Software GNSS Receiver for High-Altitude Spacecraft Applications
First Claim
1. A GNSS receiver onboard a satellite, comprising:
- an antenna for generating analog GPS signal data in response to detection of analog GPS signals;
front-end circuitry connected to receive said analog GPS signal data from said antenna, said front-end circuitry comprising an analog-to digital converter which converts analog GPS signal data to digital GPS signal data; and
a computer processor programmed to perform the following steps;
(a) buffering digital GPS signal data outputted by said front-end circuitry over a time interval that is greater than the duration of a bit of a navigation message;
(b) calculating a respective set of parameters based in part on the digital GPS signal data remaining after navigation data wipe-out for each frequency/time data point in a search array;
(c) calculating time-domain averaged I and Q signal components as a function of said respective set of parameters for each frequency/time data point in said search array;
(d) calculating respective correlation magnitudes based on said time-domain averaged I and Q signal components for each frequency/time data point in said search array; and
(e) determining an orbit state correction based in part on said correlation magnitudes.
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Abstract
A system that provides GPS-based navigation/orbit determination capabilities for high-altitude spacecraft. The system uses an existing spacecraft processor and an easy-to-space-qualify minimum-hardware front end to minimize the need for new space-qualified hardware. The system also uses coherent integration to acquire and track the very weak GPS signals at high altitudes. The system also uses diurnal thermal modeling of a spacecraft clock and precision orbit propagation to enable longer coherent integration, a special Kalman filter to allow weak signal tracking by integrated operation of orbit determination and GPS signal tracking, and a segment-by-segment, post-processing, delayed-time approach to allow a low-speed spacecraft processor to provide the software GPS capability.
7 Citations
20 Claims
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1. A GNSS receiver onboard a satellite, comprising:
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an antenna for generating analog GPS signal data in response to detection of analog GPS signals; front-end circuitry connected to receive said analog GPS signal data from said antenna, said front-end circuitry comprising an analog-to digital converter which converts analog GPS signal data to digital GPS signal data; and a computer processor programmed to perform the following steps; (a) buffering digital GPS signal data outputted by said front-end circuitry over a time interval that is greater than the duration of a bit of a navigation message; (b) calculating a respective set of parameters based in part on the digital GPS signal data remaining after navigation data wipe-out for each frequency/time data point in a search array; (c) calculating time-domain averaged I and Q signal components as a function of said respective set of parameters for each frequency/time data point in said search array; (d) calculating respective correlation magnitudes based on said time-domain averaged I and Q signal components for each frequency/time data point in said search array; and (e) determining an orbit state correction based in part on said correlation magnitudes. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of acquiring weak GPS signals onboard a satellite orbiting at high altitudes, comprising the following steps:
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(a) generating analog GPS signal data in response to detection of analog GPS signals; (b) converting said analog GPS signal data to digital GPS signal data; (c) buffering said digital GPS signal data over a time interval that is greater than the duration of a bit of a navigation message; (d) calculating a respective set of parameters based in part on the digital GPS signal data remaining after navigation data wipe-out for each frequency/time data point in a search array; (e) calculating time-domain averaged I and Q signal components as a function of said respective set of parameters for each frequency/time data point in said search array; (f) calculating respective correlation magnitudes based on said time-domain averaged I and Q signal components for each frequency/time data point in said search array; and (g) determining an orbit state correction based in part on said correlation magnitudes. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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17. A GNSS receiver onboard a satellite, comprising:
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an antenna for generating analog GPS signal data in response to detection of analog GPS signals; front-end circuitry connected to receive said analog GPS signal data from said antenna, said front-end circuitry comprising an analog-to digital converter which converts analog GPS signal data to digital GPS signal data; a computer processor programmed to perform the following steps; (a) buffering digital GPS signal data outputted by said front-end circuitry over a time interval that is greater than the duration of a bit of a navigation message; (b) propagating orbit state data of said satellite during said time interval; (c) buffering said orbit state data propagated during said time interval; (d) calculating a respective set of parameters for each frequency/time data point in a search array, the values of said parameters being based in part on position and velocity data included in said buffered orbit state data and based in part on GNSS satellite position and velocity data derived from a navigation message received from a source other than said detected analog GPS signals; (e) calculating time-domain averaged I and Q signal components as a function of said respective set of parameters for each frequency/time data point in said search array; (f) calculating respective correlation magnitudes based on said time-domain averaged I and Q signal components for each frequency/time data point in said search array; and (g) determining an orbit state correction based in part on said correlation magnitudes. - View Dependent Claims (18, 19, 20)
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Specification