Gravity Probe B data analysis: I. Coordinate frames and analysis models

Abstract

Gravity Probe B (GP-B) was a cryogenic, space-based experiment testing the geodetic and frame-dragging predictions of Einstein's theory of general relativity (GR) by means of gyroscopes in Earth orbit. This first of three data analysis papers reviews the GR predictions and details the models that provide the framework for the relativity analysis. In the second paper we describe the flight data and their preprocessing. The third paper covers the algorithms and software tools that fit the preprocessed flight data to the models to give the experimental results published in Everitt et al (2011 Phys. Rev. Lett. 106 221101–4).

Gravity Probe B data analysis: II. Science data and their handling prior to the final analysis

“…(Note that to really linearize the telescope signal in this whole range, a cubic correction had to be introduced, see [2], section 6B.) Each pair of photodiodes measured the difference in light from both sides of the roof prism.…”

“…Here ± represent the individual + and − currents for each detector pair, x and y denote the satellite body-fixed x and y axes, and A and B stand for the two redundant pairs of photodiodes corresponding to the two telescope readout electronics (TRE) boxes. These signals are combined using the telescope models described in [2]. The combined pointing noise from all four detector pairs was 0.48 mas ≈ per orbit.…”

“…The entire S/C with the science instrument rolled about the line of sight to the GS with a period of 77.5 s. Therefore, both the telescope and the SQUID signals were modulated at the roll frequency. The satellite roll phase was thus needed to demodulate these signals and transform them into the inertial North-South, West-East reference frame [1,2], and for many other purposes.…”

“…Its concept was very simple: put a star-tracking telescope and a high precision gyroscope on orbit, keep the telescope pointing at the guide star (GS) as an inertial reference, and measure the rate of change of the angle between the line of sight to the GS and the gyro spin (see figure 1 in [1] or [2]). …”

“…Before launch we had anticipated the analysis of GP-B data to be just slightly more complicated than usual (see [8] and [2], section 4F). Several unpleasant on-orbit discoveries changed this expectation drastically.…”