These pages describe various ways to use Starlink for obtaining a position fix in GPS-denied environments. The pages and programs are oriented toward cruising sailboats.
This site and associated GitHub repo is NOT intended to replace the WhatsApp group. WhatsApp is a useful discussion forum for general communication on this topic. Rather, this site is intended to be a repository for important documentation and software that will not be visible to those who join the WhatsApp group after some post has been made. It is a place for anyone to get the relevant info at any time.
Many new members of the Cruiser Connect community, and especially the Starlink Datahub GPS positioning discussion have joined and likely missed some of the earlier messages. This website is intended as a reference to bring them up to speed.
The repo from which this documentation is generated as well as the contents of this website are licensed under “The Unlicense”, reproduced here
Starlink’s ability to operate in degraded or “GPS-denied” environments is a significant area of development, both for SpaceX’s own service reliability and as an alternative navigation system for the military and researchers.
While Starlink satellites use GPS themselves to stay in orbit, the system can provide location and timing services to users on the ground even when traditional GPS is jammed or unavailable for the following reasons.
The primary reason Starlink is more resilient than GPS in degraded environments is its orbital altitude.
• GPS (MEO): Traditional GPS satellites orbit at about 20,200 km. By the time their signals reach Earth, they are extremely faint—often compared to the light of a 25-watt bulb seen from hundreds of miles away. This makes them easy to “drown out” with low-power jammers.
• Starlink (LEO): These satellites orbit at only 550 km. Because they are roughly 40 times closer, their signals are 1,000 to 10,000 times stronger than GPS. This “loudness” makes Starlink signals much harder to jam or spoof.
SpaceX has begun leaning into this capability officially. In recent FCC filings and military tests, they have highlighted:
• Star Tracker Fallback: Starlink terminals use internal “star trackers” and inertial sensors to maintain orientation. If GPS is spoofed, the terminal can often detect the anomaly (pointing errors) and switch to fallback methods to maintain a data connection.
• Dense Network: With over 6,000 satellites, a Starlink receiver almost always has a direct line-of-sight to multiple “birds.” In urban canyons where tall buildings block GPS signals, the sheer density of Starlink makes it much more likely to maintain a lock.
It is important to understand the accuracy of your navigation system. This section is based on experiences of several boats which experienced spoofing in the Red Sea Suakin and Port Sudan areas in March of 2026. The boats all had PredictWind Datahubs, and their recorded logs were analyzed by Luis from PredictWind. Full details of how different Starlink antennas performed in various spoofing scenarios, and why, are in Luis’ report here
It is not necessary to have a PredictWind Datahub to take advantage of Starlink’s resistance to spoofing - several other configurations are described on this site that will provide position data for navigation in the face of GPS spoofing.
Spoofing is when a transmitter somewhere sends out GPS data that overpowers the weak GPS satellite data and the data is specially constructed to cause receivers to report their position as somewhere they are not.
Jamming is where the GPS signal is overridden so as to be unavailable to receivers - there is no data at the receiver. That condition has not been observed. All the information below relates to spoofing.
Boats that experienced spoofing used different antenna types, and the antenna behavior in the face of spoofing differed based on antenna type and operating conditions:
It has been determined that setting “Use Starlink Exclusively” mode can cause Standard and Performance (Gen2) antennas to freeze and continuously emit their last position. That mode should not be enabled on those antennas. A difference in behavior associated with that mode has not been observed on the Starlink Mini.
The Performance (Gen3) antenna has not been evaluated.
It has been observed that when sailing into a region where spoofing is active, a vessel passes through a fringe region where the spoofing signal is not strong enough to completely overpower the genuine signal. Receivers may alternate between the genuine and the spoofing source, causing the reported position to jump between extremes. This effectively results in intermittent spoofing, and antenna performance varies based on type.
It could be a sign that you should prepare to lose GPS position (and consequently SOG, AIS display, etc.)
In the absence of spoofing, the Starlink-reported position is more or less within 20-30 meters of what GPS reports for all antenna types, both when at anchor and in motion. Errors increase when a boat is in motion but stay broadly within this range.
The table below summarizes the findings in various conditions. Intermittent spoofing means the antenna intermittently receives good GPS positions, such as in a fringe area as described above. Sustained spoofing means the antenna signal is completely overwhelmed by the spoofing source.
| Condition | Mini | Standard | Performance (Gen2) |
|---|---|---|---|
| At anchor + no spoofing | Works | Works | Works |
| At anchor + spoofing | Works | Works | Works |
| Underway + no spoofing | Works | Works | Works |
| Underway + intermittent spoofing | Works | Works | Works |
| Underway + sustained spoofing | Works | FAILS | Works |
The Starlink Mini and Performance (Gen2) antennas are the only types that have demonstrated strong resistance to spoofing while underway.
Additionally, observations while underway in the presence of spoofing suggest that spoofing may cause a standard antenna to be unable to track satellites and to lose connection to the internet.
If you think you might need to use Starlink location data, test it before you need it, and make sure Starlink’s position can make it all the way through to your navigation system.
Here are the four major approaches to using Starlink location data.
PredictWind has a plugin release for their Datahub that can read starlink position information and provide that as a source on a NMEA 2000 network (or SeatalkNG network). (The Datahub also publishes NMEA0183 over UDP and TCP on a wifi network.) The plugin
The Datahub converts Starlink location data to NMEA messages and you pipe them into a Raymarine chartplotter or OpenCPN. Use the chartplotter or OpenCPN for navigation based on Starlink location. This should bypass GPS, and should help if GPS is unavailable or spoofed.
Bruce (Wild Orchid) has tested it on a Raymarine Axiom Pro. Rui (Anne Charlotte) has tested it on an older Raymarine E120 (Wide) Classic, and also with OpenCPN.
Keep in mind, both Starlink and PredictWind may disavow this a a general purpose navigation source, for legal purposes.
After determining that the gps environment is degraded or spoofed, you could switch your chartplotter to use the DataHub with Starlink. You should still be extremely vigilant in case the starlink data is not correct and switch back to your normal GPS source as soon as it seems stable.
The original configuration that spawned all the others. Using SignalK + Signalk-Starlink plugin allows you to easily (no programming at all) broadcast your position to OpenCPN (which already has a connection specific for SignalK). It’s very easy to setup, and usable in an emergency. It’s easy enough for most (even non-techy users) that don’t have a DataHub. A downside is the position updates are not very smooth. Signalk uses its plugin that reads Starlink location data and re-publishes it.
Finn (member of the Starlink datahub positioning discussion WhatsApp group) has shared a GitHub archive that will allow a computer (laptop, raspberry pi, etc.) to run a program that extracts the starlink position and provides it to other Nav programs (OpenCPN for example). This does not require a PredictWind Datahub or Signalk, so would be a useful option for cruisers who do not have a Datahub or Signalk. It does require getting your hands a bit dirty with python configuration.
Finn’s python scripts convert Starlink location data to NMEA messages, and you pipe them into OpenCPN. You then use OpenCPN for navigation based on Starlink location. This should bypass GPS, and should help if GPS is unavailable or spoofed.
The GPS_loss_alerting folder in this software contains a program that pulls starlink and NMEA positions from signalk and compares them and sends an alert when the two gps sources disagree by more than 0.1 nautical miles. This alert could indicate you should switch from your standard chartplotter gps source to an alternate way of getting location data into your chartplotter or OpenCPN (e.g. by selecting Starlink as a location data source).
It will also detect when Starlink or GPS location becomes unavailable (data timeout). It will send an email alert. This should help warn a cruiser that they need to switch to alternate navigation solution.
This program requires that there be a computer running signalk that has access to your NMEA network. It is built to be a linux service, but can be run from the command-line or an IDE on any computer - it is intended to work on both Windows and Linux.
All these capabilities that use Starlink position data rely on the Starlink antennrereada making its position data available on the local network. Depending on the capability, other configuration or software installation may be needed.
Follow the instructions at this page to configure your Starlink antenna to make its data available on the local network.
Follow the instructions at this page to configure your Starlink location data to be forwarded via PredictWind’s Datahub to your chartplotter or OpenCPN
Follow the instructions at this page to configure Signalk and OpenCPN to use Starlink data.
Follow the instructions at this page to configure the python scripts on a Windows PC to forward Starlink location data to OpenCPN.
Follow the instructions at this page to configure the python scripts on a Mac to forward Starlink location data to OpenCPN.
Follow the instructions at this page to configure your Starlink location to be compared to GPS, and the comparison results printed and sent to email and/or Telegram if they don’t match.
The capabilities described above are supported by various software and documentation which is stored on Github at Maddox-zephyr/starlink_position.
See the repo maintainer instructions for more information about the structure of the repo and how to make changes to it.
The repo also has tabs for various purposes:
Generally, you can browse the repo, look at the issues list etc without logging into GitHub. If you wish to create discussions or issues, modify the wiki, or other activities that modify the repo contents you must be logged into GitHub. Create an account if you don’t have one at https://github.com and log in, and you’ll be more powerful, and be able to contribute to the happiness of your fellow cruisers.