals with the science data preparation for the main analysis yielding the relativistic drift estimates.
A simple pre-flight strategy of the Gravity Probe B (GP-B) data analysis has evolved in the elaborate multi-level structure after the discovery of the complex polhode motion, and of the patch effect ...torques. We describe a cascade of estimators (filters) that reduce the science data (SQUID and telescope signals) to the estimates of the relativistic drift rates. Those estimators, structured in two “floors”, are based on the polhode-related models for the readout scale factor and patch effect torque. Results of the 1
st
Floor processing—gyro orientation profiles—manifest clearly the strong geodetic effect but also the presence of classical torque. Modeling of the patch effect torque at the 2
nd
Floor provides a successful compensation of the torque contributions, and leads to consistent estimates of the relativistic drift rates.
Gravity Probe B Data Analysis Everitt, C. W. F.; Adams, M.; Bencze, W. ...
Space science reviews,
12/2009, Letnik:
148, Številka:
1-4
Journal Article
Recenzirano
This is the first of five connected papers detailing progress on the Gravity Probe B (GP-B) Relativity Mission. GP-B, launched 20 April 2004, is a landmark physics experiment in space to test two ...fundamental predictions of Einstein’s general relativity theory, the geodetic and frame-dragging effects, by means of cryogenic gyroscopes in Earth orbit. Data collection began 28 August 2004 and science operations were completed 29 September 2005. The data analysis has proven deeper than expected as a result of two mutually reinforcing complications in gyroscope performance: (1) a changing polhode path affecting the calibration of the gyroscope scale factor
C
g
against the aberration of starlight and (2) two larger than expected manifestations of a Newtonian gyro torque due to patch potentials on the rotor and housing. In earlier papers, we reported two methods, ‘geometric’ and ‘algebraic’, for identifying and removing the first Newtonian effect (‘misalignment torque’), and also a preliminary method of treating the second (‘roll-polhode resonance torque’). Central to the progress in both torque modeling and
C
g
determination has been an extended effort on “Trapped Flux Mapping” commenced in November 2006. A turning point came in August 2008 when it became possible to include a detailed history of the resonance torques into the computation. The East-West (frame-dragging) effect is now plainly visible in the processed data. The current
statistical uncertainty
from an analysis of 155 days of data is 5.4 marc-s/yr (∼14% of the predicted effect), though it must be emphasized that this is a preliminary result requiring rigorous investigation of systematics by methods discussed in the accompanying paper by Muhlfelder et al. A covariance analysis incorporating models of the patch effect torques indicates that a 3–5% determination of frame-dragging is possible with more complete, computationally intensive data analysis.
The Gravity Probe B (GP-B) Relativity Mission is a fundamental physics experiment to test Einstein’s theory of General Relativity based on observations of spinning gyroscopes onboard a satellite in a ...near-polar, near-circular orbit at an altitude of about 640
km around the Earth. The GP-B mission was designed to test two predictions of Einstein’s theory, the geodetic effect and the frame-dragging effect, to an accuracy better than 5
×
10
−4
arcsec/yr. Drag-free control technology is implemented in the GP-B translation control system to minimize support forces and support induced torques on the gyroscopes. A Global Positioning System (GPS) receiver onboard the GP-B satellite provides real-time position, velocity and timing data. The GP-B orbit is determined on the ground based on the 3-axis GPS position data and verified independently with ground-based laser ranging measurements. This paper describes the design and implementation of the drag-free translation control and orbit determination system of the GP-B satellite. The on-orbit performance of the drag-free translation control system satisfies the requirements of the GP-B science experiment. The residual accelerations from the gyroscope control efforts are less than 4
×
10
−11
m/s
2 (along the satellite roll axis) and less than 2
×
10
−10
m/s
2 (transverse to the satellite roll axis) between 0.01
mHz and 10
mHz in inertial space. The non-gravitational acceleration along the satellite roll axis, including a nearly constant component (which is kept below 1
×
10
−7
m/s
2) and a sinusoidal component (whose amplitude varies from about 5
×
10
−7
m/s
2 to less than 1
×
10
−8
m/s
2), causes the gyroscope spin axis to drift less than 9
×
10
−5
arcsec/yr. The orbit determination system is found to provide overlapping orbit solution segments having RMS (root mean square) position and velocity errors of a few meters and a few mm/s, well within the RMS mission requirements of 25
m and 7.5
cm/s.
Presented here is a hybrid digital/analog electrostatic suspension control system for the NASA/Stanford University Gravity Probe B Relativity Mission’s science gyroscopes. An adaptive LQE algorithm, ...called Authority-on-Demand (AOD), has been developed to meet the high dynamic range requirements for mission’s electrostatic suspension, while minimizing suspension induced torques on the rotor. AOD is novel because it uses plant state estimates, rather than plant parameter estimates, as inputs for adaptation. In addition minimizing disturbance torques on the gyroscope, this suspension system can also maximize and control disturbances torques to perform a post spin-up alignment of the gyroscope spin axes. A backup all-analog proportional-derivative (PD) controller subsystem is provided to maintain control of the rotor in the event of computer faults/radiation induced upsets. A precision mechanical simulation of the gyroscope’s capacitive interface and dynamic response is used to verify performance of the overall system.
The Gravity Probe B mission provided two new quantitative tests of Einstein's theory of gravity, general relativity (GR), by cryogenic gyroscopes in Earth's orbit. Data from four gyroscopes gave a ...geodetic drift-rate of −6601.8 18.3 marc-s yr−1 and a frame-dragging of −37.2 7.2 marc-s yr−1, to be compared with GR predictions of −6606.1 and −39.2 marc-s yr−1 (1 marc-s = 4.848 × 10−9 radians). The present paper introduces the science, engineering, data analysis, and heritage of Gravity Probe B, detailed in the accompanying 20 CQG papers.
This article demonstrates experimental results of a thermal control system developed for ST-7 gravitational reference sensor (GRS) ground verification testing which provides thermal stability δT < 1 ...mK/ Hz to f < 0.1 mHz, and which by extension is suitable for in-flight thermal control of the LISA spacecraft to compensate solar irradiate 1/f fluctuations. Although for ground testing these specifications can be met fairly readily with sufficient insulation and thermal mass, in contrast, for spacecraft the very limited thermal mass calls for an active control system which can simultaneously meet disturbance rejection and stability requirements in the presence of long time delay; a considerable design challenge. Simple control laws presently provide ∼ 1mK/ Hz for >24 hours. Continuing development of a model predictive feedforward control algorithm will extend performance to <1 mK/ Hz at f < 0.01 mHz and possibly lower, extending LISA coverage of super massive black hole mergers.
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