SpaceX Starlink Can Provide Super GPS With a Software Modification

There is an arxiv paper “Fused Low-Earth-Orbit GNSS”, by Peter A. Iannucci and Todd E. Humphreys of the Radionavigation Laboratory, The University of Texas at Austin, that details how low-earth orbit satellites can be modified to provide super-precise GPS.

MIT Technology Review indicates that the system would be accurate to 70 centimeters. Simple software upgrades can modify Starlink’s satellites so existing communications abilities and existing GPS signals could provide position and navigation services. Each Starlink satellite uses algorithms that are rarely found in consumer products. Spacex Starlink satellites already calculate their own location to within a few centimeters.

Here is information from the Fused Low-Earth-Orbit GNSS paper.

Low-Earth-orbiting (LEO) satellites could provide a positioning, navigation, and timing (PNT) service far more robust to interference than traditional Global Navigation Satellite Systems (GNSS). Previous proposals for LEO PNT require dedicated spectrum and hardware: a transmitter, antenna, and atomic clock on board every broadband satellite. This paper proposes a high-performance, low-cost alternative which fuses the requirements of PNT service into the existing capabilities of the broadband satellite. A concept of operations for so-called fused LEO GNSS is presented and analyzed in terms of the economy of its use of constellation resources of transmitters, bandwidth, and time. This paper shows that continuous assured PNT service over ±60° latitude (covering 99.8% of the world’s population) with positioning performance exceeding traditional GNSS pseudoranging would cost less than 0.8% of downlink capacity for the largest of the new constellations, SpaceX’s Starlink.

Previous proposals targeted positioning precision on-par with traditional GNSS pseudoranging (on the order of 3 meters), fused LEO GNSS can improve on this by more than an order of magnitude. It also offers a significant anti-jam advantage over L-band hosted-payload solutions in terms of signal-to interference ratio, thus making it attractive as a means for delivering assured PNT (A-PNT).

How is this possible?

1. We can use the massive data bandwidth in each broadband satellite transmission burst for up-to-the instant orbit and clock products. If such zero-age-of-ephemeris products are available, then expensive atomic clocks in LEO may be eliminated.
2. We can access these orbit and clock products by performing precision orbit determination (POD) on-orbit using traditional GNSS in a multi-tier architecture. This eliminates extensive ground segment to observe satellite orbits.
3. Commercial broadband signals in K-band and Vband will have both high signal-to-noise-ratio (SNR) and large bandwidth. This greatly reduces receiver noise and multipath error in L-band GPS.

It is possible to build a (relatively) compact, highly-directional receiver phased array for an additional 30 dB of anti-jam performance.

SpaceX’s Starlink could provide continuous centimeter accurate GPS service to 99.8% of the world’s population would require reserving at most 0.8% of system downlink capacity, 0.36% of system energy capacity, and a tiny amount of uplink capacity. This provisioning scenario would also reserve 5.3% of the constellation’s capacity for beam-steering, leading to at most a 0.1 dB increase in maximum pointing loss.

No atomic clocks would be needed.
No extensive ground station infrastructure is needed.
The GPS precision can ten times more accurate to about 30 centimeters or even better.
A jam resistant receiving station can be built.

SOURCES- Arxiv Fused Low Orbit GNSS, MIT Technology Review
Written by Brian Wang,