Characterization of on‐orbit GPS transmit antenna patterns for space users

Abstract

The GPS Antenna Characterization Experiment (GPS ACE) has made extensive observations of GPS L1 signals received at geosynchronous (GEO) altitude, with the objective of developing comprehensive models of the signal levels and signal performance in the GPS transmit antenna side lobes. The experiment was originally motivated by the fact that data on the characteristics and performance of the GPS signals available in GEO and other high Earth orbits was limited. The lack of knowledge of the power and accuracy of the side lobe signals on-orbit added risk to missions seeking to employ the side lobes to meet navigation requirements or improve performance. The GPS ACE Project filled that knowledge gap through a collaboration between The Aerospace Corporation and NASA Goddard Spaceflight Center to collect and analyze observations from GPS side lobe transmissions to a satellite at GEO using a highly-sensitive GPS receiver installed at the ground station. The GPS ACE architecture has been in place collecting observations of the GPS constellation with extreme sensitivity for several years. This sensitivity combined with around-the-clock, all-in-view processing enabled full azimuthal coverage of the GPS transmit gain patterns over time to angles beyond 90 degrees off-boresight. Results discussed in this paper include the reconstructed transmit gain patterns, with comparisons to available pre-flight gain measurements from the GPS vehicle contractors. For GPS blocks with extensive ground measurements, the GPS ACE results show remarkable agreement with ground based measurements. For blocks without extensive ground measurements, the GPS ACE results provide the only existing assessments of the full transmit gain patterns. The paper also includes results of pseudorange deviation analysis to assess systematic errors associated with GPS side lobe signals.

A Case Study Analysis for Designing a Lunar Navigation Satellite System with Time-Transfer from Earth-GPS

“…First, we design our simulated Earth-GPS constellation to be made up of 31 satellites with 8 satellites from Block IIR, 7 from IIRM, 12 from IIF and 4 from Block III. We model the transmit antenna of Earth-GPS satellites by utilizing the transmit power and antenna gain patterns of the L1 C/A signals, which are made available from the NASA GPS ACE study [16]. Next, we simulate a spaceborne Earth-GPS receiver with a steering antenna pointed towards the Earth so as to maximize the visibility of Earth-GPS signals at the LNSS satellite.…”

“…Several simulated works also have demonstrated the feasibility of using Earth-GPS at lunar distances [7,14,15]. Through GPS Antenna Characterization Experiment (ACE) study, NASA has characterized the GPS antenna gain patterns at high elevation angles from boresight for space users [16]. NASA has also developed a spaceborne Earth-GPS receiver [17], which will be tested on the lunar surface for the first time in 2023 [18,19].…”

Feasibility analysis of GNSS-based navigation for LUMIO mission

“…The transmitted power is then computed as (G Tx ) dBi is the gain of the GNSS satellite antenna panel toward the receiver. Two-dimensional (off-bore angle and azimuth) antenna pattern are available for GPS Block IIR, IIR-M and IIF, the first two from the ground-test antenna gain measurements performed by Lockheed Martin (the satellites manufacturer) and from experimental reconstruction of the latter [1,2]. For GPS Block III-A and Galileo, the same pattern and body reference frame of a GPS Block IIF SV has been used as modeling assumption.…”

“…For users in the space above the MEO, except for some spillover, almost the entire main lobe is covered by the Earth. In most cases, only sidelobe's signals are received with a signal power for the GPS system about 15 dB lower [1,2] with respect to main lobe ones. In addition, as the orbital height increases, the Free-Space Propagation/Path (FSP) loss becomes larger.…”

Joint navigation performance of distant retrograde orbits and cislunar orbits via LiAISON considering dynamic and clock model errors

“…Suppose that a transmitter on the DRO satellite has a power of 14.9 dBW, which is the same as the power of the GPS satellite. The effective area of the transmitter antenna is set to 0.77 m 2 , the wavelength is the same as the GPS L1 signal (0.19 m), and the corresponding gain is 24.3 dB using Equation .…”